Guinea-Bissau is a West African country with a diverse ethnic, cultural and religious history. Cantanhez NP is inhabited mostly by Balanta people, as well as the Nalu, Fulani and Sussu, among many others (Catarino and Palminha, 2018). Over the past decades, populations from different ethnic groups have been moving to this region, mainly from the Republic of Guinea (Temudo and Abrantes, 2014; Parathian et al., 2018). Land use at Cantanhez has changed over time, with the flooded rice culture developed by the Balanta now widely practised (Temudo, 2009). Small-scale production of mango and citrus trees once allowed the natural vegetation to be maintained, with limited deforestation (Temudo, 2009), but from the 1980s onwards the installation of cash fruit crops, including cashew, transformed the landscape for people and wildlife (Temudo and Abrantes, 2014; Havik et al., 2018). With the widescale introduction of fruit crops, frugivores including the chimpanzee, have gradually incorporated these new food sources into their diets, changing the nature of their interactions with people (McLennan and Hockings, 2014; Bessa et al., 2015).

In symbolic and political terms, the inhabitants of Cantanhez NP are divided between the “owners,” the Nalu, founders of the territory, and “guests,” the population of other ethnic groups to whom the Nalu have given permission to settle there. The Nalu have an intricate relationship with the landscape and wildlife. According to Nalu' pre-Islamic ontology, all beings including supernatural entities, humans, animals and plants, form a system of relations (Frazão-Moreira, 2009, 2015). Within the Nalu territory there are sacred zones that are commonly referred by the Creole term “matu sagrado” (sacred forest). These forests are a landmark of ecological, political and cultural history. The underlying components of a pre-Islamic ontology combined with Muslim beliefs are key to understanding human–chimpanzee coexistence (Sousa and Frazão-Moreira, 2010; Costa et al., 2017). Nalu people have the general belief that all non-human species have reputed access to resources in ancestral lands and the Muslim aram prevents the killing and eating of any animal with canine teeth, including primates. The Nalu believe “dari i pekador” (the chimpanzee is human) and acknowledge the physical and behavioural similarities that chimpanzees and humans share (Sousa and Frazão-Moreira, 2010). Animist ontology guides local beliefs that non-human species exist either as true animals, or some other animal form transformed by “irãs” (supernatural beings), with humans and chimpanzees being able to shape-shift into each other's physical forms (Sousa et al., 2017, 2018). Acts perceived negatively by people (such as unprovoked attacks on local persons by chimpanzees) are sometimes attributed to people taking the form of chimpanzees.

In the 1990s, on the initiative of the Non-Government Organisations Acção para o Desenvolvimento, Tiniguena and Alternag, with the support of International Union for Conservation of Nature (IUCN), a project was set up to conserve the remaining forests in the Tombali region, which in 2011 led to the creation of the Cantanhez NP (Figure 1B). Since 2011, Cantanhez NP has been managed by the Institute for Biodiversity and Protected Areas (IBAP) following an IUCN Category V protected area, acknowledging that “the interaction of people and nature over time has produced an area of distinct character with significant ecological, biological, cultural and scenic value: and where safeguarding the integrity of this interaction is vital to protecting and sustaining the area and its associated nature conservation and other values” (IUCN, 2016). The local management committee (includes 35 people from 14 villages) actively participates in the management of Cantanhez NP which is divided into three zones, including the core zones, largely consisting of protected coastal forest blocks where hunting and logging activities are forbidden, buffer zones, where hunting by local residents is allowed but felling of large trees by residents is subject to permission from IBAP, and agricultural zones (Catarino and Palminha, 2018; IBAP, 2020).

Guinea-Bissau lies within the Guinean forest-savannah mosaics, a biodiverse ecoregion buffering the Guinean moist forests in the south and the West Sudanian savannah in the north (Figure 1A). The climate in Guinea-Bissau is characterised by a rainy season from mid-May to the end of October and a long dry season from November to mid-May. Cantanhez NP hosts a wealth of wildlife species. Six diurnal primate species are present in Cantanhez NP, including the western chimpanzee (Figure 1C), Temminck's red colobus (Piliocolobus badius temminckii), king colobus (Colobus polykomos), Guinea baboon (Papio papio), Campbell's monkey (Cercopithecus campbelli) and green monkey (Chlorocebus sabaeus). Cantanhez NP is also home to numerous ungulate species including buffalo (Syncerus caffer) and bushbuck (Tragelaphus scriptus), and biomonitoring efforts have recently confirmed the presence of rare and elusive species, including the African golden cat (Caracal aurata), giant pangolin (Smutsia gigantea) and in the North of the park, the African elephant (Loxodonta africana) (Supplementary Table 1).

