Necrotising hepatopancreatitis (NHP), also known as the Texas pond mortality syndrome (TPMS), Texas necrotizing hepatopancreatitis (TNHP) and Peru necrotizing hepatopancreatitis (PNHP), is a lethal epizootic

Epizootic

In epizoology, an epizootic is a disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience . Epidemic is the analogous term applied to human populations...

 disease of farmed shrimp

Shrimp farm

A shrimp farm is an aquaculture business for the cultivation of marine shrimp or prawns for human consumption. Commercial shrimp farming began in the 1970s, and production grew steeply, particularly to match the market demands of the United States, Japan and Western Europe...

, caused by a bacterial infection.

NHP mainly affects the farmed shrimp species Litopenaeus vannamei

Whiteleg shrimp

Whiteleg shrimp , also known as Pacific white shrimp, is a variety of prawn of the eastern Pacific Ocean commonly caught or farmed for food.-Description:...

(Pacific white shrimp) and Litopenaeus stylirostris (Western blue shrimp), but has also been reported in three other American species, namely Farfantepenaeus aztecus, Farfantepenaeus californiensis, and Litopenaeus setiferus. The highest mortality rates occur in L. vannamei, which is one of the two most frequently farmed species of shrimp. Untreated, the disease causes mortality rates of up to 90% within 30 days. A first outbreak of NHP had been reported in Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 in 1985; the disease then spread to shrimp aquaculture

Aquaculture

Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

s in South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

.

NHP is caused by a small, gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

, and highly pleomorphic Rickettsia

Rickettsia

Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci , rods or thread-like . Being obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells...

-like bacterium that belongs to its own, new genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 in the alpha proteobacteria

Proteobacteria

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....

. Infected shrimps show gross signs including soft shells and flaccid bodies, black or darkened gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s, dark edges of the pleopods and uropods, and an atrophied

Atrophy

Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

 hepatopancreas

Hepatopancreas

The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods, molluscs and fish. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive enzymes, and absorption of digested...

 that is whitish instead of orange or tan as is usual.

The bacterium seems to prefer high water temperatures (above 29 °C or 84.2 °F) and elevated levels of salinity (more than 20–38 ppt). Avoiding such conditions in shrimp ponds is thus an important disease control measure.