Avian influenza virus

The avian influenza virus is a very scary virus with strong contagiousness. Everyone wants to stay away from it. There are many types of avian influenza viruses, but each one is very scary, so we must stay away from it in our daily lives and try our best to avoid contact with people and animals that may be infected with the avian influenza virus. If someone around you is infected with the avian influenza virus, you must seek medical attention in time, isolate and treat them separately to avoid cross infection.

To prevent the avian influenza virus effectively, you need to do the following: wash your hands frequently, take a shower and change clothes frequently, maintain good personal hygiene, minimize contact with poultry, and if you eat poultry, you should cook it thoroughly before eating it. Eat more nutritious food, exercise more appropriately, improve your resistance and immunity, and avoid the invasion of avian influenza virus.

Source of infection

Avian influenza virus can

Reproduces in the digestive tract of waterfowl.

The main sources of infection are poultry that are infected with avian influenza or carry the avian influenza virus. Wild birds or pigs can also become sources of infection. Many poultry can be infected with the virus and become ill: land birds such as turkeys, chickens, pigeons, guinea fowl, quail, and parrots can all be infected, but turkeys and chickens are the most susceptible, with high morbidity and mortality rates; waterfowl such as ducks and geese are also susceptible, and can carry the virus or be latently infected, and sometimes die in large numbers. Chickens and turkeys of all ages can be infected and die, and the mortality rate is higher for waterfowl such as ducklings and goslings.

In addition to wild birds such as swans, terns, wild ducks, coastal birds and seabirds, influenza viruses have also been isolated from the following birds: starlings, partridges, sparrows, crows, jackdaws, pigeons, rock partridges, swallows, herons, Canada geese and Muscovy ducks. According to foreign reports, 88 species of birds have been found to be carrying avian influenza viruses, while rodents cannot be naturally infected with influenza viruses.

Different breeds of poultry have different chances of being infected with avian influenza, but the occurrence of highly pathogenic avian influenza has not been found to be related to the gender of the birds. The highly pathogenic avian influenza virus can also be transmitted through eggs.

The spread of highly pathogenic avian influenza among poultry flocks mainly relies on horizontal transmission, such as air, feces, feed and drinking water; there is little evidence of vertical transmission. However, experiments have shown that eggs from experimentally infected chickens contain influenza viruses, so the possibility of vertical transmission cannot be completely ruled out. Therefore, eggs from contaminated chickens cannot be used for hatching.

The virus can be excreted through the respiratory tract, eye and nasal secretions, and feces of sick birds, and birds can become infected through the digestive tract and respiratory tract. Any object contaminated by sick poultry feces and secretions, such as feed, poultry houses, cages, feeding and management utensils, drinking water, air, transport vehicles, people, insects, etc., may spread the virus.

Mode of transmission

It is mainly transmitted through the respiratory tract, and infection is caused by close contact with infected poultry and their secretions, excrement, virus-contaminated water, and direct contact with the virus strain. The virus is present in high concentrations in the feces of infected waterfowl, and is transmitted by the fecal-oral route through contaminated water sources. No asymptomatic carriers of the virus have been found, and there is no definitive evidence of human-to-human transmission.

Susceptible population

It is generally believed that people of any age are susceptible, but the incidence rate is higher and the condition is more serious in children under 12 years old. People who have close contact with poultry that have died of unknown causes or are infected or suspected of being infected with avian influenza are at high risk.

Popular characteristics

Avian influenza is distributed worldwide, with outbreaks in Australia, Italy, Hong Kong, China, the Netherlands and other places in 1994, 1997, 1999 and 2003 respectively, and in 2005 it broke out mainly in Southeast Asia and Europe. Apart from the fact that avian influenza in chickens mainly occurs in winter and spring, there is no other obvious regularity. The spread of highly pathogenic avian influenza has attracted worldwide attention. Analysis of the climate characteristics of the epidemic area by my country's meteorological experts shows that avian influenza "does not like" sunny and hot weather.

The World Health Organization (WHO) believes that diseased poultry feces is the main channel of transmission, and some experts also believe that the migration of migratory birds is also one of the transmission routes.

Weather and climate conditions are an important factor in the natural environment. Their changes or abnormalities usually play a certain role in the occurrence, aggravation or alleviation of some diseases. Experts believe that avian influenza viruses prefer cold and humid environments, and that ultraviolet rays in sunlight have a certain killing effect on the virus. In late winter and early spring, cold air activities are frequent and the temperature fluctuates, which will be unfavorable for controlling and preventing the occurrence of avian influenza. In addition, as the temperature warms up, migratory birds will migrate northward, and the range of the virus spread by migratory birds will expand, which will be unfavorable for controlling the occurrence of avian influenza.

