A third confirmed case of West Nile virus has been reported in Warren County.

The Mississippi Department of Health also said Monday that cases have been reported in Claiborne, Yazoo, Hinds and 11 other counties, bringing the state total to 169 and four deaths this year.

In 2011, Mississippi had 52 confirmed cases of the virus and five deaths attributed to it.

The health department reports only laboratory-confirmed cases to the public, but as many as 80 percent of people infected with West Nile never realize they have the virus. About one in 150 people who are infected become seriously ill.

“It is very underdiagnosed,” said Dr. Jonathan Oluwatad, an infectious disease specialist at River Region Medical Center.

Symptoms of West Nile infection are often mild and may include fever, headache, nausea, vomiting, a rash, muscle weakness or swollen lymph nodes. Those who become seriously ill can contract encephalitis or meningitis, which can lead to paralysis, coma and possibly death.

City and county road crews spray almost daily for mosquitoes to help control the population of the biting insects and put larvacide in standing water.

The peak months in Mississippi for West Nile are July, August and September, but mosquito-borne illnesses can occur year-round, state health officials said.

Removing standing water is a top priority in the fight against West Nile, health officials have said.

Mosquitoes need very little water — as little as a bottle cap full — to serve as a breeding ground, according to the MSDH, and in less than three weeks’ time, depending on environmental factors, the flying bloodsuckers are ready to spread diseases including West Nile Virus.

Tips include avoiding contact with mosquitoes by repairing screens on windows and doors, wearing long-sleeved shirts and pants and using repellents containing DEET, or Environmental Protection Agency-registered repellents for use on human skin.

For more information on West Nile and other mosquito-borne illnesses, a checklist to reduce the mosquito population in and around homes and recommended mosquito repellents, visit www.HealthyMS.com/westnile or call the WNV toll-free hotline from 8 a.m. until 5 p.m. Monday through Friday at 1-877-978-6453.