Abstract:
Disclosed are an attenuated live vaccine against mycoplasmal pneumonia of swine (MPS) and use thereof. In the present invention, pathological lung tissues of swine having typical  Mycoplasma hyopneumoniae  (Mhp) infection and no obvious other pathogenic infections are screened, and subcultured 100 generations in lungs of newborn rabbits; then, Mhp strains are isolated and serially subcultured in a medium; and the Mhp strain AN306 is obtained by screening a plurality of strains, which is deposited with an accession number: CCTCC NO. M2012431. Also disclosed is a live vaccine formulation against MPS prepared on the basis of the attenuated strain and comprising live attenuated strain, a pharmaceutically acceptable carrier or excipient, and optionally an adjuvant and immunogens of other pathogens.

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to an attenuated vaccine strain against mycoplasmal pneumonia of swine (MPS), a live vaccine containing the attenuated strain, and use thereof in the protection against  Mycoplasma hyopneumoniae  (Mhp) infection related diseases. 
     Related Art 
     Mycoplasmal pneumonia of swine (MPS), common name pig asthma, is an infectious chronic respiratory disease of swine caused by Mhp, and the symptoms mainly include cough and shortness of breath. The disease mainly leads to decreased feed conversion rate and retarded growth of swine, and is characterized by high incidence and low mortality. MPS is highly prevalent worldwide, and brings about heavy economic losses to the modern swine industry. 
     Mhp generally forms, together with other pathogens, mixed infections. For example, swine enzootic pneumonia is induced by mixed infections with  Pasteurella Multocida, Streptococcus Suis  (SS),  Haemophilus Parasuis  of Swine (HPS), or  Actinobacillus Pleuropneumonia  of Porcine (APP). When mixed infections are caused by Mhp and Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Porcine Circovirus Type 2 (PCV2) and/or Swine Influenza Virus (SIV), common Porcine Respiratory Disease Complex (PRDC) takes places, which in turn causes not only respiratory system diseases, but also a decreased reproductive ability of the swine. 
     MPS is a refractory chronic infectious disease for which the therapeutic effect is less desirable, and that may easily reoccur after drug withdrawal and is difficult to be eradicated once it is epidemic in the pig farm. Therefore, the prevention, control and elimination of MPS are accomplished by means of comprehensive measures such as early diagnosis, timely isolation, antibiotic treatment or removal of affected pigs, vaccine prevention, all in and all out, and strict disinfection, where vaccine prevention plays a critical role in the control of MPS. 
     Although inactivated vaccines for MPS are currently massively used in clinic, the control effect for this disease is unsatisfactory. Moreover, the inactivated vaccines generally can lower the disease index of the lung of the affected pigs to some extent, but cannot decrease the proportion of diseased pigs effectively. MPS is accordingly considered as one of the infectious diseases of swine that are most widely epidemic, and most difficult to be eliminated. The poor effect of the vaccines may be attributed to the nature of the inactivated vaccines and the characteristics of Mhp infection. 
     Mhp binds to and is colonized on the bronchial ciliated epithelial cells through respiratory infection, thus causing persistent infection. After immunization with inactivated vaccines, systemic immune response is elicited; however, the local immune response inducing effect is poor. The circulating antibody produced needs to penetrate through the epithelium barrier, and be secreted into the tracheobronchial lumen. The process is quite difficult and suffers from low efficiency. For the purpose of effective immunization, the vaccine is required to stimulate the immune system to respond at a high level. Definitely, this necessitates relatively high dose of antigen and potent adjuvant, which lead to increased cost of the vaccine. Meanwhile, it is difficult to achieve the desirable control for the disease, because the immune response elicited by the inactivated vaccine can only inhibit the proliferation after infection with field strain and alleviate the tissue destruction, and cannot prevent the infection with field strain totally. 
     SUMMARY 
     An object of the present invention is to provide an attenuated live vaccine against MPS, which is useful in the prevention and control of diseases caused by Mhp infection, including diseases caused by co-infection with Mhp and other pathogens. 
     The attenuated live vaccine against MPS has a mechanism of action that is different from that of an inactivated vaccine, because after vaccination, the live vaccine strain proliferates in vivo to effectively activate the immune system in an organism, and is colonized on the bronchial ciliated epithelial cells after entering the respiratory system, to produce an “occupation effect”, so that the field strain cannot be colonized, and the infection with the field strain may be blocked virtually, thus having a good anti-infective effect. Moreover, because the live vaccine strain can proliferate in vivo to effectively activate the immune system, the required dose is far lower than that of the inactivated vaccine. Therefore, the present invention is obviously advantageous over the inactivated vaccine in terms of the cost control, thereby facilitating the saving of social resources. 
     It is critical in the development of a live vaccine to obtain a highly immunogenic strain and an attenuation technology that decreases the virulence of the strain while the immunogenicity is maintained during attenuation. 
     According to the characteristics of the strain, an attenuation method in which the strain is subcultured 100 generations in newborn rabbits, and then subcultured in a cell free medium after 100 generations is employed in the present invention. The method has the advantage of in-vivo subculture in animals during the early subculture process, so as to avoid the defect of excessively rapid attenuation of the strain in an early stage caused by in-vitro subculture in a medium, which is detrimental to the maintenance of immunogenicity. The strain is subcultured in a cell free medium in a later stage, which facilitates the decrease in the number of attenuated generations to some extent, and the shortening of the attenuation process. 
     The strain is derived specifically by screening pathological lung tissues of swine having typical Mhp infection and no obvious other pathogenic infections, subculturing 100 generations in lungs of newborn rabbits, then isolating Mhp strains, and serially subculturing in a medium, and screening a plurality of strains. The strain screened out is designated as attenuated Mhp strain AN306. After attenuation by long-term multiple times of subculture, the attenuated strain losses the pathogenicity, is safe to the animals, and retains good immunogenicity, thus providing immunoprotection for immunized animals and preventing the occurrence of Mhp infection related diseases. It is confirmed through five-generation virulence recovery test that the attenuated strain AN306 will not be back mutated to a pathogenic virulent strain. Therefore, the attenuated strain AN306 is useful in the preparation of vaccines or multi-valent vaccines against MPS. 
