EHP in shrimp: why the hepatopancreas looks normal until it is too late

What EHP does

EHP infects the tubule epithelial cells of the hepatopancreas, the organ that digests feed and stores energy. Infected cells produce spores instead of enzymes, so the shrimp absorbs less of what it eats. The visible result is retarded growth, wide size variation within the same pond, soft shells and, in some farms, white faeces. Mortality stays low, so the disease is often blamed on feed, water or genetics first.

The parasite was described in Thailand in 2009 and is now reported across South and Southeast Asia, China, and parts of Latin America. It is on the WOAH list of diseases of concern for crustaceans.

How it spreads

Spores leave the shrimp in faeces and are eaten by pond mates, either directly or through cannibalism of weak animals. Spores survive in pond sediment and in live feed such as polychaete worms and Artemia, which is how broodstock in a hatchery become infected and pass the parasite to post-larvae. Once a pond is contaminated, spores persist between crops unless the bottom is treated.

Why it is screened, not treated

There is no registered treatment that clears EHP from an infected shrimp, and shrimp cannot be vaccinated. Control is exclusion: stock only PCR-negative post-larvae from PCR-negative broodstock, test live feed before use, and monitor the pond during the crop so a positive result triggers an early harvest or a change of plan rather than a lost cycle.

Microscopy of hepatopancreas smears can find spores, but only at high loads and with a trained eye. Real-time PCR finds the parasite weeks earlier, at the stage when the decision still saves money.

What to sample and when

Hatchery: broodstock faeces (non-lethal) and live feed before every batch; a pooled sample of post-larvae before they are sold. Farm: a pooled hepatopancreas sample from 10 to 20 shrimp at stocking, every two to three weeks during the crop, and whenever growth falls behind the feed table. Pond: sediment from the feeding area between crops, to decide whether the bottom needs liming and drying before restocking.

Two EHP targets are in common use: the SSU rRNA gene, which is the most sensitive, and the spore wall protein (SWP) gene, which does not cross-react with related microsporidia in the pond. Laboratories often run both.

Running the test on the farm

The aquaculture line is fully lyophilised, so the kit is stored at room temperature and rehydrated with the sample extract on the day of use. An extraction-free buffer prepares tissue in five minutes; the compact 24-well analyser gives a result in about 50 minutes. Farms without a laboratory can therefore screen at the pond, and hatcheries can certify a batch the same day.

Written by the Medicare Vet product team from manufacturer data, WOAH guidance and published validation. Not a substitute for veterinary or laboratory advice in your market.