Emerging and Reemerging Diseases of Texas Beef Cattle
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This dissertation focused on three emerging/reemerging diseases posing economic impacts on Texas livestock producers. Bovine trichomoniasis is a regulated disease requiring diagnostic testing; however, current diagnostic protocols are problematic. Major obstacles resulting from variable collection procedures and discrepancies in sample handling and laboratory test accuracy need further investigation. Epizootic hemorrhagic disease primarily affects white-tailed deer; however, it is unclear why clinical disease is rarely exhibited in cattle in the same region, requiring the investigation of seroprevalence in Texas cattle. Bovine viral diarrhea (BVD) causes significant reproductive loss and complicates other diseases through immunosuppression. Although vaccination is the primary method of mitigating fetal infection, a systematic review assessing fetal protection from vaccination is needed. Methods to examine the collection, shipment, and diagnostics associated with bovine trichomoniasis included (1) testing of infected bulls for sample quality and testing accuracy related to time, collectors, and individual bulls; (2) evaluation of samples with temperature sensors in a controlled environment when shipped by common carrier; and (3) evaluation of a patented polymerase chain reaction (PCR) technique for expedient sample handling and improved diagnostic sensitivity. Methods to evaluate prevalence of epizootic hemorrhagic disease in Texas cattle were based on random blood sera collections from 11 auction markets. Methods to assess safety and efficacy of BVD vaccines for fetal protection were based on a systematic review of the scientific literature. There was little variation in bovine trichomoniasis test results due to collector or bull, indicating proper and standardized sample collection protocol increased test accuracy. Shipping samples in temperature-controlled containers to arrive at the laboratory within 24 hours also improved diagnostic accuracy. The newly patented PCR test exhibited 100% diagnostic sensitivity and 99% specificity for field samples from 56 positive and 110 negative bulls for improved test accuracy. A high seroprevalence of epizootic hemorrhagic disease (70% to 97% depending on different threshold titer positive cutoff values) was seen in Texas auction cattle, but clinical disease is rare. Much of the scientific literature dealing with BVD supports vaccination for fetal protection but lacks transparency regarding experimental design, creating a potential for bias and making evaluation of these studies difficult.
