Anthrax is an important pathogenic disease caused by Bacillus anthracis, a zoonotic rod-shaped, Gram-positive, spore-forming bacterium (1–3). The history of anthrax dates to the 1870s; it was during this period that Robert Koch discovered the bacterium. Other researchers including Louis Pasteur, Élie Metchnikoff, Max Sterne, and Harry Smith, to mention a few, contributed immensely to the current understanding of B. anthracis, including its phagocytic characteristics, zoonotic nature, toxin production, and dispersal (1–3). Interestingly, B. anthracis has also been established as a bioweapon, and was used as such for the first time in the United States in an incident in 2001 when anthrax spores were mailed to certain government officials. This was the first recorded intentional use of a bacterium as a bioweapon and was associated with the infection of 22 people, including 12 mail handlers, and the death of five people (Antonio, 2013). B. anthracis is now classified as a tier 1 biological agent as there is a very high risk associated with its misuse and it has significant potential to cause mass casualties or have a devastating effect on the economy, critical infrastructure, or public confidence; therefore, it poses a severe threat to public health and safety (4, 5; Zacchia and Schmitt, 2001). This review aims to elucidate the different host, environment, and pathogen factors contributing to the persistence and spread of B. anthracis and the occurrence of anthrax in the environment. This is pertinent because of the current wave of anthrax across both developing and developed nations across the world. Furthermore, the persistence and possible increase in trends of global warming in complicating the (re)emergence of anthrax warrant an urgent need for public understanding of the dynamics of anthrax in the environment.

Bacillus anthracis exists in two distinct forms (phases), known as the vegetative and sporulated forms/phases (7). This is a unique attribute of B. anthracis, as it exists principally in the spore form in the environment, where it can be dormant without replication over a long time (15). The environmental maintenance of anthrax over a long time is the least understood part of its life cycle. Despite the integral role of the environment, knowledge about the survival and activity of B. anthracis outside a host is still limited.

Biofilms are complex, multicellular communities of microorganisms that attach to surfaces and are encompassed in a self-produced extracellular polymeric matrix, which mainly consists of proteins, nucleic acids, and polysaccharides (27, 28). A key feature of bacterial biofilms is their contribution to bacterial virulence through the promotion of survival and persistence in hostile environments, enhancing resistance to antimicrobial agents, and facilitating chronic infections (29, 30).

Bacillus anthracis has been reported to readily form robust biofilms both under both static and shear conditions (31–33). The United States Environmental Protection Agency (EPA) reported that biofilm formation is one of the mechanisms utilized by B. anthracis to remain persistent in the soil. Furthermore, it is an essential aspect of its lifecycle and virulence (EPA, 2014). These biofilms can resist several antimicrobial agents, making B. anthracis particularly challenging to eradicate, which is a property independent of its sporulation function (31). The capability to form biofilms allows the pathogen to persist in the environment, facilitating the cycle of infection.

Moreover, research has demonstrated that the interaction between B. anthracis and bacteriophages leads to the emergence of lysogens, which are phenotypically altered bacteria with significantly improved survival capabilities. These lysogens are associated with enhanced exopolysaccharide expression and biofilm formation, further intensifying the resilience and survival capabilities of B. anthracis in soil and also in anoxic earthworm guts (33, 34).

On a molecular level, Ser/Thr protein kinase (PrkC) plays a critical role in the formation of B. anthracis biofilms. PrkC phosphorylates the chaperon protein GroEL, promoting interaction with GroES and facilitating the assembly and disassembly of structures critical to biofilm formation. Notably, the disruption of the PrkC function compromises biofilm formation, signifying the importance of the molecular signaling in this process (35).

Genetic studies by Schuch and Fischetti revealed that the genes bcp25, bcp26, wip38, and wip39 were instrumental in inducing high-level exopolysaccharide expression, leading to enhanced biofilm formation. This relationship was particularly evident in Bcp1 and Wip4 infections, signifying a strong correlation between genetic factors and biofilm development (33). Biofilm formation serves as a pivotal strategy in B. anthracis virulence by augmenting its survival in hostile environments, enabling its resistance to antimicrobial agents, facilitating its persistent environmental presence, and, ultimately, contributing to the persistent and chronic nature of anthrax infections.

