For the first time, researchers have found native birds infected with the West Nile virus in the Caribbean. The virus was probably carried by migrating birds, and its spread could prove disastrous for already endangered native bird populations.
The West Nile virus is native to Africa, Asia, and the Middle East. In 1999, scientists documented a case of West Nile in New York. In the 4 years since, the virus has spread throughout the United States. It can cause flulike symptoms, but is rarely deadly in humans. In 2001, one Cayman Island resident fell ill with West Nile encephalitis, but scientists could not find a native animal that tested positive in the Caribbean Islands.
Three years ago, animal ecologist Peter Marra with the Smithsonian Environmental Research Center in Edgewater, Maryland, began testing blood samples from migrating and native birds in Jamaica, Puerto Rico, and Mexico for the West Nile virus. Now Marra's team reports at least six cases of West Nile in native birds in Jamaica. In addition, a group led by ornithologist Mark Robbins of the University of Kansas in Lawrence announced last week that it had found five infected native birds in the Dominican Republic.
Next, the researchers hope to determine how the virus got there, how far it has spread, and what its impacts are likely to be. "I think birds are probably the best dispersers of the virus, but we still have not found the smoking gun," Marra says. Scientists need to find contagious migrating birds to prove that they are spreading the virus, he says.
Although scientists don't know which native birds are susceptible, West Nile could potentially do more damage in the tropics, because it can be transmitted year-round; winters aren't cold enough to kill off the mosquitoes that spread the virus from bird to bird, says public health veterinarian Emi Saito, at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin.
If endangered native birds are infected, their populations might be decimated by an outbreak. Robbins's team found the virus in a national park that is home to the few hundred remaining Ridgway's hawks, a close relative of North America's red tail hawk that has proved vulnerable to West Nile.