Scientists at the University of Illinois have discovered that red colobus monkeys in a park in western Uganda harbor evidence of infection with unknown poxvirus.
The study, led by Tony Goldberg, a professor of veterinary pathobiology and of anthropology at the university, found that the red colobus monkeys have been exposed to an unknown orthopoxvirus, a pathogen related to the viruses that cause smallpox, monkeypox and cowpox.
Most of the monkeys screened harbor antibodies to a virus that is similar, but not identical, to known orthopoxviruses.
This is the first effort to screen Ugandan red colobus monkeys for orthopoxviruses, said Goldberg.
"Considering that we found evidence for a new poxvirus pretty much in the first place that we chose to look is suggestive that the actual diversity of poxviruses in nature, especially in relatively unstudied areas like sub-Saharan Africa, may be much greater than we originally thought," Goldberg said.
The study was begun in 2006 when Colin Chapman, a researcher at McGill University, invited Goldberg to collaborate on a health assessment of two groups of red colobus monkeys in Kibale National Park, in western Uganda.
The agent that infected the monkeys "looked a little bit like monkeypox virus, a little bit like vaccinia virus, a little bit like cowpox virus, but not exactly like any of them," said Goldberg.
Chapman, also an associate scientist with the Wildlife Conservation Society, had spent two decades studying the behaviour and ecology of the monkeys. He wanted to broaden the study to include an analysis of the pathogens they carried.
Wildlife veterinarians from the Wildlife Conservation Society helped collect the samples, and a team from Oregon Health and Science University, led by Mark Slifka, conducted immunological analyses to characterize the virus.
An initial screening for antibodies to the vaccinia virus yielded positive results in about one-quarter of the monkeys tested. This was not clear evidence of infection with vaccinia, however.
"We found that as we screened these monkeys initially for a broad range of poxviruses, many of them came up positive," Goldberg said.
The researchers were surprised to find that the monkeys harbored antibodies to some, but not all, of the proteins associated with the known poxviruses, Goldberg said.
Whatever had infected the monkeys "looked a little bit like monkeypox virus, a little bit like vaccinia virus, a little bit like cowpox virus, but not exactly like any of them," he said.
"We were forced to conclude in the end based on a series of progressive laboratory tests that yes, these monkeys had been exposed to a poxvirus, but that it was different from any poxvirus that we were using as a reference," he added.
All the animals were healthy at the time of the study, and no recent cases of human orthopoxvirus infection have been reported in Uganda.
Little is known about the global distribution of orthopoxviruses, Goldberg said, but their potential to cross from other animals into humans warrants more attention.
The red colobus monkeys of Kibale are probably not the primary hosts of the virus that infected them, Goldberg said. None of the monkeys was sick when they were tested, an indication that their immune systems had successfully cleared the pathogen. Other mammals, such as rodents, may function as incubators of the virus, he added.
The study appears online in the journal Emerging Infectious Diseases.