The current West Nile outbreak is one of the largest ever in the United States, but Warren County has remained free of the mosquito-borne illness for half a decade.

Statewide, 85 people had been reported infected with the virus as of Thursday, according to the Mississippi Department of Health, and more than a third of those cases are just a few miles away in Hinds and Rankin counties.

So what has kept reported cases of the deadly virus from crossing the Big Black for so long? No one is quite sure, said state ep-idemiologist Dr. Thomas Dobbs with the state health department.

“It’s hard to know for sure. There’s been a lot of possibilities,” Dobbs said.

About four of five people infected with West Nile never get sick, Dobbs said. Early symptoms can include fever, headache and body aches. Some recover in a matter of days. But one in 150 infected people will develop severe symptoms including neck stiffness, disorientation, coma and paralysis.

West Nile was last confirmed in Warren County in 2007, but the lack of reported cases in Warren County might be deceiving, Dobbs said.

“Just because there aren’t any reported cases doesn’t mean there isn’t any West Nile virus there,” Dobbs said.