Acute Hepatopancreatic Necrosis Disease (AHPND/EMS)

Name

Acute Hepatopancreatic Necrosis Disease (AHPND) is often associated or equated with Early Mortality Syndrome (EMS).

Clinical signs

Clinical signs and mass mortality can occur as early as the 10th day after stocking. Shrimp affected by AHPND show an empty digestive tract, pale and shrunken hepatopancreas, soft shell, and black spots on the hepatopancreas. Unlike healthy shrimp, the hepatopancreas cannot be easily pinched between the thumb and pointer finger. Affected shrimp are weak and sink to the bottom of the pond.

AHPND cases often occur in two phases. The first is damage and peeling of the hepatopancreas, followed by inflammation and massive bacterial infection of the hepatopancreas.

Method of diagnosis

Since the signs for this disease are similar to others, confirmation is needed through a histopathology test on the hepatopancreas or by conducting a polymerase chain reaction (PCR) test. PCR can provide information up to 10 days before clinical signs appear and mass mortality occurs. This period is crucial for slowing or stopping the spread of the disease and maximizing cultivation yields.

Source: Dr. Loc Tran Example of shrimp with AHPND

Name

A unique strain of Vibrio parahaemolyticus named VpAHPND. AHPND can also be caused by V. harveyi, V. campbellii, V.owensii, and V. punensis.

Pathogen type

Gram-negative bacteria

Synonyms

None

Characteristics

VpAHPND bacteria can divide every 10-20 minutes, rapidly altering the ecosystem dynamics of the cultivation pond. The VpAHPND plasmid contains two genes, Pir A and Pir B, which produce toxins if they exist together. When these toxins enter shrimp’s digestive tract, their hepatopancreas can be damaged.

Toxicity

Can cause 100% mortality at the post-larvae (PL) stage, 30-35 days after stocking. Disease infection can occur with other diseases such as WSSV and EHP.

Predispositional factors

This disease can be triggered by high concentrations of organic matter from feed, fertilizers, and molasses, as well as high temperature, salinity, and pH, low plankton diversity in the pond, and low temperature of around 20°C for 48 hours.

Transmission

AHPND transmission can occur horizontally or vertically. Horizontal transmission (from shrimp to other shrimp) occurs through cannibalism, and vertical transmission from broodstock to shrimp.

Transmission can also occur if bacteria from farms with AHPND infection are disposed of in nature and spread to neighboring farms in the same area. The bacteria enter the digestive organs, colonize, and initially infect the stomach before moving to the hepatopancreas.

Epidemiology

AHPND was first reported in China in 2009, where it used to be called covert mortality disease. This disease was then identified in Vietnam, Malaysia, Thailand, Mexico, and the Philippines.

Host or vector

Aquatic organisms such as crabs, fish, plankton, and birds have the potential to carry the disease, although further confirmation is needed. The bacteria can be transported by zooplankton because V. parahaemolyticus can adhere to chitin (a component of shrimp shell). Polychaetes (a class of worms) also have the potential to be vectors of the pathogen.

Infectious dose

Vibrio bacteria with a population of > 1 x 10³ CFU/ml has the potential to cause this disease.

Incubation period

No data.

Susceptibility to drugs

There is no data, but the use of antibiotics is not advised to prevent resistance in shrimp. Vibrio producing biofilms at the bottom of the pond can survive despite the use of antibiotics (Chloramphenicol and Tetracycline).

Susceptibility to disinfectants/probiotics

No data.

Physical inactivation

VpAHPND can be inactivated by freezing at temperatures between -18°C and -24°C, or by heating at 55°C for 5 minutes or at 80°C for 1 minute. Additionally, inactivation can be achieved at pH 5 for 15 minutes.

Early warning

Farmers are advised to conduct thorough sampling regularly to check for shrimp’s health conditions, ensuring that they are free of Vibrio. Shrimp that show signs of weakness, changed color or behavior, or peeling in the shell when it is not in the molting stage can be an early warning of AHPND.

Prevention

AHPND prevention can be achieved by ensuring the water is sterile and in ideal conditions before entering the cultivation pond, using SPF (Specific Pathogen Free) shrimp fry, maintaining good cultivation management by keeping water quality stable without sudden changes, reducing pond size to facilitate management, and increasing aeration to enhance energy capacity.

Treatment

No data.

Eradication

If AHPND is confirmed in a pond, frequent water changes, optimizing feed amounts, and siphoning the pond bottom twice daily can stop mortality and help the population recover when the disease is diagnosed at the first signs of clinical symptoms. Shrimp that test positive for AHPND are disinfected with 100 ppm chlorine for 3-7 days and then buried. The pond bottom is cleaned from molting shrimp residues, feed, and mud. The pond is then disinfected with 100 ppm chlorine and dried for at least 15 days.

Pond equipment, such as paddles and anchors, is also disinfected with 100 ppm chlorine. Inlet and outlet channels are dried and treated with 2 tons of quicklime per hectare. Before reusing the pond, the bottom and walls are rechecked, and the water source is examined to ensure it is free of AHPND.

The spread of AHPND also occurs through the transportation of live shrimp that have the disease when carried to a different location. An example of this case is the spread of AHPND from Asia to Mexico. Another case is from live animals that have been infected with AHPND used as feed for shrimp, which happens with the Polychaete case from China to Thailand.

Shrimp that have been infected with Vibrio bacteria are highly dangerous if consumed by humans, especially if used in food incorporating raw or uncooked shrimp. In humans, Vibrio parahaemolyticus can cause gastroenteritis.

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FAO. 2018. AHPND: Acute Hepatopacreatic Necrosis Disease. Asian Fisheries Society.

Genics Pty Ltd. 2023. Genics Education Series: Early Mortality Syndrome (EMS), Acute Hepatopancreatic Necrosis Disease (AHPND), and Penaeus monodon Mortality Syndrome (PmMS).

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OIE. 2013. Acute Hepatopancreatic Necrosis Disease: Aetiology, Epidemiology, Diagnosis Prevention and Control References. OIE Scientific and Technical Department.