     The attenuated Mhp strain was deposited on Oct. 25, 2012, in China Center for Type Culture Collection (CCTCC) (University, 299 Bayi Road, Wuchang, Wuhan, Luojiashan 430072, CHINA) with an accession number: CCTCC NO. M2012431. 
     Another object of the present invention is to disclose an attenuated live vaccine against MPS, which may be a vaccine or multi-valent vaccine against MPS, and comprises the attenuated Mhp strain AN306, and a pharmaceutically acceptable carrier or excipient. The carrier or excipient mainly includes three classes of substances, which may be varied depending on the particular use and immunization route of the vaccine. One class includes a solvent or a buffer system, including sterile physiological saline and sterile phosphate buffer; one class includes a lyoprotectant, including skimmed milk powder, gelatine, and sucrose, which is added to the lyophilized system when the vaccine is prepared to have a lyophilized form, to help in the maintenance of the activity of the live vaccine; and one class includes a spray protectant, mainly including glycerol, which is added when the live vaccine is used by aerosol immunization, to help in the maintenance of the activity of the live vaccine during spraying. 
     Furthermore, the live vaccine formulation against MPS according to the present invention may further contain an immunization adjuvant. 
     Adjuvant is an ingredient commonly used in vaccines for enhancing the immunostimulatory potency of the vaccines. The adjuvant useful in the present invention is a suitable adjuvant for the live vaccine against MPS that meets the requirements for immunization against MPS without obviously compromising the viability of the live vaccine. 
     The immunization adjuvant disclosed in the present invention may be a single adjuvant ingredient or a combination of two or more adjuvant ingredients. The adjuvant ingredient may include one or more of Chinese herbal medicine polysaccharides, carbomers, chitosan, immunostimulating complex matrix, levamisole, dextran, CpG, and bursin. The mixing ratio and dosage of various immunization adjuvant ingredients vary depending on the specific dosage and route of administration of the live vaccines. 
     The live vaccine formulation against MPS according to the present invention may further contain an immunogen of at least an additional pathogen, to form a multivalent vaccine for use. The additional pathogen includes at least one of viruses, bacteria, fungi, and parasites, for example, porcine circovirus,  Haemophilus parasuis , porcine reproductive and respiratory syndrome virus,  Mycoplasma hyorhinis , swine mycoplasmal  hyosynoviae , porcine influenza virus, and others. These pathogens frequently clinically form, in respiratory tract, mixed infections with or infections secondary to Mhp, and contribute to each other, causing the disease to exacerbate and bringing about a great risk to the health of the swine. Therefore, when the vaccines against these pathogens are used in combination with the live vaccine against MPS, the mixed infections of Mhp and other pathogens can be prevented. The immunogens of other pathogens may be in the form of live or inactivated bacteria or viruses, or in the form of protein subunits. It should be noted that the carrier, excipient, and adjuvant used in the vaccines against other pathogens need to be compatible with the system of, and tolerable by the present live vaccine against MPS. 
     Immunization may be conducted with the attenuated live vaccine against MPS according to the present invention through various routes, including intrapulmonary injection, intramuscular injection, aerosol immunization, oral immunization, and nasal immunization. The attenuated live vaccine may be in the form of an intrapulmonary injectable formulation, an intramuscular injectable formulation, an aerosol, an oral formulation or a nasal drop. The route of immunization is selected depending on the animal being vaccinated, the vaccination history, the environment in the pig farm, and the convenience in operation of the person administering the vaccine. After an organism is infected with Mhp, Mhp initially binds to the bronchial ciliated epithelial cells in the lung to cause the cilium to fall off, then further invades the tissue to induce inflammation, and opens an access to infection with other pathogens. When the immunization is carried out with the live vaccine against MPS by intrapulmonary injection, the live vaccine may be directly injected into the target tissue, bind to the ciliated cells, and occupy the binding site, thereby preventing the infection with the field strain. When the immunization is carried out with the live vaccine against MPS through aerosol immunization, the live vaccine is enabled to reach the lower respiratory tract of the animal by controlling the size of the droplets, and effectively binds to the bronchial ciliated epithelial cells. Moreover, the workers needed for immunization are reduced by the use of vaccines as aerosol in a closed livestock shed or space. Intramuscular injection is a common route for immunization of animals, which is convenient and highly acceptable. When the immunization is carried out with the live vaccine against MPS by intramuscular injection, the animals are induced to produce systemic humoral and cellular immune responses, and the infection with the Mhp field strain is inhibited by the immune response mapping to the local target lung tissue. When the live vaccine against MPS is inoculated by oral or nasal immunization, the local mucosal immune response of intestinal tract or nasal cavity is induced, and the lymphocytes are nested to different mucosal site by means of the common mucosal immune system, thereby eliciting the immune response of the bronchial lung tissue in the lower respiratory tract, and achieving the protection against infection with Mhp field strain. Depending on the route of inoculation employed, the immunization adjuvant used may be varied. Therefore, the attenuated live vaccine against MPS according to the present invention is useful in the prevention and treatment of Mhp infection related diseases. The attenuated live vaccine against MPS according to the present invention is prepared by combining the attenuated Mhp strain AN306 with a pharmaceutically acceptable carrier or excipient, at least an immunization adjuvant, and an immunogen of at least an additional pathogen. 
     The live vaccine against MPS according to the present invention may be inoculated in either a single, or two or more repeated immunizations to enhance the immune response, which may be specifically determined depending on the route of immunization and the conditions of the animals. The time for single immunization is generally at an age of 3-10 days, and preferably 5-7 days. The time for the first immunization of 2 or more repeated immunizations is generally at an age of 3-10 days, and preferably 5-7 days. The interval between two immunizations is generally 2-3 weeks. 
     Matter Relating to Deposit of Sample of Biological Material 
     The attenuated Mhp strain AN306 was designated as Mhp AN306, and deposited on Oct. 25, 2012, in China Center for Type Culture Collection (CCTCC) (Wuhan University, 299 Bayi Road, Wuchang, Wuhan, Luojiashan 430072, CHINA) with an accession number: CCTCC NO. M2012431. 
    
