Risk factors associated with white spot syndrome virus infection in a Vietnamese rice-shrimp farming system

Abstract

White spot disease (WSD) is a pandemic disease caused by a virus commonly known as white spot syndrome virus (WSSV). Several risk factors for WSD outbreaks have been suggested. However, there have been very few studies to identify risk factors for WSD outbreaks in culture systems. This paper presents and discusses the risk factors for WSSV infection identified during a longitudinal observational study conducted in a Vietnamese rice-shrimp farming system. A total of 158 variables were measured comprising location, features of the pond, management practices, pond bottom quality, shrimp health and other animals in the pond. At the end of the study period WSSV was detected in 15 of the 24 ponds followed through the production cycle (62.5%). One hundred and thirtynine variables were used in univariate analyses. All the variables with a p-value ≤ 0.10 were used in unconditional logistic regression in a forward stepwise model. An effect of location was identified in both univariate and multivariate analyses showing that ponds located in the eastern portion of the study site, closer to the sea, were more likely to test positive for WSSV by 1-step PCR at harvest. Ponds with shrimp of a smaller average size 1 mo after stocking tended to be positive for WSSV at the end of the production cycle. Average weight at 1 mo was also highlighted in multivariate analyses when considered as either a risk factor or an outcome. Other risk factors identified in univariate analyses were earlier date of stocking and use of commercial feed. A number of variables also appeared to be associated with a reduced risk of WSSV at harvest including the presence of dead post larvae in the batch sampled at stocking, presence of Hemigrapsus spp. crabs during the first month of production, feeding vitamin premix or legumes, presence of high numbers of shrimp with bacterial infection and the presence of larger mud crabs or gobies at harvest. No associations were detected with WSSV at harvest and stocking density, presence, or number or weight of wild shrimp in the pond. The multivariate model to identify outcomes associated with WSSV infection highlighted the presence of high mortality as the main variable explaining the data. The results obtained from this study are discussed in the context of WSD control and areas requiring further investigation are suggested.KEY WORDS: White spot disease · Aquatic epidemiology · Risk factors · Penaeus monodon · Rice-shrimp farming systemResale or republication not permitted without written consent of the publisher

White spot disease risk factors associated with shrimp farming practices and geographical location in Chanthaburi province, Thailand

“…However, not all farms applied pond biosecurity systems to prevent entry of WSSV carriers likely to reside in the communal canals, and thus such carriers might represent a source of disease (OIE 2014). WSD outbreaks in farms in Vietnam have been associated with the introduction of WSSV-infected decapods and WSSV-contaminated zooplankton (Corsin et al 2001). The use of communal canals also increases the likelihood of ponds receiving poorquality hypertrophic or eutrophic water with potential to cause stress that could in turn induce disease (Lyle-Fritch et al 2006, Huang et al 2011).…”

White spot syndrome virus (WSSV) infectivity for Artemia at different developmental stages

“…It infects several species of penaeid shrimp cultivated in the Eastern/Western Hemispheres (Lu et al 1997, Corsin et al 2001, in addition to a wide range of other decapods and crustaceans, including crabs (Chen et al 2000, Sahul Hameed et al 2001) and fresh water crayfish (Huang et al 2001, Jiravanichpaisal et al 2001. Several studies have confirmed that many suspected decapod carriers of WSSV can transmit the virus to Penaeus monodon (Wongteerasupaya et al 1996, Chang et al 1998, Wang et al 1998.…”

Evaluation of white spot syndrome virus variable DNA loci as molecular markers of virus spread at intermediate spatiotemporal scales

“…The presence of WSSV in Vietnam was first confirmed by PCR analyses on samples collected in 1997 (Corsin et al, 2001), but it is not clear how many times the virus was introduced from abroad. Also, it is unclear where WSSV originated and how it subsequently spread to other regions in Vietnam from the original introduction site(s).…”