West Nile virus spreads to Boston

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As the summer months draw to a close, the West Nile virus is turning up in a growing number of birds and mosquitoes across the Northeast, and in areas where the flavivirus was previously unknown. Massachusetts reported its first cases of West Nile virus infection in late July in a handful of birds in and around Boston. And as New York state health officials were concluding that the mosquito-borne virus has spread to the entire state, the first case of West Nile fever this year was diagnosed in a 78-year-old Staten Island man.

New York City, thought to be ground zero of last year's outbreak, has been waging an aggressive campaign against the encephalitis-causing virus. Ground-based spraying with the pesticide Anvil has been ordered in Central Park, Manhattan, Staten Island, and parts of Queens.

West Nile encephalitis infections killed seven people and caused numerous illnesses in the New York City area last year. Bird die-off was reported there and in New Jersey, Connecticut, and Maryland. Several horses on Long Island, NY, died or were euthanatized as a result of infection.

Some speculated the virus would not last the Northeast's frigid weather, but in March it became evident that the virus had survived in Culex pipiens mosquitoes wintering in New York City. A dead red-tailed hawk, discovered in New York and tested in Connecticut, was further evidence that the virus would likely resurface with the warm weather (see JAVMA, April 15, 2000, page 1199; July 15, 2000, page 163).

As of early August, the West Nile virus was isolated in 123 birds and 38 mosquito pools in New York state, in two crows and a single pool of C restuans mosquitoes in Connecticut, and in 15 crows in New Jersey. So far, the virus has been identified only in the C pipiens, C restuans, and C Aedes japonicus species.

"We continue to find West Nile virus in birds in counties well outside the area originally affected, and it is likely that the virus is present throughout New York state," said Health Commissioner Antonia C. Novello, MD.

On July 20, an unidentified man from Staten Island became ill with symptoms of meningo-encephalitis and two days later was admitted to a local hospital. Serum and spinal fluid samples confirmed the presence of the West Nile virus. The man was treated and released a week later.

Since symptoms of the virus do not appear until five to 15 days after infection, health officials believe the man was infected before the city implemented its spraying program on Staten Island.

To the east in Massachusetts, the state department of public health announced July 26 that the virus had been confirmed by the state laboratory in a dead adult crow found four days earlier in Jamaica Plain, a Boston neighborhood where an infected robin was found a week later. Two dead crows were also discovered in nearby Brookline and in Hopkinton, a suburb 30 miles outside the city.

Infected mosquitoes have not been trapped within the state, but health officials suspect they are there. The dead robin means the virus is being transmitted locally, said Roseanne Pawelec, public relations director at the Massachusetts health department. Crows can migrate up to 200 miles, but it is unlikely that the robin was infected outside the state.