    
     DETAILED DESCRIPTION 
     The present invention is further described and discussed with reference to specific embodiments; however, the present invention is not limited thereto. 
     For the purpose of illustrating the screening, subculture, and identification of the live vaccine strain against MPS according to the present invention as well as the immunogenicity and safety of the live vaccine strain, and confirming that by using the live vaccine formulations against MPS according to the present invention that are inoculated through various routes of immunization and contain various adjuvants and immunogens of additional different pathogens, the Mhp infection can be effectively prevented and the incidence of MPS can be controlled, the following experiments and preparations are conducted. 
     Example 1: Acquisition of Mhp AN306 
     Acquisition of Virulent Strain: 
     In 1975, Jiangsu Academy of Agricultural Sciences carried out the screening of virulent and pathogenic Mhp strains by collecting the typical MPS affected tissue samples from agricultural universities and national and provincial academy of science in more than 20 provinces all over the country, according to the requirements of the Ministry of agriculture. A total of over 2 hundreds of suspected MPS affected lung tissue samples were collected all over the country, from which 10 samples having typical Mhp infection and no obvious other pathogenic infections were screened out, and lyophilized and stored as virulent MPS tissular strains. Also, the tests of disease development upon challenge and attenuation by serial subculture were conducted in animals. 
     The selected 10 virulent tissular strains were inoculated to healthy and susceptible pigs of local variety by nasal drip, and after challenge, the test animals were observed to have clinical symptoms of MPS such as cough, shortness of breath, asarcia, and dog sitting, and typical shrimp meat like consolidation was found in the apical and cardiac lobes of the lungs of the animals after necropsy. 3 strains that have the most potent virulence and the highest immunogenicity were selected from the 10 virulent tissular strains for subculture, according to the latency prior to attack, the clinical symptoms, the incidence rate, the severity of the disease, and the titer of the haemagglutination antibody of the challenged animals. 
     Attenuation by Subculture: 
     The virulent tissular strains were inoculated to healthy newborn rabbits by intrapulmonary injection. The lung tissues of challenged rabbits were collected, homogenized, and then inoculated to healthy newborn rabbits. The subculture was conducted as such. Only 1 of the 3 virulent strains was successful in subculture in rabbits. During the subculture of the strain, a parallel subculture group was additionally set respectively at Generations 20, 40, 60, and 80, and the strain was serially subcultured 100 generations. 
     Mhp was isolated from the generation 100 lung tissue of the newborn rabbits by “affected lung block immersion method”. Specifically, the animals were sacrificed by bleeding, the lung tissue was aseptically removed, cut into small blocks with a size of ½ sesame, washed with Hank&#39;s solution, and immersed in KM2 medium. Antibiotics were added, and incubation was continued at 37° C. The change in pH and the turbidity were observed every day. When the pH had an obvious change (dropped to 7.0-6.8) and homogenous turbidness was formed (at about 48 hrs), the culture was serially subcultured 4-5 generations by inoculating at a ratio of 1:5, and then subcultured by inoculating at a ratio of 1:10. After staining following Gurr&#39;s modified Giemsa staining method and examination under oil immersion microscope, the isolated microorganism was found to have a polymorphic mycelium, and have the typical morphological features of Mhp, and identified to be Mhp by particle agglutination reaction and metabolism inhibition test with standard Mhp positive serum. The isolated Mhp was purified by three times of solid cloning, identified again, lyophilized and stored. 
     The lyophilized and stored Mhp strain of generation F100 was revived, and continuously attenuated by serially subculturing in KM2 medium by inoculating at a ratio of 1:10. The strain was identified by PCR every five generations, and lyophilized and stored every 20 generations. The strain of generations F100, F140, F180, F220, F240, F280, and F320 was additionally subcultured different generations. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Preliminary screening of attenuated strains 
               
             
          
           
               
                   
                   
                 Growth during in-vitro 
                 Disease development of 
                   
               
               
                 Strain 
                 Generation 
                 culture 
                 challenged animals 
                 Remark 
               
               
                   
               
               
                 AN301 
                 F240 
                 Grow well, 10 9  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN302 
                 F110 
                 Grow slowly, 
                 — 
                 Loss in subculture 
               
               
                   
                   
                 10 2  CCU/mL 
                   
                 in medium 
               
               
                 AN303 
                 F280 
                 Grow well, 10 8  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN304 
                 F240 
                 Grow well, 10 7  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN305 
                 F32 
                 — 
                 — 
                 Loss in subculture 
               
               
                   
                   
                   
                   
                 in newborn 
               
               
                   
                   
                   
                   
                 rabbits 
               
               
                 AN306 
                 F280 
                 Grow well, 10 9  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN307 
                 F140 
                 Grow well, 10 8  CCU/mL 
                 No apparent lesion and 
                   
               
               
                   
                   
                   
                 mild inflammatory 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN308 
                 F300 
                 Grow well, 10 9  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN309 
                 F360 
                 Grow well, 10 8  CCU/mL 
                 No apparent lesion and no 
                   
               
               
                   
                   
                   
                 pathological changes 
                   
               
               
                 AN310 
                 F12 
                 — 
                 — 
                 Loss in subculture 
               
               
                   
                   
                   
                   
                 in newborn 
               
               
                   
                   
                   
                   
                 rabbits 
               
               
                 AN311 
                 F260 
                 Grow slowly, 
                 No apparent lesion and no 
                   
               
               
                   
                   
                 10 4  CCU/mL 
                 pathological changes 
                   
               
               
                 AN312 
                 F64 
                 — 
                 — 
                 Loss in subculture 
               
               
                   
                   
                   
                   
                 in newborn 
               
               
                   
                   
                   
                   
                 rabbits 
               
               
                   
               
             
          
         
       
     
     The various strains subjected to subculture was comprehensively analyzed in terms of subculture and growth abilities, and virulence, and 5 strains AN301, AN303, AN306, AN308, AN309 that grow rapidly, and have high titer and attenuated virulence were selected for the following virulence recovery test and immunoprotection assay. 
     Virulence Recovery Test of Attenuated Strain: 
     The screened strains were subjected to consecutive five-generation virulence recovery test. 3 mL of 10 8  CCU/mL Mhp culture was injected to the tracheas of 3 healthy pigs. The animals were isolated and raised for 28 days, subjected to necropsy to observe whether lesions occur to the lungs of the test pigs, and pathologically sectioned to observe whether inflammatory changes occur. The apical and cardiac lobes and 5-7 g anterior portion of the diaphragm of the lung were aseptically removed, chopped, and ground into a paste. 100 mL of Hank&#39;s solution containing 1000 IU/mL penicillin was added, to formulate a 50 g/L lung suspension. The supernatant was aspirated and inoculated to 3 healthy pigs in an amount of 3 mL/pig on the same day. The strain was subcultured 5 generations as such, to observe whether virulence recovery takes places. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Screening of attenuated strains by virulence recovery test 
               
