Purification and Control of Classical Swine Fever in large scale Pig Farm

Purification and Control of Classical Swine Fever in standardized Pig Farm

Purification and Prevention of Classical Swine Fever in standardized Pig Farm Classical swine fever (CSF) is caused by the infection of classical swine fever virus belonging to Flaviridae. It is one of the main infectious diseases in large-scale pig farms in China, and it is also an important infectious disease that needs to be prevented and controlled. According to the classified list of Animal pathogenic microorganisms issued by decree No. 53 of the Ministry of Agriculture of the people's Republic of China in May 2005, classical swine fever virus is classified into class II animal pathogenic microorganisms and belongs to highly pathogenic venereal disease. It is worth noting that although the epidemic of typical acute classical swine fever in large-scale pig farms is no longer common, the occurrence of classical swine fever, especially atypical classical swine fever, is still widespread, and the defect of diagnostic technology often leads to the neglect and misjudgment of the epidemic situation of classical swine fever. This paper will introduce the necessity, favorable conditions and purification strategies of classical swine fever purification in the working practice of large-scale pig farms. 1 purification of classical swine fever in large-scale pig farms 1.1 Pig farms are divided into three large-scale pig breeding farms in northern China (Hebei A), central China (Henan B) and southern China (Jiangxi C), with good geographical conditions and isolation measures, normal feeding and management and strict disinfection measures. the basic sows are all more than 600, self-breeding and self-breeding. 1.2 the tonsil samples of breeding pigs were collected by tonsil sampling method. The whole production line was sampled within 1-2 days, and sent to the laboratory for testing at low temperature within 24 hours. The contact piece was made in the laboratory. Classical swine fever virus antigen was detected by classical swine fever fluorescent antibody (purchased from China Institute of Veterinary Drug Supervision). The detection was completed within 1-2 days, and all positive pigs were eliminated within 1-2 days of delivery of the test report. Then the whole breeding population was generally immunized with swine fever attenuated tissue vaccine (adult rabbit splenic lymphoid vaccine, 2 portions per head), and then the tonsil of the reserve pigs were examined in vivo, and the positive pigs should not be used as breeding. The results of purification and detection of classical swine fever in three pig farms are shown in Table 1. After half a year of purification in Hebei A pig farm, the positive rate decreased by 70.09%. Statistical analysis (χ 2 test, SPSS software) showed that the virus-carrying rate of classical swine fever decreased significantly (P < 0.01). At the same time, through purification, the production index of the pig farm was significantly improved, the sow delivery rate increased by 0.8%, the live birth rate increased by 4%, the average litter size increased by 1.3, and the overall mortality decreased by 13.6%. Henan B pig farm was tested twice every 5 months. The positive rate of swine fever virus in breeding pigs decreased by 83.3% (P < 0.01). After the first test, the average litter size of healthy piglets increased from 9.28 to 9.56, and the survival rate of growing pigs increased from 81.4% to 83.9%. In Jiangxi C large-scale pig farm, the author first immunized the whole breeding group against swine fever attenuated tissue vaccine (adult rabbit spleen vaccine, 2 portions per head), and then detected and eliminated the pig herds with reproductive disorders. When the whole herd was tested for the second time, the positive rate of pigs decreased by 90.20% (P < 0.01), and the positive breeding pigs were also eliminated. At the same time of purification of classical swine fever, pseudorabies was purified by gE- ELISA surveillance results, and targeted prevention and control measures were taken for porcine reproductive and respiratory syndrome (PRRS). In a very short period of time, the production performance of the breeding population has been greatly improved, the average number of live births per litter has increased from 5.2 to 9.2, the proportion of dead, disabled and weak offspring has been reduced from 49.50% to 10.44%, and the production efficiency of pig farms has been greatly improved. The purification practice of classical swine fever in the above three large-scale pig farms shows that the strategy of "detection and elimination" is an effective measure to control classical swine fever in large-scale pig farms. 2 the necessity of purification of classical swine fever 2.1 the epidemic situation of classical swine fever is still widespread in China due to the wide application of classical swine fever attenuated vaccine, which has effectively controlled the epidemic of classical swine fever, but the epidemic situation of classical swine fever is still widespread at the present stage. Liu Youchang and others detected classical swine fever virus in more than 600 blood samples of male and female pigs from 10 pig farms in Hebei, Tianjin, Beijing, Liaoning and Inner Mongolia from January to August 2005 using the ELISA kit produced by IDEXX Company of the United States. It was found that there were virus-carrying breeding pigs in all 10 pig farms. Except for suspicious pigs, the positive rate of each pig farm is 3%-70%, and there are more than 10%-20%, with an average of 20.5% [1]. Qiu Huishen, a researcher from China Veterinary Drug Supervision Institute, and others have tested breeding pigs in 29 large and medium-sized pig farms in 13 provinces and cities in China in recent years. The results