Researchers Address Concerns
Over Texas Soremouth Outbreaks

By Colleen Schreiber

SAN ANGELO — Several outbreaks of soremouth were reported this past summer in West Texas. Though outbreaks are not necessarily uncommon, what was uncommon was the fact that the problems seemed to occur primarily in animals that had been vaccinated. All outbreaks reported were found in goats.

Because of concerns voiced by ranchers in the area, Drs. Andres de la Concha and Charles Taylor with the Texas A&M University Experiment Station addressed these concerns and reviewed proper procedures for handling and administering the soremouth vaccine at the recent Sheep and Goat Field Day here.

Two vaccines are available in the United States for the prevention of soremouth in sheep and goats. The Texas A&M Experiment Station at Sonora has been manufacturing and selling one for more than 60 years. This product is licensed for use in sheep. Another vaccine licensed for both sheep and goats is made by the Colorado Serum Company.

To determine if the failure of the soremouth vaccine was due to strain variation or faulty vaccination technique, the researchers conducted a basic experiment. De la Concha presented those findings.

Six "soremouth-naive" goats were used in the study. Two were vaccinated with the TAES vaccine, two with the Colorado Serum vaccine and two with a placebo, meaning that the diluent was used without the virus. All were vaccinated in the skin of the left inner thigh.

Three weeks after vaccination, all goats were exposed to a "wild-type" virus, virus that had collected from the outbreaks. Skin reactions were observed every other day and graded on a scale from zero to 35, with zero indicating no reaction and 35 a severe reaction.

All six goats, said de la Concha, showed skin reactions after being challenged with the wild-type soremouth virus. The severity of the skin reaction after the challenge was higher in the non-vaccinated group, followed by the TAES-vaccinated group and then the CSC-vaccinated group.

"Both vaccines failed to induce a strong protective immunity," de la Concha said. "We're unsure as of yet what's happening. Perhaps the virus mutated and caused the outbreak; perhaps we have a new strain of the virus and therefore we didn’t get strong protection, but that’s speculation."

Both vaccines are live vaccines, de la Concha reminded field day participants, meaning the virus present in the vaccine is infectious, can be transmitted to other animals and could eventually produce disease.

"That means that if you don't handle the vaccine properly, if you don't administer it properly, you may actually spread the disease instead of preventing it."

He reminded producers that vaccination should only be done if the infection has occurred on the premises in previous years. Also, recently vaccinated animals should not be allowed in contact with unvaccinated animals.

Taylor reviewed proper handling and vaccination procedures. All soremouth vaccines contain a bottle of dried virus and a bottle of sterile diluent for rehydrating the vaccine.

"Proper handling and storage of the vaccine," Taylor stressed, "is critical to maintain efficacy. For example, don't leave the vaccine in the sunlight on your dashboard."

He reminded producers that the expiration date is there for a reason.

"It might still work if it's past the expiration date, but how expensive is a bottle of vaccine relative to the other costs?"

Taylor also recommended vaccinating under the leg for better protection rather than using an icepick in the ear. Most likely, he said, use of the latter technique will result in poor vaccination protection. Appearance of a scab at the site of inoculation a few days later indicates a successful inoculation.

Finally, he said, if an outbreak occurs, knowing the serial number on the vaccine is important information for the Experiment Station to know.

Because reported outbreaks were found only in goats, some producers have questioned whether, perhaps, some new strain of soremouth was brought into the country with imported Boer goats.

"I think if that was the case it would make sense that we would have seen more resistance in Boer goats and more outbreaks in the Spanish goats or sheep, but that hasn't been the case," de la Concha said.

The scientist said the pros and cons of incorporating new strains into the vaccine are being considered. De la Concha is working on finding funding for a long-term research program on soremouth that eventually will lead to the development of safer and better vaccines. However, he said, such funding is hard to come by.

"It's hard to get funding from USDA because sheep and goats are not considered a national priority."

He tested the waters by asking producers whether they would be willing to pay $1 to $2 more for a bottle of vaccine to defer some of the expenses of such a research project. Response appeared generally favorable.