As a large-bodied and socio-ecologically flexible species, chimpanzees are able to adapt to complex and dynamic environments, including human-impacted landscapes if they are not hunted (Hockings et al., 2015; Bersacola et al., 2021). At Cantanhez NP, humans and chimpanzees show substantial overlap in their use of space, and encounter each other regularly on roads, paths and around the edges of villages and agricultural areas. Humans and chimpanzees use at least 27 of the same wild fruit species, including oil palm (Elaeis guineensis), velvet tamarind (Dialium guineensis), and saba (Saba senegalensis) (Hockings et al., 2020), with chimpanzee use of space driven partly by the availability of oil-palm fruit (Bersacola et al., 2021). Although the Caiquene-Cadique community of chimpanzees in central Cantanhez NP use areas away from villages and agriculture more intensively, they optimise their foraging strategies when wild fruits are scarce by increasing their use of village areas with cultivated fruits (Bersacola et al., 2021). Despite beliefs that prevent people from hunting chimpanzees and consuming their meat, negative interactions between people and chimpanzees can occur over highly valued crops such as oranges and papaya, with chimpanzees chased and shot at by local people to keep them away from crops during fruiting seasons (Sousa and Frazão-Moreira, 2010). People are more tolerant of chimpanzees foraging on cashew pseudofruit, as the commercially valuable cashew nut remains unharmed. Farmers perceive that the chimpanzees leave cashew nuts in more manageable piles making harvesting easier (Hockings and Sousa, 2012).

As part of the Biodiversity and Health Monitoring Programme (BHMP), we established transect routes and camera trap sampling points across Cantanhez NP in December 2019 (Supplementary Figure 1). Transects and camera traps covered habitat types across the landscape mosaic, including secondary forest, woodland, mangroves, orchards, shifting cultivation fields, villages, roads and remnant forest strips dominated by oil palms. We carried out monthly transect surveys using Cybertracker and checked camera traps monthly. We conducted distance sampling along line transects and recorded chimpanzee nests, direct encounters with wildlife, and animal and human signs, following standardised protocols (Buckland et al., 2015).

As of March 2021, biomonitoring surveys consisted of 400 km of transect survey effort and 11,884 camera trap days across 13 protected forest blocks and surrounding agro-forest mosaics. Supplementary Table 1 shows the confirmed presence of all wildlife species recorded during surveys. Chimpanzees are distributed across the park, with nests recorded in 44% of the transects. Nests were observed more frequently across the central part of Cantanhez NP (86%, of total N of nest observations = 72), where sub-humid forest cover is more extensive compared to the drier savannah-woodland-forest mosaic in the northern part. We analysed camera trap data collected during the first biomonitoring season between January and July 2020 (7,514 camera trap days). We extracted 901 independent events for chimpanzees, defined as images or sequences of images at least 60 mins apart from the previous images of the same species at the same location. We employed Bayesian spatial modelling and extracted a prediction map for intensity of space use by chimpanzees across Cantanhez NP (Figure 3A, see figure caption for more details on the analysis).

