Two previous cases were in Forrest County and one was in Rankin County.
West Nile virus cases tend to peak in August for North Dakota, but it is possible to occur at any time, said Michelle Feist, epidemiologist with the North Dakota Department of Health, Division of Disease Control.
An unvaccinated horse from Clark County is the first reported Wisconsin horse to have become infected with West Nile virus and euthanized this year.
Symptoms may show up suddenly, with a high fever and headache.
Mosquitoes had previously tested positive for West Nile in Berthoud in late June.
The 113 cases were up from a total of 107 listed on the department website a week earlier.
West Nile virus is a disease spread from infected crows, ravens, magpies and jays to humans through mosquito bites.
The virus is not contagious between horses, but can be carried by mosquitoes from an avian, or bird, host to horses and humans.
The best way to protect yourself from West Nile is to prevent mosquito bites.
Residents are encouraged to continue with preventive measures such as wearing mosquito repellent when they participate in outdoor activities, said Robin Iszler, unit administrator for Central Valley Health District in Jamestown.
Wear long-sleeved shirts and long trousers when outdoors. Use a repellent with DEET (N, N-diethyl-m- toluamide), permethrin, picaridin (KBR 3023), IR3535 or oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] according to the instructions on the product label. Mosquitoes breed in water, so items like bird baths, empty buckets, clogged gutters and kiddie pools should be drained regularly to keep mosquito populations down. "The mosquitos carrying the virus in Washington County were trapped at the Weiser Bass Pond located about 1.5 miles west of Weiser city limits".