The previous Animal Health column discussed some of the basic principals of bovine viral diarrhea virus (BVDV) that are important to understand when developing herd BVDV control strategies. Effective BVDV control currently involves a combination of diagnostic surveillance, biosecurity, and vaccination, with all three components tailored to meet the individual needs of an operation.
BVDV does not usually survive in the environment very long (less than 3 weeks), so direct transmission between animals is the most common route of transmission. Animals that are born persistently infected (PI) with the virus shed millions of viral particles every day, and serve as a constant source of BVDV exposure in a herd because they continuously shed virus in saliva, mucous, tears, milk, feces, urine, and any other bodily secretion. It is imperative for producers to identify PI animals and remove them from the herd, and uninfected herds must prevent introducing PI animals into the herd. Some PI animals will be poor-doers, but about 50% will look and perform like non-PI animals. Since PI animals cannot be consistently identified visually, they must be identified with appropriate diagnostic tests.
A number of tests are available to diagnose PI animals such as virus isolation, antigen capture ELISA, PCR, immunohistochemistry (IHC), and serology. The type of test your veterinarian recommends is somewhat dependent on the age, vaccination status, and previous test results of the animal. The best initial screening test currently available in terms of accuracy, cost, and convenience is the antigen capture ELISA performed on a skin biopsy (i.e. ear notch sample), which can be performed on new-born animals as well as adults. This test is currently available at the Tennessee Department of Agriculture KORD Diagnostic Laboratory. Currently, samples collected by producers are being accepted at KORD for testing. Instructions for collecting samples can be found on page 6 of the KORD lab submission guide. The web site address is: http://www.tn.gov/agriculture/publications/labguide/laboratoryguide.pdf. These samples are tested on a regular basis, so producers can expect results back in a timely manner. If you have an animal test positive as a PI, contact your veterinarian to discuss potential follow-up diagnostics to confirm the positive result before accepting a diagnosis of BVDV in your herd.
Disposal of PI animals
Biosecurity is an innovative approach to managing the risk of disease introduction to your livestock operation. A biosecurity plan is designed to help identify and manage disease risks through practical measures for common, everyday infectious agents such as BVDV. An effective biosecurity plan involves multiple components, but results in practical measures for implementation.
- Do not intentionally commingle animals from different herds.
- Provide a buffer between adjoining herds so no fence-line contact is available.
- Isolate new herd additions and test for appropriate diseases such as BVDV before allowing new animals to commingle with your herd. Identify isolation areas prior to purchase.
- Isolate animals for a designated period of time that are returning to the herd from livestock shows and other events.
- Post signs indicating that a biosecurity plan is in effect on your operation.
- Educate all visitors about the biosecurity plan in effect on your operation.
- Ensure that all visitors are dressed appropriately. Provide coveralls and boots, or make sure visitors are wearing clothing free from contact with other cattle.
- Recognize the fact that you are also a source of contamination for your herd. If you are around other cattle, shower and change clothes before working with your livestock.
- Clean and disinfect your truck and trailer after hauling cattle. Anyone hauling cattle for you should do the same.
- Apply appropriate insect control.