West Nile Virus Found in Cambridge

State health officials have discovered West Nile Virus in Cambridge mosquito populations, and yesterday announced that two new human cases have been identified in Massachusetts.

Three cases of human West Nile Virus had been found in Massachusetts earlier in the summer, but the new cases differed in that state health officials believe the residents—one from Arlington, the other from Worchester—contracted the disease in Massachusetts.

Despite the recent cases, and the discovery earlier this month of infected mosquito populations just north of Mount Auburn Cemetery, the University’s West Nile Virus Task Force does not consider it an immediate threat.

The mosquito-borne virus, which can be lethal to humans in a small minority of cases, has surfaced in the greater Boston area every year since it first appeared in the state in 2000, according to Sam Lipson, the city’s director of environmental health.

Lipson said that the development should not dramatically raise concerns about the disease.

“A number of factors point to a low risk to humans,” he said.

Lipson advised using insect repellent, wearing covering clothing, and eliminating standing water to reduce the risk of virus-transmitting bites.

Gary Alpert, Harvard’s entomology officer of environmental health, said an unusually dry August and cooling temperatures, which eliminate potentially dangerous mosquito populations, would soon put an end to the threat this year.

Harvard’s task force would convene in the event of a more urgent incident involving the virus in Cambridge, according to Alpert.

“We have not had any illness whatever with West Nile Virus at Harvard ever,” he said, noting that any cases in Cambridge would immediately trigger a response from the task force.

Alpert added that the task force responded by spraying insecticide several years ago when infected mosquito pools were discovered but that they had since decided that a greater threat is required for response.

The West Nile Virus first appeared in North America in the summer of 1999 and has since spread throughout the North American continent.

—­Staff writer Clifford M. Marks can be reached at