Avian influenza, also known as true chicken plague, is an infectious disease of various poultry caused by type A influenza virus. It has the characteristics of high incidence, high transmission rate and high mortality. In addition to poultry, highly pathogenic avian influenza can also infect birds and some mammals, and humans can also be infected.
In 2004, highly pathogenic avian influenza occurred and became prevalent in many Asian countries. From the winter of 2005 to the spring of 2006, highly pathogenic avian influenza occurred in Europe, Oceania, Africa and other places. According to data reports, highly pathogenic avian influenza is classified as a Category A animal disease by the World Health Organization due to its rapid spread and great harm. my country has classified it as a Category I animal disease, currently ranking first among major animal diseases.
The envelope of avian influenza viruses contains two different antigenic components, namely hemagglutinin (HA) and neuraminidase (NA), which are the basis for different subtypes of influenza viruses. So far, there are 16 HA subtypes and 10 NA subtypes (such as H5N1) of influenza viruses isolated from humans and various animals, indicating that the avian influenza virus genome is highly variable.
Influenza viruses are sensitive to detergents, formalin, oxidants, ether, chloroform, etc., and are easily inactivated under heating, extreme pH, non-isotonic and dry conditions. However, viruses excreted from secretions and feces are protected by organic matter, which greatly improves their resistance.
(1) Epidemic characteristics
A wide range of animals are susceptible to avian influenza viruses. Including poultry, wild birds, wild birds, waterfowl, migratory birds, mammals (cats, pigs, mink, etc.), humans can also be infected, with chickens, ducks, geese, and turkeys being the most susceptible.
The disease can be transmitted both horizontally and through eggs. The carcasses, feathers, excrement, secretions of sick poultry and their contaminated feed, water sources, utensils, etc. are all sources of infection.
The incubation period can range from a few hours to 14 days. The morbidity and mortality rate of highly pathogenic avian influenza in chickens can reach 100%; the morbidity and mortality rates in goslings are 100% and 95% respectively, and the morbidity and mortality rates in adult geese are 80% to 100% and 60% to 80% respectively. ; The morbidity and mortality of ducklings are 100% and 80% respectively. Adult ducks mainly cause severe egg loss. The morbidity and mortality of other day-old ducks are 90% and 10% to 60%.
(2) Clinical symptoms and pathological changes
Chicken influenza
is divided into high pathogenicity (such as H5N1) and low pathogenicity (such as H9N2).
①Highly pathogenic
Sudden onset and death, high depression, reduced food intake to the point of exhaustion, diarrhea of ??yellow-green or gray loose feces, difficulty in breathing, and edema of the comb and wattles turned purple Black, leg scales are bleeding; the egg production rate of laying hens drops sharply, which can drop from 90% to 20%; soft-shell eggs, thin-shell eggs, and deformed eggs increase; the mortality rate can be as high as more than 90%.
②Low pathogenicity
Drinking more water, constantly throwing mucus from the corner of the mouth, disheveled feathers, drooping the head and neck, runny nose, tears, head edema, swollen comb wattles and hair loss Black, bleeding leg scales. Difficulty breathing, coughing, wheezing, grunting, rales, and loose gray-green feces, and the egg production rate drops to 20% to 50%.
③Tracheal congestion and bleeding, with a large amount of sticky secretions, mucus in the mouth, and crop filled with sour and smelly liquid; glandular stomach swelling, nipple bleeding, and band-like bleeding at the junction of the glandular stomach and esophagus; cecum Tonsill swelling and bleeding; severe cloacal bleeding; follicle congestion and purple color, follicle deformation and rupture, fallopian tube edema, purulent or cheese-like secretions; rooster testicles swelling and bleeding.
(3) Diagnosis and epidemic confirmation
After the outbreak of highly pathogenic avian influenza, experts first conducted on-site diagnosis and epidemiological investigation, and the initial diagnosis was highly pathogenic. Avian influenza cases; the second is to use serological methods to identify the hemagglutinin subtype of the virus; the third is to send the diseased materials to the National Avian Influenza Reference Laboratory for virus isolation and identification, and determine the virus type; finally, the Ministry of Agriculture will use the national reference laboratory to The diagnostic results of the laboratory will finally confirm or exclude the highly pathogenic avian influenza epidemic.
①Isolation and identification of virus
The disease materials are generally taken from the trachea and cloaca cotton swabs of sick chickens or the visceral suspension of sick chickens, and then inoculated into 9 to 11-day-old SPF chickens. For embryos and those with positive virus isolation, hemagglutination inhibition test should be done with avian influenza type serum to determine the serosubtype of the virus.
② Serological tests
Including agar diffusion test (AGP), hemagglutination inhibition test (HI), and neuraminidase test (NIT).
HI is subtype specific and can be used for both serological surveillance and influenza A virus subtype identification, while NIT is mainly used for subtype identification.