Viral disease: infectious hematopoietic tissue necrosis of fish

[pathogen] the pathogen of infectious hematopoietic tissue necrosis in fish is infectious hematopoietic tissue necrosis virus (IHNV).

[symptoms and pathological changes] the diseased fish begin to swim slowly, float downstream, then shake and swim, then float and turn, and often die shortly after intense swimming. The diseased fish have black body color, exophthalmos, dilated abdomen, hyperemia at the base of the fin, and a long, thick white mucus stool is often dragged on the anus. The autopsy showed that there was a large amount of hydrops in the abdominal cavity, the color of liver, spleen and kidney became lighter, intestinal bleeding, oral cavity wall, skeletal muscle, adipose tissue, peritoneum, meninges, swim bladder and pericardium had hyperemia, bleeding spots and hematopoietic tissue necrosis. The spine of the fish that remains after the disease often bends.

[epidemic situation] Infectious hematopoietic tissue necrosis was prevalent in the United States, Canada and other countries. Due to lax port quarantine, it was introduced into China in 1985. It mainly harms the fry of salmon, salmon, red salmon, masu salmon, river trout and other salmon fry and species of the year. Newly hatched fish fry to 4-week-old fish are especially prone to this disease, with high mortality; 1-year-old fish can get sick, but the mortality rate is not high; 2-year-old fish do not develop the disease. The water temperature of the disease was 10-14 ℃. The incubation period of the disease varied with water temperature, and the symptoms developed slowly when the water temperature was below 10 ℃. At 10 ℃, the diseased fish generally began to die in 4-6 days, and the highest mortality rate lasted for several weeks at 8-14 days, while the incubation period was 4 days at 12.5 ℃, and the natural disease disappeared at 15 ℃. Adult fish with virus is the main source of infection of the disease. The virus can be discharged into the water with feces, urine and gonadal products, and invade the fish through Gill and digestive tract, causing the disease.

[prevention and treatment methods] the prevention and treatment measures of infectious hematopoietic tissue necrosis can refer to the prevention and treatment of infectious pancreatic necrosis of fish; it can also be impregnated with inactivated vaccine of tissue plasma of fish with infectious hematopoietic tissue necrosis disease. it is reported that the protection rate can reach 75%.