Comparative Ecology of Bartonella and Brucella Infections in Wild Carnivores

Phylogenetic sister clades Bartonella and Brucella within the order Rhizobiales present some common biological characteristics as well as evident differences in adaptations to their mammalian reservoirs. We reviewed published data on Bartonella and Brucella infections in wild carnivores to compare the ecology of these bacteria in relatively similar host environments. Arthropod vectors are the main mechanism for Bartonella species transmission between mammalian hosts. The role of arthropods in transmission of Brucella remains disputed, however experimental studies and reported detection of Brucella in arthropods indicate potential vector transmission. More commonly, transmission of Brucella occurs via contact exposure to infected animals or the environment contaminated with their discharges. Of 26 species of carnivores tested for both Bartonella and Brucella, 58% harbored either. Among them were bobcats, African lions, golden jackals, coyotes, wolves, foxes, striped skunks, sea otters, raccoons, and harbor seals. The most common species of Bartonella in wild carnivores was B. henselae, found in 23 species, followed by B. rochalimae in 12, B. clarridgeiae in ten, and B. vinsonii subsp. berkhoffii in seven. Among Brucella species, Br. abortus was reported in over 30 terrestrial carnivore species, followed by Br. canis in seven. Marine carnivores, such as seals and sea lions, can host Br. pinnipedialis. In contrast, there is no evidence of a Bartonella strain specific for marine mammals. Bartonella species are present practically in every sampled species of wild felids, but of 14 Brucella studies of felids, only five reported Brucella and those were limited to detection of antibodies. We found no reports of Bartonella in bears while Brucella was detected in these animals. There is evident host-specificity of Bartonella species in wild carnivores (e.g., B. henselae in felids and B. vinsonii subsp. berkhoffii in canids). A co-adaptation of Brucella with terrestrial wild carnivore hosts is not as straightforward as in domestic animals. Wild carnivores often carry the same pathogens as their domesticated relatives (cats and dogs), but the risk of exposure varies widely because of differences in biology, distribution, and historical interactions.


INTRODUCTION
Sixty percent of emerging infectious diseases are zoonoses and majority of these (71.8%) originate from wildlife (1). Among pathogens, Bartonella species might represent an underappreciated danger for human and animal health (2) and human brucellosis remains one of the most common zoonotic diseases worldwide, with more than 500,000 new cases every year (3).
Bartonella and Brucella are phylogenetic sister clades in the order Rhizobiales (4,5). The genus Brucella is composed of 12 recognized species defined to their preferential hosts (6,7). The more diverse genus Bartonella includes over 33 validated species exhibiting extremely high genetic diversity (8). Genome analyses of representative species of these bacterial genera have confirmed their shared ancestry. Alsmark et al. (9) identified 760 Bartonella henselae genes, for which homologs are present in one of chromosomes of Brucella suis. In addition to their genetic proximity, the Bartonella and Brucella genera present analogies in their life history and ecology that are even more important for our analysis. Whereas, most closely related species of the order Rhizobiales are symbiotic on plant roots, both Bartonella and Brucella are adapted to diverse mammalian hosts. Each Bartonella and Brucella species has one or a few closely related mammal reservoir hosts (5).
Investigations of wild animals, including predators, for Brucella infections started much earlier and were more intensive compared to studies of Bartonella infections. Research of Brucella infections in animals has been dominated by studies of domestic animals and, to a lesser degree, of wild ruminants. Although Brucella canis was identified in domestic dogs more than 50 years ago and is well known to veterinary community as a causative agent of canine abortion (10), investigations of Brucella in dogs are much fewer than those of Brucella in cattle, sheep, goats, and pigs. This is mainly due to lack of good tests for rough Brucella species, not because of lack of interest. Publications on the distribution of Brucella species among wild canids, as well as among other wild carnivores, are even more limited in the western literature. At the same time, a good number of reports on this topic are scattered across Russian literature. Most of these were published during Soviet times, sometimes in classified proceedings, and are not easily available (11)(12)(13). Identification of novel species and genotypes of Brucella in rodents, bats, marine mammals, and amphibians stimulated epidemiological research of diverse animal species, including wildlife (7).
Extensive investigations of animals for Bartonella species started in the early 1990s after the discovery that one or more Bartonella species could cause cat scratch disease in people. For this reason, most studies targeted domestic cats and dogs with limited investigations of stray dogs and feral cats (14,15). Studies on detection, identification, and characterization of Bartonella species in wild animals usually targeted small mammals: rodents (8) and bats (16). Chomel et al. (17) pioneered Bartonella research in wild carnivores and ruminants. Since then, numerous wildlife studies have been conducted in various parts of the world. However, a comprehensive analysis of the available data on prevalence and diversity of Bartonella and Brucella infections in wild carnivores has yet to be published. Such an analysis would allow comparisons to be made between the ecologies of these two bacterial groups living in similar host environments and identify possible directions for future research.
In this review we undertook such an analysis through an extensive literature review. We examined the similarities and differences in the Bartonella and Brucella ecology and, more importantly, analyzed biological features that may reveal ways of these phylogenetically close bacterial genera exhibit evolutionary adaptations to the same or related mammalian hosts, presumably during the long periods over which they have co-occurred. Considering the differences in the genera's life history, we paid special attention to possible arthropod-mediated transmission of these bacteria between mammalian hosts.
For this review, we followed the more accepted taxonomic division of the order Carnivora into suborders Feliformia ("catlike") and Caniformia ("dog-like"), with pinnipeds included as a separate superfamily level clade (Pinnipedia). We chose these divisions not for preference for a specific taxonomic scheme, but as a convenient basis for analysis of available data on Bartonella and Brucella infections in 12 families: suborder Feliformia (Felidae, Herpestidae, Hyaenidae, and Viverridae), suborder Caniformia (Canidae, Mephitidae, Mustelidae, Procyonidae, and Ursidae), and clade Pinnipedia (Odobenidae, Otariidae, and Phocidae).
We conducted a thorough literature search by using PubMed, Scopus, OVID Medline, BioOne, Crossref, WorldCat, Web of Science, Google Scholar, and other databases. In the search we used keywords: "Bartonella ecology, " "Brucella ecology, " "Bartonella AND wild animals, " "Brucella AND wild animals, " "Bartonella AND carnivores, " "Brucella AND carnivores, " "Bartonella AND predators, " "Brucella AND predators, " "Bartonella AND marine mammals, " "Brucella AND marine mammals, " "Bacteria AND wild carnivores, " "Bartonella AND fleas AND mammals, " "Brucella AND arthropods, " and their variations. We realized that all these search engines had missed numerous reports on detection of Brucella in wild animals in the Russian language literature and we conducted our own search of such sources in the Russian Internet and search engines as well as by working through the references in related articles and reviews in the Russian language.
We used the word "wild" in the meaning of "free-ranging" and apart from a few publications of particular interest, we excluded reports of Bartonella and Brucella in captive and zoo animals as the composition of bacterial communities in such animals could have been modified by separation from the natural environment or via acquisition of bacterial infections from the surrounding environment (e.g., from urban rats). The literature on Bartonella and Brucella infections in domestic carnivores (cats and dogs) is abundant, so we limited inclusion for comparative purposes only.
We collected data from serological, bacteriological, and molecular investigations of Bartonella and Brucella infections in all families of wild terrestrial and marine carnivores worldwide. Providing data from various techniques, we need to acknowledge that discrimination power of characterization of pure cultures and sequence analyses for identification of Bartonella and Brucella species is greater than that of serological procedures. However, serological methods remain an important tool in detection and identification of these infections in animals and should be taken in consideration with full awareness of their limitations.
Then we collated the obtained information in Bartonella, Brucella and combined tables by carnivore species divided into their respective families listed in alphabetical order of their Latin names. We listed information on location where the samples were collected, investigation method, prevalence and bacterial species, and reference to the study. Both positive and negative results of investigations were included. The combined table shows only references listed by carnivore species in their respective families.

