Primates and primatologists: social contexts for interspecies pathogen transmission

Zoonotic pathogens in wild Asian primates: a systematic review highlighting research gaps

Introduction

Ongoing global changes, including natural land conversion for agriculture and urbanization, modify the dynamics of human-primate contacts, resulting in increased zoonotic risks. Although Asia shelters high primate diversity and experiences rapid expansion of human-primate contact zones, there remains little documentation regarding zoonotic surveillance in the primates of this region.

Methods

Using the PRISMA guidelines, we conducted a systematic review to compile an inventory of zoonotic pathogens detected in wild Asian primates, while highlighting the coverage of primate species, countries, and pathogen groups surveyed, as well as the diagnostic methods used across the studies. Moreover, we compared the species richness of pathogens harbored by primates across diverse types of habitats classified according to their degree of anthropization (i.e., urban vs. rural vs. forest habitats).

Results and discussion

Searches of Scopus, PubMed, and the Global Mammal Parasite Database yielded 152 articles on 39 primate species. We inventoried 183 pathogens, including 63 helminthic gastrointestinal parasites, two blood-borne parasites, 42 protozoa, 45 viruses, 30 bacteria, and one fungus. Considering each study as a sample, species accumulation curves revealed no significant differences in specific richness between habitat types for any of the pathogen groups analyzed. This is likely due to the insufficient sampling effort (i.e., a limited number of studies), which prevents drawing conclusive findings. This systematic review identified several publication biases, particularly the uneven representation of host species and pathogen groups studied, as well as a lack of use of generic diagnostic methods. Addressing these gaps necessitates a multidisciplinary strategy framed in a One Health approach, which may facilitate a broader inventory of pathogens and ultimately limit the risk of cross-species transmission at the human-primate interface. Strengthening the zoonotic surveillance in primates of this region could be realized notably through the application of more comprehensive diagnostic techniques such as broad-spectrum analyses without a priori selection.

Viruses in saliva from sanctuary chimpanzees (Pan troglodytes) in Republic of Congo and Uganda

Pathogen surveillance for great ape health monitoring has typically been performed on non-invasive samples, primarily feces, in wild apes and blood in sanctuary-housed apes. However, many important primate pathogens, including known zoonoses, are shed in saliva and transmitted via oral fluids. Using metagenomic methods, we identified viruses in saliva samples from 46 wild-born, sanctuary-housed chimpanzees at two African sanctuaries in Republic of Congo and Uganda. In total, we identified 20 viruses. All but one, an unclassified CRESS DNA virus, are classified in five families: Circoviridae, Herpesviridae, Papillomaviridae, Picobirnaviridae, and Retroviridae. Overall, viral prevalence ranged from 4.2% to 87.5%. Many of these viruses are ubiquitous in primates and known to replicate in the oral cavity (simian foamy viruses, Retroviridae; a cytomegalovirus and lymphocryptovirus; Herpesviridae; and alpha and gamma papillomaviruses, Papillomaviridae). None of the viruses identified have been shown to cause disease in chimpanzees or, to our knowledge, in humans. These data suggest that the risk of zoonotic viral disease from chimpanzee oral fluids in sanctuaries may be lower than commonly assumed.

Comparative Review of Antimicrobial Resistance in Humans and Nonhuman Primates

Antimicrobial resistance (AMR) presents serious threats to human and animal health. Although AMR of pathogens is often evaluated independently between humans and animals, comparative analysis of AMR between humans and animals is necessary for zoonotic pathogens. Major surveillance systems monitor AMR of zoonotic pathogens in humans and food animals, but comprehensive AMR data in veterinary medicine is not diligently monitored for most animal species with which humans commonly contact, including NHP. The objective of this review is to provide a complete report of the prevalences of AMR among zoonotic bacteria that present the greatest threats to NHP, occupational, and public health. High prevalences of AMR exist among Shigella, Campylobacter, and Yersinia, including resistance to antimicrobials important to public health, such as macrolides. Despite improvements in regulations, standards, policies, practices, and zoonotic awareness, occupational exposures to and illnesses due to zoonotic pathogens continue to be reported and, given the documented prevalences of AMR, constitute an occupational and public health risk. However, published literature is sparse, thus indicating the need for veterinarians to proactively monitor AMR in dangerous zoonotic bacteria, to enable veterinarians to make more informed decisions to maximize antimicrobial therapy and minimize occupational risk.

