1 Pathogen
Duck viral hepatitis is a highly lethal infectious disease in chicks. The disease spreads rapidly, the course of the disease is short, and the mortality rate can reach more than 90%. Duck hepatitis virus, in the contaminated duck house can survive for more than 10 weeks, 2% bleaching powder, 1% formaldehyde, 2% caustic soda need 2 to 3 hours to kill.
2 Features of the disease
The disease is an acute, highly lethal infectious disease. Acute onset, rapid transmission, high mortality, spasm before death, head to back, showing a "horn arch recoil" characteristic posture, lesions are characterized by hepatomegaly and bleeding.
3 Popular features
In general, the disease only infects ducks, mainly endangering young ducks within 3 weeks of age, especially 5 to 10 days old is the most susceptible, 3 to 5 weeks old chicks can also be infected with the disease, adult ducks can be infected but not sick, can become a poison carrier. The incidence can reach 100%, the mortality rate of ducks within one week of age can reach more than 90%, the case fatality rate of young ducks aged 1 to 3 weeks is within 50%, and the mortality rate of ducklings over 4 weeks old is low. The disease occurs throughout the year, with no significant seasonality, but occurs mainly during the hatching season.
4 Clinical symptoms
1) The onset of the disease is urgent and the transmission rate is fast, and the general death is mostly within 3 to 4 days after the onset of the disease. At the beginning of the illness, the spirit is weak, the neck is shrunken and drooping, the movement is sluggish, the group cannot keep up, often crouches, the eyes are half closed, and the anorexia is anorexia.
2) Systemic convulsions occur from half a day to one day after the onset of the disease, and the sick duck lies on multiple sides, with its head facing the back and the horn arch reversed, so it is called "back neck disease". At the same time, the feet spasmodically kicked repeatedly, in the form of a paddle, sometimes spinning on the ground. Death occurs about ten minutes after the convulsions are found (Figure 1).
(Fig. 1. Duck virus hepatitis duck lying on its side, head to back,
The legs kick backwards in an angled arch. ）
3) The beak and claw tips are dark purple, and a few sick ducks have yellow or green thin feces before they die. When a serious outbreak of disease occurs in ducks within 1 week of age, the speed of death is staggering. 5 Autopsy lesions
Characteristic lesions are hepatomegaly, brittle, dark red and earthy yellow or reddish mottled. The surface of the liver is scattered with dark purple bleeding spots or streaked bleeding of different sizes at the tip of the needle, and in severe cases, it is like a layer of "black paint" (Figures 2 and 3).
(Figure 2. Duck liver with viral hepatitis disease.)
Bleeding, in severe cases the bleeding spots are black. ）
(Figure 3. Duck viral hepatitis disease duck liver of varying degrees.)
Lighter color and multiple bleeding spots. ）
Gallbladders are oblong in shape and filled with bile in a brown, pale brown, or pale green color. The spleen is sometimes enlarged and mottled (Figure 4). The kidneys are often enlarged, pale, and bleeding. The heart muscle is soft and cooked flesh-like.
(Fig. 4. Ducks with viral hepatitis disease in ducks with enlarged spleen and bleeding spots.) ）
6 Diagnosis
Diagnosis can be made based on epidemiological features, clinical symptoms, and pathological changes on characteristic autopsy of the liver, and confirmation requires laboratory virus isolation and identification or serological testing.
7 Prevention and control measures
After the onset of the disease or threatened ducks, subcutaneous injection of anti-duck viral hepatitis high immune serum or high egg-free yolk antibody 1ml can play a role in reducing death, stopping epidemics and preventing the onset of the disease.
1) Prevention: Use duck hepatitis attenuated seedlings to inject the female ducks of the egg-laying breeds with two injections of immunization twice, 1 ml / time. The first injection is 10 to 15 days before delivery, the second injection is given at intervals of 2 weeks, and the immunity is strengthened once before the peak of egg production, and the antibody production of the female duck is maintained for at least 4 months, and the maternal antibody of the offspring of the chick is maintained for at least 2 to 3 weeks, which can pass the dangerous period. Unimmunized breeding ducks, their offspring at 1 day of age with subcutaneous injection of 0.5 to 1 ml of weakened seedlings in the neck can be protected. In some areas with poor conditions and frequent occurrence of the disease, a booster immunization is still required when the chicks are 10 to 14 days old.
For the high incidence of viral hepatitis, chinese medicines such as astragalus, plate orchid root, and other traditional Chinese medicines for the treatment of liver disease can be added to the feed at 3 to 5 days old and 8 to 10 days old, which can reduce the incidence and add antibacterial drugs to prevent secondary duck serositis.
2) Adjuvant treatment: 100 g per 100 ducks, 100 g of herbs, rhubarb, gentian, gardenia, skullcap, cedar, and banlan root, decoction water juice and add 500 g of sugar, give ducks drinking water or mixing, 1 dose /day, for 3 days. At the same time, add 50 g of polyvitamin to poultry per 50 kg of feed, mash 100 slices of yeast and mix well.
(This article was originally published in China Animal Health Magazine, No. 8, 2015)