FEATURES OF BARTONELLA AND BRUCELLA BACTERIA RELATED TO THEIR ECOLOGY IN WILD ANIMALS Biological Characteristics
Bartonella and Brucella bacteria share some biological characteristics, yet there are evident differences in their adaptations to their animal reservoirs. Infections caused by bacteria of both taxonomic groups can lead to a long-lasting bacteremia with ability to invade specific mammalian cells and survive inside them. Via analogous mechanisms, the specialized secretion system (T4SS) works as a molecular syringe to inject effector molecules into their target cells (18,19). Bartonella and Brucella modulate their gene expression to adapt to the different environments during the infectious process (20,21). The VirB systems of Bartonella and Brucella are associated with distinct groups of effector proteins that collectively mediate interactions with host cells (19).
Bartonella bacteria infect endothelial cells and seed into the bloodstream, colonizing erythrocytes which provide a persistence niche for the bacteria. The ability of these bacteria to exploit their reservoir hosts with diminished morbidity and to cause a high level of bacteremia justifies the definition of "elegant hemotrophic parasites" given by Birtles (22) to bartonellae. In incidental hosts, Bartonella infections can cause various clinical manifestations commonly without high-level bacteremias (21). In contrast to Bartonella, Brucella bacteria invade and multiply within mammalian host's macrophages and placental trophoblasts (18,19,23). Although bacteremia is common during brucellosis, data on duration and mechanisms of Brucella persistence in animal blood are limited.

Transmission of Bartonella and Brucella Bacteria
The persistence of Bartonella bacteria in red blood cells optimizes transmission of these bacteria by blood-sucking arthropods. High prevalence and long-term bacteremia in reservoir mammals and adaptation to specific vectors seem to be the common strategy of bartonellae for transmission and host diversity (24). Many described Bartonella species are vector-borne bacteria transmitted by fleas, sand flies, lice, and biting flies depending on the bacteria species involved and their vertebrate reservoirs (24,25). Experimental studies demonstrated louse and flea transmission of B. henselae and B. quintana (26)(27)(28). Some investigators provided evidence of potential role of ticks and mites in transmission of Bartonella species, but debates continue on their role of as vectors (25,29). A 2008 study by Cotté et al. (30) showed that Ixodes spp. ticks are capable of transmitting B. henselae via salivary contents, but Telford and Wormser (31) found no convincing evidence that ticks were vectors of Bartonella species. Molecular detection of Bartonella spp. in terrestrial leeches (Haemadipsa rjukjuana) by Kang et al. (32) opens up a discussion of the pathogen transmission by land leeches.
Transcutaneous transmission of Bartonella via animal bites and scratches during hunting, as well as through butchering or handling wild meat is another possibility (33). Cat scratch disease, caused by B. henselae is the best-documented example of direct animal-to-human transmission of a Bartonella species by scratch or bite inoculation (14). Finkelstein et al. (27) showed that B. henselae can remain viable in flea feces for over 72 hours. Therefore, transmission potentially can occur via inoculation of B. henselae from infected flea feces into the skin via open wounds. Suspected Bartonella alsatica transmission from wild rabbits to humans, presumably occurring during hunting and butchering, was reported in patients with endocarditis or lymphadenitis in France (34,35). Suspected dog bite transmission of B. vinsonii to a human was reported based upon serological evidence (36). There is little information on possible vertical transmission of bartonellae in animals. However, Bartonella species were isolated from the embryos and neonates of naturally infected cotton rats (Sigmodon hispidus) and white-footed mice (Peromyscus leucopus) (37). Experimental inoculation of B. henselae to adult female cats was accompanied by decreased conception or failure to maintain pregnancy (38). Considering the extensive animal reservoirs and the large number of insects that have been implicated in the transmission of Bartonella species, animal exposure to these organisms may be more substantial than is currently believed.
Transmission of Brucella occurs mainly via close contact with placenta, aborted fetuses, fetal fluids, reproductive tract discharges, and secretions (7). Infected dogs intermittently shed low concentrations of bacteria in seminal fluids and nonestrus vaginal secretions. Postabortion vaginal fluids contain a high level of bacteria and are a source of infection for other dogs (39). In addition, dogs can shed the bacteria in the saliva, nasal secretions, and urine (40). Studies suggest that the concentration of Br. canis in urine is higher in male than female dogs; this difference is attributed to urine contamination with seminal fluid (41). However, the role of urine as a source of infection is not fully understood (39).
There is a widely accepted perception that absence of transmission of Brucella species via arthropod vectors is the most essential difference in ecology of these bacteria compared to the Bartonella species. We found a number of rarely cited publications on either detection of Brucella species in arthropods or experimental studies designed to verify a possibility of vector transmission of these bacteria. Although detection of Brucella in arthropods collected from different sources does not often directly relate to carnivores, such information can help interpret potential mechanisms of bacterial transmission. The invasion of Brucella into erythrocytes and its persistence in blood suggest a possibility for transmission by bloodsucking arthropods in nature (42). Although Brucella may be found in erythrocytes, these bacteria exhibit strong tissue tropism and replicate within vacuoles in macrophages, dendritic cells, and placental trophoblasts. Evidence that Brucella species can be spread among animals by arthropods is very limited. Some Russian authors argued that parasitic arthropods, especially ticks, could preserve Brucella in nature and transmit them within a population from one animal to another (43,44). Rementsova (43) listed 20 observations of Brucella detection in ticks. Experiments in Russia reported that both ixodid and argasid ticks were infected with Brucella at different phases of their development and could transmit the pathogen to uninfected animals during bloodsucking (43). Brucella in ticks retained their virulence even after 2 years (43). More recently, Neglia et al. (45) detected Br. abortus DNA and RNA in different stages of development of the sucking louse (Haematopinus tuberculatus).
Alimentary transmission is important for Brucella as proved by experimental studies in wild carnivores. Scanlan et al. (46) infected gray foxes with Br. abortus in dog food. Seven of eight foxes became seropositive. Neiland and Miller (47) infected six beagle dogs, two wolves (Canis lupus), one black bear (Ursus americanus), and two grizzly bears (Ursus arctos horribilis) with a strain of Br. suis biovar 4 isolated from a sled dog from Alaska. Their experiments demonstrated that canids and ursids are susceptible to the infection via intraperitoneal inoculation and through oral mucous membranes. During acute stages of the infection, Brucella congregated in these species in high numbers in lymph nodes and distributed throughout the body. Importantly, Brucella invaded salivary glands and probably also mammary glands and kidney, thus providing conditions for shedding the bacteria in saliva, milk, and urine. The authors reported reproductive failure during infection in wolves, but were not confident that the failure was a consequence of the infection (47). Morton (48) experimentally infected foxes with Br. suis biovar 4 and observed that the incidence of positive titers, positive cultures, and shedding of bacteria was related to the number of Brucella organisms experimentally fed to the animals. Lowest doses did not produce infection. Highest doses produced positive titers and cultures.
Tests on rats showed transmission of Br. abortus biovar 1 from infected male to uninfected female rats resulted from sexual intercourse (49). Vertical transmission of Br. abortus caused sterility in pregnant mice (50); Wang et al. (51) documented vertical transmission of Br. melitensis on a pregnant mouse model. Guzman-Verri et al. (52) cited the more likely modes of transmission of Br. ceti to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs.
Brucellae have high viability and can survive in the environment for 3-21 days in spring-summer and for 151-233 days in winter-fall seasons. Brucellae maintain viability in carcasses (muscles, internal organs, and lymph nodes) at −7.2 • to 38.4 • C for 1-12 months (53). Long-term survival of Br. microti in soil was described and, thus, soil might act as a reservoir of infection (54).

