What is Avian Flu?

Human infection with avian influenza is a human disease caused by the avian influenza virus. Avian influenza virus, which belongs to influenza A virus, is classified into three levels of high, medium, and low / non-pathogenic according to the pathogenicity of avian influenza virus to chickens and turkeys. Due to the hemagglutinin structure of avian influenza virus and other characteristics, birds are generally infected. When the virus undergoes gene reassortment during replication, the structure changes and the ability to infect humans can cause human infection with avian influenza. The subtypes of avian influenza viruses that have been found to directly infect humans are: H5N1, H7N1, H7N2, H7N3, H7N7, H9N2 and H7N9 subtypes. Among them, the highly pathogenic H5N1 subtype and the new avian influenza H7N9 subtype first discovered in humans in March 2013 are of particular concern, which not only caused human casualties, but also severely damaged the poultry breeding industry.

Basic Information

nickname

Human avian influenza, human avian influenza, avian influenza, human infection with highly pathogenic avian influenza

English name

influenza in birds

English alias

avian-human influenza

Visiting department

Infectious Diseases

Multiple groups

Older men

Common causes

bird flu virus

Common symptoms

Flu-like symptoms, including fever, cough, and general discomfort with headaches

Contagious

Have

way for spreading

Infected by direct contact with birds or their waste-contaminated items and the environment

Human infection with bird flu discovery history and epidemiology

It was isolated from chicken fowl in 1878. In 1901, this "fowl blast pathogen" was called "filter factor" or Fowl plague virus (FPV). Later, it was discovered that Newcastle disease virus (NDV) can also cause fowl-like disease in birds, which is commonly known as "fowl fever" in China. To distinguish between the two, the former is called true fowl fever or European fowl fever virus, and the latter is called pseudofowl fever or Asian fowl fever virus. In 1955, FPV was identified as a member of the influenza A virus based on the characteristics of the nucleoprotein antigen of the virus particle. Most of them do not cause chicken plague in poultry, and even show silent infection or health-carrying status, such as the newly discovered H7N9 avian influenza virus in China in 2013, which basically does not cause disease among birds.

The H5N1 subtype was first discovered in Hong Kong in 1997 to directly infect humans. As of March 2013, a total of 622 human infections with highly pathogenic H5N1 avian influenza have been reported worldwide, including 371 deaths. The cases were distributed in 15 countries, of which 45 were found in our country and 30 died. The majority of cases of H5N1 bird flu infection are young people and children. In March 2013, the first case of human infection with H7N9 avian influenza was detected in China. As of May 1, 2013, Shanghai, Anhui, Jiangsu, Zhejiang, Beijing, Henan, Shandong, Jiangxi, Hunan, Fujian and other 10 provinces (cities) have reported a total of 127 confirmed cases, including 26 deaths. The majority of cases are elderly, more men than women.

Current research has found that the source of human infection with bird flu is birds that carry the virus. The transmission route still needs to be clear. Studies have suggested that the main route for human infection with H5N1 subtype avian influenza is close contact with sick and dead birds. High-risk behaviors include slaughter, plucking, and processing of infected birds. In a few cases, when children are playing in areas where free-range poultry is frequent, feces exposed to poultry are also considered a source of infection. Most of the evidence from the current research indicates the existence of bird-to-human transmission, possible environmental (environment contaminated by bird excrement) -human transmission, and a few non-sustained human-to-human transmissions of H5N1. At present, H7N9 avian influenza patients are believed to be infected by direct contact with birds or their contaminated items and the environment. Human infection with H7N9 avian influenza is still sporadic. Although individual family clusters have occurred, no continuous human-to-human transmission of the virus has been found.

Clinical manifestations of human infection with avian influenza

According to the findings of existing human cases of H7N9 and H5N1 avian influenza, the incubation period is generally within 7 days.

Patients present with flu-like symptoms at the beginning of the onset, including fever, cough, and may be accompanied by headache, muscle aches, and general malaise, and runny nose, stuffy nose, and sore throat. Some patients have severe symptoms such as chest tightness and dyspnea when the lung disease is severe or the disease develops rapidly. Respiratory symptoms appear earlier, usually within 1 week after onset, and last for a long time. Some patients still have more severe cough and sputum after 1 month of treatment. In the early stages of the disease, chest tightness, shortness of breath, and dyspnea often indicate that the lung disease progresses rapidly and will quickly develop into a severe hypoxia and respiratory failure. Severe patients develop their condition rapidly, with severe pneumonia occurring mostly within 5 to 7 days. Most of their body temperature persists above 39 ° C. They have difficulty breathing and may be accompanied by hemoptysis; they can rapidly progress to acute respiratory distress syndrome, sepsis, and infectivity. In shock, some patients may have mediastinal emphysema and pleural effusion. A significant proportion of patients with severe illness are concurrently suffering from multiple other system or organ injuries or failures, such as heart failure due to myocardial injury, and individual patients also show digestive symptoms such as gastrointestinal bleeding and stress ulcers, and some patients with coma And disturbance of consciousness.

