Understanding PirA and PirB Genes in Vibrio Bacteria in Shrimp Farms

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Understanding PirA and PirB Genes in Vibrio Bacteria in Shrimp Farms

December 19, 2024 by Revfvi Al Ghaney Rizal

Shrimp farms in Indonesia often face challenges, especially diseases. Acute Hepatopancreatic Necrosis Disease (AHPND) is one of the most common diseases affecting vannamei shrimp. Also known as Early Mortality Syndrome (EMS), this disease poses a significant threat to shrimp farmers, as it can cause high mortality rates in a short time.

AHPND is caused by the Vibrio bacteria, specifically Vibrio parahaemolyticus, which carries the toxin-specific Pva1 genes, better known as pirA and pirB. Essentially, all types of Vibrio bacteria have the pirA and pirB genes with characteristics that can attack the hepatopancreas of shrimp.

**Why Do pirA and pirB Genes Exist in Vibrio Bacteria?**

The toxins contained in the plasmid of Vibrio parahaemolyticus, namely pirA and pirB, are the main factors causing tissue damage to the hepatopancreas, which can lead to mass mortality. PirA and pirB are genes located on specific plasmids within the Vibrio parahaemolyticus bacteria, playing a critical role in causing the AHPND disease in shrimp.

Image A shows healthy hepatopancreas tissue, while image B depicts hepatopancreas tissue experiencing necrosis and sloughing caused by AHPND infection.

The pirA and pirB genes originate from virulence plasmids that can be transferred between bacteria. Naturally, Vibrio parahaemolyticus bacteria live in high-salinity water environments and possess the flexible ability to adapt virulence plasmids such as pirA and pirB.

In Vibrio, pirA binds to specific ligands on cell membranes and receptors, while the pirB toxin consists of an N-terminal domain (PirBN) and a C-terminal domain (PirBC), which can bind to hepatopancreatic epithelial tissues and initiate cell death in the host through pore formation.

When pirA and pirB combine, they create a highly toxic effect. These genes are located within the plasmids of Vibrio bacteria, serving as a survival mechanism. Essentially, Vibrio bacteria inhabit competitive marine environments. Their survival strategy involves extracting nutrients from damaged cells and eliminating surrounding competitors.

**Managing Vibrio Infections Containing pirA and pirB in Shrimp Farms**

Infections caused by Vibrio parahaemolyticus in vannamei shrimp lead to decreased appetite, anorexia, slow growth, black spots on the hepatopancreas, and mortality rates of up to 100%. The emergence of AHPND in shrimp farming activities significantly impacts the economy, necessitating measures to manage the disease.

To combat AHPND, efforts to minimize the amount of Vibrio in aquaculture waters can be carried out through the following steps:

Cleaning the pond bottom regularly.
Routinely replacing water.
Disinfecting the pond when Vibrio levels increase.
Regularly applying probiotics.
Conducting frequent shrimp health checks.

Shrimp Health Monitoring with ShrimpProtect

Protect your shrimp farm from disease threats by regularly monitoring shrimp health with ShrimpProtect from Nusantics. ShrimpProtect is capable of detecting pirA and pirB genes, the primary causes of AHPND, in under 35 minutes. With fast, accurate, and reliable results across various sample types, ShrimpProtect ensures thorough shrimp health checks.

Effective early detection allows you to take preventive measures more quickly, safeguarding your shrimp's health and boosting your farm's productivity.

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References

Dinan J. 2014. Shrimp disease causes global shortage, Drives up prices. Shrimp Disease Causes Global Shortage, Drives Up Prices | The Weather Channel
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Tran L, Nunan L, Redman R M, Mohney L L, Pantoja C R, Fitzsimmons K, Lightner D V. 2013. Determination of the infectious nature of the agent of acute hepatopancreatic necrosis syndrome affecting penaeid shrimp. Dis Aquat Org. 105:45-55.
Schofield P J, Noble B L, Caro L F A, Mai H N, Padilla T J, Millabas J, Dhar A K. 2020. Pathogenicity of Acute Hepatopancreatic Necrosis Disease (AHPND) on the freshwater prawn, Macrobrachium rosenbergii, and pacific white shrimp Penaeus vannamei at various salinities. Aquaculture Research. 1-10.
Wangman P, Longyant S, Taengchaiyaphum S, Senapin S, Sithigorngul P, Chaivisuthangkura P. 2018. Pir A & Pir B discovered in archived shrimp pathogenic Vibrio campbelli isolated long before EMS/AHPND outbreaks. Aquaculture. 1-28