General Prevalence Pattern
Overall, prevalence of Bartonella infections in carnivores was higher compared to Brucella infections. In the studies of over two Feliformia animals, the highest prevalence was registered by culture in bobcats [37%, 7/19, (55)], by IFA in bobcats again [74%, (56)], and by PCR of blood in Iberian lynx [33.3%, 10/30, (57)]. In studies of over two Caniformia animals, the highest Bartonella prevalence was registered by culture in gray foxes [49%, 26/53, (58)], by IFA in coyotes [89%, 48/53, (58)], and by PCR of blood in raccoons [43%, 16/37, (59)]. A very high overall prevalence of antibodies to B. henselae (95%) was detected among Brazilian free-ranging felids (60) ( Table 1). As expected, the number of seropositive animals was usually higher than the numbers of culture or PCR positive individuals from the same study. Thus, of the 54 lions from South Africa, 5.2% were positive by culture, 3.7% were PCR positive for Bartonella DNA, and 17% had Bartonella antibodies (62). A study on golden jackals in Iraq found 14.5% of animals positive by PCR and 40.4% (23/57) by IFA (86).

Age and Gender Pattern
Prior studies usually show no statistical difference in prevalence by age or gender in felines (61,69,79). However, Chomel et al. (17) found antibody prevalence for B. henselae to increase with age in pumas in California. In contrast, Rotstein et al. (79) found antibody prevalence higher in Florida panthers under 2 years of age (40%) compared to panthers over 2 years of age (13%).

Geographic Pattern
Prevalence of B. henselae antibodies in mountain lions and bobcats varied significantly between different states of the U.S. (17). Mountain lions from Arizona, California, and Texas were more likely to be seropositive for B. henselae (26.7-40.0%) than pumas from the Northwest and Mountain states (0-11.8%) (17). In California, the highest prevalence in bobcats was from the coastal range (37.5%), while the highest prevalence in pumas was from Southern California and Sierra Nevada (17). The reported pattern was similar to the geographic distribution of Bartonella infection in domestic cats. It has been demonstrated that in cat populations (stray or pets), prevalence of infection was demonstrated to vary considerably with an increasing gradient from cold climates (0% in Norway) to warm and humid climates (68% in the Philippines) (14). In the U.S., prevalence of B. henselae antibodies in pet cats varied significantly with the highest average prevalence in the southeastern United States, Hawaii, coastal California, the Pacific Northwest, and low prevalence in Alaska, the Rocky Mountain-Great Plains region, and the Midwest (113). Comparing wild felids at four sites in California and Colorado, Bevins et al. (68) noted that seroprevalence varied considerably, but in almost all cases, it    was higher in warmer and more humid California than in Colorado. For mountain lions, suburban land use predicted increased exposure to Bartonella species in southern California (114).

Seasonal Pattern
Studies have yielded conflicting evidence about the seasonality of B. vinsonii subsp. berkhoffii infection in coyotes. First, Chang et al. (91) reported that the prevalence of Bartonella antibodies was highest in summer (42%) and lowest in spring (29%), whereas a geographically more restricted study conducted in coastal central California, U.S., by the same authors found the highest seroprevalence in winter (100%) and the lowest in summer (62%) (90). Investigating antibody prevalence in 239 coyotes from northern California, Beldomenico et al. (89) identified some environmental factors associated with the seropositivity. In that study, prevalence of antibodies against B. vinsinii subsp. berkhoffii was 44% in the summer, 40% in the spring, 27% in the winter, and 19% in the fall. The authors noticed that Bartonella seropositivity was associated with higher precipitation and proximity to the coast. In addition, coyotes seropositive for B. vinsonii subsp. berkhoffii were more likely to be seropositive for tick-borne agents Anaplasma phagocytophilum and mosquito-vectored Dirofilaria immitis (89). Interestingly, California Zoo felids of the genus Felis were found almost three times more likely to be seropositive for B. henselae than animals belonging to the genera Panthera and Acinonyx (69).

PREVALENCE OF BRUCELLA INFECTIONS IN WILD CARNIVORES General Pattern
Eighty-nine percent of Brucella studies of wild carnivores were conducted by serological and bacteriological methods, but no reports were found on culturing Brucella from representatives of suborder Feliformia. Only a few wild felid species (lion, jaguar, and bobcat), mongooses, and spotted hyena were serologically positive. Apart from one bobcat that had antibodies against Br. canis (115), the rest of seropositive Feliformia animals had antibodies against Br. abortus. We have to be cautious with the claim about presence of specific antibodies in this paper, as well in many other reports, because Br. abortus suspensions can also detect Br. melitensis. The highest seroprevalence was registered in white-tailed mongoose [33.3%, 1/3, (116)]. In evident contrast to Feliformia animals, prevalence of Brucella in various Caniformia species varied greatly, with many reporting high prevalences of positive antibody titeres. Antibodies to Brucella species were recorded in 40% of coyotes (117), 42% of wolves (118), 43% of black-backed jackals (116), 50% of Arctic foxes and 40% of red foxes (48), 64% of grizzly bears (119), 28% of Asian sea otters (120), 23% of California sea lions (121), and 74% of Australian seals (122). Brucella was cultured from 30.8% of wolves (123) ( Table 2).

Age Pattern
We could find information on age dependence only in marine Brucella. In the 2018 study on gray and harbor seals, Kroese et al. (212) noted remarkable age-dependent prevalence of Br. pinnipedialis in both serology and in the investigation of the tissues from stranded animals. The PCR positivity was 84% (26/31) in juveniles compared to 57% (4/7) in adults and Br. pinnipedialis was cultured only from juveniles and not from adults in that study. Similar age dependence was shown in harbor seals by Miller et al. (169) and Ewalt et al. (229). Nymo et al. (206) noted the age-dependent prevalence of anti-Brucella antibodies in hooded seals. Pups (<1 mo old) had a substantially lower probability of being seropositive (4/159, 2.5%) than yearlings (6/17, 35.3%), suggesting that exposure may occur post-weaning, during the first year of life. For seals over 1 year old, the mean probability of being seropositive decreased with age, with no seropositives older than 5 years, indicating loss of antibody titer with either chronicity or clearance of infection (206).

