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Primary reference(s)

OIE, 2019. . Accessed 10 October 2020.

Additional scientific description

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease that has caused mass mortalities in farmed populations of whiteleg shrimp and giant tiger prawn. The causative agent is virulent strains of Vibrio parahemolyticus and four other Vibrio species (V. harvey, V. campbellii, V. owendii, V. punensis). AHPND was listed by the World Organisation for Animal Health (OIE) as a notifiable disease in 2016 (OIE, 2019a).

AHPND first appeared in the People’s Republic of China around 2010 and was called ‘covert mortality disease’. It has since been reported from Viet Nam (2010), Malaysia (2011), Thailand (2012), Mexico (2013), the Philippines (2014), Bangladesh (2017), the USA (2017), Taiwan province of China (2018), South Korea (2019) and the Okinawa Prefecture of Japan (2020). It is also suspected to be present in, but unreported, from other countries in Asia and Latin America and the Caribbean (OIE, 2019a).

The causative agents, discovered in 2013, are isolates of V. parahaemolyticus and related Vibrio species that carry a 69-73 kbp plasmid (pVA1) containing pirABvp genes that produce proteins (12.7 kDa and 50.1 kDa) that act together to cause AHPND. The pirABvp toxin genes in these Vibrio species are similar to the pirAB toxin genes of Photorhabdus spp., which are gram-negative, luminescent, rod-shaped bacteria in the Family Enterobacteriaceae (FAO, 2018). The PirAB has an insecticidal property; its toxicity results in severe swelling and shedding of the midgut epithelium in larvae of the moth Plutella xylostella.

Clinical signs and mortality of AHPND can start as early as 10 days post-stocking. Major clinical signs involve shrimp hepatopancreas: significant atrophy, loss of colour, and the presence of black spots or streaks due to melanised tubules. Additional clinical signs include soft shells and empty stomach or near-empty midgut (OIE, 2019a).

Metrics and numeric limits

Not available.

Examples of drivers, outcomes and risk management

Acute hepatopancreatic necrosis disease is caused by unique strains of V. parahaemolyticus and four other Vibrio species. Vibrio bacteria are ubiquitous in marine and brackish-water environments, and their populations are affected in these ecosystems by temperature, salinity, and turbidity. These AHPND-related bacteria can be present in both the cultured shrimp as well as in the water, sediments, and associated organisms in the farm ponds and in the surrounding aquatic environment (OIE, 2019a).

Several therapeutic methods have been tried, with mixed results, to combat AHPND in populations of infected shrimp on farms, but there is a lack of scientific data to corroborate claims of their effectiveness. These include antibiotics, bacteriophage therapy, probiotics, etc (FAO, 2020).

Since the emergence of AHPND, shrimp producers in Southeast Asia and Latin America have changed farm designs and operation to facilitate management of this disease; such changes include the use of: smaller, lined ponds; central drains; prefiltered clean water; tilapia for removal of sediments; increased aeration; frequent feeding regimes to reduce uneaten feed; and probiotics applied to the ponds. These management strategies seem to have been effective, as global shrimp production has shown a gradual recovery since 2016 (FAO, 2020).

Good aquaculture and biosecurity practices include: farm management (screening prior to stocking; pond water and bottom preparation); proper destruction and disposal of diseased shrimp; disinfection of affected premises; vector control; containment through movement control and zoning; and avoiding sources of stress (high stocking density, poor water quality or other less optimal environmental conditions such as suboptimal temperature or salinity) (FAO, 2020).

The World Organisation for Animal Health (OIE) provides recommendations on AHPND that include advice on importation, transit and maintenance of free status from AHPND (OIE, 2019b).

A report jointly published by the Food and Agriculture Organization of the United Nations (FAO) and the Asian Fisheries Society in 2018, aimed at updating knowledge and experience in dealing with AHPND and related topics from the perspective of government, academe and producer sectors (FAO, 2018).