"African swine fever" appears in my country for the first time. How to prevent and control swine fever?

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The feared African swine fever is coming, how to prevent and control it

Released by the Information Office of the Ministry of Agriculture and Rural Affairs on August 3, Liaoning An African swine fever epidemic occurred in pigs in Shenbei New District, Shenyang City, the province. This is the first African swine fever epidemic (ASFV) in my country. After the outbreak, the Ministry of Agriculture and Rural Affairs launched a Level II emergency response in accordance with the African Swine Fever Epidemic Emergency Plan. In accordance with the requirements, the local government activated the emergency response mechanism and adopted disposal measures such as blockade, culling, harmless treatment, and disinfection. All pigs, susceptible animals, and products were prohibited from being transported into or out of the blockade area. Shenyang City has suspended the movement of pigs throughout the city. External transportation. At present, the epidemic has been effectively controlled.

The Lanzhou Veterinary Research Institute of the Chinese Academy of Agricultural Sciences has established a good cooperative relationship with the OIE African Swine Fever Reference Laboratory for the prevention, control and emergency reserves of African swine fever in my country as early as ten years ago, and has established a good cooperative relationship in agricultural and rural areas. Under the witness of Minister Han Fu, we established a laboratory with the Polish National Veterinary Institute, introduced relevant diagnostic technologies and materials, and in 2011 applied for and received permission from the Veterinary Bureau of the Ministry of Agriculture to conduct research on African swine fever diagnostic technology and diagnostic reagents. Research and development of the box (Agricultural Medicine Letter [2011] No. 596).

At present, the research and development and reserve of a complete set of African swine fever etiology and serological diagnostic technologies and kits have been completed, including conventional PCR and real-time fluorescence quantitative PCR kits, indirect ELISA antibody detection kits, for Africa A solid foundation has been laid for the prevention and control of swine fever~ A good cooperative relationship has been established with the OIE African swine fever reference laboratory, and under the witness of Minister Han Changfu of the Ministry of Agriculture and Rural Affairs, a laboratory has been established with the Polish National Veterinary Institute to introduce relevant Diagnostic technology and materials, and in 2011, we applied for and received permission from the Veterinary Bureau of the Ministry of Agriculture to conduct research on African swine fever diagnostic technology and the development of diagnostic kits (Agricultural Medicine Letter [2011] No. 596). At present, the research and development and reserve of a complete set of African swine fever etiology and serological diagnostic technologies and kits have been completed, including conventional PCR and real-time fluorescence quantitative PCR kits, and indirect ELISA antibody detection kits, laying a solid foundation for the prevention and control of African swine fever. A solid foundation.

African Swine Fever (ASF) is an acute, febrile, highly contagious and highly contagious infectious disease of pigs, also known as African swine plague or warthog disease. The clinical features are high fever, loss of appetite, high mortality rate, skin cyanosis, severe bleeding of lymph nodes and internal organs, abortion of pregnant sows, and edema. Mortality rates can be as high as 100%. The disease is an animal disease that is required to be reported by the World Organization for Animal Health (OIE) and is classified as a Class I animal disease by the Ministry of Agriculture of my country. African swine fever is one of the most terrifying epidemics in pigs, mainly due to its high contagiousness, changing modes of transmission, high morbidity, high mortality, and lack of specific vaccines. African swine fever has had a serious impact on global pork production and trade. From 2014 to 2017, 800,000 pigs died and were culled in Eastern Europe and Russia due to African swine fever. From 2014 to 2015, due to the occurrence of African swine fever, Due to the epidemic, the pork exports of Poland, Latvia, Lithuania, and Estonia alone fell by US$961 million. In Russia, losses caused by African swine fever in 2011 reached US$267 million.

1. Pathogen

African swine fever is caused by DNA virus infection. It was previously classified as a member of the iridoviridae family, but its DNA structure and replication method are very different from those of iridovirus. Similar to poxviruses, in 1995, the International Committee on Taxonomy of Viruses (ICTV) classified it as a new viral family - African swine fever (Asfarviridae) virus family. The latest eighth virus classification report published by ICTV in July 2005 clarified that African swine fever virus belongs to the DNA virus catalog (dsDNA), African swine fever virus family, and African swine fever virus genus (Asfivirus) in virus classification. ASFV is also currently The only recognized member of the African swine fever virus family. Unlike other DNA viruses, ASFV is a true arbovirus that can multiply in vertebrate and invertebrate hosts. In pigs, ASFV replicates in several types of cytoplasm, notably reticuloendothelial cells and monocytes and macrophages. The virus can multiply in Ornithodoros ticks, making them the primary vector of transmission.