             
          
           
               
                   
                 Strain 
               
             
          
           
               
                   
                 AN301 
                 AN303 
                 AN306 
                 AN308 
                 AN309 
               
               
                 Generation 
                 F240 
                 F280 
                 F280 
                 F300 
                 F360 
               
               
                   
               
               
                 1 st  test 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
               
               
                 2 nd  test 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
               
               
                 3 rd  test 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
               
               
                 4 th  test 
                 1/3 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
               
               
                 5 th  test 
                 2/3 
                 0/3 
                 0/3 
                 0/3 
                 0/3 
               
               
                   
               
             
          
         
       
     
     The results show that the strain AN301 leads to inflammatory pathological changes of the lung of the animals at the fourth and fifth generations; and no obvious clinical symptoms of MPS are observed for the animals experiencing 5 inoculations of the remaining 4 strains, no consolidation of the lung is found after necropsy, and no inflammatory pathological changes such as lymphadenosis and lymphocyte and macrophage infiltration are found through pathological section examination, suggesting that the 4 strains subcultured are attenuated strains and have no virulence recovery ability. 
     Immunoassay of Attenuated Strains: 
     The screened strains were determined for immunogenicity and assayed for immunoprotection after challenge. Lyophilized strains were prepared and determined for the titer. The lyophilized strain was dissolved in a sterile phosphate buffer, and adjusted with the sterile phosphate buffer to have the same concentrations for test. 
     Immunoprotection after challenge was assayed in healthy and negative Meishan pigs at an age of 5-7 days. The animals were grouped at random, each group having 5 animals. The animals in the immunization group was inoculated with 0.5 mL of attenuated strain (10 5  CCU/pig) by intrapulmonary injection, and challenged by intratracheal injection with virulent Mhp strain 8 weeks after immunization, and subjected to necropsy 28 days later. A healthy control group and a challenged control group were additionally set. 
     The serum antibody was detected by indirect hemagglutination test. 1:10“++” or above is determined to be positive. 
     Score at necropsy: The animals were sacrificed 28 days after challenge, and the damage to the lung of the test pigs was scored following the method reported by MADEC and KOBISCH (1982). The whole lung includes a left cardiac lobe (LCL), a left apical lobe (LAL), a left diaphragmatic lobe (LDL), a right cardiac lobe (RCL), a right apical lobe (RAL), a right diaphragmatic lobe (RDL), and an accessory lobe (IL), and there are 7 lobes in total. The damage score of the lung is a sum of the damage scores for the dorsal surface and the ventral surface of the 7 lobes, and the total score is 28. Each lobe is scored 0-4 according to the injured area, where no damage is scored 0, 1-25% of area being damaged is scored 1, 26-50% of area being damaged is scored 2, 51-75% of area being damaged is scored 3, and 76-100% of area being damaged is scored 4. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Screening of attenuated strain by immunoassay 
               
             
          
           
               
                   
                 Strain for immunization 
               
             
          
           
               
                   
                   
                 AN303 
                 AN306 
                 AN308 
                 AN309 
                   
               
             
          
           
               
                   
                 Healthy 
                 Generation 
                 Challenged 
               
             
          
           
               
                   
                 control 
                 F280 
                 F280 
                 F300 
                 F360 
                 control 
               
               
                   
               
               
                 Antibody 
                 − 
                 − 
                 + 
                 + 
                 − 
                 − 
               
               
                 Score for 
                 0.24 ± 0.15 
                 6.23 ± 3.39 
                 3.01 ± 1.45 
                 7.73 ± 4.38 
                 11.10 ± 6.77 
                 20.29 ± 5.42 
               
               
                 lesions of lung 
                   
                   
                   
                   
                   
                   
               
               
                 of pigs 
               
               
                   
               
             
          
         
       
     
