The causative agent is Baculovirus type C with DNA nucleus, can include inlusion body), virus size 72 x 310 nm, virus nucleus 36 x 250 nm.
The first sign of comatose larvae is slow activity, floating on the surface, the hepatopancreas of shrimp is milky white and the intestines along the abdomen are also milky. The disease usually appears in postlarvae 6-9 mm in length. Epidermal cells model hepatopancreatic ducts infected with BMN, the nucleus is enlarged, the nucleus is red, the chromatin moves to the edge of the nuclear membrane.
– Diagnosis is based on clinical signs.
-Based on histopathological signs, test with fluorescent antibodies, black background microscopy, electron microscope… to diagnose the disease.
Histopathological features: The epidermal cells of the hepatopancreas tubule model are necrotic, enlarged, and red to pale purple in color. The inclusion body has no definite shape, the chromosomes are reduced and moved to the nuclear membrane, not forming an occlusion body.
Examination with a black background microscope: Prepare a fresh sample of hepatopancreas, observe the enlarged hepatopancreatic nuclei (not stained or stained) showing white under black background, in the middle there are many rod-shaped bodies, nearly 1 m in length and most of them are arranged inside the nuclear membrane.
Necrotizing midgut virus disease of white shrimp was first encountered in Japanese white shrimp (P.japonicus) cultured in Japan and Korea. Then observed in black tiger shrimp (P. monodon) P. chinesis, P. plebejus and Metapenaeus ensis.
BMN causes high mortality in shrimp hatcheries and usually causes disease from Mysis 2 to postlarvae and postlarvae stages. There are cases of postlarvae 9-10 infected with BMN virus up to 98% and caused mass death in postlarvae 20.
In Vietnam, research on BMN virus has not been investigated, but in some cases of mass mortality of shrimp hatcheries, the cause is unknown and when shrimps die there are signs of disease such as BMN. Pay attention to this disease.
– Apply general preventive measures.