Research finds crows may not be big carrier of disease
HARTFORD, Conn. -- The beloved American robin, not the annoying, raucous crow, may be the more potent source for West Nile virus, according to new research.
A DNA analysis of blood taken from the abdomens of 300 mosquitoes trapped in Connecticut over the past three years found that 40 percent fed on the blood of the red-breasted songbird and only 1 percent on crows, said Theodore Andreadis, chief medical entomologist at the Connecticut Agricultural Experiment Station.
"It was quite surprising," he said. "Robins are right up there and are probably playing a pretty good role."
His findings have been turned over to the federal Centers for Disease Control and Prevention for publication.
A CDC expert on West Nile is skeptical. However, the results are similar to the studies of Charles Apperson, an entomologist at North Carolina State University. He also found robin blood, but little from crows, in mosquitoes he has tested over a four-year period in New York, New Jersey and Tennessee.
"We felt like we were expecting we would find that mosquitoes fed on crows. That didn't seem to be the case," Apperson said.
In most cases, humans infected by West Nile virus experience only mild, flu-like symptoms. But the virus also can trigger dangerous, and sometimes lethal, cases of meningitis and encephalitis.
Andreadis said the next step in research would be to catch robins in special mist nets and test their blood. The non-lethal tests would tell researchers if the birds are an effective reservoir for the disease. "It's got to be there in high levels for along period of time," Andreadis said.
But testing the theory may be tough. Robins -- the state bird of Connecticut, Michigan and Wisconsin -- are wily in avoiding the nets, researchers said.
West Nile virus has been identified in more than 200 species of birds, according to the CDC.
But Nick Komar, the CDC's lead bird West Nile researcher, is skeptical of the robin's newfound dubious distinction. It's too early to tell, he said.
"I'd be surprised if the American robin would be very important," said Komar, who had not yet seen Andreadis' data. "I wouldn't jump to the conclusion that crows are not important. If this study analyzes mosquitoes where there are lots of robins but no crows, that could be misleading.
"What mosquitoes feed on is a very complicated and very large puzzle. We need more data," Komar said. "Sometimes researchers will find one piece that fits. All the pieces are required."
West Nile was first reported in New York in 1999 and has caused 667 deaths nationwide. Cases have been reported in all contiguous 48 states. This year there have been 41 human cases nationwide and one death in Missouri, CDC spokeswoman Jennifer Morcone said.
People are urged to avoid mosquito bites, use repellent, stay indoors at dusk and dawn and clear gutters and other receptacles of standing water to avoid infection.
"Since West Nile was first identified it has rapidly spread across the United States," Morcone said. "It's here to stay. It's important that people know they can do things to protect themselves. Every state in the nation has made great strides in West Nile prevention and control efforts."
Connecticut, for example, has nearly tripled its monitored mosquito traps from 37 to 91. The traps help scientists identify if an insect is infected and whether it bites birds, humans or both.
Bird surveillance, which resulted in dead crows winding up at state labs by the hundreds, largely relied on public participation. People were asked to call their local health department if they saw a dead bird, particularly if it was a crow, Andreadis said.
He noted, however, fewer crows are dying off, leading researchers to believe they may be developing an immunity.
"I've got a feeling that the usefulness of the bird surveillance program may have passed. We always relied on mosquito data anyway," Andreadis said.