About EHP
Enterocytozoon hepatopenaei (EHP) is a eukaryotic, unicellular, and spore-forming microsporidian parasite that affects cultured shrimp. The disease was first reported in growth-retarded tiger shrimp, Penaeus monodon from Thailand, and recorded as an undesignated microsporidian. At that time, EHP did not constitute a major threat to shrimp production.
Over the last 12 years, however, EHP has appeared to become more virulent. In high stocking densities, virulent strains proliferate as there is no selective pressure against increased virulence. In 2009, EHP was reported in cultivated P. vannamei in Thailand, and has now spread throughout Southeast Asia countries including China, Vietnam, Indonesia, India, and Malaysia.
How is EHP Transmitted?
EHP can be transmitted horizontally among shrimp in rearing ponds, when shrimp come into contact or consume infected organisms. EHP-infected shrimp secrete feces containing large numbers of EHP spores. Those spores may be taken up by other shrimp in the pond. Healthy shrimp can also get infected by cannibalize those that were moribund or dead.
Much is unknown about EHP carriers, but it’s suspected that E. hepatopenaei can persist in the environment and mollusks in spore form. EHP can remain active for long periods of time. EHP spores in fecal pellets, or dried cadavers can survive for up to six months and retain virulence for over a year under aqueous conditions.
Potential sources of EHP infection include:
- Hatcheries
- Broodstock
- Live feed (such as polychaete worms, clams, and oysters)
- Artemia
- Pond crustaceans
- Contaminated water
Therefore, EHP can also be transmitted vertically from contaminated broodstock.
How Can I Identify EHP?
EHP infection severely retards shrimp growth. EHP does not typically cause mortality. During production, farmers suspect EHP if post larvae grow slower than normal rates.
EHP infects the shrimp’s hepatopancreatic tubule epithelium cells, where it takes the cells’ Adenosine Triphosphate energy. This exhausts the shrimp and damages their ability to uptake nutrients from feed. The disease also affects digestive and absorptive functions, resulting in shrimp with poor growth and lower immunity. These mechanisms make shrimp more
susceptible to other infectious diseases such as white feces syndrome. Many cases have been reported where white feces syndrome resulted from severe EHP infection.
You can detect EHP spores in hepatopancreas tissue sections by light microscopy using 100x magnification. You can also detect spores microscopically in shrimp fecal matter. You can also use histopathology for EHP detection. A more specific detection of EHP is done today using DNA
based molecular diagnostic tools, such as in-situ hybridization, polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and real-time PCR.
For information about how you can prevent EHP please read our Technical Bulletin: Preventing and Controlling EHP