Epidemiology of white spot syndrome virus (WSSV) and Taura syndrome virus (TSV) in some penaied shrimps
An epidemiology model was used to study factors that affect the likelihood and characteristics of shrimp viral epizootics. A method was presented for testing the negative binomial distribution that allows for identifying differences in hosts' dispersion pattern that may affect pathogen introductions. Differences in dispersion pattern were observed in wild penaeid shrimp populations ( Farfantepenaeus aztecus, F. duorarum , and Litopenaeus setiferus ) of the Gulf of Mexico. An experimental protocol was developed based on an epidemiology model to study the transmission, virulence, and recovery rates of white spot syndrome virus (WSSV) and Taura syndrome virus (TSV). I compared: (1) two modes of transmission for WSSV and Litopenaeus vannamei (cohabitation vs. ingestion of infected cadavers); (2) the ingestion transmission of WSSV to L. vannamei and L. setiferus ; (3) the transmission of L. vannamei (Kona stock) from exposures to WSSV and TSV. In addition, the virulence and recovery rates of WSSV and TSV to L. vannamei and of WSSY to L. setiferus were compared. The cohabitation transmission estimate was 0.01, and of ingestion transmission was much larger (0.46) suggesting that cohabitation is a much less important mode of transmission for WSSV. A statistically significant difference was detected between the estimates of ingestion transmission of L. vannamei (0.46) and L. setiferus (0.84), yet no differences in the virulence or recovery rates were detected between hosts. The estimated virulence rate was 0.34, and the recovery rate from a WSSV infection was 0.007 for both species. For the TSV and WSSV exposures to L. vannamei , the transmission rate was higher for TSV (0.61) than for WSSV (0.41); the virulence rate was higher for WSSV (0.37) than TSV (0.12); and the recovery rate was higher for TSV (0.10) than for WSSV (0). Finally the infectivity of a WSSV infected cephalothorax, abdomen, and whole shrimp was compared and assumptions of epidemiology models were tested. The results suggested that there was no difference in the viral loads of a WSSV infected cephalothorax or abdomen, but that the cephalothorax was more infectious probably because it was more palatable. In addition, the results are inconsistent with some assumptions of epidemiological models.