The environment, especially the soil, is currently known as the most important reservoir for B. anthracis. B. anthracis characteristically alternates between the dormant sporulated state in the environment and the vegetative replicating state in the host (7, 15). Specifically, an ideal soil is characterized by low-lying depressions, or eroded shallow and deep rich alluvial soils with high organic and calcium contents and a pH ranging between 6 and 8 serves as a suitable condition for the growth of B. anthracis (15, 36). These factors play key roles in the maintenance and persistence of B. anthracis for a long period of time because they increase its resistance to heat and desiccation (7). These climatic factors also serve as enablers of adequate host–pathogen–environment interaction. Sporulation occurs when the bacterium encounters free oxygen in the air, especially as exudates are released from dead or dying animals (15).

The phenomenon of global warming has the potential to exert an influence on the occurrence and dispersion of infectious diseases such as anthrax. However, it is crucial to acknowledge that this relationship is characterized by a complex and varied nature. The bacterial disease known as anthrax is predominantly caused by the microorganism B. anthracis. The occurrence of this disease is determined by a complex interplay of various elements, including environmental conditions, ecological dynamics, and human activities. The potential linkage between global warming and anthrax is worth exploring (37).

The potential impact of global warming on anthrax can manifest through the process of permafrost thawing. In certain geographical areas, spores of anthrax have been found to remain viable within frozen soil for extended periods of time, spanning several decades or even millennia. With the increase in temperatures leading to the thawing of permafrost, there is a possibility of the release of these spores into the surrounding environment, which might potentially result in the exposure of both wild and domestic animals to the disease (15). The phenomenon of global warming has the potential to induce modifications within ecosystems, which manifest as alterations in vegetation patterns, shifts in wildlife migration routes, and changes in the accessibility of water resources. The alterations have the potential to impact the dispersion of anthrax throughout wildlife communities, given that bacterial spores can persist in the environment and are consumed by herbivorous animals (15).

The process of increased animal stress can be attributed to the escalation of temperatures and alterations in climate patterns. The presence of stress in wildlife and livestock has been observed to have a detrimental effect on their immune systems, rendering them more vulnerable to many illnesses, including anthrax. This phenomenon has the potential to result in a higher frequency of breakouts within the regions that are impacted (38). The expanded range of disease vectors can be influenced by global warming, leading to changes in their distribution and behavior. These vectors include insects and other arthropods. Although anthrax is not primarily transmitted by vectors, alterations in the distribution and behavior of these species can have an indirect impact on the ecological dynamics of the illness (37).

The impact of human activities on land usage, such as deforestation and alterations prompted by global warming, can also result in increased proximity among humans, cattle, and wildlife that may serve as carriers of anthrax. The increased level of interaction between humans and wildlife has the potential to facilitate a greater occurrence of anthrax transmission from wildlife to both humans and domestic animals (7).

It is imperative to acknowledge that the dynamics of anthrax are influenced by a multitude of causes, with global warming being one of them. The management of land utilization, implementation of livestock immunization programs, and enforcement of public health measures are pivotal in effectively mitigating the transmission of the illness. Comprehending and effectively resolving the intricate relationship among climate change, ecological variables, and infectious illnesses such as anthrax is of utmost importance in formulating efficacious methods to alleviate their negative impacts on both animal and human populations.

Temperature and precipitation both contribute to the factors affecting the sporulation of B. anthracis spores at the onset of an outbreak with varying prolonged periods of hot, dry weather that are usually followed by heavy rains and flooding, or with the onset of rains ending a period of drought (15, 37, 39). The seasonal dynamics, human activities, and animal density play key roles in the occurrence of anthrax-related outbreaks, making anthrax a more complicated disease for humans and animals.

Global climate change has become increasingly concerning as it continues to change the dynamics of disease outbreaks, including the (re)emergence of diseases. Climate change, specifically in the form of dramatic temperature increases and extreme weather, impacts both the terrestrial and aquatic ecosystems, changing soil composition and nutrient availability, vegetation, distribution of both wild and domestic animals, and also animal density and movements (16, 38). The increasing number of climate-related stresses on the environment contribute to the change in the host–pathogen interactions, which consequently causes a change in disease dynamics. Anthrax is able to gain momentum, especially in most grasslands, because of the fragility and vulnerability of grasslands to the consequences of climate change (40, 41). The continual needs of the grasslands and the density of livestock, including their movement in search of pasture during scarcity, serve as a driver that increases the risk of exposure of naive cattle to anthrax (37, 39).