Bartonella Species in Wild Feliformia Animals
Wild Feliformia animals mostly carry the same Bartonella species as domestic cats, namely B. henselae (types I and II), B. koehlerae, and B. clarridgeiae (234). The same species were detected in feral cats from Georgia, U.S. (59). In Africa, free-ranging lions were found infected with B. henselae type II and B. koehlerae subsp. koehlerae and Namibian cheetah with a strain that clustered between B. henselae and B. koehlerae and was considered a new subspecies of B. koehlerae (61,63). In Japan, B. henselae was found in Iriomote leopard cats and B. clarridgeiae DNA was detected in Tsushima leopard cats (74,82). In a study on free-ranging mountain lions and bobcats from California, U.S., Chomel et al. (55) described new Bartonella strains, which were similar to but different from B. henselae and B. koehlerae, and named them B. koehlerae subsp. boulouisii and B. koehlerae subsp. bothieri. Phylogenetic analysis based on comparison of four genetic markers revealed two clusters: one with five strains obtained from bobcats and another with three strains obtained from mountain lions indicating a degree of hostspeciation of these strains (55). In Brazil, sequencing analysis revealed a Bartonella strain close to but different from B. henselae and B. koehlerae in wild-born captive margay (Leopardus wiedii) (235).
Other Bartonella species were detected in fleas collected from wild felids. For example, Bartonella alsatica was found in one of six rabbit fleas Spilopsyllus cuniculi collected from a European wildcat (F. silvestris) in Spain (65). This Bartonella species is usually associated with rabbits and possibly fleas were infected or they contained blood meal from infected rabbits, as S. cuniculi is normally found on European rabbits (Oryctolagus cuniculus). A different situation has been reported by López-Pérez et al. (67) regarding a genetic variant obtained from a flea (Pulex simulans) collected from a bobcat (L. rufus) in northwestern Mexico. This variant had ITS sequence 99.1% similar to a strain previously isolated from another bobcat from California, U.S., but distant from all other Bartonella genotypes.

Bartonella Species in Wild Caniformia Animals
In the studies, Caniformia animals were found to carry B. henselae, B. clarridgeiae, B. vinsonii subsp. berkhoffii, B.rochalimae, B. washoensis, and B. bacilliformis. In an investigation of wild carnivores from Colorado, U.S., Bai et al. (77) identified two Bartonella species, B. vinsonii subsp. berkhoffii and B. rochalimae. Striped skunks exclusively carried B. rochalimae, while coyotes, red foxes, and raccoons were infected with either or both Bartonella species. Bartonella rochalimae DNA was found in a wolf (C. lupus) in northern Spain (64). Investigating wild canids along with stray dogs throughout Iraq, Chomel et al. (86) identified a novel strain of Bartonella, which was named Candidatus B. merieuxii, in six jackals (Canis aureus). By three genetic markers, the "jackal" strain was aligned most closely with B. bovis and the other ruminant Bartonella species. Sequences closely related to Candidatus Bartonella merieuxii later were found in three jackals and one red fox (V. vulpes) in Israel (85). Besides this strain, B. rochalimae and B. rochalimae-like were found in five jackals and one fox, and one jackal harbored B. vinsonii subsp. berkhoffii (85).
Kehoe et al. (87) documented the presence of three Bartonella species in heart valves and/or spleen of free-ranging coyotes from northern California, U.S. Partial DNA sequencing showed that aortic valves from 8 (53%) of 15 coyotes were B. vinsonii subsp. berkhoffii positive, B. rochalimae DNA was amplified from the      spleen of one coyote, and B. henselae DNA was amplified from the mitral valve of another coyote. By sequence analyses, four coyotes were infected with B. vinsonii subsp. berkhoffii genotype I, three with genotype II, and one with genotype III (87). Two species of Bartonella, a novel Bartonella clarridgeiaelike bacterium and B. vinsonii subsp. berkhoffii, were isolated from rural dogs and gray foxes in northern California (58). Two B. henselae sequences detected in the spleen of raccoon dogs in Korea matched the strain Houston-1 and by ITS sequences were 99.8% similar to a strain found in dogs in China (94). Northern and Southern sea otters were found IFA positive for B. washoensis (107,108). The authors also detected B. bacilliformis by PCR in heart valves of both species. A strain close to B. washoensis was detected by PCR in Japanese marten (95). Chinnadurai et al. (109) detected a novel strain in river otters by PCR with a sequence matched a strain previously described in Southern flying squirrel. In the Netherlands, harbor seals were found to carry a strain 97% similar to B. grahamii (112).

BRUCELLA SPECIES IDENTIFIED IN WILD CARNIVORES
There are no reports on identification of Brucella species by culture or by sequence analysis in animals belonging to Felidae, Herpestidae, and Hyaenidae families. Except for one bobcat that had antibodies against Br. canis (115), the other few seropositive Feliformia animals had antibodies against Br. abortus (116,132). Since the authors did not use specific tests that identify rough Brucella species, they were not able to find antibodies.

BARTONELLA AND BRUCELLA INFECTIONS IN WILD CARNIVORES BY FAMILY Family Felidae
Genus Panthera Bartonella infection was reported in three big cats species: African lion (P. leo), jaguar (P. onca), and Far Eastern leopard (P. pardus orientalis). B. henselae and B. koehlerae subsp. koehlerae were cultured from the blood of three (5.2%) of 58 lions from Kruger National Park in South Africa (61,62). The level of bacteremia in the culture-positive lions varied from 35 to 2,000 bacteria per 1 ml of blood. Bartonella cultureand antibody-positive lions were found among semi-captive lions from three ranches in South Africa (71). Interestingly, all studied lions from Zambia and Zimbabwe were negative for Bartonella by culture and PCR (63,70). A wild-caught jaguar in Brazil, which was maintained in captivity for only a week, was found B. henselae positive (236). This finding led the authors to believe that the animal had been infected in the wild. In the Russian Far East, wild Amur tigers (P. tigris altaica) tested negative for antibodies to B. henselae (72,73), but two of five Far Eastern leopards from that area had antibodies against B. henselae (73).
Limited information exists about Brucella in the wild cats of the genus Panthera. During the investigation of Brucella infection in the human, livestock and wildlife interface in the Katavi-Rukwa ecosystem in Tanzania, Assenga et al. (130) found one of the two tested lions serologically positive for Brucella at a titer 1:200 by three different tests (RBPT, BAPA, and Riv.T). In a 1968 study in Tanzania, Sachs et al. (116) found two of 13 lions had antibodies to Brucella species by tube agglutination test. De Vos and Van Niekerk (131) were not able to detect Brucella antibodies in four lions from the Kruger National Park, South Africa. Furtado et al. (132) tested serum samples from 31 free-ranging jaguars (P. onca) from Brazil using Br. abortus as antigen and reported antibodies in one jaguar.

