Source: Qingdao Azure Biological Products Co., Ltd
The pathogen of porcine epidemic diarrhea (PED) is porcine epidemic diarrhea virus (PEDV), which belongs to the coronavirus family Coronavirus family. Since its first detection in Europe, porcine epidemic diarrhea virus has gradually progressed from the epidemic of classical strains (G1 subgroup) to the emergence of mutated strains (G2 subgroup). The main strains prevalent in China are mutated strains (G2 subgroups).
Newly produced piglets have a high rate of diarrhea infection and diarrhea mortality after infection with PEDV, which seriously affects the production order and economic benefits of pig farms.
Mainstream prevention and control measures for porcine epidemic diarrhea
The majority of farmers, farm technicians and veterinary-related scientific researchers have adopted corresponding prevention and control strategies and methods in the actual production, and the following is a brief summary of several strategies commonly used in the prevention and control of PED infection in actual production.
Back-feeding: refers to in some PED-induced pig farms, by feeding the sow infected piglet manure and intestinal tissue to stimulate the sow's immunity to PEDV, and then transfer it to the piglet through colostrum/regular milk, so that the piglets can obtain effective protection at the most susceptible stage, thereby reducing the morbidity and diarrhea mortality of piglets. The samples used for re-feeding can basically represent the types of strains prevalent in the farm, but there are the following risks: first, the materials used for re-feeding are not easy to obtain continuously; second, whether the strains prevalent in the farm have the potential to be used as vaccines still needs to be explored by relevant tests; third, the method of re-feeding is less safe, especially in the presence of other epidemics in the farm, there is a risk of cross-infection.
Drug therapy: In the event of a PED epidemic, in order to prevent secondary infection with other intestinal bacteria, antibiotics and other drugs that inhibit bacteria can be used for prevention and control. This method has a certain effect on controlling the secondary infection of intestinal diseases, but it mainly targets bacterial pathogens and does not play a role in the main pathogenesis of porcine epidemic diarrhea virus.
Vaccine prevention and emergency vaccination: At present, the vaccines used in PED prevention and control in most pig farms are injectable vaccines, which can be divided into live attenuated vaccines and inactivated vaccines according to the general category. The main principle of using injectable vaccines to prevent and control PED is to produce active immunity after vaccine immunization, including humoral immunity and cellular immunity. PEDV is cleared by antibody action produced by B cells and direct killing action by T cells. The advantages of injectable vaccines are that the safety of vaccine products is relatively reliable, the composition is relatively single, the amount of antigen added is guaranteed, and the evaluation of its efficacy is more scientific. Therefore, most pig farms choose to use vaccine immunization to prevent and control PED.
Considerations on the use of porcine epidemic diarrhea vaccine
According to the foregoing, the use of vaccine immunization is the mainstream PED prevention and control scheme generally accepted and used by most pig farms. The following author briefly introduces the principles and characteristics of several common vaccine immunization regimens:
Seedlings: There are precedents for the use of seedlings in many diseases, mainly the intestines and other tissues of pigs where PED occurs, which are broken and filtered as vaccines. Essentially, the seedlings are a hybrid inactivated vaccine that immunizes pigs. The same as the back-feeding, the antigens in the seedlings can basically represent the strains circulating in the field, and there are also shortcomings such as the inability to continuously obtain antigens, mixed infection of other pathogens, and incomplete inactivation with formaldehyde, resulting in the spread of other pathogenic microorganisms. At the same time, the content of PEDV as the main antigen in its own seedlings is also difficult to quantify. Therefore, there are certain uncertainties and risks in the use of seedlings.
Live attenuated vaccine for porcine epidemic diarrhea: Because the live vaccine is injected into the body with a live PEDV virus, the virus can continue to proliferate in the body after immunization, so the virus titer in the finished vaccine is lower than the virus titer before inactivation of the inactivated vaccine. The probability of mutation of porcine epidemic diarrhea virus is recommended, and it is recommended that pig farms pay attention to the genetic sequence comparison of the epidemic strain and the vaccine strain when using live attenuated vaccines.
Inactivated vaccine for porcine epidemic diarrhea virus: Inactivated vaccine is prepared by inactivating the porcine epidemic diarrhea virus cultured and added to the vaccine. The pre-inactivated virus titer is higher than that of live attenuated vaccines. Its main feature is that it does not contain live viruses, so there is no risk of spreading the virus. Of course, the use of inactivated vaccines should also be combined with the sequencing of strains popular in pig farms, and attention needs to be paid to the cross-protection of different strains.
