The Colorado Department of Agriculture reported Thursday that ten equine cases of West Nile Virus have been confirmed in Colorado, with four horses having to be euthanized due to its severity.

Cases were confirmed in eight counties across the state including Adams, Garfield, Larimer, Mesa, Montrose, Pueblo, Rio Blanco, and three in Weld.

West Nile Virus is transmitted to horses through bites of infected mosquitos, which can cause severe illness and death. Symptoms include fever, muscle tremors, teeth grinding, incoordination, inability to swallow, lethargy, falling down, and weakness. About one-third of horses infected die or have to be euthanized.

Prevention includes proper vaccination, mosquito repellant, and eliminating mosquito breeding sites such as stagnant water sources. Horses that have not been previously vaccinated will need a two-shot vaccination series within a three to four week period. Horses who have been fully vaccinated will still need an annual booster.

According to the report, the Colorado Department of Public Health and Environment has also confirmed 72 human cases to date in 2019, with one fatality reported.