Genus Puma
Two Bartonella species were cultured from mountain lions (P. concolor) (55). Bartonella antibodies were found in mountain lions from Arizona, California, Idaho, Oregon, Texas, Wyoming, and Florida in the U.S. (17,68,69,78,79). All 24 free-ranging Florida panthers (P. c. coryi) were seronegative for Brucella (134). Reports of Brucella in populations of pumas from elsewhere in the Americas were unavailable.

Genus Acinonyx
The cheetah (A. jubatus) is only member of its genus. Kelly et al. (63) reported isolation of B. henselae genotype II from an African pet cheetah from Zimbabwe. In 2016, Molia and colleagues (61) isolated Bartonella bacteria from blood of 5.9% (1/17) Namibian cheetahs, and the cheetah was infected with a previously unidentified Bartonella strain. The Namibian cheetah strain was close but distinct from isolates from North American wild felids and clustered between B. henselae and B. koehlerae; it was claimed to be a new subspecies of B. koehlerae (61). The same study documented that 23% of the 73 animals were positive for Bartonella DNA by PCR and 31% (23/74) of cheetahs had antibodies to B. henselae. No reports on Brucella infections in the cheetah were found.

Genus Lynx
Those are medium-sized cats represented by four species: Canadian lynx (Lynx canadensis), Eurasian lynx (L. lynx), Iberian lynx (L. pardinus), and bobcat (L. rufus). Chomel et al. (55) isolated two Bartonella species (B. henselae and B. koehlerae subsp. bothieri) from bobcats in California, U.S. A high prevalence of Bartonella antibodies (22.4-74.0%) was reported in bobcats from California, Colorado, Florida, Nevada, and Oregon in the U.S. and from Mexico (17,56,68,69). In northwestern Mexico, a Bartonella genotype was found in a flea P. simulans collected from a bobcat, but not in the blood of that animal (67). B. henselae DNA was found in 16 of 75 (21.3%) blood samples of Iberian lynx from southern Spain (57).
Antibodies against Brucella species in bobcats were reported in two studies: Br. abortus at 6.6% (5/75) in California (127) and Br. canis at 33% (1/3) in Texas (115). Serological investigations of bobcats from Alabama, Texas, and Utah in the U.S. did not result in identification of antibodies to Brucella (126,128,129). Tessaro (125) reported the absence of Brucella bacteria and anibodies in Canadian lynx.

Genus Leopardus
These are small spotted cats mostly native to Middle and South America. Representatives are the ocelot (L. pardalis), the little spotted cat (L. tigrinus), Geoffroy's cat (L. geoffroyi), and the margay (L. wiedii). Antibodies to B. henselae were reported in the ocelot (1/1) and the little spotted cat (2/2) in Brazil (60). A Bartonella sequence similar to B. koehlerae and B. henselae was detected in the captive margay in Brazil (235). The animal was born in the wild and lived in captivity prior to sampling, thus it is not possible to ascertain if the infection was acquired in the wild or in captivity. The authors claimed this animal exhibited clinical signs of bartonellosis: episodes of accentuated weight loss, dullness, dehydration, and anemia (235). The main reason why we have included the case of captive margay into our review is that the identified strain was different from all strains described in domestic and wild felines.

Genus Prionailurus
This is a genus of small spotted wild cats native to Asia. The genus includes the Iriomote cat (P. iriomotensis) and the Tsushima leopard cat (P. bengalensis euptilura), both endangered in Japan. A molecular epidemiologic survey in Japan resulted in identification of B. henselae in 6% (2/33) of Iriomote leopard cats and B. clarridgeiae in 8% (1/13) of Tsushima leopard cats (75). In the following study, four ixodid ticks collected from Tsushima leopard cats were PCR positive for B. henselae (74).

Genus Felis
The European wildcat (F. silvestris silvestris) is a subspecies of the same species that includes domestic cats (F. s. catus). This species is found in forest habitats of Europe. There are two reports of the presence of Bartonella in wildcats from Spain.

Family Viverridae
The most common species are civets and genets widely distributed in South and Southeast Asia, Africa, and Southern Europe. The first evidence suggesting that civets can host Bartonella came from a description of a human cat scratch disease case reported in 2001 in Japan. In the case, a patient scratched by a masked palm civet (Paguma larvata) developed fever and inguinal lymphadenopathy with a high antibody titer (1:1,024) to B. henselae (237). Later, Sato et al. (82) cultured B. henselae from blood of one of 50 masked palm civets collected in Chiba Prefecture of Japan. The level of bacteremia was high (7,000 bacteria per 1 mL of blood). Importantly, the multilocus sequence type detected from the isolated strain revealed a unique genotype. Though the prevalence of Bartonella in cats in Chiba prefecture was 5%, the same genotype had never been found in any B. henselae strains from cats from the same and other prefectures (82). Bartonella DNA was detected in another Viverridae species, the common genet (Genetta genetta). Reports of Brucella testing among viverrids are nearly nonexistent. No Brucella antibodies were found in two common genets (G. genetta) and three Cape genets (G. tigrina) from eastern Africa tested by tube agglutination test (116,136).

Family Herpestidae
Mongooses is the common name for the weasel-like small carnivores that live in southern Asia, Africa, and southern Europe, and are introduced to some other areas. We have information about Bartonella in one species of this genusthe small Asian mongoose (Herpestes javanicus). The only additional report of investigation of mongooses was from testing a single Egyptian mongoose (Herpestes ichneumon) in Algeria and the PCR test was negative (80).

Family Hyaenidae
The family contains four species of hyenas and phylogenetically belongs to the suborder Feliformia despite the dog-like appearance of these animals. The only available report on testing hyenas for Bartonella is from a molecular survey of 19 spotted hyenas (Crocuta crocuta) from two sites in Zambia with no positive results (70).
Serological observation of 15 spotted hyenas from Tanzania resulted in detection of antibodies against Brucella in four out of 15 (27%) animals (116). In the prior study, Sachs and Staak (135) found Brucella species exposure in two out of four hyenas in Tanzania. Another serological study did not detect Brucella antibodies in two spotted hyenas from the Kruger National Park in South Africa (131).
Most reports of Brucella infections in canids are based on detection of antibodies. Serologically positive coyotes were identified from California and Texas, U.S. (115,117,127,128,142). In wolves, evidence of Brucella infections also included Brucella isolations in Canada and Russia (13,125). Brucella was found in two jackal species: 1.9% (4/216) of golden jackals (C. aureus) in Serbia were positive for Br. canis by PCR (137) and 43% (3/7) of black-backed jackals (C. mesomelas) in Tanzania were seropositive for Br. abortus by tube agglutination test (116).

