With scientists hot on its tail, West Nile virus continues its invasive spread through the Caribbean. Recent tests confirm that WNV has arrived in Puerto Rico, and Cuba. “This is the first year we’ve seen West Nile virus in Puerto Rico,” said ecologist Peter Marra of the Smithsonian Environmental Research Center (SERC). Marra’s team has been sampling birds on that island for three years, and after sampling 1,205 birds this past winter, they found two individual birds, both year-round residents with antibodies to the virus.

“It’s the first year we’ve looked in Cuba,” Marra said, “but it’s only 90 miles from Miami, Florida, where birds have tested positive for at least two years. The researchers expected to find signs of the virus in Cuba, but the recent test results provide the first confirmed evidence that the virus is there.

Armed with this information, public health officials can take the action needed to manage the disease and prepare for its prevention. Marra and his team made a similar discovery in Jamaica when they found the first proof that the disease had arrived in 2002, after finding no virus the previous year. Because migratory birds are believed to spread the virus from one location to another, Marra began to track the disease in birds in 2001 through a collaboration with the Wadsworth Center of the New York State Department of Health . While finding antibodies to the virus in a migratory bird does not prove the region has active WNV, finding them in a year-round resident bird means the bird was exposed at one time to live virus, and that the disease is in fact in the local system.

In Puerto Rico, Marra’s team found two resident birds, a bananaquit and a green heron with antibodies to the virus, and in Cuba, two red-legged thrushes and a little blue heron tested positive for antibodies.

The good news for Puerto Rico and Cuba, if history is any indication, is that experts don’t expect to see the same impact as they’ve seen in North America where the disease has wide-ranging economic and health effects. The CDC reported more than 9,800 human cases of WNV in 2003 resulting in 264 deaths, and the American equine industry has felt the effects of the disease as horses fell ill and died, and many foreign countries issued bans on imports of American horses.

“One of the most perplexing issues in the West Nile story thus far has been its behavior in tropical regions,” said Marra, “We just aren’t seeing the same sort of bird, horse or human impacts as we did in temperate areas. This is a huge relief since wildlife and people have already been seriously impacted from the effects of habitat destruction. Understanding why West Nile’s lethal effects appear to be reduced in the tropics is something we’re preparing to study. Stay tuned.”