Duck viral hepatitis is a highly pathogenic, fast-spreading viral disease caused by the duck hepatitis virus, which has a very high mortality rate. At present, the form of measures taken against duck flocks is relatively single, and there is a lack of certain continuity in the process of control. For this viral hepatitis, the prevention and treatment goals in many areas are relatively single, and do not reflect the overall situation, which will lead to duck viral hepatitis not being controlled, thereby increasing the incidence and re-emerging disease in areas where the disease has been controlled. Emergency immunization is taken in the event of viral hepatitis, which is a good way to prevent the rapid transmission of this virus.
Duck hepatitis virus generally has a higher incidence in the duck stage, the virus is a highly pathogenic, and fast transmission rate of infectious diseases, small ribonucleic acid virus family enteroviruses one of which is the pathogen duck hepatitis virus, the abbreviation of the virus is dhv, this viral infectious disease mainly occurs in the duck flock, so in general only between ducks infected, just hatched for a week the incidence of ducks is higher, generally more than 95%, the mortality rate at this stage is as high as 80%, Therefore, the mortality rate in duck incubation for 1 to 3 weeks is also higher.
At the time of virus vaccination, there may be cases of embryonic death, many bleeding spots can be seen on the liver, then the allantoic fluid and yolk will appear green, the virus can quickly multiply on the liver, expand the scope of infection, and make healthy cells also lesions. Ether, acid and heat do not have a good effect on viruses, because the virus has a certain resistance to these, and the virus in the feces excluded from the body in ducks can generally survive for about 5 weeks.
Duck hepatitis virus is mainly direct contact with infection, such as contact with the virus feed, duck barn, bedding, etc. will cause the duck to cause viral infection. In general, duck farms where the virus infection occurs are caused by the infection of young ducks purchased from the endemic area, and the infectious disease is mainly transmitted through the respiratory and digestive tracts, and may also be transmitted through the feeding of the keeper, and possibly through the people who buy the ducks. After a long period of use, the hygiene of the mat grass and some utensils used in the duck farm has not been guaranteed, there is no regular disinfection treatment, and the duck farm has not done a good job of timely treatment of dead ducks, which may also cause virus infection.
Ducks infected by the virus will have a large liver, dull yellowish and fragile and other phenomena, and the surface of the duck's liver will also appear some bleeding spots of different sizes, which is an important basis for the discovery of duck hepatitis virus. Histopathological changes occur in the duck's liver with some vacuoles or cell necrosis, vascular hyperplasia, and at the same time accompanied by cell infiltration. After the serum is tested, the infected duck is used as the test material, then treated with chloroform, and then the hatched 1d chicks are inoculated, and the inoculated chicks will die in 2 to 3 days, and the above lesion characteristics will also be displayed.
According to the current preventive measures for viral infection of duck hepatitis in China, there are generally three kinds of prevention and control measures used:
The first is an injection of immune serum or high yolk antibodies to give the duck artificial passive immunity.
The second is the immune breeding duck, which is mainly to improve the immunity of the ducks in the process of breeding offspring.
The third is to inject the ducks with dhv-1 live strain vaccine, so that the chicks can receive artificial active immunity. There are still many problems in the process of purifying the virus, and the antigen concentration extracted does not meet the requirements, so the main antibodies so far are weak vaccines, inactivated vaccines, high-free serum and high-yolk antibodies.
3.1 Immunization against attenuated vaccines
This vaccine is mainly bred based on embryos or duck embryos. At present, the most commonly used weak vaccines in China mainly include DHV-54, DHV-fe34, etc., in addition to duck hepatitis duck plague dichotomy and weak vaccines.
The best time to immunize breeding ducks to weakened vaccines is 2 to 4 weeks before egg collection, and the optimal frequency of vaccination is twice a week. This vaccination method is mainly to pass the antibody through the egg to the chicks, after two weeks, the chicks will get the protection of the mother antibody, the immunization period of this immune vaccine is 6 months, and the second immunization is carried out after 5 to 6 months. Ducks that have been protected by maternal antibodies should be immunized to weakened vaccines at 7 to 10 days, and ducks without maternal antibody protection should be immunized to weakened seedlings within 1 day. For ducks that already have maternal antibody protection, oral immunization should be carried out, so that the effect will be better.
3.2 Inactivated seedling immunization
After a series of experiments, the effect of duck embryo inactivation seedlings is better than that of chicken embryo inactivated seedlings, but the use of weakly toxic seedlings is inseparable from the best immune effect of inactivated seedlings. In the process of experiments, it was also found that the immunity based on weak vaccines can not achieve a good antibody effect, and through comparison, it was found that the effect of first immunization with live vaccines and then immunization with inactivated vaccines was better than that of direct immunization with live vaccines or three inactivated vaccines. Therefore, in general, weak vaccines and inactivated vaccines are used together.
3.3 High immunity serum and high egg-free yolk antibody
The prevention method of intramuscular injection of high serum-free and high-yolk antibodies is generally in the mother antibody or the chicks whose situation is unknown, and the effect of immunization is guaranteed to be inseparable from the determination of immunization time and dose and antibody titer. In the process of prevention, some people have analyzed the configuration of high serum-free and high-yolk antibodies and the effect of treatment, and the results of the experiment show that the antibody titer can withstand the effect of 20 minimum strong poisons in the ducks with a maximum of 1:64 or more, and the protection rate after 14 days of injection is also very impressive, and it is confirmed that a preventive dose of serum injection in the chicks can ensure that the chicks are protected from infection. Through the study found that in order to ensure the effect of immunization, it is inseparable from the determination of immunization time and vaccination dose and antibody titer, the higher the titer, the earlier the use, the better the effect, so the use of high serum-free and high-yolk antibodies can be a good way to protect chicks from virus infection.
3.4 Relevant precautions
Purchases from diseased duck farms and hatcheries should be prohibited when purchasing young ducks, and outsiders cannot enter the duck farms without disinfection. For the mat grass and related tools in the duck farm, it should be disinfected in time, and if the duck farm is infected, it should be dealt with in time. Breeders should also be strict when feeding, and environmental hygiene must be guaranteed to ensure that the environment of feeding is clean and clean. The area around the duck farm should also be disinfected in time, and peracetic acid can be sprayed. If an infected duck is found, it is necessary to do a good job of isolation in time, and then be guarded by a special person to prohibit unrelated personnel from approaching to avoid the consequences of virus infection.
According to the current prevention of duck hepatitis virus, there are still many deficiencies in prevention and treatment, one is that a better immune vaccine has not been developed, and the other is that the duck hepatitis virus immune vaccine has not been approved. Variants of dhv-1 have been found in many regions, and there are also some problems in the use of immune vaccines, and immunization failures can also occur. Although inactivated vaccine immunity and weak vaccine vaccine immunity have a good immune effect on duck hepatitis virus, they still cannot meet the needs of the current society, so the society should also study the safety and efficiency of immune vaccines in time.