Human infection with bird flu test

The leukocyte level of most people infected with bird flu is lower than normal, and the level of lymphocytes is not high or even decreased. If the platelet level is reduced, it is necessary to consider whether the situation of disseminated intravascular coagulation due to severe infection should be combined with the results of coagulation analysis and fibrinogen level. Blood biochemical examinations often include creatine kinase, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase, C-reactive protein, and myoglobin can increase.

Imaging studies revealed flaky shadows in the lungs of patients with pneumonia. Severe disease progresses rapidly, showing multiple ground glass shadows and lung consolidation images in the lungs, which can be combined with a small amount of pleural effusion. When ARDS occurs, the lesions are widely distributed.

The most reliable is still the etiology test. Prior to antiviral treatment, conditional medical units collect as many respiratory specimens as possible (such as nasopharyngeal secretions, oral gargles, tracheal aspirates, or respiratory epithelial cells) for viral nucleic acid testing (real-time fluorescent PCR testing) and viruses Separation.

In addition to bird flu virus infections in humans, people infected with avian influenza often have early or secondary bacterial infections. After long-term or large-dose use of antibacterial drugs and inappropriate use of glucocorticoids, fungal infections can also be combined. Therefore, sputum culture and respiratory tract culture should be performed multiple times in the clinic to check the types of bacteria and / or fungi, as well as their sensitive or drug-resistant types, in order to rationally choose antibiotics and guide clinical treatment.

Human infection with bird flu diagnosis

According to the standards in the "Diagnosis and Treatment Program for Human Infection with Avian Influenza (2008 Edition)" released in May 2008 and the "Diagnosis and Treatment Program for Human Infection with H7N9 Avian Influenza (2013 Edition)" released in April 2013, Contact history, clinical manifestations, and laboratory test results can make a diagnosis of human infection with H5N1 or H7N9 avian influenza. In the case of unknown epidemiological history, according to clinical manifestations, auxiliary examinations and laboratory test results, especially the isolation of avian influenza virus from specimens of respiratory secretions of patients, or positive detection of avian influenza virus nucleic acid, or dynamic detection of duplicates Serum avian influenza virus-specific antibodies are positively transformed or show a 4-fold or more increase, which can be used to diagnose human infection with avian influenza.

Etiological testing should be mainly used to distinguish it from other unexplained pneumonia, such as seasonal influenza (including H1N1 influenza), bacterial pneumonia, severe acute respiratory syndrome (SARS), new coronavirus pneumonia, adenoviral pneumonia, chlamydia Pneumonia, mycoplasma pneumonia and other diseases.

Human infection with bird flu treatment

Under appropriate isolation conditions, treatments such as symptomatic maintenance, anti-infection, ensuring tissue oxygen supply, and maintaining organ function are given.

Symptomatic maintenance includes bed rest, dynamic monitoring of vital signs, and physical or drug cooling. Anti-infective treatment includes antiviral treatment (such as oseltamivir, zanamivir, paramivir, etc.), but it is emphasized that clinical treatment should be "early, fast and accurate". In particular, antiviral drugs should be obtained from respiratory tract specimens before use, and should be used within 48 hours of onset as far as possible. For cases that are clinically considered to require antiviral drugs, they can also be used for more than 48 hours.

Ensuring tissue oxygenation is the core to maintain the normal function of important organs in critically ill and critically ill patients. It can be performed by sequential methods such as nasal canals, mouth / nasal masks, non-invasive ventilation and invasive ventilation.

Specific treatment methods should be carried out under the guidance of a professional doctor to avoid drug abuse and improper operation, resulting in drug resistance and misdiagnosis.

Human infection with bird flu prevention

Based on the characteristics of avian influenza virus and existing research, it is currently believed that birds carrying the virus are the main source of human infection with avian influenza. It is particularly important to reduce and control the spread of avian influenza virus among birds, especially poultry. With the improvement of China's social and economic development level, there is an urgent need to accelerate the transformation and upgrading of traditional poultry breeding and circulation to modern production methods, and change from free-range breeding to centralized large-scale breeding, slaughter treatment and scientific transportation, and improve poultry and livestock breeding. 2. Circulate the level of biological safety, thereby reducing the exposure of live or sick and dead birds in the population. At the same time, we must continue to carry out health education, advocate and cultivate personal respiratory hygiene and prevention habits, and wash hands frequently, keep the environment clean, and properly process cooking food. Health education and health protection for people at high risk of human infection with bird flu and medical staff need to be strengthened.

At the same time, surveillance of influenza in animals and humans should be done well. In time to detect animal infections or disease outbreaks, and the state of the virus cycle in the environment, take early measures to eliminate the source of infection, such as animal immunization, culling, and closing the market, and stop the virus from spreading between birds. Early detection and early diagnosis of bird flu patients, and timely, effective and reasonable implementation of case isolation and diagnosis and treatment. Do a good job of epidemiological investigation and virological monitoring of the disease, continuously improve the scientific understanding of avian influenza, timely detect clustered cases and virus mutations, and then take appropriate intervention and response measures.

While doing scientific prevention and control, we must also seriously prepare for the pandemic. ^[1-2]