Zoo workers who come in close contact with nonhuman primates, such as apes and monkeys, are at increased risk for exposure to simian virus 40 (SV40), suggest the results of a study of North American zoo workers.

However, the investigators emphasize that larger studies are needed to determine the precise level of risk and to determine whether there are health consequences of SV40 infection in humans.

SV40 causes cancer in laboratory animals and SV40 DNA has been observed in some human tumors although possible routes of infection are unknown, Dr. Eric A. Engels from the National Cancer Institute in Bethesda, Maryland and colleagues report in The Journal of Infectious Diseases.

They tested 254 zoo workers for antibodies to SV40. Twenty-five of 109 of the workers who had direct contact with primates (23 percent) tested positive for SV40 compared with 15 of 145 (10 percent) workers who had no direct contact with primates.

The increased rate of SV40 exposure in primate handlers remained after an “added level of stringency” was incorporated, the team notes, namely, a test to eliminate possible false-positive results that may have picked up two SV40-related human viruses.

The “mostly low-level” of SV40 exposure observed in the workers suggests that there is no ongoing replication of SV40, Engels and colleagues note.

They emphasize that the current study cannot provide a reliable estimate, in absolute terms, of the risk to zoo workers of exposure to or infection with SV40.

The author of a related editorial also points out that while humans who come in contact with primates may become infected with SV40, there is currently no evidence to suggest that SV40 has spread outside of zoo environments or that it plays a role in the development of cancer in humans.

However, due to uncertainties in available data on SV40 in humans, further studies are warranted, Dr. Keerti V. Shah, from The Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, concludes.

SOURCE: The Journal of Infectious Diseases, December 15, 2004.