Duck viral swollen head hemorrhagic disease

Duck viral swollen head hemorrhagic disease is an acute septic infectious disease caused by duck viral swollen head hemorrhagic disease virus. It is characterized by duck head swelling, conjunctival congestion and bleeding, extensive skin bleeding, enlarged liver with bleeding spots, body temperature above 43 ℃, green defecation, etc., with an incidence of 50% to 100% and a mortality rate of 40% to 80% or even 100%. It is a new infectious disease that seriously harms the industry.

1 Epidemiological diagnosis of duck viral swollen head hemorrhagic disease

Cheng Anchun et al (2003) reported the outbreak of infectious diseases in 5000 Tianfu ducks at the age of 33 weeks raised in a duck farm in Wenjiang, Sichuan Province in 1998. These ducks were immunized with duck plague, duck viral hepatitis, pasteurellosis and colibacillosis at the age of 18 to 23 weeks. At that time, due to the phenomenon of duck head swelling and tears, the ducks were treated according to duck plague. On the third day of the disease, each duck without symptoms was injected with three times the dose of duck plague attenuated vaccine and treated with broad-spectrum antimicrobials. the incidence rate was 100%, the epidemic period was 32 days, and the infected ducks died. The isolated serum of duck blood in the later stage of the disease was negative by Agar diffusion reaction with avian influenza antigen. In the autumn of 1999, the disease began to spread in the surrounding areas, reached its peak in winter, remained prevalent in the spring of 2000, naturally subsided in summer, and began to appear again in autumn, and peaked in winter of 2000 and spring of 2001. The disease also occurred in almost all duck-raising areas in Sichuan Province, Chongqing, Guizhou and Yunnan Province. More than 7 million commercial meat ducks and breeder ducks raised in a town in Chengdu from December 2000 to January 2001 alone died. Caused serious economic losses.

The area of the duck farm where the disease occurred for the first time showed an acute outbreak, and the morbidity and mortality often reached 100%. A small number of diseased ducks suddenly appeared in the duck flock, a large number of diseased ducks and deaths occurred in 2 to 3 days, and the death reached the peak in 4 to 5 days, and the course of disease was usually 4 to 6 days. In areas and duck farms where the disease occurs again or repeatedly, the morbidity is 50% or more, and the mortality rate is 40%, 80% or more. Ducks of all ages and breeds can be infected. Through the investigation of more than 3 million species of ducks and more than 50 million commercial meat ducks in 18 regions of Sichuan Province, Chongqing, Guizhou and Yunnan, the breeds involved are Tianfu meat duck, Aobaixing duck, Cherry Valley duck, Beijing duck, Sichuan Ma duck, Sichuan white duck, Jianchang duck, muscovy duck, wild duck, lace duck, hybrid duck and so on. There are still some cases at the age of 500 days. The use of antibacterial drugs such as penicillin, streptomycin, colistin, ciprofloxacin, ofloxacin, florfenomycin, difloxacin, sulfonamides, or antiviral drugs such as ribavirin, amantadine, Banlangen, antiviral granules can prolong the epidemic period of the disease without effective treatment effect. Emergency injection of rabbit anti-superimmune serum or rehabilitation duck serum prepared by isolated virus to ducks without clinical symptoms can prevent the further development of the disease, and 40% to 90% cure rate can be obtained for ducks with clinical symptoms, while superimmune sera against duck plague, duck viral hepatitis, Pasteurella multocida (5 ∶ A), goose plague, Muscovy duck parvovirus and avian influenza have no such emergency prevention or therapeutic effect.

2 Clinical diagnosis of duck viral swollen head bleeding.

The incubation period of natural infection was 4-6 days. After the introduction of diseased ducks in a duck farm or area, other ducks began to develop clinical symptoms after 4-6 days, and the incubation period of artificial infection was 3-4 days. Diseased duck early mental atrophy, unwilling to exercise, with the development of the disease lying on the ground, no light and covered with dirt, do not eat but a lot of water, diarrhea, discharge of grass-green loose stool, dyspnea, eye and face congestion, bleeding and severe swelling, eye and nose serous or bloody secretions, all diseased ducks head obvious swelling, body temperature rose to more than 43 ℃, later body temperature dropped, rapid death.