Injectable live attenuated vaccine for porcine epidemic diarrhea combined with inactivated vaccine prevention and control plan for porcine epidemic diarrhea virus: As the name suggests, this scheme is to first immunize the live vaccine and then inject inactivated vaccine, which can only cause humoral immunity and cellular immunity in theory, and also pay attention to the matching of the strain.
The above are commonly used vaccine immunization regimens against porcine epidemic diarrhea. The injectable vaccine regimen lacks the immunological theory of artificial stimulation of the body's mucosal immunity. Mucosal immunity is the first battleground against viral infections. Effective weapons of mucosal immunity are secretory IgA dimers (sIgA), as well as antigen-activated dispatch-resident T cells and B cells. sIgA provides additional protection in addition to IgG in the mucosa of the respiratory tract and digestive tract, neutralizing viruses earlier and more effectively. Resident memory B cells and T cells activated in the mucous membrane encounter antigens earlier than phylogenetic memory cells, respond faster, hinder viral replication, and reduce virus shedding and spreading. At the same time, the immune stimulation of the mucous membrane will also cause the body to produce corresponding humoral immunity and cellular immunity. Therefore, the development and use of the mucosal drug delivery route to gently stimulate the body to produce mucosal immunity, humoral immunity and cellular immunity is an important direction of PED vaccine immunity.
At the same time, in the actual production process, the common phenomenon is that the passive immune protection of piglets brought by breast milk is particularly critical. Its theoretical basis lies in the theory of the common mucosal immune system. Specific manifestations are to stimulate the specific mucosal immunity of PEDV in the mammary gland of sows, produce high concentrations of sIgA antibodies into milk, and continuously deliver exogenous sIgA antibodies to the piglets' intestines through breastfeeding after sow calving, forming a high-concentration antibody environment against PEDV in the piglet intestine, preventing the colonization and infection of invading pathogens, thereby achieving passive immune protection for piglets.
Evaluation of immunization against porcine epidemic diarrhea vaccine
In the actual production process, porcine epidemic diarrhea has the greatest impact on newborn piglets, and the monitoring of passive immune antibodies after vaccine immunization is particularly important. Among them, in passive immunity, sIgA is the main immunoglobulin in mucosal secretions, and the synthesis rate is higher than that of IgG, while the structure of sIgA is stable, and it can tolerate changes in physical and chemical states such as local temperature and pH of the intestine and the digestion of proteases. Theoretically, sIgA in colostrum is the main active ingredient that provides passive immunity to piglets. Therefore, the monitoring of sIgA antibodies after vaccine immunization can basically reflect the strength of passive immunity for piglet protection after vaccine immunization.
Empirical evidence of the scientific prevention and control model of porcine epidemic diarrhea detected by oral + injection + mucosal immune antibody
Qingdao Azure Biotech has innovatively established a new scientific immune prevention and control model for diarrhea: mucosal immune induction + vaccine immunization fortification + colostrum sIgA antibody level evaluation. In order to verify the prevention and control effect of the azure pig epidemic diarrhea prevention and control plan on pig epidemic diarrhea virus disease after use in large-scale pig farms, this empirical evidence follows the sampling standards for major animal diseases in the selection of large-scale pig farms, and selects 1-2 empirical pig farms in each province for distribution, immunization and sampling in many densely bred provinces nationwide, including Shandong, Jiangxi, Henan, Guangdong and other provinces. At the same time, the prenatal sow was applied to the blue pig epidemic diarrhea prevention and control immunization program and the pig epidemic diarrhea immunization program of other mainstream animal vaccine manufacturers, the piglet diarrhea rate and diarrhea mortality rate of the sow after immunization were counted, and the sIgA in the colostrum of the empirical sow was monitored, and finally the indicators and data detected were statistically analyzed.
Empirical immunization regimens:
Blue pig epidemic diarrhea virus prevention and control program: one serving: 35-40 days before the birth of sows, oral PED-specific functional microecological preparations. Two exemptions: 30 and 15 days before the birth of the sow, 2 ml of Qingdao Azure pig epidemic diarrhea and infectious gastroenteritis dual inactivated vaccine (abdominal health) were injected intramuscularly.
Vaccination of live attenuated vaccine for porcine epidemic diarrhea: pregnant sows are first exempted 35-50 days before delivery, 1 dose of live attenuated vaccine for porcine epidemic diarrhea is injected intramuscularly, two exemptions are carried out 7-14 days before delivery, and 1 serving of live attenuated vaccine for porcine epidemic diarrhea is injected intramuscularly.
