With nearly 50 confirmed cases of equine West Nile virus reported in Arizona, several East Valley veterinarians have been working to cure diseased horses despite the high cost and limited availability of an FDAapproved antidote.
Of the 48 equine cases reported by the Arizona Department of Health Services, only seven were in Maricopa County. However, Valley veterinarians say they have treated many more than that.
One reason for the low number of reported cases is that some veterinarians don’t notify state officials after treating horses with West Nile, said Rae Chornenky, legislative liaison to the Arizona Department of Agriculture.
Queen Creek veterinarian Melanie Rettler said she has treated three horses so far that tested positive for the disease, and all three have recovered.
Cheryl Rahal, medicine specialist for Chaparral Animal Hospital in Phoenix, also has treated three horses successfully. Chaparral ran out of the approved antiserum earlier this week, she said, but has since restocked.
Queen Creek Vice Mayor Lisa Coletto-Cohen, who also runs a family-owned veterinary clinic, traveled to California on Sunday to get more doses of the antiserum but was unsuccessful because of its limited supply. Still, no horses have been reported dead from the encephalitiscausing disease as a direct result of the serum being unavailable.
The treatment, a hyperimmune plasma, is created by injecting healthy horses with large doses of a West Nile vaccine, then extracting their highly immune blood plasma.
The plasma is further refined so that only the disease-fighting proteins remain. Horses injected with the antiserum should quickly develop the immunity of a vaccinated horse, Rahal said. The technology is impressive but not cheap, she added, at $600 a dose.
"It’s kind of scary because the bottle is only 250 (milliliters)," Rahal said.
The actual vaccine is much less expensive, but it takes two to three months for the horse to build up a defense to West Nile. Those who haven’t vaccinated their horses have little choice but to buy the hyperimmune plasma, she said.
Rettler said as long as horse owners seek treatment within the first day of the disease’s onset, there is a good chance of full recovery.
One potential problem with the recently developed antiserum is that a horse’s body could reject it like a blood transfusion of the wrong type, Rahal said.