Primates and infectious disease
Primates, both human and nonhuman, share a complex relationship concerning infectious diseases, characterized by the potential for cross-species transmission. This occurs through various pathways, including hunting, butchering, and direct contact, leading to significant health implications for both groups. A notable example is the transmission of the HIV virus from chimpanzees to humans, which has resulted in a global AIDS pandemic with over 40 million fatalities. In contrast, diseases such as Ebola primarily affect nonhuman primates and can spill over to humans through similar interactions, although they do not sustain human-to-human transmission.
The increasing overlap between human populations and primate habitats, exacerbated by activities like deforestation and bushmeat trade, heightens the risk of disease exchange. Moreover, human diseases, such as polio and respiratory viruses, can severely impact primate populations, contributing to conservation challenges. The fragmentation of tropical forests and the rise of ecotourism further complicate the dynamics between humans and primates, as they increase the frequency of encounters. Understanding these transmission pathways is crucial for conservation efforts, public health education, and preventing future pandemics, emphasizing the need for a respectful coexistence between humans and primates in shared environments.
Primates and infectious disease
Definition
Human primates can infect or be infected by nonhuman primates through a complicated and not completely understood process of pathogenic (parasitic, fungal, bacterial, viral) transmission from animal to human or human to animal. The widely similar physiologic and genetic characteristics shared by the two species support a susceptibility that can lead to cross-species transmission.
Nonhuman-to-Human-Primate Transmission
In ancient times, the contamination of humans by nonhuman primates through hunting or the sharing of water carried a threat to humankind that was quite small compared with the relatively recent pandemic of human immunodeficiency virus (HIV) infection, which leads to AIDS (acquired immune deficiency syndrome). Beginning about one hundred years earlier in Cameroon, Africa, HIV was transmitted, in the form of a chimpanzee virus, to the blood of a hunter who butchered the animal and ate its meat. First recognized in 1981, statistics published by UNAIDS in 2024 stated that AIDS has killed roughly 42.3 million people worldwide. No cure exists, though; antiretroviral therapies taken once a day can lead to a person infected with HIV/AIDS to suppress the virus to undetectable levels.
The Ebola virus, although frequently reaching epidemic levels through accidental human contact or through unsanitary medical care, can be traced to individual contact involving hunting, butchering, or eating nonhuman primate bushmeat (meat from forest animals), which also is linked to monkeypox and simian foamy virus. However, the Ebola virus, unlike HIV, cannot establish itself through human transmission and dies after a few cycles.
Transmission can also occur between nonhuman primates and persons who care for them in zoos and related settings. Other persons in danger of infection are those who have nonhuman primate pets.
Human-to-Nonhuman Primate Transmission
As human and nonhuman primates share a pathogenic susceptibility that can lead to the transmission of nonhuman diseases to humans, this same susceptibility promotes the transmission of human diseases to nonhuman primates in the wild. As disease transmission from nonhuman primates to humans portends dire human health issues, the transmission of disease from human to nonhuman primates also exacts a heavy toll on the health of nonhuman primates; ill health also affects animal conservation.
Increased contact between human and nonhuman primates, accomplished largely through the rise in human populations, adds to the number of wild primates eliminated through the deadly diseases transmitted by humans. Poliomyelitis (polio), a human disease, is one of the most lethal to chimpanzees, as is a variant of human paramyxovirus, which causes respiratory diseases in humans and leads to death in chimpanzees. Ebola virus, yellow fever virus, intestinal parasites, and a respiratory virus linked to the measles virus, all thought to be of human origin, kill apes. Mountain gorillas are especially vulnerable to respiratory diseases transmitted to them by a growing human population engaged in the habituation of apes for research and ecotourism (such as gorilla watching).
Deforestation and Climate Change
The shared habitat of nonhuman primates and humans that existed for centuries has changed. Home to wild primates, tropical forests are being destroyed by road-building and logging, for example, which increases the human population and devastates primate populations, degrading the environment and natural primate habitats. The fragmented tropical forests and increased human populations in these habitats have widened the interface between primates and humans, creating increased health risks to both primates and humans.
Aided by these new logging roads, subsistence hunting, which had maintained indigenous peoples for centuries, is being replaced by the business of primate meat export. Hunters now supply bushmeat to local eateries, and primate meat is sold to distributors in cities, where the meat is sold at a premium. Cross-species transmission has become a special concern, as nearly thirty different species of primates are killed, butchered, and eaten. The enormous number of contacts with animal blood and bodily fluids easily promotes disease transmission. Also, widely accessible air travel provides a network of potentially infected persons who move around the world and infect others.
Impact
Understanding the basis of primate transmission of infectious disease allows for the much-needed conservation of wild primates, educating persons about the consequences of butchering and eating primate meat, improvements to the health of primate communities in the grasp of human-made changes in land use (that threaten primate existence), and stopping pandemics before they begin.
Bibliography
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"HIV." World Health Organization (WHO), July 2022, www.who.int/data/gho/data/themes/hiv-aids. Accessed 4 Feb. 2025.
Huffman, Michael, and Colin Chapman, eds. Primate Parasite Ecology: The Dynamics and Study of Host-Parasite Relationships. New York: Cambridge University Press, 2009.
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