An elderly West Haven woman has contracted the West Nile virus, the first case of the sometimes-fatal, mosquito-borne disease in New Haven County, state health officials said Friday.

She is in critical condition with brain inflammation at the Hospital of St. Raphael on Chapel Street.

The virus infected Connecticut and New York with a rash of fear in summer 1999, and cities and counties blanketed their roadsides and woods with bug poison to kill the mosquitoes whose bite transmits it. Sixty-two people contracted the virus that year, and seven died.

The West Haven woman, who is in her 70s but whose name has not been released, was confirmed Friday to be the third person in Connecticut this year to contract the virus. Though the mosquito season is winding down, health officials are again warning the public to use insect repellent and to eliminate pools of standing water where mosquitoes tend to breed and form clusters.

“The individual can play the greatest role in minimizing exposure to mosquitoes,” said William Gerrish, a spokesman for the Connecticut Department of Public Health.

The woman checked herself into the emergency room Sept. 1 with a high fever, headache and confusion. Blood and spinal test results Friday confirmed that she was infected.

The West Nile virus can only be transmitted through mosquito bites and not person-to-person. Far fewer than one percent of mosquitoes are infected with the virus, and infected mosquitoes transmit the virus to less than one percent of those bitten.

The West Haven woman was likely infected during the last two weeks in August. Since she was traveling around Connecticut at that time, health officials are not sure where in the state she contracted the virus.

The two others who were infected were hospitalized in the third week of August and recently discharged. Both in their 60s, one patient was a resident of Fairfield, and the other was a tourist who was vacationing in Staten Island, N.Y., and Norwalk, Conn., before falling ill.

Gerrish said the state has been working throughout the year to inform the public on how to avoid mosquitoes. Precautions include keeping screens intact, wearing light-colored clothing and avoiding outdoor activity at dusk and standing pools of water.

“We are informing the public that they can play a very important role in preventing the West Nile virus,” Gerrish said.

Of those cases that are reported to public health authorities, three to 15 percent result in fatalities, with the elderly and those with compromised immune systems most at risk.

Mosquitoes become infected when they feed on infected birds. These infected mosquitoes can then transmit the virus to humans and animals. In addition to the three human cases this year, a horse was also infected.

The virus first appeared in North America in the early summer of 1999. In 1999, 62 cases of severe West Nile virus, including seven deaths, were reported in the New York area. In 2000, 21 cases were reported, with two deaths.