Infectious bursal disease (IBD) of chickens is an acute, highly contact and lympholytic infectious disease in chickens caused by infectious bursal disease virus (IBDV) of the double-stranded RNA virus family of the double-stranded RNA virus family. Its genome is composed of two segments, A and B. Segment A encodes the four proteins VP5, VP2, VP4 and VP3 in sequence, and segment B encodes VP1 protein. Among them, the VP2 protein is the main structural protein and host protective antigen of IBDV. Studies have shown that the mutation of amino acids in the hypervariable region of VP2 is one of the important factors for changes in viral antigens and virulence. IBDV mainly damages the bursa of Fabricius, causing degeneration and necrosis of the pre-B lymphocytes of the chick’s bursa of Fabricius, leading to varying degrees of immune function suppression and unable to produce a normal immune response to the vaccine, causing the immune failure of a variety of vaccines (such as Newcastle disease, poultry) Influenza) and cause secondary infections with other pathogens (coccidia, E. coli, Salmonella, adenovirus); vaccination is one of the key steps to control chicken bursal disease. However, there are many types of bursal virus vaccines. There are differences in the strength of the virus strains, as well as the difference between live vaccines, whole virus inactivated vaccines, and genetic engineering vaccines, causing the majority of chicken farmers to blindly select vaccines and unscientific immunizations, resulting in immune failure. This article introduces the hazards of infectious bursal disease in chickens, the reasons that cause the immune failure of infectious bursal disease in chickens, the characteristics of different bursal bursal disease vaccines and the recommended immunization procedures, so as to facilitate the reference of chicken farmers.

1. The harm of infectious bursal disease in chickens

With the emergence of vvIBDV and the high-intensity use of vaccines, the virulence and antigens of the virus have changed, and new characteristics of IBD appear: (1) The super-virulent bursa strain can cause typical chicken bursal symptoms in chickens. And pathological necropsy lesions; (2) The bursal mutation strain infects chickens, which mainly causes immunosuppression, and the immune vaccine cannot produce a good immune response, and multiple pathogen infections are secondary to it; (3) the immune failure is serious, The resistance of IBDV to physical and chemical factors is enhanced, and vIBDV and vvIBDV can evade the antibodies produced by chickens immunized with classic strains, resulting in chickens immunized with classic strains that can still develop disease.

2. Reasons for immune failure of chicken infectious bursal disease

There are many reasons for the immune failure of infectious bursal disease in chickens. There are not only factors related to the unreasonable selection of vaccines (strains), but also incorrect immune methods, and the immune effect is not reliable; there are also factors of the chicken body itself (such as immunity). The existence of suppressive disease, the level of maternal antibody in chickens is uneven), these are all factors that lead to immune failure, but the root cause of the immune failure of infectious bursal disease in chickens is mainly the following two aspects:

2.1 The level of maternal antibody in chicks is too low or uneven. The level of maternal antibody in chicks directly determines and affects whether the chicken flock can resist the attack of chicken bursal bursal virus; the level of maternal antibody is uneven, and the level of maternal antibody is low. Chickens infected with Fabry-Xiang virus will carry the virus for a long time and detoxify, causing the whole flock of chickens to become sick.

2.2 Highly virulent infections or live vaccines have high virulence, which can cause fascinating shrinkage, resulting in severe immunosuppression, leading to immune failure. In actual production, if the chicken farm uses the highly virulent live bursal vaccine for a long time or the flock is infected with the virulent bursal virus, it will inevitably cause the chicken's bursa atrophy and reduce the chicken's immune response to the vaccine. , Resulting in immune failure.

3. The characteristics of different bursa vaccines

3.1 Live vaccines

Live vaccines (virulent strains, moderately virulent strains and attenuated strains) There are many types of vaccines, the strains are mixed, and the attenuated strain live vaccines are difficult to break through the maternal antibody, the moderately virulent strains and the virulent strain live vaccines Although it can break through the maternal antibody, it can cause irreversible damage to the flock, cause widespread immunosuppression and induce respiratory diseases in chickens. It is difficult to balance the prevention of super-virulent strain infection and the safety of chickens.

