The characteristics of the avian flu pandemic and its control strategy

2008-12-26

Avian influenza is referred to as avian influenza, Newcastle disease, also known as polycythemia, are sticking by the Virus Unit A certain type of influenza virus subtypes caused mainly consisting mainly of poultry infected with an acute, highly contagious diseases.

Since 1878 Italy confirmed the outbreak of disease is by A-type bird flu virus since the disease is currently in Europe, the Americas, Asia, Africa and other places have taken place. In the history of poultry, bird flu is a devastating disease, every time an outbreak of the poultry industry, supplies are causing huge economic losses, especially in recent years in Asia, Europe and the highly pathogenic avian influenza epidemic, not only to the poultry industry brought about a fatal blow, but also a serious threat to human health, has been widespread concern.

1 the characteristics of the avian influenza pandemic virus
1.1 spectroscopy (host range) wide has now been confirmed infected with the avian flu virus around the world can be many types of poultry (such as turkey, chicken, ducks, geese, quails, pigeons, guinea fowl, Shek chickens, ostriches, pheasants, parrots, starlings, etc.), wild (such as swans, terns, ducks, geese, puffins, sea Hatoyama, etc.) and birds (such as swallows, chukars, crows, sparrows, herons, etc. ) and so on, caused or was hidden after the incidence. Poultry chickens, turkeys, ducks, geese under natural conditions is the most susceptible species of birds. In addition, the avian flu virus can also be infected pigs, horses and people as well as whales, ferrets and other animals.
As the virus infected a broad spectrum of avian flu caused more source of infection for avian influenza prevention and control very difficult.

1.2 virus serotypes, and easy to variation based on two types of avian influenza virus-specific surface antigens - hemagglutinin (HA) and neuraminidase (NA) of different, can be divided into several subtypes. HA now know there are 16 kinds of antigens (H1-H16), NA has nine kinds of antigens (N1-N9), between the two subtypes may constitute a number of levels. Caused by avian influenza virus subtype serum mainly H7N7, H5N1, H5N2, H7N1, H7N3 and so on. Is generally believed that H7, H5 highly pathogenic strains, of course, not all H5 and H7 are vMDV. Although the highly pathogenic avian influenza virus strains of only a small minority, but as a single unit because of its negative chain BNA viruses, and gene structure is from 8 to separate copy of the gene fragment combination, together with numerous virus subtypes, So when different strains infected the same host, they will occur between the gene rearrangement, complementary, mixed and other phenotypic variation genome so that the original low-pathogenic strain may mutate into highly pathogenic strains. Once the virus mutates, the vaccine in the past will fail to control avian influenza considerable difficulties.

(more)1.3 level and faster dissemination of the main avian influenza is generally believed that the main mode of transmission is the level of communication, the principal means of infection of the respiratory and digestive tract. Poultry and poultry infected by respiratory and digestive tract from the virus, through the dust, feed, water, tools Insemination, eggs egg baskets disk, means of transport, such as the spread of bird species, so the spread very fast. Once the chickens are infected, the entire group easily cause the outbreak, and even spread to the nearby chicken farms and rural households. Waterfowl and birds infected with avian flu, the clinical symptoms do not usually show, but can be infected and long-term detoxification, especially migratory birds in the course of a very wide-ranging散毒, once the virus is highly pathogenic strain can be caused by Fulminant epidemic. This shows that water birds and birds in the spread of this disease are important.

1.4-induced factors and the prevalence of the season from the previous occurrence of the avian flu epidemic areas of environmental conditions, the usually warm and humid, rich in water resources, densely populated, highly mobile, disease defense system is weak, poultry primitive conditions, poor sanitation, lack of Science defensive measures, coupled with a variety of mixed poultry rearing and so on, is the spread of the disease constitute a predisposing factor. Avian influenza can occur throughout the year, but the outbreak in the winter and spring festival, especially in autumn, winter and spring at the turn, climate change, big time. Under normal circumstances the summer less morbidity, mostly sporadic, the incidence of symptoms is also lighter chickens.

1.5 avian flu and more complicated with other infectious diseases or secondary avian influenza itself is a kind of immune suppression of the disease, poultry disease incidence is extremely poor and often complicated by or secondary to other infectious diseases, a common complication following the pathogenesis of E. coli and disease, Newcastle disease, infectious bronchitis, diseases such as mycoplasma.