     It can be known from analysis of the results that the attenuated strain AN306 has a high immunogenicity, and a high protection effect as confirmed by the challenge test. Moreover, the test shows that the strain grows rapidly when cultured in vitro, and has a high titer and a high safety. Therefore, the strain AN306 is selected and used as the live vaccine strain, and the primary generation is F280. 
     Example 2: Culture of Attenuated Mhp Strain AN306 
     Preparation of KM2 liquid medium (2050 mL): 1000 mL of Eagles medium, 10 g of hydrolyzed milk protein, 400 mL of swine serum, 20 mL of fresh yeast extract, 600 mL of Dulbecco phosphate buffer, 4,000,000 units of penicillin, and 3.5 mL of 0.4% phenol red, pH 7.4 7.6 (adjusted with 10 g/L NaOH). 
     1 vial of lyophilized attenuated Mhp strain AN306 was dissolved in 0.5 mL medium, and then 0.5 mL was inoculated in 4.5 mL medium, and incubated in a closed penicillin bottle at 37° C. When the color of the medium was changed from red to yellow, the culture was harvested in time, and inoculated into a fresh medium at a volume ratio of 1:10 for expansion culture. When the color of the medium was changed from red to yellow, the culture was harvested in time. Following this process, the strain was expansion cultured to 5000 mL and the culture was collected. 
     A lyoprotectant was formulated, which comprised 1.5 g of gelatine, 12.5 g of sucrose, 100 mL of double distilled water, and was sterilized in an autoclave for 15 min at 115° C., and adjusted to pH 7.0 with sterilized 1% NaOH. The culture was harvested and determined for the CCU level. The culture to be inoculated was added with the sterilized lyoprotectant at a volume ratio of 3:2, mixed fully, and packaged in ampoules in an amount of 0.5 mL/ampoule. The ampoule with packaged culture therein was placed in a lyophilizer, and lyophilized. After lyophilization, the bottle was sealed with nitrogen, and stored at −40° C. 1 mL culture was removed for DNA extraction and identification by PCR. 
     The culture of the attenuated strain AN306 thus obtained has a titer up to 10 9  CCU/mL, and a production at liter level. 
     Example 3: Evaluation of Immunoprotection of Attenuated Live Vaccine Strain AN306 Against MPS Inoculated by Intrapulmonary Injection, and Comparison with Other Commercial Live and Inactivated Vaccines 
     Preparation of Vaccines: 
     Lyophilized attenuated live vaccine strain AN306 against MPS was dissolved in a sterile phosphate buffer, to formulate a vaccine solution in which the live vaccine has a titer of 2×10 5  CCU/mL. Each animal was dosed 0.5 mL by intrapulmonary injection, that is, 10 5  CCU/animal. 
     Commercial live vaccines: In this test, the only two live vaccines against MPS available in the market were used as control live vaccines, that is, (1) the live vaccine against MPS manufactured by Jilin Zhengye Biological Products Co., Ltd, which is chick embryo yolk sac tissue containing lapinized attenuated Mhp strain, referred to as Commercial vaccine 1 hereinafter, and used following the operations described in the instruction of the vaccine; and (2) Zhibining (trade name), which is a in-vitro culture of attenuated Mhp strain 168, referred to as Commercial vaccine 2 hereinafter, and used following the operations described in the instruction of the vaccine. 
     Commercial inactivated vaccine: In this test, two inactivated vaccines against MPS currently widely available in the market were used as control inactivated vaccines, that is (1) RespiSure (trade name), which is referred to as Commercial vaccine 3 hereinafter, and used following the operations described in the instruction of the vaccine; and (2) MycoFLEX (trade name), which is referred to as Commercial vaccine 4 hereinafter, and used following the operations described in the instruction of the vaccine. 
     Immunization and Challenge of Animals: 
     70 healthy piglets were assigned to 7 groups at random, where Group G1 is a healthy control group, which is not immunized and challenged; Group G7 is a challenged control group, which is not immunized, but challenged; and Groups G2-G6 are groups with immunization of vaccines. The specific grouping and immunization method was as shown in a table below. The animals were immunized and then challenged. 8 weeks after immunization, the animals in Groups G2-G7 were challenged by intratracheal injection with virulent Mhp strain, and subjected to necropsy 28 days later. 
     The test was the experiments were done in duplicate with two varieties including Suzhong pig and Topigs. 
     Result: 
     The MPS lesion in the lung of the animals was scored following the method described in Example 1. The result shows that the animals immunized with attenuated live vaccine strain AN306 against MPS have obviously lessened lesions in the lung, and the statistical difference is highly significant (P&lt;0.01) compared with the challenged control group (by One-way ANOVA). The average disease index is obviously lower than that of the commercial live and inactivated vaccines (Commercial vaccine 1, P&lt;0.01; Commercial vaccine 2, P&lt;0.05; Commercial vaccine 3, P&lt;0.01; and Commercial vaccine 4, P&lt;0.01) currently widely available in the market, suggesting that the attenuated live vaccine strain AN306 can help the immunized animals to resist Mhp infection effectively, with a protection being superior to that of the vaccines widely available in the market. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of attenuated live vaccine strain AN306 against MPS inoculated by 
               
               
                 intrapulmonary injection, and comparison with other commercial live and inactivated vaccines 
               
             
          
           
               
                   
                 Group No. 
               
             
          
           
               
                   
                 G1 
                 G2 
                 G3 
                 G4 
                 G5 
                 G6 
                 G7 
               
               
                   
               
               
                 Group 
                 Healthy 
                 Live vaccine 
                 Commercial 
                 Commercial 
                 Commercial 
                 Commercial 
                 Challenged 
               
               
                 division 
                 control 
                 group 
                 vaccine 1 
                 vaccine 2 
                 vaccine 3 
                 vaccine 4 
                 control 
               
               
                   
                 group 
                   
                   
                   
                   
                   
                 group 
               
               
                 Route of 
                 — 
                 Intrapulmonary 
                 Intrathoracic 
                 Intrapulmonary 
                 Intramuscular 
                 Intramuscular 
                 — 
               
               
                 immunization 
                   
                 injection 
                 injection 
                 injection 
                 injection 
                 injection 
                   
               
               
                 Score of 
                 0.50 ± 0.71 
                 2.60 ± 0.84 
                 5.00 ± 1.15 
                 3.80 ± 1.14 
                 10.60 ± 2.37 
                 11.90 ± 3.41 
                 21.90 ± 2.02 
               
               
                 lesions of the 
                   
                   
                   
                   
                   
                   
                   
               
               
                 lung (test 1) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Score of 
                 0.40 ± 0.70 
                 2.80 ± 1.40 
                 5.10 ± 2.18 
                 4.00 ± 1.25 
                  8.30 ± 2.41 
                  6.00 ± 2.17 
                 17.90 ± 3.21 
               
               
                 lesions of the 
                   
                   
                   
                   
                   
                   
                   
               
               
                 lung (test 2) 
               
               
                   
               
             
          
         
       
     
     Example 4: Evaluation of Immunoprotection of Attenuated Live Vaccine Strain AN306 Against MPS Inoculated by Aerosol Immunization 
     Preparation of Vaccine Diluent: 
     Sterilized 5%-10% glycerol solution in deionized water, pH 6.8-7.5. 
     Formulation of Vaccines: 
     Lyophilized attenuated live vaccine strain AN306 against MPS was dissolved in the vaccine diluent, to formulate a vaccine solution in which the live vaccine has a titer of 10 6  CCU/mL. 
     Immunization and Challenge of Animals: 
     40 healthy and negative Topigs at an age of 5-7 days were assigned to 4 groups at random, where Group G1 is a healthy control group, which is not immunized and challenged; Group G2 is a group with aerosol immunizations of live vaccine strain AN306 in an amount of 0.5 mL (5×10 5  CCU/animal), in which 2 weeks after the first immunization, the immunization is conducted again, followed by challenge; Group G3 is a commercial vaccine group, in which the commercial inactivated vaccine RespiSure against MPS currently widely available in the market is inoculated, the operation is following the instruction of the vaccine, and challenge is performed after immunization; and Group G4 is a challenged control group, which is not immunized, but challenged. The animals in Groups G2, G3, and G4 were challenged by intratracheal injection with virulent Mhp strain 8 weeks after the first immunization, and subjected to necropsy 28 days later. 
     Result: 
     The MPS lesion in the lung of the animals was scored following the method described in Example 1, specifically as shown in a table below. The result shows that the animals with aerosol immunization of attenuated live vaccine strain AN306 against MPS have obviously lessened lesions in the lung, the statistical difference is highly significant (P&lt;0.01) compared with the challenged control group, and the lesions are obviously reduced compared with the case in which the commercial inactivated vaccine is inoculated (P&lt;0.01), suggesting that the attenuated live vaccine strain can help the immunized animals to resist Mhp infection through aerosol immunization, with a protection being superior to that of the inactivated vaccine widely available in the market. 
     
