Some urban performing monkeys in Indonesia are carrying several retroviruses that are capable of infecting people, according to a new study led by University of Washington researchers. The results indicate that contact with performing monkeys, which is common in many Asian countries, could represent a little-known path for viruses to jump the species barrier from monkeys to humans and eventually cause human disease. Performing monkeys are animals that are trained to produce tricks in public.
While scientists have conducted extensive research on primate-to-human viral transmission in Africa, where they believe HIV originated, few have researched this topic in Asia.
"People aren't looking at Asia, and they need to do so, because viruses are emerging on that continent," explained Dr. Lisa Jones-Engel, leader of the study and a research scientist in the Division of International Programs at the UW's Washington National Primate Research Center. "There is a large, diverse population of primates there, and a huge human population in dense urban centers, so there's the potential for viral transmission across the species barrier."
The study's authors are urging more research on the different settings in Asia where people have contact with non-human primates – zoos, animal markets, monkey forests, pet ownership, and urban street performances. Most previous research on viral transmission has focused on bushmeat hunting and consumption, a practice in which local residents hunt wild monkeys for food. HIV, the virus that causes AIDS in humans, is believed to have originated as a primate virus and jumped the species barrier to humans when African bushmeat hunters came into contact with blood from infected animals.
However, in Asia other forms of primate/human contact, among them urban monkey performances, may be more prevalent than bushmeat hunting. Asia has a long history of performing monkeys, and initial studies indicate that the performances can include very close, physical contact between the animals and human spectators – monkeys crawling on people, for instance. Such contact might increase the risk of a bite, scratch, or other interaction that could lead to exposure to monkey body fluids.
"The risk of viral transmission in this context is unclear," said Dr. Michael Schillaci, professor of social sciences at the University of Toronto at Scarborough and lead author on the study. "But the contact here can be very intense."
Also troubling are the animal markets where many performing monkeys are acquired by their trainers. The markets typically bring together many different species of wild monkeys, as well as many other types of animals, in very close, unnatural quarters and unsanitary conditions.
"The market is a condensed area for mixing species and pathogens," explained Dr. Gregory Engel, an attending physician at Swedish/Providence Hospital in Seattle, Wash., a clinical instructor of family medicine at the UW, and a co-author on the study. "The animals may be sick or in bad shape there, and they're mixed with other animals that potentially could have pathogens, and then they're put into contact with a dense human population."
In this study, the researchers drew blood from 20 urban performing macaques in Jakarta, Indonesia, and tested those samples for various simian viruses. They found that about half of the macaques tested positive for simian foamy virus (SFV), a primate retrovirus that so far has not been shown to cause disease in humans, but that has been detected in other monkey-human interaction settings in Asia. Two of the monkeys tested positive for simian retrovirus (SRV), which, though it has been shown to infect humans in a laboratory setting, has yet to be associated with any disease in humans. However, both SRV and SFV are retroviruses, which are typically slow-acting in their host, so it could be many years before physicians know the effects of those virus exposures.
One monkey tested positive for simian T-cell lymphotropic virus (STLV), which is believed to be the primate ancestor to the human version of the virus, HTLV, a known cause of T-cell leukemia in people. One macaque tested positive for herpes B virus, also known as CHV-1, which rarely infects humans, but, in the 40 known human cases, was associated with an 80 percent fatality rate.
The researchers still do not know the prevalence of such simian viruses across larger urban performing monkey populations in Indonesia, or elsewhere in Asia. Urban performing monkeys can be found in India, Pakistan, Thailand, Vietnam, China, Japan and Korea. They hope to learn more about the risk of primate to human viral transmission in future studies of owners and their monkeys. However, they urge people to take precautions around performing monkeys, by preventing the animals from climbing on them and by keeping food away from the macaques. Such precautions can help reduce the risk of bites and scratches from the monkeys.
This study included researchers at Bogor Agricultural University in Bogor, Indonesia, and the Southwest National Primate Research Center in San Antonio, Texas. It appears in the December issue of the journal Tropical Medicine and International Health, published on Dec. 8, 2005.
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