Rethinking Human-Nonhuman Primate Contact and Pathogenic Disease Spillover

Zoonotic transmissions are a major global health risk, and human-animal contact is frequently raised as an important driver of transmission. A literature examining zooanthroponosis largely agrees that more human-animal contact leads to more risk. Yet the basis of this proposition, the term contact, has not been rigorously analyzed. To understand how contact is used to explain cross-species spillovers, we conducted a multi-disciplinary review of studies addressing human-nonhuman primate (NHP) engagements and pathogenic transmissions and employing the term contact. We find that although contact is frequently invoked, it is employed inconsistently and imprecisely across these studies, overlooking the range of pathogens and their transmission routes and directions. We also examine a related but more expansive approach focusing on human and NHP habitats and their spatial overlap, which can potentially facilitate pathogenic transmission. Contact and spatial overlap investigations cannot, however, explain the processes that bring together people, animals and pathogens. We therefore examine another approach that enhances our understanding of zoonotic spillovers: anthropological studies identifying such historical, social, environmental processes. Comparable to a One Health approach, our ongoing research in Cameroon draws contact, spatial overlap and anthropological-historical approaches into dialog to suggest where, when and how pathogenic transmissions between people and NHPs may occur. In conclusion, we call for zoonotic disease researchers to specify more precisely the human-animal contacts they investigate and to attend to how broader ecologies, societies and histories shape pathogen-human-animal interactions.

Disease and Human/Animal Interactions

Understanding pathogen exchange among human, wildlife, and livestock populations, and the varying ecological and cultural contexts in which this exchange takes place, is a major challenge. The present review contextualizes the risk factors that result from human interactions with livestock, companion animals, animal exhibits, wildlife through nature-based tourism, and wildlife through consumption. Given their phylogenetic relatedness to humans, primates are emphasized in this discussion; primates serve as reservoirs for several human pathogens, and some human pathogens can decimate wild primate populations. Anthropologists must play a central role in understanding cultural variation in attitudes toward other species as well as perceived risks when interacting with animals. I argue that the remediation of emerging infectious diseases will be accomplished primarily through human behavioral changes rather than through efforts in pathogen discovery. Given the history of human interactions with wildlife, candid discussions on zoonotic diseases will be increasingly important for our combined survival.

Dental disorders in brown howler monkeys (Alouatta guariba clamitans) maintained in captivity

BACKGROUND

The aim of this study was to investigate dental disorders of brown howler monkeys maintained in captivity. The hypothesis is that the identification and diagnosis of the lesions may contribute to control and prevention.

METHODS

Sixteen intact brown howler monkeys (Alouatta guariba clamitans), eight females and eight males, weighing from 3.9 to 6.8 kg, were studied. Under general anesthesia, the teeth were evaluated by visual inspection, probing, palpation, and intra-oral radiographic exam. The findings were registered on a dental chart specific for primates.

RESULT

Of the 16 monkeys evaluated in the present study, 94% (n = 15) had some type of dental disorder. The lesions observed were dental calculus (88%), dental wear (81%), missing teeth (38%), gingivitis (19%), gingival recession (6%), dental fracture (19%), pulp exposure (19%), and dental staining (25%).

CONCLUSIONS

Alouatta guariba clamitans maintained in captivity have a high rate of dental problems.

New World simian foamy virus infections in vivo and in vitro

Foamy viruses (FV) are complex retroviruses that naturally infect all nonhuman primates (NHP) studied to date. Zoonotic transmission of Old World NHP simian foamy viruses (SFV) has been documented, leading to nonpathogenic persistent infections. To date, there have been no reports concerning zoonotic transmission of New World monkey (NWM) SFV to humans and resulting infection. In this study, we developed a Western blot assay to detect antibodies to NWM SFV, a nested PCR assay to detect NWM SFV DNA, and a β-galactosidase-containing indicator cell line to assay replication of NWM SFV. Using these tools, we analyzed the plasma and blood of 116 primatologists, of whom 69 had reported exposures to NWM. While 8 of the primatologists tested were seropositive for SFV from a NWM, the spider monkey, none had detectable levels of viral DNA in their blood. We found that SFV isolated from three different species of NWM replicated in some, but not all, human cell lines. From our data, we conclude that while humans exposed to NWM SFV produce antibodies, there is no evidence for long-term viral persistence.

Social processes and disease in nonhuman primates: introduction to the special section

Most nonhuman primate species are remarkably social, but their social nature presents many challenges, including increased opportunities for pathogen transmission and development of disease (both physical and psychological). An interdisciplinary symposium was convened at the 2010 annual meeting of the American Society of Primatologists on the topic of social processes and disease in nonhuman primates, and four articles from that session, as well as a fifth that was separately solicited, appear in this special section. The articles reflect a variety of disciplines and perspectives that highlight the many ways that social processes can impact disease processes (and vice versa) in this highly social taxon. This is an increasingly active area of research interest as a consequence of technological developments and the availability of long-term field data. The continuing loss of primate habitat in the wild, climate change, and the need to manage high densities of primates in captivity, however, all add urgency to our need to better understand the bidirectional relationship between social factors and disease processes.