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of attenuated live vaccine 
               
               
                 strain AN306 against MPS inoculated by aerosol immunization 
               
             
          
           
               
                   
                 Group Division 
               
             
          
           
               
                   
                   
                   
                 G3 
                 G4 
               
               
                   
                 G1 
                 G2 
                 Commercial 
                 Challenged 
               
               
                   
                 Healthy 
                 Live vaccine 
                 inactivated 
                 control 
               
               
                   
                 control group 
                 group 
                 vaccine group 
                 group 
               
               
                   
               
               
                 Score of 
                 1.08 ± 0.27 
                 3.83 ± 2.48 
                 8.25 ± 4.14 
                 20.34 ± 3.45 
               
               
                 lesions 
                   
                   
                   
                   
               
               
                 of the lung 
               
               
                   
               
             
          
         
       
     
     Example 5: Evaluation of Immunoprotection of Attenuated Live Vaccine Strain AN306 Against MPS Inoculated by Intramuscular Injection 
     Preparation of Vaccines: 
     Lyophilized attenuated live vaccine strain AN306 against MPS was used. The adjuvant used was a mixed adjuvant of 5 mg/mL carbomers and 30 mg/mL.  Astragalus  polysaccharides formulated in a sterile phosphate buffer. The lyophilized vaccine strain was dissolved in the adjuvant solution, to formulate a vaccine solution in which the live vaccine has a titer of 2.5×10 5  CCU/mL. 
     Immunization and Challenge of Animals: 
     40 healthy and negative Suzhong pigs at an age of 5-7 days were assigned to 4 groups at random, where Group G1 is a healthy control group, which is not immunized and challenged; Group G2 is a group immunized with a live vaccine by intramuscular injection in an amount of 2 mL (5×10 5  CCU/animal), in which 2 weeks after the first immunization, the immunization is conducted again, followed by challenge; Group G3 is a commercial vaccine group, in which the commercial inactivated vaccine RespiSure against MPS currently widely available in the market is inoculated, the operation is following the instruction of the vaccine, and challenge is performed after immunization; and Group G4 a challenged control group, which is not immunized, but challenged. The animals in Groups G2, G3, and G4 were challenged by intratracheal injection with virulent Mhp strain 8 weeks after the first immunization, and subjected to necropsy 28 days later. 
     Result: 
     The MPS lesion in the lung of the animals was scored following the method described in Example 1, specifically as shown in a table below. The result shows that the animals immunized with attenuated live vaccine strain AN306 against MPS by intramuscular injection have obviously lessened lesions in the lung, the statistical difference is highly significant (P&lt;0.01) compared with the challenged control group, and the lesions are obviously reduced compared with the case in which the commercial inactivated vaccine is inoculated (P&lt;0.01), suggesting that the attenuated live vaccine strain can help the immunized animals to resist Mhp infection through intramuscular injection, with a protection being superior to that of the inactivated vaccine widely available in the market. 
     
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of attenuated live vaccine 
               
               
                 strain AN306 against MPS inoculated by intramuscular injection 
               
             
          
           
               
                   
                 Group Division 
               
             
          
           
               
                   
                   
                   
                 G3 
                 G4 
               
               
                   
                 G1 
                 G2 
                 Commercial 
                 Challenged 
               
               
                   
                 Healthy control 
                 Live vaccine 
                 inactivated 
                 control 
               
               
                   
                 group 
                 group 
                 vaccine group 
                 group 
               
               
                   
               
               
                 Score of 
                 0.98 ± 0.43 
                 4.57 ± 2.32 
                 7.88 ± 4.78 
                 20.65 ± 7.51 
               
               
                 lesions of 
                   
                   
                   
                   
               
               
                 the lung 
               
               
                   
               
             
          
         
       
     
     Example 6: Evaluation of Immunoprotection of Attenuated Live Vaccine Strain AN306 Against MPS Inoculated by Nasal Immunization 
     Preparation of Vaccines: 
     Fresh culture of Mhp strain AN306 having a titer of 5×10 6  CCU/mL was used. A vaccine containing chitosan as an adjuvant was prepared as follows. Chitosan was dissolved in a 1% acetic acid solution, to formulate a stock solution containing 1% chitosan, which was adjusted to pH 6.5 with a 0.1 M NaOH solution. The stock solution containing chitosan was diluted with 0.1 M NaAc—HAc (pH 6.5) solution to give a final concentration of chitosan of 0.2%. The fresh culture of the Mhp strain AN306 was concentrated at 12000 rpm for 30 min, to collect the pellet, which was resuspended in 1 mL of 50 mM Na 2 SO 4 , to give a titer of 6.66×10 6  CCU/mL. 5 mL of 0.2% chitosan solution was added with 1 mL of the Na 2 SO 4  solution containing Mhp, and mixed by stirring. 660 μL of sodium tripolyphosphate (4 mg/mL) solution was added slowly with stirring, to obtain a cream white homogeneous suspension. 
     Immunization and Challenge of Animals: 
     32 healthy and negative Topigs at an age of 5-7 days were assigned to 4 groups at random, where Group G1 is a healthy control group, which is not immunized and challenged; Group G2 is a group with nasal immunizations of live vaccine strain AN306 in an amount of 0.5 mL (5×10 5  CCU/animal), in which 2 weeks after the first immunization, the immunization is conducted again, followed by challenge; Group G3 is a commercial vaccine group, in which the commercial inactivated vaccine RespiSure against MPS currently widely available in the market is inoculated, the operation is following the instruction of the vaccine, and challenge is performed after immunization; and Group G4 is a challenged control group, which is not immunized, but challenged. The animals in Groups G2, G3, and G4 were challenged by intratracheal injection with virulent Mhp strain 8 weeks after the first immunization, and subjected to necropsy 28 days later. 
     Result: 
     The MPS lesion in the lung of the animals was scored following the method described in Example 1, specifically as shown in a table below. The result shows that the animals immunized with attenuated live vaccine strain AN306 against MPS have obviously lessened lesions in the lung, the statistical difference is highly significant (P&lt;0.01) compared with the challenged control group, and the lesions are obviously reduced compared with the case in which the commercial inactivated vaccine is inoculated (P&lt;0.01), suggesting that the attenuated live vaccine strain can help the immunized animals to resist Mhp infection through nasal immunization, with a protection being superior to that of the inactivated vaccine widely available in the market. 
     
