Infectious disease remains an important obstacle for shrimp aquaculture in Latin America. While overall production has increased over the past decade, emergence of new diseases, and reemergence of existing ones, is a growing concern. The effect of these diseases is often reflected in growth retardation rather than large scale die-offs. Here, we report a case study from Latin America where severe growth retardation was documented in Penaeus vannamei. Clinical signs included high size variation (e.g. 4 gm to 20 gm), soft cuticle, weakness, dark body coloration and red tails and pleopods. Survival rates at harvest were 30-50%. Fecal strands could be seen floating on the water, similar to what is observed in shrimp affected with white feces syndrome. Since hepatopancreatic microsporidiosis had been recently reported in the region, there was concern this facility might had also been affected.
Juvenile shrimp samples were submitted to our laboratory for a complete health assessment by conventional H&E histology. Samples were also submitted for PCR analysis. By H&E, the most significant finding included the presence of lesions diagnostic of infection by Hepatobacter penaei, the agent causative of necrotizing hepatopancreatitis or NHP (Fig. 1). Additionally, intranuclear inclusion bodies indicative of infection by Decapod Hepanhamaparvovirus (DHPV) were found in the mucosal epithelium of the anterior midgut caecum. No other known lesions/pathogens of concern to penaeid shrimp were detected in these samples, including Enterocytozoon hepatopenaei (EHP). Neither did we find any intranuclear inclusion bodies associated with white spot disease (WSD), which is widely reported in Latin America.
PCR analysis mirrored H&E findings. There were very high levels of NHP and DHPV in samples displaying growth retardation and white feces. EHP were not detected. The DHPV isolate detected in these samples represented the currently circulating DHPV genotype in Latin America, not the isolate reported from Asia in the past. This case study exemplifies why health assessment of farmed shrimp should combine histological and molecular analysis. Had only PCR analysis for EHP been requested for these samples, based on the presumptive clinical signs, NHP would not have been detected.