Genus Vulpes
There are more reports on detection of Bartonella in red foxes (V. vulpes) than in any other species of wild carnivores. Bartonella DNA was identified in red fox tissues from Australia, Austria, France, Israel, Spain, and U.S. (64,77,83,85,88,103,105). Most sequences were identified as B. vinsonii subsp. berkhoffii and B. rochalimae. Out of two red foxes positive for Bartonella DNA in Israel, one harbored DNA sequences that were 100% identical to B. rochalimae and the other was positive for Candidatus B. merieuxii (85) There are several reports about screening of ectoparasites from red foxes. DNA of a Bartonella strain, closely related to B. rochalimae, was found in fleas (Pulex irritans) from red foxes in Andalusia, Spain (65). PCR tests detected B. clarridgeiae and B. henselae in 20/34 and 4/34 fleas (Ctenocephalides felis), respectively, from red foxes in Australia, where it is an introduced species (105). Sréter-Lancz et al. (106) found Bartonella DNA in 4.2% (4/95) pools of fleas (P. irritans) from red foxes in Hungary, but all ticks from foxes were negative.
Similarly, there are numerous reports of Brucella infections in red foxes in Austria, Canada, Ireland, Russia, the U.S., and the UK (115,125,(159)(160)(161). Tessaro (125) cultured Br. abortus from red foxes in Canada. Morton (48) cultured Br. suis biovar 4 from three out of 38 red foxes from Alaska. Scholtz et al. (161) cultured Br. microti and the proposed novel species Br. vulpis from red foxes in Austria in 2016. Br. suis biovar 4 cultures were obtained from arctic foxes from Alaska and Russia (11,13,48). McCue and O'Farrell (158) conducted a serological survey of San Joaquin kit foxes in California, U.S. and reported antibodies to Br. abortus in 8% in 1981-1982 and 3% in 1984 and to Br. canis in 14% in 1981-1982 and none in 1984.

Genus Cerdocyon
Investigators tested another fox species, the crab-eating fox (Cerdocyon thous), in Brazil and found B. rochalimae DNA in all nine P. irritans fleas collected from one animal (92). In another study by De Sousa et al. (66), none of the 78 sampled crab-eating foxes showed presence of Bartonella DNA in blood samples by qPCR.

Genus Urocyon
This genus contains two species of Western Hemisphere foxes: the gray fox (U. cinereoargenteus) and closely related island fox (U. littoralis), which is a dwarf cousin of the gray fox (239).There is a comprehensive study of Bartonella in gray foxes in northern California, U.S., conducted by Henn et al. (58). A novel B. clarridgeiae-like bacterium was isolated from 22 (42%) of 53 gray foxes and B. vinsonii subsp. berkhoffii from five gray foxes (9.4%). Serology showed that 48 gray foxes (89%) had detectable antibodies against Bartonella. The authors made the conclusion that the high prevalence of bacteremia and seroreactivity in gray foxes suggests that they may act as a reservoir species for the B. clarridgeiae-like species in this region. In another study of gray foxes in northern California, 14 (64%) of 22 foxes were infected with Bartonella species at one or more of the capture dates (97). Fleas collected from gray foxes in the study were identified as P. simulans, and 39% of the fleas were PCR positive for Bartonella, with B. rochalimae and B. vinsonii subsp. berkhoffii identified in 81% and 19% of the PCR positive fleas, respectively.
A culture of Br. abortus was obtained from one gray fox (U. cinereoargenteus) from Alabama, U.S. (126) while there were no positive results in foxes of this species in Arkansas, Florida, and South Carolina, U.S. (115,156).

Genus Lycalopex
Several investigations of the South American foxes for Brucella infection have been published, including those investigating the pampas gray fox (L. gymnocercus) and Patagonian gray fox (L. griseus). Szyfres and González Tomé (154) found evidence of Brucella in both species from Argentina and isolated B. abortus biovar 1 from a pampas gray fox.

Genus Nyctereutes
The DNA identified as B. henselae was detected in spleens of two out of 142 raccoon dogs (N. procyonoides) in Korea, but not in any of 51 blood samples tested (94).

Family Ursidae
We found research on Bartonella and Brucella in three bear species, namely black bear (U. americanus), brown bear (U. arctos), and polar bear (U. maritimus). Bartonella DNA was not detected in seven black bears from Colorado, U.S. (77). All other research was focused on Brucella in bears (119,147,148,179,180,(182)(183)(184)(185). Despite high seroprevalence levels for Br. abortus antibodies in all investigated bear species, we could not find any report on successful isolation of Brucella from these animals. Serological tests of 61 black bears for Br. canis by Bronson et al. (178) were negative.

Family Mephitidae
Twelve skunks of two species, the hooded skunk (Mephitis macroura) and the striped skunk (M. mephitis), from Colorado, U.S., and Mexico were found infected with B. rochalimae and one skunk from Mexico was infected with B. vinsonii subsp. berkhoffii (67,77).

Family Procyonidae
The common raccoon (Procyon lotor) has a natural range from southern Canada to Panama. Of 37 raccoons trapped on St. Simon Island in Georgia, U.S., 12 were positive for B. henselae and one for B. koehlerae (59). Interestingly, raccoons from the western regions of the U.S. carried different species of Bartonella. Two Brucella strains cultured from raccoons from Alabama were identified as Br. abortus biovar 1 (126,177). Raccoons seropositive to Brucella species were found in California, Alabama, Florida, and Texas in the U.S. (115,(126)(127)(128). None of 63 raccoons from Nebraska, U.S., had antibodies to Br. canis (139). In South Korea, Brucella DNA was found in blood (1/9) and tissues (2/5) of introduced raccoons (172). Three (8.8%) of 34 brown-nosed coatis (Nasua nasua), which also belong to family Procyonidae, were serologically positive for Brucella in the Brazilian Pantanal (149).

Family Mustelidae
Mustelidae is the largest family in the order Carnivora. Many terrestrial species of this genus were tested for Bartonella,  Table 1). However, out of 16 mustelid species tested for Bartonella DNA, only two cultures were obtained: one from a Japanese badger (Meles anakuma) and another from a Japanese marten (95). The isolate from the marten was close to Bartonella washoensis, a species typically found in squirrels, suggesting that it could have potentially "jumped" from a squirrel to its natural predator. The isolate from the Japanese badger was unique, with the closest match being to B. clarridgeiae and B. rochalimae (95). Bartonella clarridgeiae or related sequences were also detected in a beech marten and in European badgers, all from Spain (64,83).
In North Carolina, U.S., Chinnadurai et al. (109) revealed a novel Bartonella species in 19 (29%) of 65 tested river otters (Lontra canadensis). Bartonella infection was detected in 45% (23/51) and 10% (3/30) of heart valves of northern and southern sea otters (Enhydra lutris kenyoni and E. l. nereis), respectively, by PCR (108). Analysis of the Bartonella ITS region identified two Bartonella species in those animals: a novel species closely related to Bartonella washoensis and Candidatus B. volans, whereas another genotype was molecularly identical to B. henselae. Sera from 50% of necropsied and 34% of presumed healthy, live-captured northern sea otters and in 16% of necropsied southern sea otters contained antibodies against Bartonella species (107).
Antibodies against Brucella species were detected in the American badger (Taxidea taxus), American mink (Neovison vison), European mink (Mustela lutreola), Eurasian otter (Lutra lutra), wolverine (Gulo gulo), and northern, southern and Asian sea otters (Enhydra lutris keyoni, lutris, nereis) from Europe, Asia, North and South Americas (11,124,125,127,174). We found only one report of successful culturing of Brucella (Br. abortus) from terrestrial mustelids (farmed European mink) and only one report of PCR detection of Brucella DNA in tissues of Asian badger (Meles leucurus) (172,240). Similar to Bartonella, sea otters carry different species of Brucella than terrestrial mustelids. Investigating rectal swab samples of Asian sea otters (E. l. lutris) from Russia (168) found DNA of three Brucella species (Br. abortus, Br. melitensis, and Br. pinnipedialis). Miller et al. (169) isolated marine Brucella from a southern sea otter (E. l. nereis) with osteolytic lesions that was stranded on the central California coast. Antibodies to Brucella were detected in Northern sea otters (E. l. keyoni) from Alaska in the U.S. and Russia (120).