of tonsillar classical swine fever fluorescent antibody staining technique show that swine fever virus exists in all tested pig farms. The national average positive rate of swine fever antigen is 11.12%, the highest is 30.7%, and the lowest is 4.4% [2]. Wei Xiuyu and others used enzyme labeling method to detect classical swine fever antigen in 234 pig farms in 2004. the results showed that 64 samples were positive, with a positive rate of 27.4%. At the same time, 4735 serum samples were detected by indirect hemagglutination method. the qualified rate was only 69.1% [3]. The author investigated the virus-carrying situation of breeding pigs in some large-scale pig farms in northern China in 2005, and found that the virus-carrying rate of breeding pigs was 5% and 20%. In addition, 65% of weak piglets in pig farms and conservation of swine swine fever antigen also showed positive clinical monitoring results [4]. It shows that the virus-carrying phenomenon of sows in pig farms in China is quite common, but the degree is different, so classical swine fever is still an important epidemic disease that must be paid attention to in large-scale pig farms at the present stage. 2.2 the occurrence of classical swine fever is characterized by reproductive disorders and mild types of breeding pigs. Due to low immune level, frequent presence of low virulence classical swine fever virus or other reasons, classical swine fever virus forms persistent infection in breeding pigs. Classical swine fever virus exists in pigs for a long time. Antibodies and antigens of classical swine fever virus can be detected at the same time. Only through laboratory methods can we detect infected pigs. Persistent infection of breeder pigs is characterized by virus-carrying syndrome in pregnant sows and semen transmission in boars, which is the root cause of the persistence of classical swine fever in pig herds. In clinical practice, except for reproductive disorders, breeding pigs often do not show obvious clinical symptoms. However, miscarriage and stillbirth, mummified fetus and weak piglets may occur in breeding sows, and congenital infection in piglets often forms immune tolerance [5]. Clinically, it is often found that the levels of antibodies to classical swine fever virus and other pathogens in some breeds are very low, but the antigen detection results are positive. If the infected reserve pigs enter the production group, it will form a vicious circle chain of classical swine fever in the pig farm, so in order to control the classical swine fever epidemic in the large-scale pig farm from the source, the breeding pig herd must be purified [2]. 2.3 Classical swine fever often occurs mixed infection with other diseases in large-scale pig farms in recent years, with the development of large-scale pig industry, some immunosuppressive infectious diseases such as porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 bring great harm to pig production. Classical swine fever virus usually forms mixed infection with these pathogens, on the one hand, it aggravates the harmfulness of classical swine fever. On the other hand, it brings difficulties to the diagnosis. This requires laboratory methods to identify the types of pathogens, specific analysis of specific pig herds, objective and scientific analysis of the epidemic situation, while purifying classical swine fever, the harm of other pathogens should not be ignored and comprehensive prevention and control measures should be taken. 3 favorable conditions for purification of classical swine fever 3.1 convenient in vivo sampling technology because the virus-carrying breeding pigs are the root cause of the persistence of classical swine fever virus in pig farms, therefore, the strategy of "detection and elimination" for breeding pigs can purify classical swine fever from the source. At present, there are special living sampling instruments for pig tonsils in China, which can be very convenient for live sampling of breeding pigs (figure 1). The method is simple and easy to learn. Tonsil samples were taken from each pig for about 30 mg, stored at low temperature, and then sent to the conditional laboratory to detect classical swine fever virus antigen by immunofluorescence or PCR. It should be noted that the sampling site must be accurate, and each pig should be disinfected in time after sampling. Disinfectants can generally use 2%-3% sodium hydroxide or phenolic disinfectants. 3.2 efficient and economical detection methods of classical swine fever antigen and antibody must be pointed out that at present, some pig farms only rely on the results of antibody detection to monitor classical swine fever virus, and even diagnose classical swine fever according to the titer of antibody. Laboratory and clinical practice show that there is a big misunderstanding in antibody detection and diagnosis, because so far, the existing serological methods can not distinguish between vaccine antibodies and wild virus antibodies. Therefore, the diagnosis of classical swine fever only depends on the titer of antibody, the result is often uncertain. Therefore, the detection of persistent infection of classical swine fever virus in breeding pigs must focus on the detection of virus antigen [6]. Among them, classical swine fever virus immunofluorescence assay is not only a national standard method, but also an international general method. Classical swine fever virus antigen was detected directly by fluorescence labeled antibody, and the cytoplasm of porcine tonsillar crypt epithelial cells showed specific fluorescence (figure 2). Immunofluorescence method can quickly and effectively detect continuously infected pigs [6jue 7], but also can detect samples in batches, and the detection cost is relatively low. Fluorescent antibodies can be ordered from specialized