3.2 Whole virus inactivated vaccine: It has the shortcomings of slow antibody production speed and long immune blank period.

3.3 Traditional VP2 protein subunit vaccine: Its antigen is recombinant VP2 protein with a single structure, and its epitope is conformation-dependent. Detergents and heating can easily destroy its conformation and lose its ability to bind to neutralizing antibodies; in addition, only It can provide a single humoral immunity, but can not provide good protection to chickens.

3.4 New genetic engineering subunit vaccine: Purified VP2 protein is used as the antigen for vaccine production. VP2 protein can be assembled into virus capsid-like particles (VLPs), which fully mobilizes the immune system of the chicken body. VL Ps and natural viruses are in morphological structure and It is very similar in antigenicity and has a normal spatial conformation. VLPs can not only induce the body to produce strong humoral immunity, but also induce a strong cellular immune response. The challenge of mutant strains can provide strong protection; the antigen volume (VLPs is greater than r-VP2) increases, which leads to accelerated macrophage recognition, and the antibody production time is earlier than simple VP2 protein; virus-like particles (VLPs) do not contain viruses Nucleic acid does not carry out virus replication, and there is no risk of spreading the virus. It is especially suitable for the purification of bursal bursal virus and the purification of bursal virus.

4. Advantages of Huizhong Biological Bursa Subunit Vaccine:

4.1 Strain characteristics: Using purified VP2 protein as an antigen for vaccine production, VP2 protein can be assembled into virus capsid-like particles (VLPs), which fully mobilizes the immune system of the chicken body, and is highly virulent against chicken infectious bursal disease Challenges with mutant strains can provide strong protection and are more suitable for use in areas with severe epidemics.

4.2 Process characteristics The protein purification process optimizes the cell fragmentation and protein purification process, so that the purity of VP2 protein can reach more than 40% (ordinary protein purity is about 8%). Endotoxin removal process: Aqueous two-phase extraction to remove endotoxins. The endotoxin content of each feather can be no more than 20EU, which can effectively prevent the occurrence of side reactions.

4.3 Immune efficacy The antibody production speed is fast, and the high antibody lasts for a long time. 10 days after injection, the standard virulent attack of infectious bursal disease of chickens can provide 60% protection, and 14 days after injection, it can provide more than 90% protection. Especially suitable for broilers and breeders. For chickens aged 7 to 14 days, each 0.3ml, the immunization period can last for 4 months; for chickens over 14 days old, each injection of 0 5ml, the immunization period can last 6 months.

4.4 Safety: Immunize laying hens with 2 times the dose and 7-day-old chicks with 3 times the dose. There is no adverse reaction to the production performance of the laying hens and the growth performance of the chicks, and the vaccine is well absorbed.

5. Prevention and control strategies for chicken infectious bursal disease

The above analysis of the main factors that cause the failure of the bursal immunity, combined with the characteristics of various bursal vaccines and the characteristics of the genetic engineering subunit vaccines of the bursa of Fabricius, provides the following prevention and control strategies:

5.1 In order to obtain a high level of bursal antibody or maternal antibody in the early stage of the chicken flock, it is recommended that the chicken be immunized 1 day after birth with Huizhong Biological's new-flow method triple inactivated vaccine 0.15ml/ This vaccine is not affected by maternal antibodies, which is immune to immune suppression caused by atrophy of the bursa of Fabricius, and helps To produce active immunity faster.

5.2 Breeding hens and chicks are recommended to use Huizhong's new-flow method triple inactivated vaccine: If chicken farms use live bursal vaccines, especially live vaccines against virulent strains, for a long time, in view of the long survival time of the virus in vitro It is difficult to clear that the Fabry virus in chicken farms can exist for a long time and infect chickens with low bursal antibody, causing chickens to be continuously infected with Fabry virus for a long time. The bursa of fabric VP2 subunit in the new-flow method triple inactivated vaccine produced by Huizhong Biology belongs to the virus capsid-like particle vaccine, which can fully adjust the body's immune system, produce cellular immunity and humoral immunity, and does not contain viral nucleic acid. There is no virus replication, and there is no risk of spreading the virus. It is especially suitable for the purification of bursal bursal virus seriously polluted fields and bursal bursal virus.