Families Phocidae, Otariidae, and Odobenodae
There is only one report on the identification of Bartonella in any of the pinnipeds, including walruses, eared seals, and true seals. Morick et al. (112) tested spleen samples and seal lice (Echinophtirius horridus) collected from seven harbor seals (Phoca vitulina). One spleen of 48 tissue samples and one of six lice pools were positive. The Bartonella species identified in the spleen and lice were found to be identical to each other by two genetic loci. One genetic marker identified the genotype as B. henselae, while another marker indicated 97% sequence similarity with B. grahamii.
In contrast to Bartonella, there is abundant evidence of Brucella infections in various species of the clade Pinnipedia. In family Phocidae (true seals), cultures of Brucella species were obtained from hooded seals (Cystophora cristata), gray seals (Halichoerus grypus), ringed seal (Phoca hispida), harp seal (Pagophilus groenlandicus), and harbor seal (Ph. vitulina) (170,171,206,208,214,223,224,226,231,233). All identified cultures from true seals were Br. pinnipedialis. Serological evidence of Brucella was reported from investigation of even more species of true seals, including the bearded seal (Erignathus barbatus), There are multiple reports of Brucella antibodies in fur seals and sea lions of the family Otariidae-nine species of the genera (Arctocephalus, Callorhinus, Eumetopias, Neophoca, Phocarctos, and Zalophus) ( Table 2).

DIFFERENCES IN DISTRIBUTION OF BARTONELLA AND BRUCELLA SPECIES IN WILD CARNIVORES
Carnivores have regular exposure to both Bartonella and Brucella bacteria through predation on pathogen hosts, scavenging, and arthropod vectors. As with plague caused by Yersinia pestis (241), testing one carnivore for Bartonella and Brucella species could be equivalent to sampling a large number of its prey animals and give an idea of the epidemiological situation in the local environment. Overall, both Bartonella and Brucella are common in wildlife. Our review demonstrated numerous reports of infections caused by bacteria of both taxa in wild carnivores. We analyzed over 170 Bartonella and Brucella studies covering 109 species and subspecies of carnivores ( Table 3). Eighty-four species of carnivores were tested for Brucella and 79% of these species were found positive by serological, bacteriological, or molecular methods. Out of 51 species examined in Bartonella studies, 71% tested positive.
Although no species of wild carnivores were tested for both pathogens in a single study, 26 species were tested for both pathogens in different studies. Of those, 15 (58%) species were positive for both Bartonella and Brucella (among them bobcat, African lion, golden jackal, coyote, wolf, foxes, striped skunk, sea otters, raccoon, and harbor seal), meaning these carnivores can harbor either pathogen or potentially both. We know that other mammalian groups [bats for example, (242)] can be co-infected with Bartonella and Brucella species, and we speculate that this is also possible in carnivores, a hypothesis that definitely needs more investigation.
The most commonly identified Bartonella species was B. henselae, which was found in at least 23 species of wild carnivores, followed by B. rochalimae in 12, B. clarridgeiae in ten, and B. vinsinii subsp. berkhofii in seven species. Similarly, Br. abortus led the list of Brucella species, being identified in 36 terrestrial carnivore species, followed by Br. canis in eight. However, most of the reports are based on serology that cannot reliably discriminate these species until there are bacteriological data or sequences of PCR amplicons. Br. pinnipedialis is prevalent in marine carnivores, and some of the early reports of antibodies to Br. abortus in marine animals probably can be attributed to Br. pinnipedialis as well.
The analysis revealed some striking differences in distributions of these infectious agents in wild populations belonging to different carnivore families. One of the evident differences is abundance of several species of Bartonella practically in every explored species of wild felids. In contrast, very few reports of Brucella in the same species are available and those are limited to detection of antibodies that may indicate an exposure to the agent rather than direct involvement of these animals in the circulation of Brucella. At the same time, we could not find any report of Bartonella in bears while the presence of Brucella in these animals was well documented. An even more evident difference was found in marine carnivores, such as seals and sea lions, with practically every species reported infected with a specific species of Brucella (Br. pinnipedialis). In contrast, there is only one report of detection of Bartonella DNA in one tissue sample of a seal and there is no evidence of a Bartonella strain specific to marine mammals. A comparison with other marine mammals, such as dolphins, porpoises, and whales, which were not the subjects of our paper, also indicated a presence of specific Brucella species in blood of these animals, known as Brucella ceti. Whereas, the cat pathogen B. henselae was found in cetaceans, albeit less commonly than species of Brucella (243,244).
Prevalence and the spectrum of bacterial species present depends on a potential exchange of bacteria between domestic and wild terrestrial carnivores. Wild carnivores are often infected with the same pathogens as their domesticated relatives (cats and dogs) though the risk of exposure varies widely because of differences in biology, distribution, and historical interactions. Confirmation of the identity of the bacterial species, however, remains critical for making such a statement regarding host specificity. Using a rapid test for differentiation of Bartonella     (55). The authors who described the novel strains noted that these strains appear highly adapted to their particular species of wild cats and likely originated from a common ancestor.
There are some limitations in the analysis provided herein on the distribution of Bartonella and Brucella species in wild carnivores. The timing of samples collection for the animals listed in our review varied among studies and this factor could influence prevalence of infections. Differences in diagnostic methods used for identification can significantly affect comparison of the results. For a number of reasons, the number of Brucella studies relying on detection of antibodies in wild carnivores was much higher compared to the number of Bartonella studies in the same species that included either culturing or molecular detection. Several species of Brucella (Br. suis, Br. abortus, and Br. melitensis) are select agents and culturing of these species requires BSL-3 level capacity. Investigations of Brucella in wildlife started much earlier than similar investigations of Bartonella when DNA amplification techniques were not available. We should be carefull with interpretation of Brucella antibodies since available serological tests cannot identify all species of Brucella. There are separate tests for rough Brucella species (Br. canis) and for smooth Brucella species (Br. abortus, Br. melitensis, and Br. suis), and reported serology depends on the used tests.There are more described species of Bartonella (>35) and multiple diverse strains exist within this genus than for Brucella species. For many decades, the genus Brucella included six species, with some experts arguing that this genus is monospecific. In the past decade, new and more diverse Brucella species have been described (7). Recognition of the ubiquitous presence of Brucella in the environment will most likely continue (6). Nevertheless, reports of Brucella in wildlife without discrimination between species and biovars are still common, whereas future studies of Bartonella infections are more likely to be accompanied by proper identification down to species or subspecies level. Clearly, serological investigations are less informative for identification of bacterial species because of possible crossreactivity between different antigens. The analysis presented in this review demonstrates the need for more information on genetic polymorphism of bacterial pathogens for the purposes of making comparison of strains from domestic and wild carnivores.

