Thirteen more human cases of West Nile virus have been reported by the North Dakota Department of Health.

So far this season, 125 human cases have been reported, surpassing the 86 cases reported in 2005.

"The season is starting to wind down," West Nile Virus Surveillance Coordinator Michelle Feist said.

The lab at the department of health is conducting fewer tests for the virus, she said.

In Burleigh County, 58 people have been reported infected with the virus and in Morton County, 13 people have been reported infected with the virus.

Horses also are susceptible to the virus. So far, four horses have tested positive. Horses can be vaccinated for the virus. It is a yearly vaccination, Feist said.

Reports of horse infections can vary year to year depending on how many horses are tested, she said.

In Burleigh County, one horse was reported infected and no horses have been reported in Morton County.

Mosquito numbers continue to dwindle with the colder weather. It was a dismal season for mosquitoes compared to last year to begin with. Conditions, however, favored the disease-transmitting culex tarsalis mosquito. This species likes hot, dry weather, and breeds in shallow, stagnant water, Feist said.

More of the culex tarsalis mosquitoes is only part of the reason for their being more reports of human infection of West Nile. The mosquitoes get the virus by feeding on birds that are infected with the virus. The virus spreads when they feed on other hosts, like birds, humans and horses.

Additionally, more people could be getting tested for the virus. This could be because of more public awareness about the virus or healthcare providers doing a better job recognizing the symptoms, Feist said.

Only one person has died this year from the virus and 32 people have been hospitalized.

It takes three days to two weeks from the time of infection for people to show symptoms of the virus. Most people who are infected, however, do not have symptoms. Those who do have nausea, headache, fever and feel achy. The most severe symptoms, which are rare, can affect the central nervous system. It can be fatal.

The way to prevent a West Nile infection is to not get bit by a mosquito. Insect repellent with DEET, long-sleeved shirts and pants, and staying inside at dusk and dawn can reduce a person's risk.

"As long as someone is outside, they are considered at risk," Feist said.

The health department will track West Nile numbers through the end of the year. The virus reaches its peak in late August or early September. The Web site is www.ndwnv.com.

(Reach reporter Sara Kincaid at 250-8251 or sara.kincaid@bismarcktribune.com.)