RESEARCH Primate-to-Human Retroviral Transmission in Asia Lisa Jones-Engel,* Gregory A. Engel,† Michael A. Schillaci,‡ Aida Rompis,§ Artha Putra,§ Komang Gde Suaryana,§ Agustin Fuentes,¶ Brigitte Beer,# Sarah Hicks,** Robert White,** Brenda Wilson,** and Jonathan S. Allan** We describe the first reported transmission to a human of simian foamy virus (SFV) from a free-ranging population of nonhuman primates in Asia. The transmission of an exogenous retrovirus, SFV, from macaques (Macaca fasci- cularis) to a human at a monkey temple in Bali, Indonesia, was investigated with molecular and serologic techniques. Antibodies to SFV were detected by Western blotting of serum from 1 of 82 humans tested. SFV DNA was detect- ed by nested polymerase chain reaction (PCR) from the blood of the same person. Cloning and sequencing of PCR products confirmed the virus’s close phylogenetic relation- ship to SFV isolated from macaques at the same temple. This study raises concerns that persons who work at or live around monkey temples are at risk for infection with SFV. Rtory syndrome (SARS) have changed the way we ecent epidemics such as HIV and severe acute respira- view emerging infectious diseases; these epidemics show that animal reservoirs are important sources of new infec- tious threats to humans. Contact between humans and ani- mals is a crucial rate-limiting step in this process, although data describing the variables that influence animal-to- human transmission are relatively scarce. Nonhuman pri- mates, by virtue of their genetic, physiologic, and sometimes social similarities to humans, are particularly likely sources of infectious agents that pose a threat to humans (1,2). Data on simian immunodeficiency virus (SIV)/HIV dramatize this point; scientists now theorize that SIVs were transmitted from primates to humans on *University of Washington National Primate Research Center, Seattle, Washington, USA; †Swedish/Providence Hospital Family Practice Residency, Seattle, Washington, USA; ‡University of Toronto at Scarborough, Toronto, Ontario, Canada; §Udayana University, Denpasar, Bali, Indonesia; ¶University of Notre Dame, Terre Haute, Indiana, USA; #Southern Research Institute, Frederick, Maryland, USA; and **Southwest Foundation for Biomedical Research, San Antonio, Texas, USA several occasions (3,4). As a result, concern is increasing that other infectious agents enzootic in primate popula- tions may endanger humans (5). The family of SIV is 1 of 4 primateborne retroviruses known to infect humans (6). Simian T-cell lymphotropic viruses, enzootic in both Asian and African Old World monkeys and apes, may have repeatedly crossed the species barrier (7,8). The resulting human form of the virus, HTLV, is the etiologic agent of 2 human diseases, adult T-cell leukemia and tropical spastic paresis (9). Serologic studies have demonstrated evidence of primate- to-human transmission of simian retrovirus (SRV), a retro- virus enzootic among Old World monkeys, in laboratory workers exposed to captive primates (10). To date, no dis- ease has been linked to human infection with SRV. Finally, in the past decade, evidence of infection with simian foamy virus (SFV) has been identified in 1% to 4% of per- sons who come into frequent contact with primates in zoos and primate laboratories and among 1% of bushmeat hunters in Central Africa (11–15). SFV SFVs are exogenous retroviruses enzootic in both New and Old World primates (16–18). Phylogenetic analyses of SFVs indicate a species-specific distribution of virus strains not unlike that of SIV among some African primate species (19–23). Among captive primate populations, sero- prevalence of antibodies to SFV may reach 100% in adults, with many animals seroconverting before the onset of sex- ual maturity (19,24; J. Allan, unpub. data). Fewer data are available on the seroprevalence of antibodies to SFV among free-ranging populations of primates. SFV is pres- ent in highest concentrations in the saliva of infected labo- ratory macaques (Macaca mulatta and M. fascicularis) and African green monkeys (Cercopithecus aethiops), which suggests that bites, scratches, and mucosal splashes with 1028 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 7, July 2005