[2] The highest mortality rates occur in L. vannamei, which is one of the two most frequently farmed species of shrimp.
A first outbreak of NHP had been reported in Texas in 1985; the disease then spread to shrimp aquacultures in South America.
[2] NHP is associated with a small, gram-negative, and highly pleomorphic Rickettsia-like bacterium that belongs to its own, new genus in the class Alphaproteobacteria.
[3] 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.
[4] The pathogen that causes NHP seems to prefer high water temperatures (above 29 °C or 84 °F) and elevated levels of salinity (more than 20–38 ppt).