EVOLUTIONARY ASPECTS
Another issue that may influence the choice of methods for discriminating among Bartonella species is the effective level of association between these bacteria and their mammalian hosts, ranging from host species to host genus (245). Presumably, such a close bacteria-host association relates to the long-history of coadaptation between Bartonella and their mammalian hosts and possibly arthropod vectors (245). An association of these bacteria with rodents, bats, and ruminants is described elsewhere, but analysis of the literature on Bartonella in wild carnivores also supports some degree of host-specificity (e.g., B. henselae in felids and B. vinsonii subsp. berkhoffii in canids).
A co-adaptation of Brucella with terrestrial wild carnivore hosts is not as straightforward as in domestic animals. A clear exception to this observation is Br. pinnipedialis, a species found in true seals only. Typical for domestic dogs, Br. canis may be expected to be commonly shared with wild canids, such as wolves and coyotes. However, this bacterial species has not been cultured from these predators and only few serological findings are available (115,128,139). Noticing the absence of Br. canis in wolves and coyotes, Moreno (7) proposed that this bacterial species evolved in the dog's ancestor after its predation on Br. suis biovar 4 infected animals (e.g., caribou/raindeer). This can be also explained by lack of specific serological tests available and low yield of culture.
Recent phylogenetic reconstructions and diversification analyses of prokaryotes have led to a better understanding of patterns of bacterial macroevolution. According to the analysis of prokaryote evolution based on the 16S rRNA gene (246), the common ancestor between the Brucella and the Bartonella genera split from the common ancestor with Phyllobacteriaceae in the order Rhizobiales about 567 million years ago and diverged about 507.4 million years ago (247) around the time of the Cambrian explosion and diversification of life during the Paleozoic Era, still on the giant supercontinent Pangea. As the species of the order Rhizobiales most closely related to Bartonella and Brucella are symbionts on plant roots, we can speculate that the ancestor of the two genera may have been a plant symbiont as well.
Bartonella evolved around 134 million years ago during Early Cretaceous Period around the time the flowering plants appeared in the middle of the dinosaur era (247). Segers et al. (248) suggest that the last common ancestor of the Bartonella was a gut symbiont of insects that produced its own amino acids and vitamins and that the adaptation to blood-feeding insects facilitated colonization of the mammalian bloodstream. Indeed, Bartonellaceae species were identified in honeybees (248,249) and ants (250) filling the gap between the pathogenic Bartonella clade and more ancient bacterial symbionts. The honeybee strains of B. apis form a clade basal to species of the genus Bartonella (249). However, the B. apis genomes are almost twice as large (2.6 to 2.9 Mb) as the ant symbionts, suggesting that the association with the bee is more recent or that the association is less intimate (251). The phylogenetic trees show that the ant-related bacterial clade is a sister group to bee-related clade and other mammal-related Bartonella species (249,252). Ants predate bees by some 35 million years in the order Hymenoptera which is 325 million years old itself (246). We can only speculate how the Bartonella ancestor adapted from a plant symbiont to gut symbiont through possible consumption routes and suggest looking into other "ancient" insect orders, like Archaeognata, or the orders that have maintained connection with water in their metamorphosis, like mayflies or dragonflies; and the ones that include sap-sucking insects.
Genomic and functional similarities between Br. suis and organisms from the Rhizobium Agrobacterium group suggest that the Brucella may have evolved from a soil plant-associated ancestral bacteria and speculatively, it may be metabolically active outside of a mammalian host (253). According to the analysis of prokaryote evolution based on the ribosomal gene, the genus Brucella is much younger than Bartonella and diverged about 230 thousand years ago (247) during Middle Pleistocene epoch. Previously it was hypothesized that Brucella species diverged roughly 20 million years ago following the divergence of their bovine and goat hosts (254). However, whole-genomebased phylogeny (255) supports the ribosomal gene analysis suggesting a much younger age for Brucella than previously estimated. Their rooted phylogeny suggests that brucellosis in various mammalian species emerged from infected sheep roughly in the past 86,000 to 296,000 years. This analysis has also suggested that transmittal of Brucella from pigs to canids likely happened within the past 22,500 years from infection of wolves or other canids feeding on pigs that were themselves infected (255). So, while possible paleo-brucellosis cases in the Bronze Age and later (256) fit perfectly within the timeframe, the possibility of brucellosis in a 2.5-million-year old hominid (257) brings an exciting prospect of an ancestral Brucella-like strain that either became extinct or has not been detected yet.

CONCLUSION
We can only speculate that a longer period of evolution of Bartonella has resulted in higher diversity and better co-adaptation to specific mammalian hosts compared to Brucella. Asymptomatic persistence of Bartonella bacteria in their natural reservoir animals contrasts with the welldocumented pathological manifestations of Brucella in host animals. The only until the present time association of Bartonella infection with fatal cases of clinical disease in wild carnivores was reported in Florida pumas (76). Three diseased pumas had spent time in captivity prior to being released in the wild and were found later exhibiting respiratory signs and reluctance to move. Autopsy findings included necrotizing interstitial pneumonia and suppurative myocarditis associated with B. henselae infection (76). There is much more information on pathology caused by Brucella in domestic animals than in wildlife in general and even less in wild carnivores. Describing a range of pathologies caused by Brucella in sea mammals, Foster et al. (208) listed subblubber abscesses, hepatic and splenic necrosis, macrophage infiltration in liver and spleen, possible abortion, epididymitis, and meningitis.
In spite of shared mammalian reservoirs, the difference in transmission cycles presents distinct ecological traits. While Bartonella species use arthropod vectors as a main mechanism for transmission between mammalian hosts, the role of arthropod vectors in transmission of Brucella remains disputed. In our review, we provided some data, mostly from Russian sources, which support a potential role of ticks and other arthropods in transmission of Brucella. Nevertheless, it is hard to argue that such means of transmission are significant, let alone dominant, in transmission of these bacteria. Commonly, wild terrestrial predators contract brucellosis through consumption of infective tissues during predation and scavenging (258). Considering potential modes of Brucella transmission between marine mammals, Foster et al. (208) also included social interactions, sexual activity, maternal transmission, physical trauma, ingestion during feeding, and carriage by parasites.
We realize that our analyses create more questions than answers; the current review brought up significant parallels and differences in Bartonella and Brucella ecologies in wild carnivores and we hope it will prove to be useful for a wide range of specialists and can stimulate interest in comparing the ecologies of Bartonella and Brucella in wildlife and, at a larger scale, in investigating ecological trends of phylogenetically related zoonotic agents; benefitting epidemiological research and wildlife conservation.