Enterocytozoon hepatopenaei (EHP) Microsporidiosis in Shrimp

Enterocytozoon hepatopenaei (EHP) is a microsporidian of the shrimp hepatopancreas. It rarely kills directly but causes severe growth retardation and major economic loss.

Overview

Enterocytozoon hepatopenaei (EHP) is a microsporidian, an intracellular spore-forming parasite, that infects the hepatopancreas of farmed shrimp and causes hepatopancreatic microsporidiosis (HPM). Unlike acutely lethal shrimp viruses, EHP rarely kills shrimp directly. Instead it causes severe growth retardation and uneven size, which translates into major economic losses, and it is increasingly recognized as an emerging problem in shrimp aquaculture worldwide.

Affected species and impact

EHP infects the principal farmed penaeid shrimp, including Penaeus vannamei (Litopenaeus vannamei) and Penaeus monodon. The parasite replicates within the cytoplasm of the hepatopancreatic tubule epithelial cells, impairing nutrient absorption. Infected populations show slow, irregular growth and pronounced size variation, and EHP is also associated with white feces syndrome and can predispose shrimp to other diseases such as AHPND.

Clinical signs

• Slow growth and marked size variation within a pond (the main impact)
• No obvious external signs in early or light infections
• Lethargy and reduced feed intake in advanced cases
• Soft shells and an empty midgut
• White feces in association with white feces syndrome

Transmission

EHP is transmitted horizontally by the oral route, including cohabitation with infected shrimp and cannibalism of infected hepatopancreas tissue, and the environmentally resistant spores can persist in ponds. Contaminated live or frozen feeds have also been implicated, as EHP has been detected in frozen Artemia biomass. The spores' durability makes thorough pond and equipment disinfection important.

Diagnosis

Diagnosis relies on PCR assays, including spore-wall-protein and beta-tubulin targets, performed on hepatopancreas and faeces, where copy numbers are highest. Histopathology and in situ hybridization reveal basophilic inclusions and spores within the hepatopancreatic tubule epithelial cells. Because infected shrimp often look normal, molecular screening is essential for early detection.

Treatment, control and prevention

There is no curative treatment for EHP. Control depends on excluding the parasite and on rigorous pond preparation and biosecurity.

• Stock specific-pathogen-free (SPF) and PCR-screened postlarvae from certified hatcheries
• Screen broodstock and avoid EHP-positive sources
• Disinfect ponds between cycles, including drying and treatment with quicklime (calcium oxide) to destroy spores
• Use safe, screened feeds and avoid potentially contaminated live feeds
• Maintain strict biosecurity and remove and dispose of infected animals