1.6 incidence rehabilitation easy to relapse, many flocks of chickens in the incidence of recovery or rehabilitation after 1 ~ 2 months and morbidity. Rehabilitation chicken antibody levels decreased gradually over time, the current dropped to a certain level, the body will not be able to protect chickens against bird flu vMDV invasion, at this time if the environment in the presence of avian influenza virus, chicken is still possible to re-infection morbidity. However, the second incidence of the same flock, the symptoms are often lighter, and mortality rates are low.

2 bird flu epidemic clinical manifestations of clinical manifestations because of sick poultry species, age, sex, feeding and management, with or without complications, as well as strain virulence and other conditions vary, which can be divided into low pathogenic avian influenza and highly pathogenic avian influenza.

2.1 low pathogenic avian influenza long incubation period, the incidence compared to ease, the spread of slow, long course, morbidity and mortality is relatively low. Reflected mainly in poultry digestive tract, respiratory tract, reproductive tract as well as the systemic symptoms. Poultry feed intake decreased, the spirit of gloomy, loose feathers chaos, necking,呆立; conjunctival redness, eyes in tears, there are secretions; nasal secretions out there; head swelling, and some crown and meat beard edge congestion due to dark purple, meat beard can thicken, harden, touch it thermal; leg scales have symptoms such as bleeding spots. Respiratory symptoms are usually lighter, poultry and some coughing, respiratory啰音, some difficulty in breathing, mouth伸颈issued screams. Individual poultry diarrhea symptoms, and some water samples from稀便, which has not been completely digested with feed; some from yellow, green or light green稀便. Poultry egg production decrease in the extent and duration of the severity of infection vary. Under normal circumstances, egg production dropped by 30% to 70%, serious production may drop to near level.

At the same time, soft-shell eggs, eggs fade, sand preserved eggs, deformed eggs increased. General in the 7 ~ 10 days, dropped to the lowest level, at this level to stay about two weeks before a slow recovery. Egg drop, picked up the pace with sick birds infected with the virulent strain of strong or weak, feeding and management good or bad, is it timely symptomatic treatment is closely related to such factors. Autopsy shows that the lower end of the trachea, bronchial congestive top tracheal ring, tracheal there exudation; a small portion of the heart can see the size of fat have a tip of the bleeding point; individual can be seen catarrhal enteritis. Adult birds eggs congestive, atrophy, and a large quantity of congestive tubal inflammatory exudation quite common. Atypical for avian flu if it does not take active measures, the virus difficult to be eradicated in the affected areas, the epidemic will gradually spread to the periphery, so that the growing epidemic, but the virus still strong (become highly pathogenic) possible.

2.2 short incubation period of highly pathogenic avian influenza, the incidence urgency, the spread of fast, high morbidity and mortality. Incidence of acute clinical poultry are often no obvious symptoms and sudden death. Longer course, the performance is not to reclaim the body temperature rise and high fever, loss of appetite waste must, laying rate can be seen a sharp decline and a large number of soft-preserved eggs, shell eggs, deformed eggs. Head and neck, facial swelling, purple cockscomb and肉垂or see edema, tears eyes, mouth, nasal mucus containing or outflow, a high degree of difficulty breathing and issued screams, the majority of yellow-green稀便row, a considerable portion had neurological symptoms , manifested as ataxia or paralysis, bleeding legs scaly patches. Breeder of the fertilization rate and hatching rate also dropped significantly. A very short time a large number of deaths. A large group of very high prevalence, morbidity, mortality, mortality rates up to 100%.

Autopsy shows that sick body subcutaneous bleeding. Trachea and throat hyperemia, hemorrhage, mucosal surface of how the volume of sticky secretions or cheese-like structures, pipe-ming site bleeding spot, pulmonary hemorrhage, necrosis, balloon membrane thickening, with cellulose exudative or cheese-like objects. Proventriculus nipples bleeding, there are purulent secretions, proventriculus and esophagus and the stomach muscle at the junction with or bleeding ulcers, muscular stomach hemorrhage cuticle; duodenal and intestinal mucosa have different levels of bleeding; cecal tonsil enlargement , bleeding; rectal mucosa and cloacal hemorrhage. Pericardial thickening, heart冠状沟epicardial fat and bleeding, and sometimes see strips or myocardial necrosis. Liver, spleen can be seen bleeding or necrosis, mucosal surface there are varying degrees of bleeding or bleeding spots. Pancreas bleeding spots and necrotic foci. Kidney enlargement, and urate deposition. Mother poultry and eggs ovarian hemorrhage, and some follicles deformation, rupture, abdominal yolk liquid flows, the formation of yolk peritonitis; tubal hyperemia, hemorrhage, containing a large number of mucus. Rooster testicular swelling, bleeding.