African swine fever virus does not produce neutralizing antibodies after infecting animals, so there is only one serotype. The latest research shows that there are 23 genotypes of African swine fever. Among them, genotype 1 was first diagnosed in Kenya in 1921 and was mainly prevalent in East and Central Africa. It then invaded Europe from 1957 to 1960 and became popular in Spain, Portugal and other countries. Genotype II invaded Georgia in 2007 and was later introduced to Russia, Ukraine, Poland, Latvia, Lithuania, Estonia, Moldova, the Czech Republic, and Romania. The disease was first introduced to Cuba in 1971; it invaded Brazil in 1978, and epidemics have appeared in American countries.

2. Epidemiology

ASFV only infects pigs and wild boars. Infected pigs and infected pigs (recovered pigs and latent infected pigs) are the main sources of infection, and wild boars and soft ticks of the genus Ornithodoros are the storage hosts of the virus. Sick pigs can detoxify before they develop fever; some chronically infected pigs can detoxify for life; the virus can persist in the recovered pigs for a year and detoxify for more than 6 months. The disease is mainly transmitted through the digestive tract and respiratory tract. Contact transmission, food transmission, and soft tick bites are the main transmission routes of the disease. There are other transmission routes, and research shows that ASFV can be transmitted through the air at close range (within 2m). There are other possible potential routes of transmission, such as via birds and rodents. There is no difference in susceptibility among pig breeds and pig groups of different ages. The incubation period after direct contact with infected pigs is 5-19 days, and the incubation period after being bitten by an infected tick does not exceed 5 days, with symptoms appearing in 5-7 days.

In Africa, ASFV can infect warthogs, bush boars and large forest boars. Several species of wild boar are susceptible to ASFV, but usually do not show obvious clinical symptoms. Wild boars in Europe and North America are susceptible to ASFV, with clinical symptoms and mortality similar to those seen in domestic pigs. The exception is the American pied boar, which is not susceptible to ASFV. The pathogenicity of different strains is different. Infection with super virulent strains of ASFV can cause 100% death of pigs within 4 to 14 days. The virus content in the blood of sick pigs is greater than 108 virus particles/mL, which mainly invades lymphocytes and causes lymphocytes to be infected. Apoptosis, endothelial cell damage, and hemorrhage. The mortality rate caused by moderately virulent strains is generally 30% to 50%, while infection by low-virulence strains only causes the death of a small number of pigs.

African swine fever is not a disease of humans or animals. Currently, there is no evidence that ASFV can infect humans. Although African swine fever does not infect humans, because my country is a big breeding country and accounts for more than half of the world's pigs, it cannot be effectively controlled in a timely manner after it invades our country. Once it spreads over a large area, it will cause catastrophic consequences and seriously affect the economy and social stability.

3. Pathogenesis

ASFV can enter the pig body through the mouth and upper respiratory system, and infection occurs in the nasopharynx or tonsils. The virus quickly spreads to the mandibular lymph nodes and passes through the lymph and blood All over the body. Afterwards, the virus was detected in almost all tissues, with the highest viral content in tissues including the monocyte-macrophage system, reticuloendothelial cells such as the spleen and lymph nodes. ASFV causes hemorrhagic lesions due to the release of cytokines from infected monocytes/macrophages rather than directly causing endothelial cell loss. ASFV infection is accompanied by thrombocytopenia, which may be caused by impaired platelet production or peripheral vascular platelet consumption. Cells change rapidly during virulent infection, and cells die before an obvious stimulatory response occurs. During attenuated infection, stimulatory reactions are easily observed, with enlarged cell nuclei and widespread mitosis.

IV. Clinical symptoms

It can occur in pigs of different breeds and ages. The most acute type of pigs dies suddenly without obvious clinical symptoms. Some sick pigs have the same clinical symptoms as the acute type. The case fatality rate is as high as 100%. The incubation period after acute infection with ASFV is 5-15 days, and the first symptom is an increase in body temperature (41-42°C). Symptoms include depression, anorexia, hemorrhage, extensive bleeding and bleeding points in the skin and mucous membranes of the ears, nose, limbs, and abdomen, cyanosis and even bleeding clots in the skin of peripheral parts; blood and mucus covering the surface of the feces; and dystaxia Or the gait is stiff and breathing is difficult. Sick pigs usually die 7 days after fever and 1-2 days after symptoms appear. Abortion in pregnant sows. The case fatality rate is as high as 100%. The symptoms of the subacute type are the same as those of the acute type, but the symptoms are milder, the mortality rate is low, and the duration is long. The mortality rate of piglets is relatively high, and the duration of the disease is 5-30 days.

