Quantitative analysis of the dose-response of white spot syndrome virus in shrimp.

Thuy T N Ngo,Just M Vlak,Eduardo S A Santos,Alistair M Senior,Mark P Zwart,Antica Culina

doi:10.1111/jfd.12877

Abstract

White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose-response by a combination of experiments, modelling and meta-analysis. We performed dose-response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models-differing in whether they incorporated heterogeneous host susceptibility to the virus or not-were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose-response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose-response, which can elucidate the most basic virus-host interactions and help to avoid underestimating WSSV infection at low virus doses.

Highlights

In the 1990s, shrimp aquaculture was devastated by a new pandemic disease, with a causal agent named white spot syndrome virus (WSSV; Escobedo‐Bonilla et al, 2008; Walker & Mohan, 2009)
It has been suggested that WSSV virus particles might be acting independently during the infection process because dose–response is similar to predictions of the independent action hypothesis (IAH) model (Dieu, Zwart, & Vlak, 2010)
Our approach is conceptually similar to the dependent action (DA) model: For parsimony, we introduce heterogeneity only in the infection step, so thatthe effe1c=tνs carryover from infection to mortality

Summary

| INTRODUCTION

In the 1990s, shrimp aquaculture was devastated by a new pandemic disease, with a causal agent named white spot syndrome virus (WSSV; Escobedo‐Bonilla et al, 2008; Walker & Mohan, 2009). Other factors that are known to affect WSSV virulence are host species (Escobedo‐Bonilla et al, 2008; Waikhom et al, 2006), water temperature (Rahman et al, 2006, 2007), interactions with bacteria (Phuoc et al, 2008), different levels of replication in different host tissues (Rahman et al, 2008) and previous exposure to WSSV The latter can result in long‐lived protection to the virus (Johnson, van Hulten, & Barnes, 2008; Venegas, Nonaka, Mushiake, Nishizawa, & Muroga, 2000). It has been suggested that WSSV virus particles might be acting independently during the infection process because dose–response is similar to predictions of the independent action hypothesis (IAH) model (Dieu, Zwart, & Vlak, 2010). To gauge the generality of our conclusions, we performed a meta‐regression analysis on reanalysed published dose–response data for WSSV in shrimp

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION