Concept, incidence and epidemic characteristics of highly pathogenic avian influenza
1 What is avian influenza? What is highly pathogenic avian influenza?
Avian influenza is the abbreviation of avian influenza, and it is an infectious disease of poultry (poultry and wild birds) caused by influenza A virus. Avian influenza virus infection can show mild respiratory symptoms and digestive symptoms, and the mortality rate is low; Or manifested as more serious systemic, hemorrhagic and septic symptoms, and the mortality rate was higher. This difference in symptoms is mainly determined by the virulence of avian influenza virus.
According to the pathogenicity and virulence of avian influenza virus, avian influenza can be divided into highly pathogenic avian influenza, low pathogenic avian influenza and non-pathogenic avian influenza. There are different subtypes of avian influenza virus. The diseases caused by H5 and H7 subtype strains (represented by H5N1 and H7N7) are called highly pathogenic avian influenza (HPAI). Recently, avian influenza caused by H5N1 subtype at home and abroad is highly pathogenic avian influenza, with high morbidity and mortality and great harm.
How long is the incubation period of highly pathogenic avian influenza? Can it be contagious during the incubation period? The incubation period of avian influenza ranges from several hours to several days, and the longest is 21 days. The incubation period is influenced by many factors, such as virus virulence, infected virus amount, resistance of poultry, age and breed, feeding management, nutritional status, environmental sanitation and stress factors. Highly pathogenic avian influenza has short incubation period, rapid onset and high morbidity and mortality. There is the possibility of infection during the incubation period.
What is the route of transmission of avian influenza?
There are two kinds of transmission of avian influenza: direct contact between sick birds and healthy birds and indirect contact with virus pollutants. Avian influenza virus exists in the digestive tract, respiratory tract and organs of sick and infected birds. Therefore, the virus can be excreted with eye, nose, oral secretions and feces, and any objects contaminated by virus-containing secretions, feces and dead poultry carcasses, such as feed, drinking water, poultry houses, air, cages, feeding management appliances, transport vehicles, insects and various birds carrying viruses, can be mechanically transmitted. Healthy birds can be infected through respiratory tract and digestive tract, causing illness. Avian influenza virus can spread through the air, and the migration of migratory birds (such as wild ducks) can spread avian influenza virus from one place to another, and it can cause infection and illness of birds through polluted environment (such as water source). The circulation of poultry flocks and poultry products with avian influenza virus can cause the spread of avian influenza.
What are the main clinical manifestations of highly pathogenic avian influenza? What is the difference with Newcastle disease? Highly pathogenic avian influenza has no specific clinical symptoms, which is characterized by sudden onset, loss of appetite, sudden rise of body temperature, high mental depression, edema and cyanosis of comb and wattle, accompanied by a large number of deaths, and the mortality rate can reach more than 90% within a few days. Newcastle disease and avian influenza are obviously different, and their pathogens are completely different viruses. Avian influenza virus belongs to orthomyxoviridae and Newcastle disease virus belongs to paramyxoviridae. Typical clinical symptoms of Newcastle disease virus infection can be seen in the early stage: long incubation period, respiratory symptoms, diarrhea, loss of appetite, mental fatigue, and neurological symptoms in the later stage. Under the current breeding conditions, chickens immunized with Newcastle disease vaccine will not have typical Newcastle disease, and infected chickens generally show mild respiratory symptoms, neurological symptoms and decreased egg production of laying hens, with low mortality.
What are the epidemic characteristics of highly pathogenic avian influenza?
Highly pathogenic avian influenza can occur all year round, but it occurs frequently in winter and spring because the avian influenza virus has strong resistance at low temperature. All kinds of birds with different ages can be infected with highly pathogenic avian influenza, which has an acute onset and rapid spread, and its mortality rate can reach 100%.
Is the occurrence of highly pathogenic avian influenza related to the age, sex and variety of poultry? Many poultry, such as chickens, turkeys, guinea fowl, quails, ducks and geese, can be infected, but chickens, turkeys, ducks and geese are more common, and turkeys and chickens are the most susceptible, with high morbidity and mortality. Waterfowl such as ducks and geese have low susceptibility, but they can be infected with virus or recessive infection, and sometimes cause a large number of deaths. Chickens and turkeys of various breeds and different ages can be infected and die, but the mortality rate of waterfowl such as ducklings and goslings is higher. It has not been found that the occurrence of highly pathogenic avian influenza is related to the sex of poultry.
7 Will highly pathogenic avian influenza spread through eggs?
The transmission of highly pathogenic avian influenza among flocks mainly depends on horizontal transmission, such as air, feces, feed and drinking water. The current evidence shows that highly pathogenic avian influenza will not be transmitted through eggs. However, some experiments have shown that the eggs of experimentally infected chickens contain influenza virus, so the possibility of vertical transmission cannot be completely ruled out. The eggs of infected and diseased chickens cannot be used for hatching.
Why do highly pathogenic avian influenza occur in winter and spring?
Highly pathogenic avian influenza can occur all year round, but it occurs frequently in winter and spring. The main reasons are:
First, the avian influenza virus is sensitive to temperature. With the increase of environmental temperature, the survival time of the virus is shortened. In addition, the light intensity is relatively higher in summer and autumn, and the ultraviolet rays in the sun have a strong killing effect on the virus.
Secondly, the ventilation intensity of poultry houses in summer and autumn is much higher than that in winter and spring, and good ventilation can greatly reduce the number of viruses in poultry houses. Therefore, the chances and quantity of virus invading chickens are obviously reduced, and the probability of infection is reduced. At the same time, good ventilation also reduces the stimulation of bad gas to the respiratory mucosa of chickens, which is of great significance to maintain the resistance of respiratory mucosa.
When did the bird flu happen?
In 1878, it was first reported that a serious disease broke out in Italian chickens, which was called chicken plague at that time. In 1955, it was confirmed that this kind of fowl plague virus was actually a type A avian influenza virus. It has been proved that avian influenza virus is widely distributed in many poultry (including turkey, chicken, guinea fowl, stone chicken, quail, partridge, ostrich, pheasant, goose and duck, etc.) and wild birds (including duck, goose, sandpiper, three-toed snipe, tern, swan and stork) all over the world. Among them, bird flu is the most serious harm to domestic turkeys and chickens.
What is the harm caused by avian influenza in history?
In the recorded history of poultry diseases, avian influenza is a devastating disease, and every serious outbreak has caused huge economic losses to the poultry industry. At present, it has occurred in many countries and regions in the world such as America, Europe, Asia, Africa and Australia. Before 1990s, there were eight outbreaks of avian influenza in Scotland (1959), Britain (1967), Australia (1975), Britain (1979), Iceland (1983), the United States (1983), and the United States (1985). Since 1990s, there have been four outbreaks of avian influenza, namely, H7N9 and H7N9 in Australia, H7N9 in Pakistan, H5N2 in Mexico and H7N1 in Italy.
The outbreak of avian influenza in Mexico in 1994 was more complicated and unforgettable than that in Pennsylvania in 1983. In 1981-1982, Mexico conducted a nationwide serological survey of poultry, and found no infection of avian influenza virus. In May 1994, an epidemic of low virulence H5N2 was discovered, which suddenly became a highly virulent strain in January 1995, and spread in Puebla and Queretaro states, and then spread to 12 states. In order to control the epidemic situation, 18 million chickens were eliminated, 32 million chickens were blocked and 1.3 billion chickens were vaccinated urgently, resulting in direct economic losses of $1 billion.
Are waterfowl also infected with bird flu?
Waterfowl has not only become a highly susceptible bird to natural infection and death, but also can infect terrestrial birds horizontally and become the source of infection, which is a problem that should be paid great attention to at present.
Avian influenza virus was first isolated from commercial ducks in Canada by Walker in 1952, but its subtype was not identified.
Since 1999, the fact that geese and ducks have high morbidity and mortality caused by highly pathogenic avian influenza virus has broken the traditional understanding that waterfowl are only carriers of influenza virus and do not get sick and die. Waterfowl is not only a huge repository of avian influenza virus, but also has become a naturally infected and dead bird that is highly susceptible to avian influenza virus.
What are the h and n of avian influenza virus?
Both H and N refer to the glycoprotein (protein) of the virus. One glycoprotein is called hemagglutinin (HA) and the other is neuraminidase (NA). Because these two glycoproteins are easy to mutate, HA can be divided into fifteen different types from H1 to H15, and NA can be divided into nine different types from N1 to N9. Among them, H5 and H7 are highly pathogenic subtypes.
Is the avian influenza virus resistant?
Generally speaking, avian influenza virus is not resistant to the external environment, sensitive to high temperature, ultraviolet rays and various disinfectants, and easy to be killed. The virus can be inactivated in a few minutes at 70℃. Generally, disinfectants can kill viruses quickly, but viruses existing in organic substances such as feces, nasal discharge, tears, saliva and corpses can survive for a long time. Seriously polluted feces is the main problem to control avian influenza. It should be emphasized that avian influenza virus can survive for a long time in natural environment, especially in cool and humid conditions, such as the virus in feces and nasal secretions, and its infectivity can be maintained for 30~35 days at 4℃ and 7 days at 20℃. The virus can survive for a long time in polluted water source at low temperature, and once healthy chickens come into contact with the environment and water source polluted by sick poultry feces, they can cause illness.
What are the susceptible animals of avian influenza virus?
Many poultry, wild birds and birds are sensitive to avian influenza virus, and the virus has been isolated from their bodies. Turkey, chicken and duck are the most commonly infected birds in natural conditions. Other species include guinea fowl, domestic goose, quail, pheasant, pigeon, partridge, parrot, budgerigar, etc., as well as wild birds and wild waterfowl, such as geese, terns, wild ducks, mandarin ducks, coastal birds and seabirds. In addition to seabirds and waterfowl, influenza viruses were isolated from the following birds: starlings, pheasants, sparrows, crows, Western jackdaw, sandpipers, snipes, pigeons, songbirds, starlings, rock partridges, swallows, herons, Canadian geese and gourds. According to foreign reports, 88 species of poisonous birds have been found. Rats can’t be naturally infected with influenza virus.
What is the relationship between avian influenza and other animal influenza?
Influenza is an infectious disease caused by influenza virus, which endangers people and poultry. Its pathogenic influenza virus belongs to orthomyxoviridae of RNA virus and is divided into three types: A, B and C.. Among them, influenza A virus is mostly found in poultry, and some subtypes can also infect other animals and humans. Influenza B and C viruses are found in seals and pigs respectively.
Influenza A virus can infect various animals, including humans, pigs, horses, various marine mammals and poultry. There are 15 subtypes of hemagglutinin (HA) and 9 subtypes of neuraminidase (NA) in waterfowl, especially ducks and geese. Influenza virus can propagate in the digestive tract of waterfowl. Therefore, there is a high concentration of virus in the feces of infected waterfowl, and the influenza virus is transmitted from feces to mouth through polluted water sources.
Excerpted from "Questions and Answers on Prevention and Control of Highly Pathogenic Avian Influenza" by China Agricultural Publishing House.