Understanding EHP Disease: A Growing Concern in Shrimp Farming

EHP disease has emerged as a silent yet significant challenge in shrimp farming, affecting shrimp growth and causing substantial economic losses. This article delves into the origins, symptoms, impacts, and control measures for EHP disease, providing essential insights for shrimp farmers to protect their stock and maintain sustainable practices.

What is EHP Disease?

Enterocytozoon hepatopenaei (EHP) is a microsporidian parasite responsible for what is now commonly referred to as EHP disease in shrimp. This intracellular parasite primarily affects the hepatopancreas (HP) of shrimp, hindering nutrient absorption and leading to stunted growth rather than direct mortality. First identified in cultured tiger shrimp (Penaeus monodon) in Thailand in 2004, EHP has since become a widespread issue in shrimp farming across Asia and beyond.

EHP disease in shrimp is particularly problematic because it does not directly cause death, making it difficult to detect in the early stages. Instead, the disease disrupts the growth of shrimp, leading to size variations within farming ponds and significant economic losses for shrimp farmers.

What is EHP Disease?

Origins and Spread of EHP Disease

EHP was first observed in Penaeus monodon but later found to infect the widely farmed Litopenaeus vannamei. Initially thought to be an exotic pathogen, studies revealed that EHP is endemic to Australasia. Its transmission method—direct shrimp-to-shrimp infection via oral routes—differs from earlier known microsporidian diseases, which often required intermediate hosts.

Since 2009, outbreaks have been reported in China, Indonesia, Malaysia, Vietnam, and Thailand, with recent PCR-positive cases in India. The pathogen’s silent but damaging nature has led to its classification as an emerging problem requiring urgent control.

EHP Disease Symptoms

Identifying EHP disease in shrimp is critical for effective management. Symptoms include:

• Slow growth and size disparity within ponds.
• White feces syndrome (WFS) characterized by white strings of feces in infected shrimp.
• Reduced appetite and weakened shells.
• The hepatopancreas and midgut are empty.
• Epithelial cells in the hepatopancreatic tubules showing basophilic cytoplasmic inclusions (microsporidian sporocysts).

Transmission occurs horizontally through cannibalism and contaminated water containing EHP spores released from infected shrimp feces. Early detection via PCR testing can differentiate EHP from other shrimp diseases.

EHP disease symptoms

Impacts of EHP on Shrimp Farming

While EHP does not directly cause mortality, its economic impact stems from reduced shrimp growth and the resulting variation in harvest sizes. This growth retardation in Penaeus vannamei and other shrimp species complicates production efficiency and profit margins. Additionally, farms recovering from other diseases like early mortality syndrome (EMS) or acute hepatopancreatic necrosis disease (AHPND) often face compounded challenges when EHP becomes prevalent.

Preventing and Controlling EHP Disease

While EHP disease poses significant challenges to shrimp farming, proactive measures can help mitigate its impact and safeguard shrimp populations. Here are key strategies to prevent and control this emerging threat.

1. Quarantine and Monitoring

Quarantine infected shrimp to prevent the disease from spreading. Monitor for symptoms like reduced appetite and slow growth. Regular PCR testing on days of culture (DOC) 20, DOC 40, and DOC 60 can detect EHP early.

2. Water Quality Management

Frequent water replacement and the removal of pond waste are critical. Maintaining optimal parameters for temperature, salinity, and dissolved oxygen reduces stress and strengthens shrimp immunity, thereby lowering the risk of EHP infection.

3. Quality Feeding Practices

Feed high-quality, microsporidian-free diets. Avoid unverified or contaminated feeds to prevent introducing EHP spores into the environment.

4. Biosecurity Measures

Adopt the strictest biosecurity protocols. Avoid using live feed such as polychaetes and clams, which may carry EHP spores. If live feed must be used, ensure it is frozen or pasteurized to eliminate pathogens. Gamma irradiation is another effective method to treat frozen feed.

5. Hatchery and Pond Preparation

Hatcheries should ensure broodstock is EHP-free through PCR testing. Clean hatchery equipment with 2.5% sodium hydroxide solution, followed by drying and chlorine treatment. For ponds, use quicklime (CaO) at 6 tonnes/ha to disinfect sediment and raise the soil pH to 12, effectively inactivating EHP spores.

Advanced Diagnostic Methods

EHP detection is possible through light microscopy or PCR testing. While light microscopy can identify spores in hepatopancreatic tissue, PCR testing is preferred due to its accuracy and ability to detect EHP at low infection levels. Nested PCR and LAMP methods can confirm EHP presence in shrimp feces and post-larvae (PL).

EHP Disease in Vannamei Shrimp

Litopenaeus vannamei, or vannamei shrimp, is highly susceptible to EHP, making the disease a significant concern for farmers cultivating this species. The slow growth caused by EHP affects productivity and profitability. Regular screening of broodstock and PL, coupled with stringent biosecurity measures, is essential to mitigate the impact on vannamei shrimp farming.

EHP Disease in Vannamei Shrimp

Global Perspective and Future Outlook of Shrimp Diseases

Shrimp diseases, including EHP, continue to challenge global shrimp farming. While production has recovered in some regions after EMS outbreaks, EHP remains a persistent threat. Its ability to silently spread and cause growth retardation underscores the need for proactive measures.

Scientists recommend adding EHP to the list of pathogens screened during quarantine and SPF certification processes. Enhanced diagnostic techniques and farmer education on biosecurity can limit EHP’s spread and impact. Collaborative efforts between researchers, farmers, and governments are vital to safeguard the shrimp industry.

Conclusion

EHP disease in shrimp is a pressing issue that demands attention and action from shrimp farmers worldwide. By understanding its symptoms, transmission, and control methods, farmers can take proactive steps to mitigate its impact. Implementing stringent biosecurity measures, maintaining optimal water quality, and adopting advanced diagnostic tools are crucial in managing EHP disease effectively.

As the shrimp farming industry continues to grow, addressing challenges like EHP is essential for sustainable development. Early detection, prevention, and research will play pivotal roles in protecting shrimp populations and ensuring the industry’s resilience against future outbreaks.