February 15, 2015

 

 Study models FMD vaccine strategies

Posted Jan. 28, 2015

Findings of a recent study indicate that, in a foot-and-mouth disease outbreak, vaccinating susceptible animals living in a broad geographic area could result in a shorter outbreak with fewer herds depopulated.

Biosecurity measures, early detection of infections, and control of contacts between farms also could decrease the duration and harm from such an outbreak.

A scientific article published in December in the journal Preventive Veter­inary Medicine (Prev Vet Med 2014;117:487–504) states that, in a series of models that simulated FMD outbreaks in the U.S., the size of the vaccination zone was most important in affecting the outbreak duration and number of herds depopulated. The study considered 17 scenarios, each of which was run 200 times to compare median outcome values of outbreaks that started with latent infections in a northeastern Colorado feedlot containing 17,000 cattle.

The 16 scenarios that involved vaccination ranged in median duration from six months to 20 months, with median numbers of animals depopulated ranging from 1 million to 10 million.

Dr. Michael W. Sanderson, one of the study authors and a professor of diagnostic medicine and pathobiology for the Kansas State University College of Veterinary Medicine, said that variability was a function of modeling the scenarios and the uncertainty in outbreaks.

“On average, you’re better off—in our model, at least—vaccinating over a wide area and, to some extent, focusing on large feedyards,” he said.Eight scenarios had vaccination zones with a 10-kilometer radius, and eight had a 50-kilometer radius.

Dr. Sanderson also said that, in most scenarios, every day later that an outbreak was detected resulted in the need to depopulate substantially more herds.

“Early detection is really important, and producers and practicing veterinarians are the front line for recognizing signs and promptly reporting them,” he said. During an outbreak, “They could really make the difference between us getting an early start and getting ahead of it or being behind and ending up with a large outbreak that takes much more effort to stop.”

The study’s sensitivity analysis showed that the outbreak results also were affected by controls intended to limit animal and human movement between farms and add biosecurity and disinfection practices. Tight controls on contact between farms, such as movement of feed trucks between operations, decreased the sizes of outbreaks. But Dr. Sanderson said those controls could harm animal welfare, increase the difficulty of delivering feed, and increase the difficulty of picking up milk.

Increasing biosecurity through measures such as improving hygiene and truck washing also could control FMD transmission and reduce outbreak sizes, whereas low amounts of biosecurity produced larger outbreaks and left few effective vaccination protocols, he said.

Dr. Sanderson said he would like veterinarians to talk with clients about implementing practical biosecurity in the absence of an outbreak and plan for changes in biosecurity the day they receive notification FMD is found in the U.S.