Research Sheds New Light on Herpes Virus Transmission Among Trafficked Peruvian Primates

Thousands of Neotropical primates have been illegally trafficked from the Peruvian Amazon, extracted from their habitats and exposed to humans and other species they have not had previous contact with—heightening the risk of zoonotic disease transmission and spillover. A new study examines trafficked Peruvian Neotropical primates with herpes simplex virus 1 (HSV-1), a lethal disease for some primate species, that, if undetected, can spread among trafficked animals and to those in rehabilitation centers and in the wild.

Featured in the May issue of the Centers for Disease Control and Prevention (CDC) journal, Emerging Infectious Diseases, “Herpes Simplex Virus 1 in Trigeminal Ganglia of Trafficked Neotropical Primates, Peru, 2024” is a unique study because of its focus on the trigeminal ganglia, an area of the brain where HSV-1 commonly resides in humans latently infected with the virus. Currently, common diagnostic assays used to detect HSV-1 in Neotropical primates include oral swab PCR and serology, which may miss infections that are latent or not active. 

Dr. Fernando Vilchez-Delgado, VG27, Ph.D. student at Cummings School of Veterinary Medicine at Tufts University, is the lead author of the study. His mentor and co-author, Dr. Marieke Rosenbaum, V14, MG14 (M.P.H.), assistant professor in the Department of Infectious Disease and Global Health at Cummings School, serves as the principal investigator for this project and has published extensively on zoonotic disease transmission among illegally trafficked animals. 

Much more devastating to primates than humans, HSV-1 can cause neurological and hemorrhagic disease and death in some species, often within days. With no proven treatment options, if an animal tests positive, it is often euthanized, along with any other animals exposed in its group, to prevent further spread. 

Vilchez-Delgado and Rosenbaum pulled together an international research team to examine the trigeminal ganglia of 37 trafficked carcasses across seven species of Peruvian Neotropical primates. While all the primates were asymptomatic prior to their deaths, four were found to have HSV-1 in the trigeminal ganglia even though the virus was not detected in oral swabs, indicating that Neotropical primates infected with HSV-1 may not exhibit symptoms or test positive on a typical PCR test. According to the paper, “Our findings suggest latency and raise concerns about diagnostic standards, viral reactivation, and spillover risks.” 

Rosenbaum has spent more than two decades researching zoonotic disease transmission and public health risk stemming from primate trafficking, starting with her student research project in 2010 on detecting Mycobacterium tuberculosis complex in Peruvian Neotropical primates, while earning her D.V.M. and M.P.H. at Cummings School.

Growing up in Peru, Vilchez-Delgado was inspired by his father, a veterinarian who helped wildlife agents who rescue animals. “That exposed me when I was very young to this reality—how wildlife trafficking affects animals and, in the end, how this can also affect humans.”

After earning his veterinary degree in Peru, Vilchez-Delgado witnessed an outbreak of yellow fever in primates in Brazil before joining a virology lab, turning his focus fully to studying viruses that infect trafficked primates. Vilchez-Delgado and co-author of the study, Dr. Ana Patricia Mendoza, postdoctoral research associate of biological anthropology at Washington University, previously collaborated on research into infectious disease spread among trafficked primates in Peru. Mendoza connected Vilchez-Delgado with Rosenbaum, and for the past four years, they have combined their research efforts.

Primates are primarily trafficked as exotic pets and for biomedical research, according to Rosenbaum and Vilchez-Delgado. Despite strict regulations on transporting wild species across borders, the animals are trapped in Peru and exported to other South American countries, where they are shipped to laboratories abroad. Trafficked primates are also sold for consumption, medicinal or ritualistic purposes, or to attract tourists to commercial establishments. 

Beyond disease transmission, trafficking primates devastates populations and their ecosystems.

“Trafficking affects the balance that exists in nature,” says Vilchez-Delgado. “Spider monkeys, for example, are very important for spreading seeds, and there are areas in the Amazon jungle where these species were simply exterminated. Rehabilitation sanctuaries are trying to bring some of these species back to their natural habitats and re-establish this balance.” 

The impact on humans is also significant. Rosenbaum notes, “Wildlife trafficking is lucrative, and that money is often used to fund other illegal trafficking activities, like arms, drugs, and people, which all take advantage of the same porous borders. It's a complicated and complex problem.” 

After primates are trapped, they are held in overcrowded crates, sometimes for several days, while in transit on riverboats. Many die under these stressful conditions, often without ample water, food, or space. During trafficking, they may come in close contact with other species—and consequently exposed to pathogens from humans and other animals. Wild species rescued from traffickers and wet markets are typically euthanized by the government or sent to privately funded sanctuaries for rehabilitation; however, as a result of trafficking, they may be infected with and at risk for spreading infectious diseases normally found in other species.

“The Amazon Basin in Peru is one of the richest regions in the world for primate species diversity, many of which are endangered or threatened, so this is something we're actively trying to understand better, specifically looking at herpes virus transmitting from humans to monkeys in this context,” says Rosenbaum.

The researchers partnered with Universidad Peruana Cayetano Heredia in Peru (Vilchez-Delgado’s alma mater), utilizing their laboratories to perform necropsies and PCR tests, and the National Forest and Wildlife Service in Lima, which provided the carcasses. Several Cummings School students from the D.V.M. and Master of Science in Conservation Medicine programs assisted with PCR testing in Peru and the U.S. for their summer research projects. Additionally, Vilchez-Delgado trained on genomic sequencing of HSV-1 with experts at Penn State University. 

“Finding that DNA of the virus in the ganglias of the primates might represent a risk for other species,” says Vilchez-Delgado. “How many other animals in rescue centers might be false-detected negatives when they are actually positive in the ganglia for HSV-1?” 

The study not only reinforces that HSV is spilling over from humans to monkeys but also revealed slightly different genomic sequences of the virus, indicating separate spillover events.

On the implications of their findings, Rosenbaum says, “There are more questions we need to answer to better understand what's happening. We're working on developing a naturally occurring animal model for viral spillover, where we can study the evolution of alpha herpes viruses like HSV-1 when they jump from one host to another.” 

Vilchez-Delgado and Rosenbaum are currently focusing on the genomic component of these spillovers in relation to observable symptoms in affected primates, how the viruses are mutating, and how pathogenic they become if they mutate in a new host. These findings in primate animal models will provide insight into herpes virus transmission in humans.

“In detecting these cases of spillover and studying them more in depth, we'll better understand how viruses adapt to new hosts and what host factors facilitate or prohibit infection. We’re trying to understand how cross-species spillover impacts viral evolution, mutation, and pathogenicity in the host,” says Rosenbaum. 

On bringing this issue of detecting HSV-1 to the forefront of primate conservation, Vilchez-Delgado says, “I feel very proud of these efforts and results we obtained. I value these studies being able to provide this extra layer of information to better understand what's happening in Peru.”