Eradicating Diseases in Cattle

Livestock Update, June 2001

Dee Whittier, Ext. Veterinarian, Cattle, VA-MD Regional College of Veterinary Medicine

The Foot and Mouth Disease (FMD) outbreak worldwide has brought the subject of disease eradication to the forefront in many discussions since vivid pictures of dead animals have been common in the news media. A review of the great advantages and details of eradication programs in cattle disease may serve to remind cattle producers of some important principles.

Significant programs for cattle disease eradication began as early as the late 1800's. It was then apparent that there were some diseases that had characteristics that would allow their complete elimination from a country's borders. In general, these characteristics include:

• The disease organism only survives in a limited number of hosts. A disease caused by an agent that infects large numbers of animal species would be very hard to eradicate.
• The disease organism must not be able to survive outside the animal host for long periods of time. Disease organisms that can survive in the environment for months or years would be nearly impossible to eradicate.
• There must be a precise way to identify infected animals and distinguish them from non-infected ones. In some cases, infected animals can be readily recognized but generally tests that identify infected animals must be developed and applied.
• The disease must be serious enough that it motivates the large effort that must typically be mounted to eradicate it.
• Eradication of the disease is judged to be less expensive, in the long run, than other approaches to controlling the disease.

A number of diseases have been or are being eradicated from cattle in the US. These include Foot and Mouth disease of current interest as well as Brucellosis (Bangs Disease), scabies and Tuberculosis which are in the final stages of eradication. Other diseases are less familiar to cattle producers but, had they not been eradicated would have still been important causes of animal loss. These include such diseases as Contagious Bovine Pleuropneumonia and Piroplasmosis (tick fever). Mad Cow Disease is currently being eradicated from Europe at a huge cost.

A number of approaches to eradication exist. Sometimes more than one of these tools is used for eradicating a disease. Approaches include:

• Test and slaughter. Although this is a harsh approach, with many diseases where no effective treatments exists or where spread is very rapid, removing infected or high-risk animals from the population is the only effective track towards eradication.
• Treatment. Dipping cattle to kill the mites that cause scabies is the major thrust to eradication with this skin disease.
• Vaccination. Only very rarely is vaccination effective enough to totally eradicate a disease (human small pox is a very fortunate exception). Sometimes, however, vaccination can be coupled with test and slaughter. Bruccellosis is an example of this approach. In some cases with Foot and Mouth disease eradication, cattle in the area of the outbreak are immediately vaccinated to slow the spread of the disease, then later (when there may be more resources for carcass removal), these animals are slaughtered. Vaccination alone does not completely prevent animals from becoming infected with the FMD virus nor from them shedding it. Vaccination does prevent severe disease and decrease shedding of virus.
• Some novel approaches. Screwworm has been eradicated from the US and Mexico by releasing sterile male flies.

As livestock producers in the US, we have great reason to appreciate former and current eradication efforts that make our cattle population quite disease free and thus allow the economical production of animal products. This disease freedom allows us to keep large numbers of animals in a small area and to move them around for breeding, sale and exhibition very freely.

Are cattle disease eradication efforts in the US now almost history? This question is an interesting one. There are still diseases that are eradicable and have been eradicated in some countries. The US approach to these diseases has either been to live with them or to practice wide scale vaccination. Diseases that fit this category are Johne's Disease, Bovine Leukosis Virus, Anaplasmosis and even BVD.

Whether additional eradication programs are begun in the US will depend on a number of factors. One of these is producer's interest in such programs. Whether we embark on additional eradication or not there will always be the need for surveillance to be sure that the diseases have not returned. There should also be great appreciation for the freedom that past eradication efforts have afforded us in our livestock programs.

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