3 pathological diagnosis of duck viral swollen head hemorrhage.

3.1 gross pathological changes

Dead ducks of all ages have swollen head, swelling and congestive eyelids, yellowish transparent serous exudate under the head, extensive skin bleeding, gastrointestinal and respiratory tract bleeding, liver swelling and crisp yellowish color with bleeding spots, splenomegaly, epicardial and crown fat with a small amount of bleeding spots, pulmonary hemorrhage, renal swelling, intestinal serosa and other serous membrane bleeding spots. The ovaries of laying ducks are severely congested and bleeding.

3.2 histopathological changes

There were hemorrhagic foci in the intima and myocardial layer of the heart, as well as rupture of myocardial fibers, red staining of the cytoplasm, disappearance of nucleus and necrosis. Steatosis and granular degeneration of hepatocytes in the early stage, focal necrosis in the later stage, loose arrangement of hepatocytes, red staining of cytoplasm, nuclear pyknosis and infiltration of inflammatory cells. Splenic bleeding, necrotic foci and arterial smooth muscle degeneration. The pulmonary capillaries were congested and the interstitial edema widened with hemorrhagic foci. Congestion of renal venule, congestion of capillaries and granular degeneration of renal tubular epithelial cells. Degeneration and necrosis of neurons in brain tissue and widening of vascular space. The mucosal epithelium of the duodenum completely fell off, the lamina propria was inflammatory and edema, and the residual chorionic membrane filled the intestinal cavity. The inflammatory cells of the lamina propria of the rectal villi invaded, the pyknosis of the intestinal gland tended to be necrotic and separated from the basement membrane.

4 laboratory diagnosis of duck viral swollen head hemorrhagic disease

4.1 etiological diagnosis of duck viral swollen head bleeding

4.1.1 pathogen characteristics: duck viral swollen head hemorrhage was confirmed as a new disease through epidemiological investigation, observation of clinical symptoms and pathological changes, histopathological examination, isolation and identification of pathogen, artificial infection experiment, electron microscope observation, prevention and treatment experiment. Duck viral swollen head hemorrhagic virus is considered to be a kind of reovirus. The virion is spherical or oval in diameter, about 80nm in diameter, without envelope, and the nucleic acid is RNA. It does not agglutinate the erythrocytes of chicken, duck, goose, pigeon, yellow cattle, buffalo and pig. It is stable in pH4.0~8.0 and resistant to chloroform. Neutralization test and cross protection test showed that it had no antigenic correlation with duck plague virus and duck viral hepatitis virus. Agar diffusion test confirmed that there was no antigenic correlation with Muscovy duck parvovirus, influenza virus, infectious bursal disease virus, avian viral arthritis virus and goose paramyxovirus. The isolated virus infected ducks by oral administration, subcutaneous injection, intramuscular injection and nasal drip could successfully replicate the symptoms and lesions consistent with clinical cases, but could not infect SPF chickens (chicken embryos) and geese.

4.1.2 pathogen isolation: after routine treatment and sterilization, the liver, heart, spleen and brain tissues of typical dead ducks were inoculated with duck embryo fibroblasts and cultured for 37 ℃. After 10 days of observation, the patients with disease were further identified: those without disease were passed on blindly for 7 generations. The isolated virus with cytopathic effect was repeatedly frozen and thawed for 3 times, and the supernatant was observed under Hmur600 transmission electron microscope after negative staining.

4.1.3 experiment of artificial infection of ducks: 80 60-day-old commercial meat ducks were randomly divided into two groups with 40 ducks in each group. Each duck in the experimental group was subcutaneously injected with 0.5ml and the control group was subcutaneously injected with 0.5ml sterilized saline. 90% of the infected ducks died, and the control ducks survived.

4.2 Serological diagnosis of Duck viral swollen head hemorrhagic Disease

Neutralization test and cross protection experiment: duck embryo fibroblasts or susceptible ducklings can be used.

