Estimation of prevalence of
white spot syndrome virus (WSSV) by polymerase chain reaction in Penaeus
monodon postlarvae at time of stocking in shrimp farms of Karnataka,
India: a population-based study
P.C. Thakur, F. Corsin, J.F. Turnbull, K.M. Shankar,
N.V. Hao, P.A. Padiyar, M. Madhusudhan, K.L. Morgan, C.V. Mohan-2002
Diseases of Aquatic Organisms, 49(3): 235-243
Abstract:
White spot disease (WSD) is at present the most
serious viral disease affecting cultivated shrimp species globally. The
causative agent, white spot syndrome virus (WSSV), is extremely virulent,
has a wide host range and can also be transmitted from broodstock to their
offspring. The shrimp postlarvae (PL) act as asymptomatic, latent carriers
of the virus, and stocking of WSSV-infected PL has been reported as a risk
factor for WSD outbreaks in culture ponds. However, there is no
population-based study on WSSV prevalence in PL of shrimp. The present
manuscript documents the approaches and the results in the estimation of
prevalence of WSSV in PL populations of Penaeus monodon at the time
of stocking. A maximum of 300 PL from each of the 73 batches of PL stocked
at various farms in the west coast of India during September 1999 to January
2000 were tested for the presence of WSSV by 2-step nested PCR. Thirty-six
(49%) of the 73 batches tested positive for WSSV either by 1-step alone (3
batches) or after 2-step nested PCR (33 batches). Sub-samples of 5 PL each
or 1 PL each tested to quantify the proportion of infected PL within batches
showed that WSSV prevalence was very high in 1-step PCR-positive batches and
low in 2-step PCR-positive batches. The study also showed that appropriate
sampling and sample size were major factors in determining the prevalence of
WSSV in PL populations, underlining the need for testing large samples of PL
to reduce errors from falsely negative results.
(Fish Pathology & Biotechnology Laboratory,
Department of Aquaculture, University of Agricultural Sciences, College of
Fisheries, Mangalore 575002, India, e-mail of C.V. Mohan: cv_mohan@yahoo.com)