agencies, but some experience is needed to determine the results. The purification of classical swine fever by immunofluorescence has been successful in some pig farms, and the epidemic situation of classical swine fever has been effectively controlled after purification. The ELISA method for antigen detection is based on the principle of double antibody sandwich method, in which classical swine fever virus serum is coated with a micro reaction plate, which binds to classical swine fever virus antigen in the tested sample, and then forms a sandwich upper layer with specific monoclonal antibody of classical swine fever virus. Horseradish peroxidase is used to detect the absorbance of the substrate is proportional to the content of virus antigen. The detection methods of antibody to classical swine fever virus include ELISA and indirect hemagglutination. Due to the standardization of determination reagents and methods, the ELISA method can quantify the test results, at the same time, it can detect samples with high throughput, and it is also gradually used in clinical monitoring. However, because most of the kits are imported, the cost is relatively high, and the process of sample treatment is also complicated. It should be noted that the test process requires the strict establishment of positive and negative controls, and the technical requirements for the test personnel are relatively high. At present, indirect hemagglutination is the most commonly used method for the determination of antibodies to classical swine fever virus in China. This method uses sensitized red blood cells of classical swine fever virus to directly determine the titer of serum antibodies. The required equipment is relatively simple, and the result is intuitive, so it is suitable for grass-roots application. According to experience, 1 ∶ 16 or 1 ∶ 32 is generally taken as the critical standard. It should be noted that the relationship between antibody titer and protection is inconclusive, and like other serological methods, it is impossible to distinguish between wild virus antibodies and vaccine antibodies. However, through regular antibody monitoring, we can know the immune status of pigs in time and evaluate the immune effect of the vaccine. Therefore, regular antibody surveillance is an indispensable important link in the comprehensive control measures of classical swine fever in pig farms. 3.3 the application practice of qualified classical swine fever vaccine with attenuated classical swine fever virus shows that the existing vaccine strain (strain C) still has strong protective effect against field strains with different virulence, that is, there is no need to doubt the efficacy of the vaccine strain. However, a highly effective vaccine strain does not represent an effective commercial vaccine. It should be pointed out that the reasons for the occurrence of classical swine fever in immunized pigs should be analyzed in detail, in which virus-carrying pigs and congenital infection in piglets are important reasons. In addition, there may be some differences in the toxicity price of vaccines from different manufacturers, and improper measures in the process of transportation, preservation and use of vaccines will affect the effectiveness of vaccines, and unreasonable immunization procedures are also important factors. such as the interference of maternal antibodies. In view of the current epidemic situation of classical swine fever, the pig farms that purify classical swine fever still need to use classical swine fever vaccine. Qualified and efficient attenuated classical swine fever vaccine can provide strong protection for the purification of pig herds. (4) the summary and discussion practice shows that classical swine fever is still an infectious disease that needs to be prevented in the current large-scale pig farms, and continuous infected pigs is a key factor in the occurrence of classical swine fever. Therefore, as long as the production group is purified from the population, adopting the strategy of "detection and elimination" to breeding pigs will control the vicious circle chain of classical swine fever in pig farms from the source. Large-scale pig farms should fully understand the new characteristics of the epidemic of classical swine fever, renew their ideas, focus on the long-term development of pig farms, focus on the purification of the population, and detect each batch of reserve pigs by purifying the population for 2 or 3 times. it will significantly reduce the positive rate of breeding pigs, so as to fundamentally control the epidemic situation of classical swine fever. At the same time, we should fully realize that the prevention and control of classical swine fever is a systematic and comprehensive project, and pig farms should take strict biosafety measures to control the mechanical transmission of personnel, vehicles, instruments and treatment tools, and strengthen disinfection. It is necessary to adopt high-quality and efficient classical swine fever vaccine, regularly monitor the level of classical swine fever antibody, establish an immune procedure suitable for this farm and strictly implement it, and establish a regular epidemiological surveillance mechanism in large-scale pig farms to understand the latent infection of swine epidemic disease in time. While purifying classical swine fever, it is necessary to strengthen the prevention and control of other serious epidemic diseases such as swine pseudorabies, porcine reproductive and respiratory syndrome and circovirus disease. when conditions permit, many kinds of epidemic diseases can be purified at the same time. the real establishment of a healthy and stable breeding group will effectively improve production efficiency and enhance brand image. This method is troublesome. Whose method is simpler. Tell me.