Necrotising hepatopancreatitis

Necrotising hepatopancreatitis (NHP), also known as the Texas pond mortality syndrome (TPMS), is a lethal epizootic disease of farmed shrimp, caused by a bacterial infection.

NHP mainly affects the farmed shrimp species Penaeus vannamei (Pacific white shrimp) and P. stylirostris (Western blue shrimp), but has also been reported in three other American species, namely P. aztecus, P. californiensis, and P. setiferus. The highest mortality rates occur in P. 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 in 1985; the disease then spread to shrimp aquacultures in South America.

NHP is caused by a small, gram-negative, and highly pleomorphic Rickettsia-like bacterium that belongs to its own, new genus in the alpha proteobacteria. Infected shrimps show gross signs including soft shells and flaccid bodies, black or darkened gills, dark edges of the pleopods and uropods, and an atrophied hepatopancreas that is whitish instead of orange or tan as is usual.

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

Research on NHP
The NHP bacterium (NHPB) has been successfully transmitted to experimental shrimp by intra-hepatopancreatic injection of purified infectious material into healthy shrimp. Feeding of infectious material to healthy shrimp is currently the standard approach for maintaining the organism in a laboratory setting. There have been no successful attempts to culture NHPB in vitro, requiring infectious material to be obtained from infected shrimp.