Maximal predicted duration of viremia in bluetongue virus-infected cattle

Central to the development of rational trade policies pertaining to blueton gue virus (BTV) infection is determination of the risk posed by ruminants p reviously exposed to the virus. Precise determination of the maximal durati on of infectious viremia is essential to the development of an appropriate quarantine period prior to movement of animals from BTV-endemic to BTV-free regions. The objective of this study was to predict the duration of detect able viremia in BTV-infected cattle using a probabilistic modeling analysis of existing data. Data on the duration of detectable viremia in cattle wer e obtained from previously published studies. Data sets were created from a large field study of naturally infected cattle in Australia and from exper imental infections of cattle with Australian and US serotypes of BTV Probab ility distributions were fitted to the pooled empirical data, and the 3 pro bability distributions that provided the best fit to the data were the gamm a, Weibull, and lognormal probability distributions. These asymmetric proba bility distributions are often well suited for decay processes, such as the time to termination of detectable viremia. The analyses indicated a > 99% probability of detectable BTV viremia ceasing after less than or equal to 9 weeks of infection in adult cattle and after a slightly longer interval in BTV infected, colostrum-deprived newborn calves.