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of attenuated live vaccine 
               
               
                 strain AN306 against MPS inoculated by nasal immunization 
               
             
          
           
               
                   
                 Group division 
               
             
          
           
               
                   
                   
                   
                 G3 
                 G4 
               
               
                   
                 G1 
                 G2 
                 Commercial 
                 Challenged 
               
               
                   
                 Healthy control 
                 Live vaccine 
                 inactivated 
                 control 
               
               
                   
                 group 
                 group 
                 vaccine group 
                 group 
               
               
                   
               
               
                 Score of 
                 0.21 ± 0.18 
                 3.03 ± 2.68 
                 8.72 ± 4.19 
                 22.68 ± 4.67 
               
               
                 lesions of 
                   
                   
                   
                   
               
               
                 the lung 
               
               
                   
               
             
          
         
       
     
     Example 7: Evaluation of Immunoprotection of Divalent Vaccine of Attenuated Live Vaccine Strain AN306 Against MPS and Inactivated HPS Vaccine 
     Preparation of Vaccines: 
     Fresh culture of Mhp strain AN306 having a titer of 1×10 6  CCU/mL was used. 
     Fresh culture of HPS strain XX0306 serotype 5 (which is isolated by Veterinary Research Institute, Jiangsu Academy of Agricultural Sciences, has a good immunogenicity, and is proved through tests to be suitable for the preparation of inactivated vaccines of HPS, with the protection effect being good) was inactivated for 12 hrs with a formaldehyde solution having a final concentration of 0.2% after viable count. Then the inactivation was terminated by adding 0.2% sodium metabisulfite. The cells were concentrated to 1×10 10  CFU/mL. 
     The adjuvant used was a mixed adjuvant of 5 mg/mL carbomers and immunostimulating complex matrix (containing QuilA 500 μg/mL, cholesterol 100 μg/mL, and phospholipid 100 μg/mL) formulated in a sterile phosphate buffer. 
     0.5 mL of fresh Mhp culture was mixed fully with 0.5 mL of inactivated HPS strain XX0306 serotype 5 and the adjuvant at a ratio of 1:1:2, with which the animals were immunized. 
     Immunization and Challenge of Animals: 
     30 healthy and negative Suzhong pigs at an age of about 10 days were assigned to 4 groups at random, where Group G1 is a healthy control group having 10 animals, which is not immunized and challenged, and in which 5 of 10 animals are subjected to necropsy at the same time with the animals in Groups G2 and G3, and the other 5 animals are subjected to necropsy at the same time with the animals in Groups G4 and G5; Group G2 is a group having 5 animals and immunized with the bivalent vaccine and challenged with Mhp, where the immunization is performed by intramuscular injection of 2 mL of the prepared bivalent vaccine (AN306 live vaccine: 2.5×10 5  CCU/mL, inactivated HPS strain XX0306 serotype 5: 2.5×10 9  CFU/mL), immunization is performed again 3 weeks after the first immunization, and challenge with virulent Mhp is conducted by intratracheal injection 8 weeks after the first immunization; Group G3 is a control group challenged with Mhp and having 5 animals, which is not immunized, but challenged in the same way as that for the animals in Group G2; Group G4 is a group having 5 animals and immunized with the bivalent vaccine and challenged with HPS, where the immunization is performed by intramuscular injection of 2 mL of the prepared bivalent vaccine (AN306 live vaccine: 2.5×10 5  CCU/mL, inactivated HPS strain XX0306 serotype 5: 2.5×10 9  CFU/mL), immunization is performed again 3 weeks after the first immunization, and challenge with virulent HPS is conducted by intraperitoneal injection 6 weeks after the first immunization; and Group G5 is a control group having 5 animals and challenged with HPS, which is not immunized, but challenged in the same way as that for the animals in Group G4. 
     Result: 
     (1) Protection Against Mhp Infection 
     The animals were subjected to necropsy 28 days after challenge, and the MPS lesion in the lung of the animals was scored following the method described in Example 1. The results are shown in a table below and suggest that after immunization with the bivalent vaccine, the lesion in the lung is obviously lessened (P&lt;0.01). 
     (2) Protection Against HPS Infection 
     The clinical symptoms of HPS infection include reduced appetite, roughened hair coats, ear and body skin flushing, increased nasal discharge, and respiratory distress, swelling joint, and failure to stand occurring in a later stage. At necropsy, pleural effusion, abdominal effusion, different degrees of pleural and peritoneal adhesion, swelling joint, increased mucus in articular cavity, bleeding lung, lymph node enlargement and other physiological changes may be found. The disease status of HPS infection in the animals in each group was determined based on the above criteria, and outlined in a table below. The results suggest that after immunization with the bivalent vaccine, the incidence of HPS infection in the animals are obviously lessened (P&lt;0.01). 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of divalent vaccine of attenuated live vaccine strain AN306 
               
               
                 against MPS and inactivated HPS Live vaccine 
               
             
          
           
               
                   
                 Group division 
               
             
          
           
               
                   
                   
                 G2 
                   
                 G4 
                   
               
               
                   
                   
                 Group immunized 
                   
                 Group immunized 
                   
               
               
                   
                   
                 with the bivalent 
                 G3 
                 with the bivalent 
                 G5 
               
               
                   
                 G1 
                 vaccine and 
                 Control group 
                 vaccine and 
                 Control group 
               
               
                   
                 Healthy 
                 challenged with 
                 challenged 
                 challenged with 
                 challenged 
               
               
                   
                 control group 
                 Mhp 
                 with Mhp 
                 HPS 
                 with HPS 
               
               
                   
               
               
                 Immunization 
                 Not 
                 Immunized with 
                 Not immunized 
                 Immunized with 
                 Not immunized 
               
               
                   
                 immunized 
                 the bivalent 
                   
                 the bivalent 
                   
               
               
