IHHN Virus as an Etiological Factor in Runt-Deformity Syndrome (RDS) of Juvenile Penaeus vannamei Cultured in Hawaii

Runtdeformity syndrome (RDS) is an economically significant, frequent disease problem of cultured Penaeus vannamei . RDS is characterized by variable, often greatly reduced, growth rate of up to 30% of a cultured population and many shrimp with cuticle deformities of the rostrum, anterior appendages or other parts. The cause of RDS is undetermined.
Nursery trials comparing histologically IHHN-positive and histologically IHHN-negative Penaeus vannamei cultured under identical conditions were conducted at The Oceanic Institute. The IHHN-positive populations developed RDS symptoms including increased individual size variation, reduced population growth, and high prevalance of rostrum, antennae or cuticle deformity, while the IHHN-negative groups displayed none of these symptoms. No other diseases or parasites were identified in the IHHN-positive populations that would account for the RDS symptoms.
A single commercialele nursery was stocked with histologidly IHHN-positive P. vannamei and a high prevalence of RDS was observed. Shrimp growth was bimodal with a subpopulation growing normally and a subpopulation growing slowly. Significant relationships between shrimp harvest size and IHHN prevalance, selected individual organ IHHN severity grades and IHHN severity index (six organs evaluated) were found. Large, apparently normal shrimp were less severely infected with virus and did not display any cuticle deformities.
In sum, these data provide epidemiological and histopathological evidence for the hypothesis that infection by IHHN virus is the cause of RDS in cultured P. vannamei .