3 bird flu control measures in view of the characteristics of the avian flu epidemic and the serious harm, should take the following comprehensive measures to control the occurrence of avian flu.

3.1 加强检疫
3.1.1 加强国境口岸检疫。 State Customs to deal with the import of poultry, wild, ornamental birds, poultry breeding eggs, semen, poultry, as well as biological products from poultry and related products. Strict quarantine, at the same time respond to the epidemic situation in the exporting country to understand, observe good of the country, to do a good job in import customs clearance, to prevent the epidemic imported abroad.

3.1.2 enhance domestic production, transport links and quarantine. Veterinary and quarantine departments should do a good job in poultry production, distribution, slaughtering and processing plant of railways, highways, docks, ports, airports and other circulation disease outbreak detection and quarantine, if infected poultry or their products should be reported promptly, in order to take corresponding timely and effective measures to control the spread of avian flu and spread.

3.2 poultry farm biosecurity measures should be implemented biosecurity measures to control infectious diseases is the most economical and most effective way, but also a prerequisite for the prevention of all infectious diseases. Broadly speaking its contents, including the introduction of disease pathogens to cut off the channels of all the methods. On integrated prevention and control of avian flu is concerned, should include the following aspects.

3.2.1 poultry farms should be built away from rivers, lakes, where poultry farms around the other livestock and poultry rearing should not avoid the raising of poultry and other livestock and poultry and wild birds contacts, in particular, should be avoided and water birds such as ducks, geese, ducks and other contacts, at the same time to prevent wild birds out.

3.2.2 strict sanitation and disinfection measures, non-production personnel shall not enter the production areas, production personnel should be in strict accordance with the requirements for disinfection before entering the production area, at the same time should be strengthened into the appearance of vehicles, egg baskets and appliances, as well as the surrounding environment disinfection regular sterilization; Furthermore, it should be a regular basis to eradicate harmful insects inside poultry, such as mosquitoes, flies and rodents, etc.; dead birds should be burned or buried, their feces and litter should be carried out innocuous treatment.

3.2.3 poultry farms should insist on self-support and self-Fan all-in all of the rearing methods to enable the vaccination of poultry to obtain more consistent immunity and prevent the cycle of the spread of infectious diseases.

3.2.4 strengthen poultry husbandry management, minimize the occurrence of stress factors and improve the capacity of poultry disease resistance; attention to autumn and winter, spring and winter climate change, prepare warm cold and ventilation work.

3.2.5 strengthen immunization. Vaccine to prevent avian influenza outbreaks and an important measure to control the disease and the key link, the current avian influenza virus known to the different subtypes have no or only a low cross-protective and they would have to get good protection must use the specific serum subtype vaccines. China has developed for different subtypes of avian influenza virus vaccine.

3.3 after the occurrence of bird flu measures in case of suspected bird flu should immediately report to the higher authorities. Once diagnosed, should take immediate and decisive measures to control and fight.

3.3.1 of highly pathogenic avian influenza control and the fight against the measures. Early diagnosis, delineation of affected areas, strict blockade, culling infected poultry, the affected areas are likely to be infected premises to carry out a thorough disinfection of infected areas and threatened areas susceptible to carry out emergency vaccination of poultry.

3.3.2 low pathogenic avian influenza control measures. Confirmed for the low-pathogenic avian flu, should be taken to control the highly pathogenic avian influenza and similar measures, the incidence of avian quarantine blockade or poultry house, strengthen disinfection work to improve the management of poultry rearing, add material in poultry immunoenhancer to enhance the body resistance. Because of the avian flu is still no reliable specific therapy, and therefore the course of the bird flu epidemic are not in favor of treatment, to prevent the spread of the epidemic. Author: Henan University of Science and Technology Co., Ltd. in Luoyang benefits of veterinary drugs