The first likely case of human West Nile infection in 2004 was reported in Ohio on Tuesday, health officials said.

The Ohio Department of Health said a 79-year-old man was believed to be infected with the virus, which first appeared in the United States in 1999 and which has spread coast to coast and to Canada and Mexico.

“Today’s development should remind us all of the importance of taking personal protection measures and working to eliminate mosquito breeding sites on and around our properties,” Dr. Nick Baird of the Ohio Department of Health said in a statement.

Last year the U.S. Centers for Disease Control and Prevention reported 9,858 West Nile cases, with 262 deaths in 45 states and the District of Columbia.

No one knows how the virus was brought to the Western Hemisphere, but it is carried by birds and transmitted to people by mosquitoes that first bite infected birds and then bite humans. Experts say it is in North America to stay, although as mosquitoes go dormant in winter the virus disappears for a while before coming back.

Each year it has re-appeared earlier than before in many places. Health experts say the best way to protect against it is to avoid mosquito bites by wearing long sleeves and trousers and staying inside when mosquitoes are most active.