Lyme Disease Treatment and Vaccine

Nearly 50% of adult horses in areas of the northeastern United States are or have been infected with Borrelia burgdorferi, the causative agent of Lyme disease. Thomas Divers, DVM, Dipl. ACVIM, Dipl. ACVECC, and others at Cornell University recently completed research that confirmed the value of tetracycline treatment and efficacy of a recombinant outer-surface protein A (rOspA) vaccine against B. burgdorferi.

Researchers found that tetracycline given intravenously once daily is superior to orally administered doxycycline once daily or intramuscular ceftiofur (Naxcel) twice daily, both of which have been used in Lyme disease cases. They think this might be because tetracycline achieves higher tissue concentrations compared to relatively low levels of oral doxycycline. The efficacy of tetracycline might not be as good in horses infected for longer than five months.

It was shown the rOspA vaccine is effective in preventing Lyme disease in ponies challenged with infected ticks three weeks after a three-dose vaccination series. The vaccine seems to inhibit the spirochete within the tick, since there was no serologic conversion in vaccinates. This is probably because when the tick feeds on vaccinated horses' blood, the spirochete, which inhabits the gut lumen of the tick, is exposed to antibodies in the horse's plasma.

"We do not know how frequently to vaccinate" in order to maintain protection against B. burgdorferi, Divers said. The vaccine would be of questionable value once the animal is infected, and safety studies need to be completed on it before it becomes widely used.

The researchers also confirmed the consistency and predictability of how B. burgdorferi infects ponies. (See article #4973 online.)

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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