We first observed clinical signs of leprosy in chimpanzees through the analysis of camera trap data in 2015. We then conducted molecular analyses of chimpanzee faecal samples and confirmed M. leprae as the causative agent of the lesions observed in chimpanzees (see Hockings et al., 2021, for details). From 2015 to 2021, we were able to determine the occurrence of advanced leprosy (multibacillary) in five chimpanzee communities across the park, with M. leprae likely transmitted between individuals within this population. We identified seven affected individuals (three adult females, two adult males and two adults of unconfirmed sex), and possible cases of leprosy in three other individuals. Advanced leprosy symptoms in chimpanzees include hair loss, plaques and nodules that cover different areas of their body (limbs, trunk and genitals), facial skin hypopigmentation, facial disfigurement as well as ulcerated and deformed hands (claw hand) and feet (Hockings et al., 2021) (Figure 3B). Paucibacillary cases in chimpanzees, where bacterial levels are low, can easily go undetected as minor physical manifestations of leprosy such as localised hair loss are challenging to observe on camera trap footage. Data collection using additional camera traps in affected chimpanzee communities, as well as faecal sampling for determining the prevalence of leprosy in chimpanzees are ongoing. These long-term data allow us to determine changes in physical symptoms displayed by individuals over time and any changes in community prevalence of the disease.

Guinea-Bissau is strongly dependent on agriculture and fisheries and is among the poorest countries on Earth, with 67% population living below $1.90 USD/day. The health sector in Guinea-Bissau suffers from a lack of financial and material resources, as well as a lack of specialised human resources (Guerreiro et al., 2017, 2018a,b; Russo et al., 2017; Guerreiro, 2019). The national health system is organised into three levels: central, regional and local (Supplementary Table 2). In 2017, 66% of the population did not have geographic access to services, i.e., they live beyond 5 km from the nearest primary health care delivery structure (Guerreiro et al., 2017). According to the latest available data, in 2016, the number of doctors stood at 1.3 per 10,000 people, and the number of nurses and midwifery personnel at 5.9 per 10,000 people (WHO, 2021b). At regional and local levels, there are also some health facilities under the responsibility of non-governmental, religious or other organisations.

The government of Guinea-Bissau has established sectoral action plans, following World Health Organization (WHO) guidelines. These include the Master Plan for the Control of Neglected Tropical Diseases in Guinea Bissau, which takes into consideration 13 priority diseases in Africa, including leprosy, and the National Tuberculosis and Leprosy Control Programme (MINSAP, 2014). Leprosy, according to the criteria of the WHO, is considered to be eliminated at the national level in Guinea-Bissau, because the number of patients on multidrug therapy is <1 case per 10,000 inhabitants (a value considered as the elimination target by the WHO). Nevertheless, leprosy is endemic with official figures showing between 50 and 70 new cases of leprosy detected each year (MINSAP, 2014). Importantly, not all cases of leprosy are identified; in its early stages the disease is easily confused with other conditions.

Cumura Hospital, located near Bissau, is the only health structure dedicated to the treatment of leprosy in Guinea-Bissau. It was founded in 1952 with the support of Catholic missionaries (particularly Italian Franciscan missionaries) to isolate leprosy patients, according to the medical knowledge of the time and the stigmatisation of the disease (Costa, 2010). Nowadays, the Cumura Hospital is managed by the Catholic Mission of Cumura and funded by the NGO AIFO (Amici di Raoul Follereau), following international scientific procedures concerning leprosy. Patients are mainly treated on an outpatient basis, although Cumura remains a permanent residence for some leprosy patients with disabilities. Beyond hospital work, the Cumura team has trained some nurses and community health agents. Cumura Hospital has treated patients from the Tombali region, although we do not currently have reliable counts of people with leprosy in Cantanhez NP. The population of Cantanhez NP locally receives support from “Type C” health centres (Supplementary Table 2), as well as from health facilities belonging to religious missionaries. If a patient with suspected leprosy is identified by a community health agent, the agent directs the patient to a “Type C” health centre. If treatment cannot be carried out there, the patient is directed to a “Type B” health centre at Cacine or Quebo, or to the Catió Regional Hospital. If a suspected leprosy case is identified, the patient should expect to be referred to Cumura Hospital.

Traditional medicinal systems are also present in Guinea-Bissau and are particularly important in contexts where the public health system is lacking or inefficient. In these systems, medicine cannot be dissociated from ontology and religious dimensions. In Cantanhez NP, there are various types of traditional healers: curandeiros (healers who can be from any ethnic group with different religions), djambakus (healers that perform divination and ritualised treatments based on traditional and pre-islamic Nalu beliefs), and marabouts (Muslim medicine-men). Healers have a refined knowledge of medicinal plants and treatments (Frazão-Moreira, 2009, 2016; Catarino et al., 2016). Patients consult these healers, seeking explanations for their health problem and its cure, either before going to the health centre or at the same time as consultations with nurses or doctors. Here, as in other parts of Africa, treatment itineraries are complementary and simultaneous, and are not culturally perceived as contradictory (Augé, 1984; Janzen and Green, 2003; Ribera, 2007).

