A young horse in Fresno County tested positive for West Nile virus. The test was confirmed by Fresno County Health Department and California Department of Food and Agriculture. It was Fresno County's first case of WNV in a horse this year.
The vaccinated yearling developed symptoms of West Nile virus last week; it was still alive Friday.
The Fresno County Ag Commissioner's office reported on Friday that it was not clear if the horse received the initial series of two vaccinations or a single "booster" vaccination.
Although Madera County has had no reported cases of horses testing positive this year for WNV, horses have been reported in previous years.
"West Nile Virus activity in the Central Valley remains high," said Fresno Agricultural Commissioner Jerry Prieto Jr.
"I urge all horse owners to ensure that their horses have been vaccinated to protect them against West Nile virusinfection," he said. All owners of unvaccinated or partially vaccinated horses are advised to contact their veterinarian for guidance.
Aside from this newest case, 12 other California horses have tested positive for WNV so far in 2007; four of those have either died or been euthanized. Last year in California, 58 cases of equine WNV were confirmed with 24 horses dead or euthanized, a mortality rate of 41 percent.
A report released in October 2002 from UC Davis said most horses exposed to the virus do not become ill. No significant age, gender or breed predisposition has been noted among infected horses and their disease outcomes do not appear to be affected by these factors.
Horses that do show symptoms typically suffer from neurological disease.
"The severity and nature of clinical signs," the report stated, "depend on the area of the nervous system affected by the virus and the extent of the resulting lesions."
The Center for Equine Health outlines the vaccination recommendations for West Nile virus.
It states that the optimal time to vaccinate previously unvaccinated horses is spring (March) of each year with a two-dose primary series, three to four weeks apart.
As a general rule, UC Davis veterinarians recommend that horse owners avoid vaccinating pregnant mares in the first trimester of gestation whenever possible. Consulting a veterinarian about the best options for vaccinating horses is recommended.
Vaccinations are recommended for all horses under one year of age in the spring of each year with the three-dose primary series, allowing three to four weeks between doses one and two, and allow six to eight weeks between doses two and three.
If a foal is born to an unvaccinated mare or a mare that was not booster vaccinated four to six weeks before foaling, begin a vaccination series at three months of age.
If a foal is born to a mare that was booster-vaccinated with two months of foaling, UC Davis recommends starting the vaccination series at four to six months of age.
If a horse was fully vaccinated last year or if the primary vaccination series was completed this year, UC Davis recommends a booster follow-up every six months.
UC Davis urges owners to give booster to all horses that have not been vaccinated within the previous six to eight weeks and follow with boosters every six months from the date of the last vaccination.
Horse owners can give additional protection to their animals by reducing the animals exposure to mosquitoes. Putting horses in stables during active mosquito feed times and using fans, barrier cloths, screens, flysheets, repellent sprays and insecticide misting systems will help minimize animal exposure. Following the general guidelines for mosquito control as outlined by Madera Mosquito Abatement department will help increase safety.
Clinical signs of WNV in horses vary, but the most common symptoms include lack of coordination, stumbling, weak limbs, partial paralysis, muscle twitching (especially around the nose and lips), hypersensitivity to touch or sound, head drooping, lethargy and unresponsiveness. A transient fever sometimes precedes these signs by about 10 days.
West Nile virus in horses can be diagnosed by testing blood, cerebral spinal fluid, or certain tissues. The California Animal Health and Food Safety laboratory provides free testing of suspected WNV cases in horses, ostriches, rheas and emus. Call 916-654-1447 in Sacramento for information or contact a local veterinarian. For more information, visit www.cdfa.ca.gov/ahfss/ah/wnv_infor.htm.
To receive a free brochure with information on ways to protect your horse from West Nile Virus, contact the Fresno County Department of Agriculture at 456-7510.
To report mosquito problems call Madera County Mosquito and Vector Control at 674-6729. To report dead birds online, visit the California Department of Public Health website at www.westnile.ca.gov or call 1-866-922-BIRD.
Ramona Frances Ramona Frances is a staff columnist, writer and photographer for the Madera Tribune. You may contact Ramona at 674.8134 ext. 222 or by e-mail ramona (at) maderatribune.net