WHO believes that the H5N1 avian influenza virus strain in sick chicken feces can be spread in the air and carried by the wind, spreading avian influenza. Judging from the number of sunshine hours, analysis materials show that areas with less sunshine are more prone to avian influenza. This is consistent with the view put forward by agricultural experts that the avian influenza virus can only survive for 24 to 28 hours in the sun, generally spreads in winter and spring, and basically subsides from May to October.

Highly pathogenic avian influenza virus is mainly transmitted through the air. With the help of the hemagglutinin (H) on the surface of the virus, it binds to the corresponding receptors on the surface of the respiratory mucosal epithelial cells and adsorbs to the host's respiratory epithelial cells. The neuraminidase (N) on the surface of the virus acts on the receptor of the nucleoprotein, causing the virus to combine with the nucleoprotein of the epithelial cells, forming an RNA-type soluble antigen in the nucleus, which then seeps out to the cytoplasm, replicates progeny viruses, and is expelled from the epithelial cells by budding through the action of neuraminidase. The replication cycle is 4 to 6 hours. The excreted viruses spread to nearby cells, causing an inflammatory response. Clinically, systemic toxemia-like reactions such as fever, muscle pain, and leukopenia appear.

The virus mainly invades the epithelial cells of the respiratory mucosa, causing catarrhal lesions such as epithelial cell hyperplasia, necrosis, local mucosal congestion, edema and superficial ulcers. After 4 to 5 days, lesions in the basal cell layer may extend to the bronchi, bronchioles, alveoli and peribronchial tissues, causing mucosal edema, congestion, lymphocyte infiltration, accompanied by microvascular embolism, necrosis, small aneurysm formation and bleeding, triggering a systemic toxemia-like reaction. In a small number of severe progressive pneumonia, in addition to bronchiolar inflammation changes, there may be congestion and edema of the alveolar wall, fibrin exudation, mononuclear cell infiltration and hyaline membrane formation, as well as pulmonary hemorrhage, which may cause many complications.

Highly pathogenic avian influenza virus is highly toxic, and the infectious allergic reaction (type IV allergic reaction) it triggers is the root cause of serious complications such as progressive pneumonia, acute respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS).

Relationship with humans

Humans have been studying and preventing avian influenza for more than 100 years. Current research results show that the avian influenza virus lacks the genetic fragments of the human influenza virus. Unless the avian influenza virus undergoes genetic recombination with the human influenza virus, it is difficult for it to invade humans and cause human-to-human transmission. The occurrence of avian influenza in humans can only be caused by contact with sick poultry. The chance of a person being infected with the virus is very small.

Avian influenza virus belongs to influenza A virus. Influenza virus belongs to the Orthomyxoviridae family of RNA viruses and is divided into three types: A, B, and C.

Simple influenza

There are only catarrhal inflammatory changes in the upper respiratory tract, with congestion, edema and lymphocyte infiltration in the mucosa. Fibroepithelial cells degenerate, necrotize, and fall off.

Pneumonia-type influenza

The lungs are dark red and edematous. There are bloody secretions and mucosal congestion in the trachea and bronchi, the ciliated epithelial cells are necrotic and fall off, there is focal hemorrhage, edema and leukocyte infiltration in the submucosal layer, and there is fibrin exudate in the alveoli, containing neutrophils and lymphocytes. There is bleeding in the alveoli of the middle lobe of the lungs, transparent membranes may be present in the alveoli, and influenza viruses can be easily isolated from the lung tissue.

Serious complications

The main pathological change is pulmonary consolidation. Due to pulmonary interstitial edema and decreased interstitial negative pressure, the tendency of small airways to close increases, leading to atelectasis; the surfactant of the alveolar membrane decreases, and the alveoli also collapse and close; coupled with pulmonary congestion, the lung capacity decreases and the lung compliance decreases, leading to serious complications such as acute respiratory distress syndrome.

Pathogenicity

Generally speaking, there are differences in receptor specificity between avian influenza viruses and human influenza viruses, and avian influenza viruses are not easily transmitted to humans. Some avian influenza viruses that cause human infection may be mutated viruses. The possibility of mutation is that two or more viruses enter the same cell for recombination. For example, pigs can be infected with both human influenza virus and avian influenza virus. Each virus has 8 gene segments. Theoretically, 256 new recombinant viruses can be formed. The second is that the viral gene site is affected by certain factors. In April 1983, an outbreak of low pathogenic avian influenza caused by the H5N2 virus occurred in chickens and turkeys in Pennsylvania, USA. Because it was not effectively controlled in time, by October of the same year, the same H5N2 strain suddenly changed from low pathogenicity to high pathogenicity, causing the death of a large number of poultry.

We all know about the avian influenza virus. There have been many cases of avian influenza virus in recent years, and everyone is very familiar with it. Therefore, we must develop good living habits in our daily lives and try to keep ourselves away from the source of infection to ensure our health.