5 differential diagnosis

5.1 differential diagnosis from duck plague

For many years, people have regarded head swelling ("big head plague") as one of the typical bases for clinical diagnosis of duck plague. In clinical diagnosis and prevention, habitual thinking treats "swollen head and tears" according to duck plague without thinking. In fact, there is a significant difference between the two: (1) Duck plague virus belongs to herpesvirus, has envelope and is sensitive to chloroform; (2) nearly 100% of the cases of this disease have head swelling, and only part of the duck plague has enlarged head and neck. (3) both of them have gastrointestinal mucosal bleeding lesions, but this disease lacks characteristic lesions such as gastrointestinal mucosal necrosis and fibrous pseudomembrane covering of duck plague. (4) the gross changes of liver are obviously different from histological changes. The disease lacks gray-white necrotic spots of duck plague liver and shows yellowish swelling, brittleness and bleeding spots, and there are obvious inclusion bodies in the histological changes of duck plague liver. (5) in the natural epidemic of duck plague, the morbidity and death of adult grazing ducks are more serious, the incidence and death of ducklings under 1 month old in captivity are rare, but the morbidity and death of duck plague in all age groups are very serious, especially the ducklings.

In the production practice, it is worth paying attention to the high frequency of mixed infection of this disease and duck plague, especially in the duck flocks that are not vaccinated with duck plague vaccine in the vast rural areas. using the polymerase chain reaction (PCR) method established in our laboratory to detect duck plague virus, it is confirmed that 40% of them are mixed infection or secondary infection in the later stage of the epidemic. Its characteristic is that in all cases of mixed or secondary infection with duck plague virus, necrotic foci and yellow fibrous pseudomembrane can be observed in the esophagus and rectum, as well as gray necrotic spots in the liver and inclusion bodies under histology. Four annular bleeding zones can often be found on the serous surface of the small intestine in ducklings under 1 month of age after death. The results showed that esophageal and rectal necrotic foci, yellow fibrous pseudomembrane and grayish-white necrotic spots of liver and small intestine of ducklings were diagnostic lesions of duck plague.

5.2 differential diagnosis from duck viral hepatitis

The liver of this disease is yellowish, swollen and brittle with bleeding spots and easy to be confused with duck viral hepatitis, but duck viral hepatitis virus belongs to the family MicroRNA viridae, with a diameter of about 25nm, and has obvious age characteristics (mainly infecting ducklings less than 3 weeks). The histological changes of liver are necrosis, inflammatory cell infiltration and bile duct epithelial cell proliferation.

5.3 differential diagnosis from avian influenza

Avian influenza virus can cause the disease of many kinds of poultry and birds, such as chickens, turkeys, ducks and quails, and belongs to the family Orthomyxoviridae, with capsule and hemagglutination, but there is no disease in the infected ducks and chickens when raised with sticks, and there is no avian influenza in the chickens in the epidemic area. the isolated virus has no hemagglutination and does not infect SPF chicken embryos (chicks), geese and so on.

6 Prevention and treatment of viral swollen head disease in ducks

According to the existing research and clinical practice, the common broad-spectrum antibacterial and antiviral drugs have no definite effect on the disease, but the epidemic period of the disease is prolonged due to the control of bacterial secondary infection to a certain extent. Strengthening veterinary hygiene measures and environmental disinfection are indispensable or effective measures to control the occurrence of the disease. Emergency injection of rabbit anti-superimmune serum or rehabilitation duck serum into ducks without clinical symptoms can prevent the further development of the disease. 40% and 90% cure rate can be obtained for ducks with clinical symptoms. The tissue inactivated vaccine prepared by the internal organs of the dead duck and more than 10 million portions of oil inactivated vaccine prepared by isolated virus were applied in the epidemic area of the disease, and a good preventive effect was obtained. As the effective immunity of tissue and oil inactivated vaccine is often more than 15 days, ducks with early onset in serious epidemic areas often need to use superimmune serum and inactivated vaccine at the same time in order to obtain good preventive effect.