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Reducing early impact of WSSV in shrimps

Reducing early impact of WSSV in shrimps

White Spot Syndrome Virus (WSSV) is a major shrimp pathogen, present in most of the producing regions and causing considerable economic losses to farmers. A new feed solution however showed strong reduction in mortality and improvement of growth in moderate WSSV pressure.

White Spot Syndrome Virus (WSSV) is a dsDNA virus of the Nimaviridae family affecting all Penaeid shrimps. This enveloped virus leads to high mortality in shrimp farms all over the world and is highly contagious. WSSV characteristically causes small white spots to appear on the inside surface of the cuticle, carapace and appendages, supposedly being the result of a dysfunction of the integument, leading to an accumulation of calcium salts in the cuticle.

The epithelium of the gills, integument and the stomach are the most severely damaged and the related dysfunctions lead to death in the last stage of the infection. Other clinical signs include a loose cuticle, a sudden reduction in feed consumption and lethargy. Common routes of infection are through contact with infected tissue, cannibalism and by water-borne routes. It can also be vertically transmitted to offspring. Once the virus has reached a threshold concentration, the outbreak is extremely rapid, forcing farmers to carry out emergency harvests. Therefore, early detection of the virus by quantitative or nested PCR as well as improving the immune system of the host and decreasing the development of the virus is of primordial importance.

Annual loss of one billion US dollars

First reported in 1992, its rapid expansion throughout all shrimp production regions makes it one of the main pathogens in the shrimp industry. Total losses for this virus alone have been estimated to be in the range of US$ 1 billion per year since the middle of the 1990s. The spread of WSSV over the years has hampered the development of shrimp farming in many tropical areas, which cut smallholder farmers from a new source of income. Researchers are therefore very much focused on finding solutions that can reduce the mortality rates, caused by the diseases. The nutritional supplements that are being developed for shrimp are often targeted at improving the immune function and/or improving the gut health of the animals.

This suits well with the non-antibiotic approach seen in aquaculture, followed by the global trend in other livestock sectors as well to reduce antibiotic use. One of the in-feed solutions that has been developed is a patented Copper-exchanged Clay (CeC). This product is based on an ion activated clay, aiming at securing digestive process. CeC acts as a microflora modulator in the gut, thus helping monogastric animals to face challenging periods. As demonstrated in scientific literature (CAI-HONG et al, 2006) CeC combines the technical properties of a clay and copper. Copper compounds such as CuSO4 are one of the traditional inorganic antibacterial materials with a wide usage. However Cu2+ ions are difficult to connect with bacteria. Thanks to the specific layer structure of the clay, the cations present between the structure sheets can be readily replaced by other cations or compounds such as bacteria. The clay also serves as a carrier of the coper in the intestinal lumen.

Trial in field conditions

A WSSV-infection trial was carried out at Incabiotec ConceptoAzul facilities in Peru, applying a mild WSSV challenge to L. vannamei juveniles during six weeks in 15 litre tanks containing 100 PostLarvae/tank. Two successive inoculations were performed, first at week one (stage PL26), and then at week four with an inoculum prepared from a biomass of live shrimp that were infected with WSSV and positive for WSSV at second PCR, in order to mimic field conditions in which the virus progressively develops...

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Posted in: Animal health VIV Asia