A horse has tested positive for West Nile virus in Burleigh County.

It is among one of five reports of West Nile virus in animals. No humans have been reported to have West Nile. So far, 13 people were tested for the virus by the North Dakota Department of Health Laboratory.

The horse that tested positive is alive. Blood tests are used to detect West Nile, according to the state veterinarian's office.

West Nile is spread by certain species of disease-transmitting mosquitoes. The virus affects horses, birds and humans, and causes headaches, fever and nausea in some people.

The health department tracks mosquito numbers and looks for the primary culprit of spreading the disease, the female mosquito culex tarsalis. The health department started setting out traps over Memorial Day, and data was to be tracked on the West Nile Web site this week.

Besides the horse, one dead bird and three sentinel chickens have tested positive for the virus. The dead bird was found in Cass County. Two of the infected sentinel chickens were found in Grand Forks County, and one of the sentinel chickens was found in Ramsey County.

"We like to use dead birds and sentinel chickens to monitor" West Nile, surveillance coordinator Michelle Feist said.

Most people infected with West Nile - 80 percent - do not show symptoms. Those with symptoms may have a fever, headache and nausea, which will last a few days. More severe symptoms, such as tremors, disorientation and muscle weakness, can occur. People with more severe symptoms should visit their health care providers, Feist said. West Nile can be fatal.

Reports of animals with West Nile show it is in the area, and now it's a matter of prevention. Insect repellent, wearing light-colored clothing, removing standing water and keeping grass trimmed around buildings will help limit mosquito bites and mosquito habitat.

In past years, the first human cases usually have been reported in June, Feist said.

There were 86 cases of humans with West Nile in North Dakota in 2005.

Nationwide this year, four people have tested positive for the virus, 58 birds have died from the virus, 16 sentinel chickens have tested positive and 53 mosquito pools are positive for the virus.