Vaccination of live attenuated porcine epidemic diarrhea vaccine combined with porcine epidemic diarrhea virus inactivated vaccine prevention and control program: pregnant sows are exempted for the first time at 21-28 days before delivery, intramuscular injection of live attenuated vaccine for porcine epidemic diarrhea virus is 2 ml, secondary immunity is carried out 7-14 days before delivery, and intramuscular injection of porcine epidemic diarrhea virus inactivated vaccine is 2 ml.
Vaccination of porcine epidemic diarrhea virus inactivated vaccine prevention and control program: 21-28 days before delivery for one exemption, intramuscular injection of porcine epidemic diarrhea virus inactivated vaccine 2 ml, 7-14 days before delivery for two exemptions, intramuscular injection of porcine epidemic diarrhea inactivated vaccine 2 ml.
Non-immunization regimen: No porcine epidemic diarrhoeal virus vaccine immunization is given.
The source of the samples collected empirically: from 2018 to 2019, from the main pig breeding areas in the country: including large-scale self-breeding pig farms in Jiangxi, Shandong, Henan, Guangdong and so on. 1 small-scale pig farm (300 ≤ sow stock) collected and detected a total of 26 colostrum samples; medium-sized pig farms (300 ≤ sows with a < of 1,000 heads) collected and tested a total of 23 colostrum samples; large-scale pig farms (sow stock ≥ 1,000 heads) collected and detected a total of 163 colostrum samples. After statistics, the number of sows involved in this empirical work reached more than 30,000, and more than 2,000 were included in the trial, and a total of 201 samples were collected and tested for pigs with porcine epidemic diarrhea virus, and after collecting samples, they were sent to a third-party testing laboratory for immune antibody testing in the laboratory.
In each of the farms involved in this demonstration, the sow population included in the trial collected colostrum samples at a rate of 5% of the number of immunized sow populations when the sows were littered. All the colostrum samples collected by the evidence are sent to a third-party testing agency to detect sIgA antibody, and the test results are grouped according to 1-2 births, 3-4 births, 5-6 births, and 7-8 fetal cycles, and the antibody level of sow colostrum is counted, forming a large-scale pig farm sow colostrum antibody consumption law, the specific results are shown in Figure 1.
Figure 1 Statistical diagram of the extinction law of colostrum sIgA antibody in sows
Statistics of piglet diarrhea rate and diarrhea mortality rate of sow production after using different pig epidemic diarrhea virus vaccine immunization programs in large-scale pig farms, compared with the protection rate of piglets by different programs, the specific results are shown in Figures 2 and 3.
Figure 2 Statistical map of sow littering diarrhea rate
Figure 3 Statistical map of diarrhoea mortality rate of sows
For the farms involved in each of the demonstrations, sows using different diarrhea regimens were collected colostrum samples at the rate of 5% of the number of immunized sow populations during littering. All the colostrum samples collected by the empirical evidence were sent to a third-party testing agency to detect sIgA antibodies, and the test results were grouped according to 1-2 births, 3-4 births, 5-6 births, and the antibody levels of sow colostrum of different immunization regimens were counted, and the specific results were shown in Figure 4.
Fig. 4-1 Comparison of sIgA antibody levels in different diarrhea prevention and control regimens 1-2 fetal sows
Fig. 4-2 Comparison of sIgA antibody levels in different diarrhea prevention and control regimens 3-4 fetal sows
Fig. 4-3 Comparison of sIgA antibody levels in different diarrhea prevention and control regimens 5-6 fetal sows
Based on the data collected in this empirical large number of samples, the following analysis was made: First, through the big data comparison of colostrum sIgA antibody after sow immunization, it can be seen that the level of colostrum sIgA antibody in 1-6 fetal sows increases with the increase of fetal frequency, and the level of colostrum sIgA antibody in sows of 7 and 8 fetuses decreases rapidly, which shows that the immunization effect of porcine epidemic diarrhea vaccine must be divided into fetal stages. Through this empirical evidence, Qingdao Azure's new scientific immune prevention and control model for diarrhea has formed a more scientific and meticulous evaluation system. Second, compared with the clinical symptoms (diarrhoea rate and diarrhea mortality rate of newborn piglets) of sows after using different immunization regimens, the diapermic virus prevention and control program of azure pigs has lower diarrhea rates and diarrhea mortality rates in primary piglets produced by sows after immunization. Third, the gestational age of sows is basically controlled at 1-6 births, so the empirical detection of colostrum sIgA antibody levels in sows is mainly concentrated in 1-6 births, and is grouped according to 1-2 births, 3-4 births, and 5-6 births. The big data collection and analysis of sow colostrum sIgA antibody verified that Qingdao Azure's new scientific immune prevention and control model for diarrhea has certain advantages.