With the outbreak of West Nile virus last summer, the drone of mosquitos has become a threatening, not just annoying, sound.

For horse owners in Freeborn County, the vaccination against West Nile has become a necessity, not just an option.

Fred Harris, owner of Red Rail Ranch in Freeborn County, said he didn’t have to think twice about getting the West Nile shot for his 13 horses.

&uot;All the horses here were vaccinated last summer,&uot; he said.

Harris had some advice for those who haven’t bought the vaccine.

&uot;If they aren’t vaccinating their horses they should think about it and get it done,&uot; he said. &uot;It’s not a pretty sight when one gets it.&uot;

West Nile virus, which is usually found in Africa and southern Europe, was first detected in the United States in New York City in 1999. It has spread westward to 44 states, infecting thousands of horses and people &045; including 284 human deaths &045; according to 2002 data from the Centers for Disease Control and Prevention.

The virus first appeared in Minnesota on July 9, 2002, when a dead crow was discovered near Isle. Since then, it spread to all but two counties &045; Lake and Cook in northeastern Minnesota &045; and 48 people tested positive for the virus. Of those, at least 25 were hospitalized, but none died.

After the virus made its first appearance in the state last year, nearly 1,000 horses tested positive for it. About 300 died.

The West Nile virus is transmitted by mosquitoes to animals and humans, and causes encephalitis, or inflammation of the brain. Most people who are bitten by an infected mosquito will not get sick.

The virus does, however, pose a serious threat to horses, and state health officials are urging people to vaccinate before the mosquito season arrives in earnest.

&uot;The vaccine is critical because if you get your horses protected adequately before the mosquito season, the vaccine is effective and it will protect your horses,&uot; said Bill Hartmann, the state veterinarian and executive director of the Minnesota Board of Animal Health.

Horses six months and up require two separate injections, one month apart; horses two to six months old require three, also about one month apart. The cost per dosage varies among veterinarians, but generally ranges from $15 to $20.

Mike Bjorklund, a veterinarian at the Clarks Grove Veterinary Clinic, said he hasn’t seen a dramatic rise in the number of vaccinations he’s given out, but says he has given out more.

&uot;It’s not a dramatic increase (over last year) because most people got theirs done last summer,&uot; he said.

Bjorklund has been going from farm to farm this spring giving horses the vaccination. He said he expects to see an increase in number of patients as the summer draws closer.

Signs to watch for in horses include weakness in the back end of the horse, fever, walking in circles and impairment of the central nervous system, such as disorientation.

Last fall, two horses in the Freeborn County area were diagnosed with West Nile virus.

In August, the Minnesota Department of Health reported two horse infections in the county, one in the south central area and the other in the southwest part of the county, near the Iowa border.

Fred Harris said said most of the people he knows who own horses have taken the precaution.

Harris said weighing the cost of the vaccine versus a horse’s life is a no brainer.

&uot;I’m sure there are still people that haven’t but they’re foolish,&uot; he said.

The Associated Press contributed to this report.