Using physical contact heterogeneity and frequency to characterize dynamics of human exposure to nonhuman primate bodily fluids in central Africa

Emerging infectious diseases of zoonotic origin constitute a recurrent threat to global health. Nonhuman primates (NHPs) occupy an important place in zoonotic spillovers (pathogenic transmissions from animals to humans), serving as reservoirs or amplifiers of multiple neglected tropical diseases, including viral hemorrhagic fevers and arboviruses, parasites and bacteria, as well as retroviruses (simian foamy virus, PTLV) that are pathogenic in human beings. Hunting and butchering studies in Africa characterize at-risk human social groups, but overlook critical factors of contact heterogeneity and frequency, NHP species differences, and meat processing practices. In southeastern Cameroon, a region with a history of zoonotic emergence and high risk of future spillovers, we conducted a novel mixed-method field study of human physical exposure to multiple NHP species, incorporating participant-based and ecological methodologies, and qualitative interviews (n = 25). We find frequent physical contact across adult human populations, greater physical contact with monkeys than apes, especially for meat handling practices, and positive correlation of human exposure with NHP species abundance and proximity to human settlement. These fine-grained results encourage reconsideration of the likely dynamics of human-NHP contact in past and future NTD emergence events. Multidisciplinary social science and ecological approaches should be mobilized to generate more effective human and animal surveillance and risk communications around neglected tropical diseases. At a moment when the WHO has included “Disease X”, a presumably zoonotic pathogen with pandemic potential, on its list of blueprint priority diseases as, new field-based tools for investigating zoonotic disease emergence, both known and unknown, are of critical importance.Author summary: Animal diseases that infect humans are a major threat to human health. Nonhuman primates’ genetic relatedness to human beings makes them an important source of disease spillovers into human populations. The central African rainforest has witnessed many infectious spillovers from primates, including multiple neglected tropical diseases. Previous studies have focused on hunting and butchering of primates as risky practices that expose central Africans to their diseases. These studies have not investigated how different kinds and frequencies of contact or the abundance of different monkey and great ape species affect these risks. We examined these factors in southeastern Cameroon, conducting a social sciences study of human physical contacts with nine different primate species. We found that Cameroonian adults had frequent physical contact with primates, and more with monkeys than apes, especially through handling meat for butchering, marketing, and preparation. People also had more contact with more abundant primate species living closer to villages. National and international authorities should support improved surveillance of humans and abundant monkey species, as well as popular messages to promote safe meat handling practices. Multidisciplinary social science and ecological approaches should be used to improve surveillance and communications with forest populations about neglected tropical diseases.