In 2004, highly pathogenic avian influenza occurred and prevailed in many countries in Asia, and from the winter of 2005 to the spring of 2006, highly pathogenic avian influenza occurred in Europe, Oceania and Africa. According to data reports, highly pathogenic avian influenza has been listed as a class of animal diseases by the World Health Organization because of its rapid spread and great harm, and it has been listed as a class of animal diseases in China, ranking first among major animal diseases at present.
The envelope of avian influenza virus contains two different antigenic components, namely hemagglutinin (HA) and neuraminidase (NA), which are the basis of different subtypes of influenza virus. So far, HA subtype 16 and NA subtype 10 (such as H5N 1) have been isolated from humans and various animals, which indicates that the genome of avian influenza virus has great variability.
Influenza virus is sensitive to detergent, formalin, oxidant, ether and chloroform. It is easy to be inactivated under the conditions of heating, extreme pH, non-isotonic and drying. The virus excreted by secretions and feces has greatly improved its resistance because of the protection of organic matter.
(1) epidemic characteristics
Animals susceptible to avian influenza virus are very extensive. Including poultry, wild birds, wild birds, waterfowl, migratory birds, mammals (cats, pigs, minks, etc. ), people can be infected, especially chickens, ducks, geese and turkeys.
The disease can be transmitted to eggs through horizontal transmission. The carcasses, feathers, excreta and secretions of sick birds and their contaminated feed, water sources and utensils are all sources of infection.
The incubation period ranges from several hours to 14 days. The incidence and mortality of highly pathogenic avian influenza in chickens can reach100%; The morbidity and mortality of goslings are 100% and 95% respectively, and the morbidity and mortality of adult geese are 80% ~ 100% and 60% ~ 80% respectively. The morbidity and mortality of ducklings were 65438 000% and 80% respectively. Adult ducks mainly cause serious egg drop, while the morbidity and mortality of other day-old ducks are 90% and 10% ~ 60% respectively.
(2) Clinical symptoms and pathological changes
fowl plague
It can be divided into high pathogenicity (such as H5N 1) and low pathogenicity (such as H9N2).
① High pathogenicity
Sudden death from illness, high depression, reduced food intake to waste, yellow-green or gray stool, dyspnea, purple-black edema of cockscomb and bleeding of leg scales; The laying rate of laying hens dropped sharply, from 90% to 20%, and the number of soft-shell eggs, thin-shell eggs and deformed eggs increased, with a mortality rate of over 90%.
② Low pathogenicity
Drink plenty of water, keep spitting mucus in your mouth, unkempt feathers, drooping head and neck, runny nose, tears, swollen head, swollen comb and black leg scales. Dyspnea, cough, wheezing, snoring, rales and watery gray-green feces reduce the egg laying rate by 20% ~ 50%.
(3) Trachea congestion, bleeding, a large number of viscous secretions, mucus in the mouth, crop filled with sour and smelly liquid; Swelling of glandular stomach, nipple bleeding, banded bleeding at the junction of glandular stomach and esophagus; Swelling and bleeding of cecal tonsil; Severe bleeding in cloaca; Follicle congestion is purple, follicular deformation and rupture, tubal edema, purulent or caseous secretion; Testicular swelling the rooster bleeds.
(3) Diagnosis and confirmation of epidemic situation
After the outbreak of highly pathogenic avian influenza, experts first conducted on-site diagnosis and epidemiological investigation, and initially diagnosed it as a highly pathogenic avian influenza case; The second is to identify the hemagglutinin subtype of the virus by serological method; Third, send the pathogenic materials to the National Avian Influenza Reference Laboratory for virus isolation and identification to determine the virus type; Finally, according to the diagnosis results of the National Reference Laboratory, the Ministry of Agriculture finally diagnosed or ruled out the highly pathogenic avian influenza epidemic.
① Isolation and identification of virus
Generally, cotton swabs in trachea and cloaca of sick chickens or visceral suspension of sick chickens are used as sick materials. After treatment, 9 ~ 1 1 day-old SPF chicken embryos were inoculated. In order to determine the subtype of the virus, the patients with positive virus isolation did hemagglutination inhibition test with avian influenza stereotypes serum.
② serological test
Including agar diffusion test (AGP), hemagglutination inhibition test (HI) and neuraminidase test (NIT). HI has subtype specificity and can be used for serological monitoring and subtype identification of influenza A virus, while NIT is mainly used for subtype identification.