Shrimp Disease Research

The Southern Miss Crustacean Disease Laboratory at the Gulf Coast Research Laboratory investigates diseases of wild and aquacultured shrimp and crabs.

Shrimp Diseases

Marine shrimp aquaculture is the most valuable marine aquaculture industry in the world at about $15 billion annually. The United States imports more than 80 percent of the shrimp it consumes, creating a trade deficit of $3.5 billion dollars.

A primary impediment to growth of a shrimp aquaculture industry in the United States is control of diseases. The shrimp diseases of most importance to the U.S. are: Taura syndrome virus (TSV), white spot syndrome virus (WSSV), and the necrotizing hepatopancreatitis bacterium (NHP-B).

Taura Syndrome Virus (TSV)

Taura Syndrome Virus (TSV) has had a devastating economic impact on the shrimp aquaculture industry of the Americas since its initial recognition in the early 1990s. TSV is a 30 to 32 nm, icosahedral virus particle containing positive-sense, single-stranded RNA of about 10.2 kb in length. Initially the virus was allied with the family Picornaviridae. However, TSV is more closely related to the cricket paralysis-like viruses (CrPV-like viruses) and is a member of the “picornavirus superfamily,” the family Dicistroviridae and the genus Cripavirus.

At the Gulf Coast Research Lab we are dedicated to the eventual eradication of TSV by means of exploring further the ecological and epidemiological characteristics of this disease. Recent work at our lab includes the modeling of the pathogen’s epidemiology, estimating viral vital rates, TSV-resistant selective breeding, the effect of host size on TSV virulence, and disease control via an SPF-based shrimp aquaculture industry.

Tissue damage due to TSV infection in L. vannamei.
Tissue damage due to TSV infection in L. vannamei.

Sea Gulls feeding on shrimp dying during a TSV outbreak in Texas
Sea Gulls feeding on shrimp dying during a TSV outbreak in Texas

White Spot Syndrome Virus (WSSV)

White spot syndrome virus is the most virulent pathogen of penaeid shrimp. WSSV was recognized in the early 1990s in eastern and southeastern Asia. WSSV is an ovoidal, enveloped particle about 80- 20 nm wide by 250-380 nm long with a small tail-like appendage at one end. The virion’s genome consists of a single, circular, double-stranded DNA molecule of about 300 kb in length The virus belongs to the viral family Nimaviridae and the Genus Whispovirus.

The progression of a WSSV infection in affected ponds begins when shrimp become anorexic; after 1 -2 days, mass mortalities ensue. By 3 -10 days following onset of mortalities, deaths typically reach 80 percent and frequently all of the population succumbs

At the Gulf Coast Research Lab we are investigating the ecological and epidemiological characteristics of this disease. Recent work at our lab include the modeling of the pathogen’s epidemiology, estimating viral vital rates, pathogenesis, the geographic variation, and disease control via an SPF-based shrimp aquaculture industry.

WSSV infected cell nuclei in hypodermis of L. vannamei (Solid arrow). Dashed arrow indicates normal cell nucleus.
WSSV infected cell nuclei in hypodermis of L. vannamei (Solid arrow). Dashed arrow indicates normal cell nucleus.

Above. White spots on shell are gross signs of white spot syndrome viral disease.
Above. White spots on shell are gross signs of white spot syndrome viral disease.

Necrotizing Hepatopancreatitis (NHP)

Necrotizing Hepatopancreatitis, NHP, is a severe bacterial disease affecting penaeid shrimp aquaculture. NHP was first reported in 1985 from shrimp ponds in Texas, USA, and resulted in significant mortalities and devastating losses to shrimp crops. NHP has since been observed in penaeid shrimp aquaculture in Central and South American countries and is possibly in the Eastern Hemisphere as well. Elevated salinity and temperature appear to be factors associated with NHP outbreaks. Reported hosts are Litopenaeus vannamei, L. setiferus, L. stylirostris, Farfantepenaeus aztecus and F. californiensis.

The NHP-bacterium (NHPB) is a gram-negative, pleomorphic, obligate intracellular bacterium that is non-culturable through established cell lines or traditional bacteriological methods. Therefore, laboratory research of NHP is dependent on maintaining the disease agent in live animals. Gross signs of NHP include reduced feed intake, empty gut, lethargy, anorexia, and a pale and atrophied hepatopancreas.

Above. Shrimp affected by NHP. Note pale hepatopancreas and empty gut.
Above. Shrimp affected by NHP. Note pale hepatopancreas and empty gut.

Our research on NHP involves experimental infection in Kona stock Specific Pathogen Free L. vannamei to estimate epidemiological parameters of NHP spread in a shrimp population. We will use what we learn to generate predictive mathematical epidemic models of NHP infection in shrimp ponds. In addition, bioassays examining salinity and temperature will be attempted to elucidate the role of these environmental factors in NHP outbreaks.