Arizona has three confirmed cases of West Nile in horses

A third case of West Nile Virus has been discovered in a horse near Lavine, Arizona.

Two other cases were earlier diagnosed in Mesa, on April 20, and in Buckeye, on June 3.

Last year, in Arizona alone, 109 cases of West Nile Virus were discovered in horses.

Although West Nile affects horses far more often than any other domestic animal, many do not develop any illness, but of those horses that do become ill, about one-third die or need to be euthanized.

On the whole, other livestock and poultry do not appear to show any illness if infected with the West Nile virus.

Mosquitoes become infected with West Nile virus after feeding on an infected bird; they cannot get the virus from an infected horse.

Horses like humans become infected with West Nile virus by the bite of infectious mosquitoes.

After the transmission by an infected mosquito, West Nile virus, can cause a mild, transient, self resolving fever, or it may infect the brain causing inflammation or "encephalitis".

However most horses that are bitten by infected mosquitoes do not become ill, but those that do develop severe encephalitis and often die.

As West Nile virus is transmitted by infectious mosquitoes, an infected horse is not contagious to humans or to other horses.

However routine infection control precautions should be followed when caring for a sick horse.

To date there is no documented evidence that West Nile virus is transmitted between horses.

In order to protect horses the insects in the area must be controlled and the horse vaccinated.