New theory may explain West Nile virus spread

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The invisible pathogens of the West Nile virus may have more in common with grazing herds of cattle than one might think - even in the far from bucolic borough of Queens.

Some in the medical community believe West Nile has been traveling - probably via birds and mosquitoes - to areas where there are more birds and mosquitoes to infect to propagate itself.

This "herd immunity" theory is being considered as one of the ways to explain why the virus, which ravaged Queens in 1999, appears to have skipped the borough in 2000, said Dr. Stephen Ostroff of the Centers for Disease Control in Atlanta.

In a telephone interview last Thursday, Ostroff suggested that because of the large numbers of birds and mosquitoes in Queens infected by West Nile in 1999, there might not be enough susceptible animals this year to allow the virus to flourish.

But, he stressed, don't count on West Nile to make a quiet exit.

"The areas most impacted last year don't seem to be particularly involved this year," said Ostroff, the federal West Nile "czar." But he cautioned that "it's too soon to tell . . . the way the virus is going to behave."

Overall, Queens has had relatively little West Nile activity this year. In 1999, several people in the borough died from the virus, but this year there have been no human cases of the disease reported in Queens.

According to statistics released by the city Health Department Friday, a total of seven people and a dead horse have been found with the virus, as well as 88 dead birds and 81 mosquito pools. The majority of human cases, birds, mosquito pools and the horse were from Staten Island, the agency said.

Ostroff said it is possible "there simply aren't enough susceptible birds in some areas to allow the natural viral cycles to occur. It could be the virus basically found someplace else to keep itself in circulation."

This would explain why areas like Staten Island - which seemed to have been one of the least affected places in 1999 - have been so hard hit in 2000. That borough has been a virtual hotbed of West Nile activity, Ostroff said, possibly because birds and mosquitoes in that area had less exposure to the virus last year.

The theory has not stopped the Health Department from spraying pesticides at each discovery of West Nile in birds or mosquitoes in Queens, a practice which Ostroff endorses. Several sections of the borough were sprayed over the holiday weekend after more dead birds infected with the virus were found.

The West Nile virus made its first appearance in the Western Hemisphere in College Point in August 1999, killing four people in the borough and sickening dozens throughout the city. It travels from infected birds to mosquitoes, which then transmit the virus to humans. The elderly, young children, and those with compromised immune systems are most vulnerable.

Ostroff, who has been with the CDC since 1986 and serves as the federal agency's outbreak coordinator, emphasized that the "herd immunity" theory was just one of the possible explanations for the behavior of West Nile. He also urged residents to continue to limit their contact with mosquitoes.

To stop doing so, he said, would be "a recipe for disaster."

Because West Nile is a new pathogen in a new environment, Ostroff said, research surrounding the virus has focused on discovering how potent it is.

Ostroff said one question before the medical community about the virus is why it has infected humans in Staten Island, but not in Suffolk County where there have been a similar number of contaminated birds and mosquitoes.

"It begs the question," he said. "What's different?"

Other West Nile mysteries include: which birds species and/or other mammals are most vulnerable; how it maintains itself in nature; and how much of a risk to humans is posed by a single dead infected bird.

"Is every single find of a dead bird as risky as finding 50?" Ostroff said. "We really do need to understand that."

Until the scientists find an answer, he said, residents in infected areas must continue to take precautions, which include reporting findings of dead birds to the city Health Department.

"It remains quite important," he said. "Even if they don't pick up and test them, they'll still have a record."

Last Thursday the city Health Department announced schedules for ground spraying of the pesticide Anvil in Queens over the holiday weekend.

On Friday night, the Health Department sprayed pesticides in Woodhaven, Kew Gardens, Glendale, Richmond Hill, Ozone Park and parts of Forest Hills.

On Saturday, parts of Hunters Point, Long Island City, Dutch Kills and Queensbridge were sprayed, and on Sunday parts of Jamaica, Hollis, St. Albans, Springfield Gardens, and Cambria Heights were sprayed.

For more information about the virus call the Health Department toll free at (877) WNV-4NYC, or go to

Posted 7:05 pm, October 10, 2011
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