July 01, 2003

 

 Vaccines may be key to controlling FMD - July 1, 2003

Posted on June 13, 2003
 

Researchers, get ready. A new study indicates that scientists need to intensify their research into the use of vaccination to control an outbreak of foot-and-mouth disease in the United States. This includes the development of vaccines, response to vaccination, and diagnostic tests that can distinguish animals naturally infected with FMD virus from those that were vaccinated. From an economic standpoint, vaccination may be a viable option for controlling the disease, according to a study in the July issue of the American Journal of Veterinary Research.

"Despite a previous reluctance of the United States and other countries to consider using vaccination as a means to control FMD, it appears that vaccination could well be an important tool," said Dr. Mark Thurmond, a professor in the Department of Medicine and Epidemiology at UC-Davis School of Veterinary Medicine and an author of the study.

"Results also suggest, on the other hand, that preemptive slaughter, which is a strategy that we have held onto for a long time, would be very expensive and not cost-effective."

UC-Davis researchers, led by Thomas Bates, PhD, formerly a researcher at the university and now at Lawrence Livermore National Laboratory, came to these conclusions after developing a model for 2,238 herds and five sale yards located in Fresno, Kings, and Tulare counties in California. In their model, the scientists took into account direct costs associated with indemnity, slaughter, cleaning and disinfecting livestock premises, and vaccination, comparing them in various eradication strategies. Based in part on results of published model simulations, the researchers estimated the net benefit and benefit-cost value for each supplemental strategy.

They concluded that vaccination with a highly efficacious vaccine could be a cost-effective strategy for controlling foot-and-mouth disease during an outbreak, providing vaccinated animals are not subsequently slaughtered and adverse economic impacts on trade are mitigated by tests that would be able to differentiate between vaccinated and naturally infected animals.

In addition to ethical and environmental considerations associated with slaughter strategies, several supplemental control strategies involving the use of vaccination were economically efficient and feasible. Supplemental strategies involving preemptive slaughter of nearby herds, however, were not economically efficient. When implemented rapidly with appropriate vaccines, vaccination was the economically preferred strategy for controlling one of the most economically important diseases that affect livestock.

Investigators determined that it would cost $5.2 million to slaughter all cattle in only two average-sized dairy herds, which was almost as much as the estimated $6.6 million it would cost to vaccinate all of the herds in the study region. Vaccination cost was estimated to be $2,960 per average-sized livestock herd.

"It really hinges on the success of the vaccination program," Dr. Thurmond said. This includes making sure that the appropriate amounts and types of vaccines are available, the vaccines are efficacious, and there is a workforce that has been trained and can be put in place to administer them immediately when needed. Researchers also need to better understand when and why vaccinated animals can occasionally become FMD virus carriers.

"In the near-term, we need to pursue diagnostic test research much more aggressively, including test validation acceptable to international animal health organizations," Dr. Thurmond said. "Under the somewhat optimistic conditions assumed in the model, vaccination would be a cost-effective strategy, but if we don't have internationally accepted diagnostic tests that can be used to distinguish vaccinated animals from those that were naturally exposed, a vaccination strategy is not likely to be approved."