Veterinary Updates by Tom Clark, DVM

WEST NILE UPDATE

Despite mosquito and dead bird testing in central and southern Arizona, only one mosquito sample from Mesa was positive for West Nile Virus through mid-May in 2005. Recently, however, several mosquitos have tested positive for WNV in the Yuma area. In 2004 there were 1305 confirmed cases of equine WNV disease in the USA. 109 confirmed cases were in Arizona and 534 cases in California. The death rate from the disease or euthanasia was 24.8% in Arizona and 43% in California. Scientists have not been able to explain the differences in the mortality rate from various states.

Dogs and cats are easily infected with the WNV, but usually suffer no consequences. The peak season for equine infection is late summer/early fall with August and September producing the largest number of cases. There is no cross protection for WNV from vaccination for Western or Eastern Encephalitis. There are 2 excellent vaccines available for the prevention of WNV in horses. It is recommended to vaccinate prior to peak risk, i.e. June or July for Arizona horses. Foals should start their vaccinations at 3 months of age, and healthy adult horses can receive their initial vaccinations at any time. A new Texas A & M study found no connection between foal losses and vaccination against WNV. This study was based on 595 mares from 4 different farms in Texas and Kentucky. Horses who have recovered from clinical infections should be vaccinated 1 year after recovery.

RABIES UPDATE

As of March 25th, 43 animals have been confirmed to be infected with rabies in 2005 by the Arizona State Health Laboratory. The vast majority of these rabid animals have been skunks with 34 of the 38 found in Pima County. Only 3 bats and 2 foxes have tested positive for rabies as of March 25th. Pima County usually reports the most cases of rabies. Historically, bats and skunks are the most frequently infected animals.

One of the recent rabid skunks joined a group of campers as they enjoyed a campfire at Patagonia Lake State Park in Santa Cruz County. Another rabid skunk was found by a trail rider in Saguaro National Park east of the Rincon Mountains, southeast of Tucson.

On April 17th, Coconino County Health Department, USDA Wildlife Services, Flagstaff Animal Control, and other collaborators started distributing oral rabies vaccine in bait covered sachets for skunks. In the past few years over 44.5 million oral rabies vaccine/baits have been distributed in the USA for the control of rabies in raccoons. You should check with your veterinarian as to their recommendation for vaccinating your horse. It is out there!

VESICULAR STOMATITIS UPDATE

As you may have learned from TV news, the Arizona Department of Agriculture has confirmed over 30 cases of Vesicular Stomatitis throughout the state in 2005. The first case was confirmed on April 20th, 2005. Last year Texas, New Mexico, and Colorado had a problem with VS, but Arizona managed to escape without any cases. This year Arizona is the second state to detect the disease which normally occurs in 5 to 8 year cycles, the last peak being 1998/1999. So far, Colorado has not reported any cases, but Texas and New Mexico have. VS is most likely to occur during the warm months in the southwestern USA, particularly along river ways and valleys.

VS is an acute, highly contagious, viral disease of horses, sheep, goats, cattle, swine, camelids, wildlife, and humans. Any sex, age, or breed can be affected. Gnats and biting flies are suspected carriers of the disease and direct contact with affected animals can be a source of the infection. Humans are most commonly infected when handling affected animals. In horses blisters and ulcers in the mouth, around the muzzle, and on the coronary bands are the most common signs. The disease can also cause blister like lesions to form on the dental pad, tongue, lips, nostrils, external genitalia, and teats. These blisters swell and break leaving raw tissue that is so painful that infected animals may slobber, bleed from the nose, and generally refuse to eat or drink. Some lesions on the coronary band may produce signs of significant lameness. Severe weight loss usually follows. There is no vaccination for VS and, fortunately, most all infected animals eventually recover within 1-5 weeks with supportive care and "tincture of time." VS can mimic Hoof and Mouth disease which has been eradicated from the USA since 1929. The only way to tell these diseases apart is via laboratory testing, therefore, the state veterinarian requires all suspected cases of VS to be reported to his office.

Infected animals must be quarantined and not allowed to move off the premises for at least 30 days after the last lesion has healed. What is important for us as trail riders, is that states not currently having problems with VS, such as Colorado, want to make sure we do not bring infected animals into their state. When traveling out of state your health certificate may be required to be less than 48 hours old, include a specific statement concerning VS, and have a permit number issued by the state, as is currently required by Colorado. Check with your veterinarian before traveling out of state to get the latest requirements in order to avoid unnecessary delays.