Humans infected via research primates
Cases show monkey virus can cross species lines
Five animal caretakers and biomedical researchers working with non-human primates are now known to be infected with simian viruses after occupational exposures such as bites and needlesticks, the Centers for Disease Control and Prevention reports.1
The infections are asymptomatic but persistent in the five humans, leaving open the key question as to whether the viruses can cause disease in humans that could be subsequently transmitted. Nonetheless, documentation of the infections raises additional questions about the wisdom of proceeding with xenotransplants involving baboons and other non-human primates.
Workers remain asymptomatic
Adding three U.S. cases to two previously reported cases in Germany, the CDC reported that the workers were infected with non-human primate retroviruses such as simian immunodeficiency virus (SIV) and simian foamy virus (SFV), explains Louisa Chapman, MD, medical epidemiologist in the CDC retroviruses diseases branch. Though DNA sequencing confirmed the presence of the animal virus, none of the five workers has reported symptoms and no known transmission has occurred to contacts, she says. In the three cases most recently documented, spouses of two of the workers tested negative for the virus. In addition, some of the infections may have occurred as far back as the early 1970s, the CDC reports.
"We don’t have any evidence so far among the five infected people to suggest that it either transmits from person-to-person or that it causes disease, but I think it would be erroneous to turn that into a positive statement," she says.
That is in part because of the small number of known cases, and the fact that retroviral infections can sometimes take years to manifest disease symptoms. It is known, however, that SFV is so common in baboons that excluding animals with the virus from xenotransplants would leave very few baboons available as sources for human transplants, Chapman says. Natural SFV infections have not been definitively associated with disease in non-human primates, but other retroviral infections have resulted in a broad clinical spectrum of symptoms that include life-threatening immunodeficiency in the infected animals, the CDC reports.
"It is one more piece of evidence that needs to be taken into consideration in [xenotransplant] discussions," she says. "We have been working hard here at CDC over the past two years to develop a scientific basis for assessing these concerns. I think it would be inappropriate for me to speculate on what policy decisions will come out of that consideration."
In 1995, the CDC surveillance program for such infections was expanded beyond SIV to include voluntary testing and counseling for exposure to SFV and other simian retroviruses. As of Nov. 20, 1996, samples from 231 of the participating volunteer biomedical workers had been tested for SFV and infection was documented in three (1.3%).
"Our data suggests that these infections may exist in humans occupationally exposed to non-human primates at a level of 1% or higher," she says.
Reference
1. Centers for Disease Control and Prevention. Nonhuman primate spumavirus infections among persons with occupational exposure United States, 1996. MMWR 1997; 46:129-131.
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