The presence of suitable pH and organic carbon alongside calcium further aids the germination of the anthrax spores while also contributing to optimal grassland ecosystems and agricultural cultivation (15; Gaitanis et al., 2015, Wall et al., 2015; 37). This type of environment, which naturally attracts a high density of livestock because of the numerous pastures/vegetation utilizable by livestock, serves as an important springboard for an increased risk of anthrax.

Increasing temperature anomalies have been linked to increased suitability for B. anthracis, and they also contribute to water stress (15). The divergence of temperature over the years, especially around the latitudes, is now known to change habitat suitability across intercontinental regions and contribute immensely to the emergence of diseases such as anthrax. The warming temperature trends not only change grassland diversity and increase livestock movement, but also increase the melting rate of permafrost in the Arctic, which in turn leads to the release of spores from dead frozen animals into the environment (42, 43). These spores then become available for livestock for ingestion, and they germinate and thus cause infection. On another note, the warming temperature in the arid shrubland in the middle or southern latitudes, especially in the summer, favors the dissemination of anthrax spores, particularly when there is intermittent precipitation (Gaitanis et al., 2015, Wall et al., 2015). Furthermore, the increasing temperature also affects the host by increasing disease immunocompetence, which eventually increases disease susceptibility in the host (44). This is due to the significant impact of stress on both the host’s immunity and the enhanced chains of disease transmission.

Climate change is undoubtedly a huge contributor to the trends currently predominantly caused by anthrax. The significant roles of temperature and consequential stressful environmental conditions, including water stress and grassland as drivers of anthrax in a population, could be a major reason for the (re)emergence of anthrax beyond the norm (16, 45). The impact of climate change on infectious diseases is indeed inexhaustible, especially for anthrax, the distribution of which is driven by salient environmental changes. Climate change complicates anthrax more because of the force with which it exerts changes on animal and human distribution and movement, the availability of foods and consequential increasing search for foods, and the increasing exposure of humans and animals to anthrax spores.

Bacillus anthracis poses a persistent threat to public health, animal populations, and national security. As we look to the future, several factors contribute to the ongoing concern surrounding B. anthracis. B. anthracis has been weaponized in the past and remains a potential bioweapon. Its ability to form highly resilient spores and the devastating impact of anthrax on human health make it an attractive option for bioterrorism (69).

The continuous monitoring of antimicrobial susceptibility patterns is essential, as B. anthracis may develop resistance to current treatment options. The emergence of drug-resistant strains could complicate disease management and limit effective therapeutic interventions. Bruce et al., 2021 identified 10 antimicrobial resistance genes (bla1, fosB, bla2, vmlR, mphL, cfrC, oxa-59, dfrG, tem-116, and bcll) in 356 genomes of B. anthracis from GenBank, which further corroborates the need for a more careful antimicrobial stewardship approach.

The persistence of B. anthracis spores in soil and animal remains presents a significant challenge (59). Environmental reservoirs allow the sporadic reemergence of anthrax, leading to sporadic outbreaks and potential zoonotic transmission, as spores can survive for more than 10 years in soil, which can trigger the reemergence of the disease many years after the death of the host (59, 70). Shifting climate patterns, including increased temperatures and extreme weather events, may influence the geographic distribution of B. anthracis. These changes could expand the areas conducive to anthrax outbreaks and introduce the disease to new regions.

The prevention of anthrax has been proven achievable through vaccination against the anthrax toxin components of the disease. The anthrax vaccine approved by the US Food and Drug Administration (FDA) is approved for use in three groups of adults aged 18 years to 65 years who may be at risk of encountering anthrax because of their job. The vaccine can be administered in two different situations: routine occupational use (before possible exposure) and post-event emergency use (after possible exposure) (21, 71–73). The prevention and management of anthrax necessitate the implementation of a multifaceted approach encompassing hygienic measures, surveillance, the avoidance of contact with diseased animals or contaminated substances, educational initiatives, heightened awareness, and the use of antibiotics. Anthrax is a pathogenic bacterial infection attributed to the microorganism B. anthracis. While its primary impact is observed in animals, it is also capable of infecting human hosts.

