"The issue of primate-to-human viral transmission has been studied extensively in Africa, largely because that is where HIV originated," explains Dr. Lisa Jones-Engel, lead author of the study and a research scientist in the Division of International Programs at the Washington National Primate Research Center. "But there has not been much work on the topic in Asia, which has huge primate diversity and large human populations."
Jones-Engel and her co-authors also argue for more research on diverse contexts of human-primate contact. The vast majority of previous viral transmission research focused on bushmeat hunting and consumption, a practice in which local residents hunt monkeys for food. HIV, the virus that causes AIDS in humans, is believed to have originated as simian immunodeficiency virus (SIV), and jumped the species barrier to humans when African bushmeat hunters came into contact with blood from infected animals.
Though bushmeat hunting and consumption may be a significant factor in viral transmission in Africa, Jones-Engel says, people in Asia have many other contexts in which they come into contact with primates, including animal markets, primate pet ownership, urban performing primates, and zoos. In addition, monkeys are significant symbols in both Buddhism and Hinduism, and monkey temples - places of religious worship that have become refuges for populations of primates - are common throughout much of South and Southeast Asia. In these areas, protected macaque populations have thrived alongside dense human settlement for centuries.
On the island of Bali alone, there are more than 40 such temples, which are frequented by tourists from around the world. About 700,000 international tourists visit the island's four main monkey temples every year. Temple workers and people who live near the temples also have a great deal of contact with monkeys at the religious sites.
"In Asia, the amount of contact between humans and primates in temple settings dwarfs the contact due to bushmeat hunting," says Jones-Engel. For this study, the researchers tested blood samples from 82 people who work in or around a temple in Bali, as well as samples from macaques in the area. They found antibodies for simian foamy virus in the blood of one 47-year-old farmer who visited the temple every day. They confirmed the tests by performing a DNA analysis of the man's blood, and found that the SFV strain he carried was the same strain found in the temple's macaques. The man denied owning a monkey as a pet, or hunting monkeys for food. He had been bitten once and scratched more than once by the temple's macaques.
Researchers still don't know the long-term effects of SFV on humans - there are about 40 known cases of people being infected, through laboratory or zoo contact, or through bushmeat hunting in Africa. There are no known cases of human disease yet.
However, Jones-Engel and her fellow researchers warn that there are other primate viruses known to be harmful that could jump the species barrier. They don't want people to be afraid of coming in contact with macaques or other primates, but they do urge people to be cautious and careful when interacting with monkeys. Feeding the animals, or even carrying food into a temple, can greatly increase the risk of a bite or scratch, which can lead to transmission of infection. Visitors occasionally engage in other risky behavior, such as touching animals or trying to hold baby monkeys. Limiting such behavior can reduce the risk of bites and scratches.
"If you look at free-ranging monkeys in Singapore's nature reserves, you see that feeding by visitors is not allowed, and it is actively discouraged," says Gregory Engel, an attending physician at Swedish/Providence Hospital in Seattle, Wash., a clinical instructor of family medicine at the University of Washington, and a co-author on the study. "Interspecies interaction there is very different, and rates of human-monkey contact are much lower."
Limiting dangerous contact between primates and humans can have other benefits, as well, such as reducing the transmission of human infections to monkeys. Human measles, for instance, can cause disease in monkeys and can even kill them. Other primate species have already seen significant population losses because of infection by human illnesses.
Also participating in the study were researchers at the University of Toronto; Udayana University in Denpasar, Bali, Indonesia; the University of Notre Dame; the Southern Research Institute, Frederick, Md.; and the Southwest Foundation for Biomedical Research, San Antonio, Texas.