Prince George's County authorities reported yesterday that a resident has likely contracted West Nile virus, the first human case of the mosquito-borne illness in the region this year.

Patricia Sullivan, a spokeswoman for the Prince George's County Health Department, said preliminary tests by the state concluded that the person did have West Nile. Additional tests, which will be completed in two to three weeks, are needed to confirm the diagnosis, she said.

Health officials said residents should take precautions, such as wearing insect repellent when outside, using screens on open windows and removing standing water from around homes. The region generally sees most of its West Nile activity between mid-July and the end of October. Culex mosquitoes, which carry the virus and can spread it to humans, usually proliferate in August and September.

"This is about the time we'd expect to see something," said John Hammond, a spokesman for the Maryland Department of Health and Mental Hygiene.

Sullivan provided no information about the county resident, who is recovering at home. She said she was unaware of the patient's condition at the time of diagnosis.

The majority of West Nile patients do not become severely sick. Many who contract the virus are unaware they have it. Typically, only the most severe cases get reported. The population at risk for infection, mainly the elderly, is small.

Symptoms can appear three to 15 days after an infected mosquito bites. They can range from mild, flulike discomfort to encephalitis and meningitis.

Health officials said West Nile activity in the region has been minimal this year. For example, prior to the report of the human case, Prince George's has had only pools, or samplings, of mosquitoes test positive for the virus.

Seventy-three people contracted West Nile in Maryland in 2003; eight died. Virginia had 26 human cases of West Nile and one death. The District had three cases and one death.

"Our point right now is protection and prevention," Sullivan said. "That's what people need to be reminded of."