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EMS/AHPNS: Causes and Prevention

EMS/AHPNS Introduction

 

Shrimp Early Mortality Syndrome (EMS)
Acute Hepatopancreatic Necrosis Syndrome (AHPNS)

Since Shrimp Early Mortality Syndrome (EMS) / Acute Hepatopancreatic Necrosis Syndrome (AHPNS) emerged in China in 2009, many monodon and vannamei deaths have been reported in several Asian countries, especially in China, Vietnam, Malaysia, and Thailand. Many, if not all, infected post-larvae (PL) die within 30 days of farming. In 2013, Thailand expected shrimp farming production would decrease by 30% or even up to 60% in certain regions. (FAO, 2013)

Pathogeny tests in these shrimp identify vibrio infections (V. parahaemolyticus, V. harveyi, or V. vulnificus) in their livers or pancreases. Bacteriophage and other viruses (WSSV, YHV, TSV or IHHNV) are also identified. However, symptoms are not triggered by these viruses. Lightner (2013) points out that if healthy shrimp are infected by V. parahaemolyticus, EMS/AHPNS symptoms will appear. If certain bacteriophages exist at the same time, shrimp will die. This combination creates toxins and impacts livers and pancreas. The mechanism is similar to cholera infections in humans, as Vibrio cholerae and bacteriophages both trigger lethal diarrhea.

 

EMS/AHPNS Pathological Features

Shrimp with EMS/AHPNS are inactive or swimming in circular paths, especially vannamei. Diseased shrimp also eat less and grow slower; their stomachs and intestines are empty; their livers and pancreases are pale and shrinking with black lines. When observing tissues, mitosis activities appear insufficient in E-cells in livers and pancreases, while B, F, R cells exhibit functional disturbances. Epithelium of nephric tubules falls off extensively. (Lightner et al., 2012).

 

Juvenilie Penaeus Vannamei from Vietnam. Left with EMS; right appears normal. (Photo by Dr D. V. Lightner)

Biopsy of Penaeus Vannamei infected with EMS/AHPNS displays pathological changes in hepatopancreas. (Photos by Dr T. W. Flegel)

EMS/AHPNS Symptoms

 
  • Behavior
    • Lack of appetite, empty intestine
    • Inactive
    • Abnormal swimming patterns
Abnormal swimming patterns
  • Symptoms
    • White hepatopancreas and pancreas, and organ necrosis
    • Black scabs on shrimp shell
    • Disease outbreak within 7 to 30 days from introducing PL to the pond
    • Smaller size
 

Atrophic and deformed tubules / necrotic hepatopancreas

 

EMS/AHPNS Preventive Measures

 
  • PL management
    • Ensure with PCR tests that shrimp are not infected
    • Ensure cleanness of organic feed

  • Tool sanitization
    • Use sanitized tools in the farm

  • Environmental and water quality management
    • Enhance sewage processing to maintain proper water quality
    • Add probiotics to water to avoid proliferation of pathogenic bacteria
    • Avoid liver and pancreas damage due to drug misuse

  • Disease management
    • Use Grobest functional feed at the initial stage of farming to increase immunity
    • Remove dead shrimp to avoid cross-infection
    • Choose superior and healthy PCR-negative PL

  • Grobest functional feed:
    • enhances intestinal immunity, protects intestines, increases palatability and resistance to diseases;
    • improves nonspecific immunity in shrimp, reduces infection rates, effectively prevents shrimp diseases;
    • contains vitamins and amino acids which supplement nutrition needed for enzymes and trace elements and facilitate metabolism for shrimp’s health and growth;
    • contains glucans which improve bacterial colony structures in intestines, facilitate metabolism, protect cells against free radicals, and enhance resistance;
    • facilitates digestive enzymes, improves digestive capabilities and enhances growth with antioxidant functions;
    • improves resistance to diseases and cell recovery.
 

How to use feeds

Water quality indicators: ammonia < 0.3 ppm, nitrite < 1 ppm, DO > 4 ppm, pH 7.5-8. When water quality is abnormal, apply Grobest PSB and EM products to improve water quality, and use functional feed.

 
  • Usage instructions::
    • During PL stage (< DOC 30): 15 consecutive days
    • Prevention: 5 to 7 consecutive days every two weeks
    • Before high-risk season: 15 consecutive days before environmental changes or disease seasons