In terms of hygiene, when engaging in activities involving animals or their derived products, it is imperative to adhere to appropriate hygiene and safety protocols. This entails the utilization of protective attire, such as clothing, gloves, and masks, during the manipulation of items that may be contaminated. When ingesting animal-derived items such as meat, it is imperative to ensure that they are cooked completely so that any potential spores of bacteria are eliminated. It is also advisable to refrain from consuming raw or undercooked meat and dairy products, particularly those of uncertain origin.

For surveillance, it is important to establish and deploy a comprehensive surveillance system to identify and track the occurrence of outbreaks in both animal and human populations. The rapid identification of a condition or issue is crucial for prompt intervention, as is encouraging healthcare providers and veterinarians to promptly report any suspected instances of anthrax to the appropriate local health authorities.

For the act of refraining from making connections or engaging in interpersonal interactions, it is advisable to refrain from any form of interaction with animals that are infected. It is important to avoid handling or having close proximity to animals that are unwell or deceased, particularly when there is suspicion of their having anthrax. It is also advisable to refrain from contacting soil or materials that may be contaminated and to exercise caution when working in regions where diseased animals have been present or when handling substances such as bone meal or animal hides that could potentially harbor anthrax bacteria.

Public awareness campaigns are important because they disseminate information to the general population, particularly in regions where anthrax is prevalent, regarding the potential hazards linked to the disease and effective preventive measures against it. It is imperative to ensure that healthcare practitioners possess comprehensive knowledge on the clinical manifestations of anthrax and the corresponding treatment guidelines.

It is important to note that anthrax is a very uncommon occurrence in numerous regions across the globe, and the appropriate preventive actions may differ depending on the local prevalence and associated risk factors. It is therefore advisable to seek information from local health authorities and specialists regarding region-specific measures for the prevention and control of anthrax. Moreover, it is imperative to adhere to the prescribed vaccination schedules for livestock in regions where anthrax poses a recognized threat to mitigate the occurrence of animal outbreaks, hence diminishing the potential for human exposure to the disease.

To mitigate the bioweapon threat posed by B. anthracis, it is crucial to implement comprehensive measures aimed at prevention and preparedness. It is also recommended that the security measures and regulations for handling and storing B. anthracis cultures and spores are enhanced. Strict control and oversight should be enforced to prevent unauthorized access and theft from laboratories or research facilities. In addition, implementing robust surveillance systems to monitor the acquisition, transport, and potential misuse of B. anthracis to enable the timely detection of suspicious activities and effective sharing of intelligence among relevant agencies is vital.

Additionally, it is important to provide comprehensive training to laboratory personnel on biosafety practices, including the proper handling, storage, and disposal of B. anthracis and when doing so, it is important to lay emphasis on the need to strictly adhere to biosafety protocols and conduct regular risk assessments. It is also recommended that the public are educated about anthrax, its transmission, and the signs and symptoms associated with it. Promoting awareness campaigns to encourage the reporting of suspicious activities and emphasize the importance of early detection and response would also be advisable.

Fostering international collaboration and information sharing to prevent the proliferation of B. anthracis bioweapons and strengthening diplomatic efforts and engaging in multilateral agreements to ensure global cooperation in biodefense is also crucial. However, implementing these recommendations requires a coordinated effort among governments, law enforcement agencies, public health authorities, and research institutions. By prioritizing prevention and preparedness measures, we can enhance our ability to mitigate the potential bioweapon threat posed by B. anthracis.

Despite significant advances made in the detection, prevention, and treatment of infections caused by it, B. anthracis remains a global concern. Vigilance in biodefense, continuous surveillance, and research into new therapeutic strategies are imperative to mitigate future threats posed by this pathogen. Collaborative efforts across disciplines, international borders, and public health agencies will also be vital for effective preparedness and response to B. anthracis-related risks in the coming years.

SO: Conceptualization, Writing – original draft, Writing – review & editing. MO: Conceptualization, Writing – original draft, Writing – review & editing. KF: Conceptualization, Writing – original draft, Writing – review & editing. ATA: Writing – original draft, Writing – review & editing. OCA: Writing – review & editing. AA: Writing – review & editing. BO: Writing – review & editing. AB: Writing – review & editing. ML: Writing – review & editing. OA: Writing – review & editing. EC: Writing – review & editing.