                   
                   
                 vaccine 
                   
                 vaccine 
                   
               
               
                 Challenge with 
                 Not 
                 Challenged 
                 Challenged 
                 Not challenged 
                 Not challenged 
               
               
                 Mhp 
                 challenged 
                   
                   
                   
                   
               
               
                 Challenge with 
                 Not 
                 Not challenged 
                 Not challenged 
                 Challenged 
                 Challenged 
               
               
                 HPS 
                 challenged 
                   
                   
                   
                   
               
               
                 Score of MPS 
                 0.54 ± 0.28 
                 5.37 ± 4.36 
                 19.81 ± 6.57 
                 Not evaluated 
                 Not evaluated 
               
               
                 lesion 
                   
                   
                   
                   
                   
               
               
                 Evaluation of 
                 0/5 
                 Not evaluated 
                 Not evaluated 
                 1/5 
                 5/5 
               
               
                 disease status of 
                   
                   
                   
                   
                   
               
               
                 HPS infection 
               
               
                   
               
             
          
         
       
     
     Example 8: Evaluation of Immunoprotection of Divalent Vaccine of Attenuated Live Vaccine Strain AN306 Against MPS and Live PRRSV Vaccine 
     Preparation of Vaccines: 
     A mixed adjuvant containing 10 mg/mL chitosan and 10 mg/mL levamisole was formulated in a sterile phosphate buffer. Lyophilized live vaccine strain AN306 against MPS was dissolved in 1.5 mL adjuvant, to obtain a live vaccine against MPS as a solution having a specification of 1 dose (5×10 5  CCU)/1.5 mL. 
     Commercial live PRRSV vaccine (strain ATCCVR-2332) was dissolved in saline, to obtain a live PRRSV vaccine as a solution having a specification of 2 dose/mL. 
     The two vaccine solutions were mixed at a ratio (by volume) of 3:1, with which the animals were immunized by inoculating 2 mL per animal, that is, 1 dose of the live vaccine against MPS and 1 dose of the live PRRSV vaccine. 
     Immunization and Challenge of Animals: 
     30 healthy and negative Suzhong pigs at an age of about 10 days were assigned to 4 groups at random, where Group G1 is a healthy control group having 10 animals, which is not immunized and challenged, and in which 5 of 10 animals are subjected to necropsy at the same time with the animals in Groups G2 and G3, and the other 5 animals are subjected to necropsy at the same time with the animals in Groups G4 and G5; Group G2 is a group having 5 animals and immunized with the bivalent vaccine and challenged with Mhp, where the immunization is performed by intramuscular injection of 2 mL of the prepared bivalent vaccine, immunization is performed again 2 weeks after the first immunization, and challenge with virulent Mhp is conducted by intratracheal injection 8 weeks after the first immunization; Group G3 is a control group challenged with Mhp and having 5 animals, which is not immunized, but challenged in the same way as that for the animals in Group G2; Group G4 is a group having 5 animals and immunized with the bivalent vaccine and challenged with PRRSV, where the immunization is performed by intramuscular injection of 2 mL of the prepared bivalent vaccine, immunization is performed again 2 weeks after the first immunization, and challenge with virulent PRRSV is conducted by intraperitoneal injection at the neck 6 weeks after the first immunization; and Group G5 is a control group having 5 animals and challenged with PRRSV, which is not immunized, but challenged in the same way as that for the animals in Group G4. 
     Result: 
     (1) Protection Against Mhp Infection 
     The animals were subjected to necropsy 28 days after challenge, and the MPS lesion in the lung of the animals was scored following the method described in Example 1. The results are shown in a table below and suggest that after immunization with the bivalent vaccine, the lesion in the lung is obviously lessened (P&lt;0.01). 
     (2) Protection Against PRRSV Infection 
     After challenge, the animals were observed and detected for the body temperature every day. The criteria for determining the attack of PRRSV infection include consecutive 3 or more days of high fever of 41° C. or higher, lassitude, reduced appetite, occurrence of conjunctivitis and respiratory symptoms such as cough and shorthness of breath, death, and lamellar consolidation of the lung at necropsy. The results show that the animals in the control group challenged with PRRSV all suffer from the disease, and two of them are dead; and the animals in the group immunized with the bivalent vaccine have no obvious symptoms of the disease and all survive. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Evaluation of immunoprotection of divalent vaccine of attenuated live vaccine strain AN306 
               
               
                 against MPS and live PRRSV vaccine 
               
             
          
           
               
                   
                 Group division 
               
             
          
           
               
                   
                   
                 G2 
                   
                 G4 
                   
               
               
                   
                   
                 Group immunized 
                   
                 Group immunized 
                   
               
               
                   
                   
                 with the bivalent 
                 G3 
                 with the bivalent 
                 G5 
               
               
                   
                 G1 
                 vaccine and 
                 Control group 
                 vaccine and 
                 Control group 
               
               
                   
                 Healthy 
                 challenged with 
                 challenged 
                 challenged with 
                 challenged 
               
               
                   
                 control group 
                 Mhp 
                 with Mhp 
                 PRRSV 
                 with PRRSV 
               
               
                   
               
               
                 Immunization 
                 Not 
                 Immunized with 
                 Not 
                 Immunized with the 
                 Not immunized 
               
               
                   
                 immunized 
                 the bivalent 
                 immunized 
                 bivalent vaccine 
                   
               
               
                   
                   
                 vaccine 
                   
                   
                   
               
               
                 Challenge with 
                 Not 
                 Challenged 
                 Challenged 
                 Not challenged 
                 Not challenged 
               
               
                 Mhp 
                 challenged 
                   
                   
                   
                   
               
               
                 Challenge with 
                 Not 
                 Not challenged 
                 Not challenged 
                 Challenged 
                 Challenged 
               
               
                 PRRSV 
                 challenged 
                   
                   
                   
                   
               
               
                 Score of MPS 
                 0.22 ± 0.15 
                 5.05 ± 3.89 
                 23.24 ± 3.72 
                 Not evaluated 
                 Not evaluated 
               
               
                 lesion 
                   
                   
                   
                   
                   
               
               
                 Evaluation of 
                 0/5 
                 Not evaluated 
                 Not evaluated 
                 0/5 
                 5/5 
               
               
                 disease status of 
                   
                   
                   
                   
                   
               
               
                 PRRS