COVID-19 and Ebola health campaigns are being conducted across Guinea-Bissau, including in Cantanhez NP. To avoid campaigning about another infectious disease, leprosy, and risking low engagement with local communities, we chose to develop a campaign to publicise One Health messages more broadly with leprosy used as one example of possible zoonotic infection. Delivering One Health concepts is complex; to reduce the risks of miscommunication regarding the disease threat posed by wildlife and the possible dangers to human health, we opted to reduce the geographical scale of the campaign to initially trial messages in selected villages. The focus on only six selected villages enables us to explore and identify effective ways to deliver One Health messages which will be incorporated into a One Health campaign strategy report for future application. Pre- and post-campaign interview questionnaires with participants from the selected villages will be used to evaluate changes in understanding of the links between environmental, animal and human health (see Measurable Indicator for Output 1, Figure 2 caption). Additionally, working alongside Cumura hospital and AIFO, we will involve health workers as well as local health agents and healers in clinical training to identify all stages of leprosy disease with clear instructions for the referral protocol.

The BHMP has achieved increased wildlife monitoring capacity in Cantanhez NP through intensive training of local staff in data collection, including deploying and maintaining camera traps, recording direct and indirect animal observations and measuring habitat type using datasheets, GPS and Cybertracker. Guinean researchers are trained in data entry, management and analysis to ensure the sustainability of the monitoring programme. To promote good practise, staff have received training in the necessary health precautions during data collection.

A One Health environmental management plan will promote healthy human–wildlife coexistence and strengthen multi-stakeholder decision-making capacity in Cantanhez NP. The plan aims to reduce possible risks of disease transmission within and between-species and to inform future management strategies, including replanting and re-organising chimpanzee food sources across risk areas to reduce spatial overlap and conflicts. Key wildlife habitat and corridors, as well as areas of high human–wildlife interactions and potential disease transmissions are identified (see Measurable Indicator for Output 3, Figure 2 caption) using data from the BHMP and participatory mapping. With additional GIS layers, including 2017–2021 vegetation cover and health landmarks (graded health centres, health units, healers), these data will help inform the development of the plan. Maps will be shown and discussed during meetings with local stakeholders, including the management committee, women's groups, farmers, and hunters. Maps will also be discussed with local people to identify aspects of human–wildlife interactions related to One Health that will need to be taken into consideration, such as sites where resources are shared (water points, cultivated foods). We use this opportunity to ask people to propose measures to minimise contact with wildlife. These meetings will be used to inform the content of the One Health environmental management plan.

An effective infectious disease response plan requires coordination, communication and collaboration amongst conservation and health stakeholders. An increase in multi-stakeholder knowledge of leprosy occurrence in humans in Cantanhez NP and how to respond to conservation conflicts over disease will be achieved through multi-stakeholder collaboration in developing a leprosy response plan. The plan will be developed from published literature, knowledge exchange between project partners, including consideration of the socio-political context in Cantanhez NP, and the revision and development of a communication chain from local to national level (Cumura Hospital) and WHO. To reduce the risk of pathogen transmission and increase scientific knowledge on other infectious diseases present in Cantanhez NP, the response plan also involves the development and implementation of a protocol for the handling and management of dead chimpanzees and other wildlife. The plan will involve establishing a communication chain for when animal carcasses are found in the forest or information is received about a retaliatory wildlife killing. Information will need to be shared from residents to park guards, and then to IBAP managers and the Cantanhez Chimpanzee Project. Carcass swabbing, which involves taking biological samples from a carcass by inserting a sterile swab into natural body orifices or wounds, will then be carried out exclusively by trained staff using the appropriate PPE (FFP3 mask, goggles, and gloves). A detailed protocol for data and sample collection, decontamination, and waste disposal will be followed.