The chronic type has a low mortality rate, manifesting as respiratory and pneumonia symptoms. Most pigs can recover after infection, but they will carry the virus for life. Sick pigs can usually survive for several months, but due to low immunity, they are prone to secondary bacterial infections and are difficult to recover. The course of disease is 2-15 months.

5. Diagnosis

Make a preliminary judgment based on clinical symptoms and pathological changes. Since the clinical symptoms of African swine fever and swine fever are very similar clinically, if there are no typical symptoms and characteristics Sexual bleeding is almost impossible to identify based on clinical symptoms and visual lesions alone. Laboratory testing is necessary for differential diagnosis. In addition, it can be distinguished from diseases such as highly pathogenic PRRS, porcine dermatitis nephritis syndrome (PDNS), bacterial sepsis, mycotoxin poisoning and coumarin poisoning. Laboratory diagnosis includes the following methods: Since the disease often manifests as the most acute or acute form, people often die before specific antibodies appear. Therefore, the detection of virus etiology is very important in the diagnosis of African swine fever epidemics. Virus isolation is the most commonly used etiological diagnostic technique. However, diagnosis must be carried out under high security conditions in the P3 laboratory. In addition, serological tests such as erythrocyte adsorption and erythrocyte adsorption inhibition tests, immunofluorescence, enzyme-linked immunosorbent assay, and agar diffusion can also be used for the diagnosis of this disease. At present, the Lanzhou Veterinary Research Institute of the Chinese Academy of Agricultural Sciences has completed the research and development and reserve of a complete set of African swine fever etiology and serological diagnostic technologies and kits, including conventional PCR and real-time fluorescence quantitative PCR kits, indirect ELISA antibody detection kits, and is in large quantities. Production, different kits are very convenient to use, and have the advantages of high accuracy and short time, and can be widely used in laboratory diagnosis. The Lanzhou Veterinary Research Institute's African swine fever etiology (PCR, real-time fluorescence quantitative PCR) and serology (antibody detection indirect ELISA) diagnostic kits provide strong technical support for the prevention and control of African swine fever.

Differential diagnosis: ASFV lesions are very similar to swine fever. The most acute form is often characterized by severe bleeding from internal organs. The disease usually does not show clinical symptoms in the early stage when the body temperature rises; the most significant lesion in the acute form is splenomegaly, which can reach several times the original size. The spleen is large, black, extremely soft and fragile. Intra-abdominal lymph node bleeding is severe, similar to hematoma, and edema occurs in many parts of the colon mucosa, mesentery, etc. There is no vaccine or drug for emergency vaccination and treatment of this disease.

Obvious clinical symptoms of swine fever appear when body temperature rises; lymph nodes are marble-shaped; edema lesions are not obvious; when swine fever occurs in a large area, emergency vaccination with swine fever vaccine can reduce the epidemic alleviate. It can be seen that African swine fever usually shows an increase in body temperature first and then other symptoms, while swine fever shows other symptoms almost at the same time as the body temperature rises, which can be used as a differential diagnosis between the two.

6. Prevention and Control Methods

Strengthen the quarantine of imported breeding pigs and pig products, and resolutely do a good job in the destruction and disposal of waste and garbage at international airports and ports. Once suspected African swine fever occurs, decisive culling measures must be taken, strict blockade and thorough disinfection must be carried out. The virus has strong resistance to the environment and can survive for 120 days at 23°C. In the tropics, viruses can survive in pig pens for at least 2 weeks. There are fewer types of effective disinfectants. Currently, the most effective disinfectant is 10% benzene and phenol. Other disinfectants recommended by the OIE include 0.8% sodium hydroxide, 0.3% formalin, and 2.3% hypochlorite. Pig breeders are strictly prohibited from transporting pigs from epidemic areas, pay attention to daily disinfection work, raise pigs in a closed enclosure as much as possible, adopt isolation and protective measures, try to avoid contact with wild boars and Ornithodoros ticks, and are strictly prohibited from using restaurants and canteens that have not been treated with high temperatures Feed pigs swill or meal waste. Once there is an abnormal increase in unexplained deaths and symptoms similar to swine fever, the local veterinary department should be reported promptly.