Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2005
Publication Date: 2/15/2006
Citation: Fulton, R.W., Hessman, B., Johnson, B.J., Ridpath, J.F., Saliki, J.T., Burge, L.J., Sjeklocha, D., Confer, A.W., Funk, R.A., Payton, M.E. 2006. Evaluation of diagnostic tests used for detection of bovine viral diarrhea virus and prevalence of subtypes 1a, 1b, and 2a in persistently infected cattle entering a feedlot. Journal of the American Veterinary Medical Association. 228(4):578-584. Interpretive Summary: Infections with bovine viral diarrhea viruses (BVDV) result in significant economic losses for feedlot producers. Most of these losses are associated with an increased incidence of respiratory disease. The most common way in which BVDV gets into a feedlot is by the introduction of an animal that is persistently infected (PI) with BVDV. The faster one can identify and eliminate a PI animal, the fewer animals it can infect. In this study we looked at several different types of tests and found that they could all detect PI animals. However, one of the tests called an ELISA gave results much faster than the others. Because it is faster, it may be the best choice to use in feedlots. We tested 21,743 animals entering feedlots and found 86 PI animals. This number may look small, but when we looked at how the animals were housed we found that more than 30% of all the animals at this lot would be in direct contact with a PI animal. This just counts the animals that would be in the same pen as the PI animals. When we looked at animals, that would be in pens next to the PI and might have nose to nose contact, then that percentage was a lot higher. Two other findings in the study are important to the control of BVDV. One is that most of the PI animals (77.9%) were infected with a variety of BVDV, called BVDV genotype 1b. At this time there are very few vaccines that contain this variety of BVDV. Therefore we need to see if our vaccines will protect against this BVDV variety or if we need to add this variety to the vaccine. The second is that there is a lot of virus in nasal secretions. It appears that BVDV may spread between pens when animals make nose to nose contact over fences.
Technical Abstract: Feedlot cattle are at a high risk for exposure to bovine viral diarrhea virus (BVDV). Control of BVDV in feedlots centers on: (1) enhancement of BVDV immunity by vaccines; and (2) biosecurity using methods to identify and remove cattle persistently infected with BVDV (PI). Several diagnostic tests are available for screening for PI animals. The objective of this study was to evaluate multiple tests designed to detect PI calves entering a feedlot; determine the prevalence of PI animals and characterize the BVDV genotypes found in PI calves. Test used included virus isolation from serum, polymerase chain reaction from serum, immunohistochemistry on ear notches and ELISA on ear notches. There were 86 PI calves out of 21,743 giving a 0.4% prevalence PI rate. There was 100% agreement among on the tests used on detection of the 86 PI animals. The ELISA test also detected transient infections in 2 additional animals. Results from the ELISA were obtained much faster than results from the other tests. Distribution of BVDV subgenotypes for the 86 noncytopathic BVDV strains are as follows; 77.9% BVDV1b, 11.6% BVDV1a, and 10.5% BVDV2a. The level of viral titer in serum and nasal swab samples were similar (100 – 10,000 viral infectious doses per ml). The high level of virus in nasal swab samples indicate that nasal secretions can be a significant means of viral spread.