In May of 2009, one of the species of monkeys housed in a facility at the University of California in Davis began falling ill, showing symptoms of pneumonia and hepatitis. Despite efforts to limit the spread of any infectious agent, a third of the monkeys eventually came down with the ailment; most of them died or had to be euthanized. Researchers have now identified the cause of the outbreak, a new species of a well-known virus family. Once they knew what to look for, they found evidence that the virus had been transmitted to one of the researchers at the facility and spread to one of his family members.

In the wake of the epidemic, researchers went looking for a cause using a DNA chip that can help identify sequences from a variety of pathogens. A number of viruses appeared to be present, but most weren't known to cause the symptoms exhibited by these monkeys, so the authors focused on one family that does: the adenoviruses. Sequencing DNA from samples of the lungs of infected monkeys eventually allowed the researchers to reconstruct parts of an adenovirus genome. Targeted cloning and sequencing then enabled them to reconstruct the whole virus.

Adenoviruses strike many different vertebrate species, and a number of families of the virus have been identified that are specific to humans or other primates. This new virus, which has been termed TMAdV, was only distantly related to the known viruses that infect humans and other primates, and resided on a branch all its own between the primate viruses and those that infect other groups, like birds or carnivores. So it was very clear the researchers had found something new.

What does this new virus normally infect? Most adenoviruses have been found to be fairly specific to a small range of species in the lab, but there's evidence that this isn't the case in the real world; the viruses that infect humans and other primates are mixed in among each other on an evolutionary tree, and people who live in areas where other primate species are endemic have antibodies to their versions of the virus.

The new virus showed a complex pattern of infectivity. The primates it initially targeted, titi monkeys, are from the western hemisphere, and are distant relatives of humans. Other primates in the facility didn't seem to get infected, and it wasn't possible to grow the virus in cultured cells from other monkey species. But it could grow in a culture of human cells and, disturbingly, the virus appears to have spread to humans during the outbreak. One of the technicians who worked with the monkeys had an extended respiratory infection around the same time as the outbreak, and one of the technician's relatives had a milder case of a similar ailment.

Using a less-specific test, antibody reactivity, the authors found that one of the macaques in the same building had antibodies that reacted with TMAdV, and other antibodies showed up in a few samples taken from human blood donors.

Overall, the results don't really clarify much. Based on a variety of factors, the authors think that the virus was transmitted from the titi monkeys to their handler, but they can't rule out transmission in the opposite direction. They do think it isn't endemic to the monkeys, since viruses that cause that many fatalities don't tend to exist as background infections. And there's little sign that it came from any of the other species housed in the facility. Plus there's the antibody results, which suggest it (or a close relative) might be circulating in the background of the local human population.

All of that might suggest that TMAdV doesn't even normally infect primates at all, but that humans and the monkeys have gotten it from the same source. In any case, the authors say they are working very hard to identify the normal host of the virus. It might be tempting to panic, but the virus didn't spread too far from the infected worker, and none of the people who had it required hospitalization.

The fact that we can pick up viruses from our fellow primates (and other mammals) shouldn't surprise anyone at this point. We hadn't known that adenovirus could make these sorts of hops but, as noted above, we had reason to think it might. But following up on this case could help us understand the conditions that foster these jumps, which might help us to make them less common in the future.

PLoS Pathogens, 2011. DOI: 10.1371/journal.ppat.1002155 (About DOIs).