EHP (Enterocytozoon hepatopenaei) is a microsporidian parasite belonging to the Microsporidia group, commonly affecting farmed shrimp, especially white-leg shrimp and black tiger shrimp. Unlike Early Mortality Syndrome (EMS) or White Spot Disease, EHP does not cause mass mortality. However, it severely impacts shrimp growth rates and overall productivity. Since there is no specific treatment for EHP, it has become a major threat to the global shrimp farming industry.
EHP: A Dangerous and Widespread Disease in Shrimp Farming
Mechanism of EHP Infection
EHP directly attacks the digestive system of shrimp, particularly the hepatopancreas—an essential organ responsible for digestion and nutrient absorption. Once infected, EHP spores invade the epithelial cells of the hepatopancreatic tubules and reproduce intracellularly, gradually destroying these cells. This process severely impairs digestive functions, preventing shrimp from fully absorbing nutrients, leading to slow growth, stunted development, and reduced farming efficiency.
A particularly dangerous aspect of EHP is its strong ability to spread through contaminated water and infected feed. The spores can persist in pond environments for a long time, increasing the risk of infection for the entire shrimp population.
Symptoms of EHP-Infected Shrimp
Unlike viral diseases that cause rapid mortality, shrimp infected with EHP do not exhibit immediate clear symptoms. However, over time, some noticeable signs include:
- Slow growth: Shrimp in the same pond develop unevenly, with many individuals being smaller than usual.
- Empty intestines and segmented feces: Damage to the hepatopancreas impairs digestion, leading to empty intestines and discontinuous fecal strands.
- Thin shell and weak immunity: Shrimp become more susceptible to environmental stress and secondary infections such as white feces disease and acute hepatopancreatic necrosis disease (AHPND).
Causes and Transmission Pathways
EHP can spread through multiple pathways, including:
- Infected broodstock and postlarvae: Shrimp larvae from hatcheries may already carry the pathogen if not strictly monitored.
- Contaminated feed and pond sediment: The spores can persist in dead shrimp remains or pond sludge from previous farming cycles.
- Unsanitized farming equipment: EHP spores can attach to shared tools and spread between ponds.
- Infected pond water: If the water source is contaminated or exchanged with infected ponds, EHP spores can quickly disperse.
Effective management and biosecurity measures are crucial in controlling EHP outbreaks and minimizing its impact on shrimp farming operations.
Impact of EHP on the Shrimp Farming Industry
Although EHP does not directly kill shrimp, it severely affects productivity and profitability for farmers. Some major consequences include:
- Reduced growth rate: Shrimp infected with EHP may reach only 10-40% of the weight of healthy shrimp of the same age.
- Increased farming costs: Due to slow growth, the farming cycle is prolonged, leading to higher expenses for feed, pond management, and increased disease risks.
- Export market challenges: Shrimp batches detected with EHP may be rejected by importers, causing significant financial losses for the seafood industry.
Prevention and Control Measures for EHP
Since there is currently no specific treatment for EHP, the most effective approach is strict prevention and management during shrimp farming. Key solutions include:
Seed Quality Control
- Purchase shrimp postlarvae only from reputable hatcheries that conduct PCR testing to ensure they are disease-free.
- Quarantine and randomly test shrimp samples before introducing them into ponds.
Pond Environment Management
- Clean and treat ponds before each farming cycle, removing bottom sludge and organic residues.
- Maintain stable water quality to limit the proliferation of harmful bacteria and parasites.
- Use probiotics to improve water conditions and reduce disease pressure.
Feed and Nutrition Control
- Avoid feeding raw seafood such as bivalve mollusks (clams, mussels, oysters), which may carry EHP spores.
- Supplement immune-boosting products like beta-glucan, vitamin C, and digestive enzymes to support shrimp gut health.
Implementing these preventive measures can significantly reduce the risk of EHP outbreaks and ensure sustainable shrimp farming operations.
Implementing Biosecurity Measures
- Minimize direct water intake from uncontrolled sources.
- Disinfect tools, equipment, nets, and clothing before use in shrimp ponds.
- Limit human and vehicle movement between ponds to prevent disease transmission.
EHP: A Major Challenge in Shrimp Farming
EHP remains one of the biggest threats to the shrimp farming industry, negatively impacting growth and economic efficiency. Controlling EHP requires a comprehensive approach, including strict seed quality control, environmental management, and rigorous biosecurity measures. Only through these combined efforts can shrimp farming achieve sustainability and long-term development.
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