Necrotising hepatopancreatitis (NHP), also known as the early mortality syndrome (EMS), acute hepatopancreatic necrosis syndrome (AHPNS), Texas pond mortality syndrome (TPMS), Texas necrotizing hepatopancreatitis (TNHP) and Peru necrotizing hepatopancreatitis (PNHP), is a lethal epizootic disease of farmed shrimp. It is not very well researched yet, but generally assumed to be caused by a bacterial infection.
NHP mainly affects the farmed shrimp species Litopenaeus vannamei (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 percent 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, in 2009 to China and subsequently Southeast Asia, followed by massive outbreaks in that region in 2012-2013.
NHP is associated with a small, gram-negative, and highly pleomorphic Rickettsia-like bacterium that belongs to its own, new genus in the alpha proteobacteria. However, in early-2013 a novel strain of Vibrio parahaemolyticus was identified as a more likely causative agent, though involvement of a virus cannot be definitely ruled out yet.
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.
Whichever of the two bacteria associated with NHP actually causes it, the pathogen seems to prefer high water temperatures (above 29 °C or 84 °F) and elevated levels of salinity (more than 20–38 ppt). Avoiding such conditions in shrimp ponds is thus an important disease control measure.