OVERVIEW
Highly pathogenic avian influenza virus infection, known as avian influenza virus infection, is an acute respiratory infection of humans caused by certain subtypes of avian influenza A virus. The severity of the disease varies, and in severe cases, it can lead to sepsis, shock, multiple organ failure, and Reye’s syndrome and other complications leading to death. The new “Law of the People’s Republic of China on Prevention and Control of Infectious Diseases”, which came into effect on December 1, 2004, has included human infection with highly pathogenic avian influenza in Category B infectious diseases for management and stipulated that it should be handled in accordance with the precautionary measures for Category A infectious diseases. Avian influenza virus infection can manifest as mild respiratory and gastrointestinal symptoms with a low mortality rate, or as more severe systemic, hemorrhagic and septic symptoms with a high mortality rate.
Etiology
Avian influenza virus belongs to the genus Influenza A (A) virus of the family Orthomyxoviridae, and the common shape is spherical, with an average of 100 nm, a diameter of 80-120 nm, and an envelope. The newly isolated or not many viruses are filamentous, varying in length, up to 4000 nm long. according to the different antigenicity of its outer membrane hemagglutinin (HA) and neuraminidase (NA) proteins, avian influenza viruses have many subtypes. Fifteen HA subtypes (H1 to H15) and nine NA subtypes (N1 to N9) have been identified from birds. Highly pathogenic avian influenza is caused by the H5 and H7 subtypes of influenza A viruses, both of which are often stabilized in a low pathogenic form in the natural host, and the viruses are transmitted to susceptible poultry, where they can mutate to a highly pathogenic form after several rounds of cyclic infection.
Symptoms
H5N1 virus infected people are mostly acute onset of disease, early performance similar to ordinary influenza, mainly fever, body temperature is mostly sustained at 39 ℃ or more, fever duration of 1 to 7 days, usually 3 to 4 days, can be accompanied by runny nose, nasal congestion, cough, sore throat, headache, muscle aches and general discomfort, some patients may have nausea, abdominal pain, diarrhea, dilute watery stools and other gastrointestinal symptoms. Most of the mild cases have good prognosis, but the condition of severe patients develops rapidly, and there may be pneumonia, acute respiratory distress syndrome, pulmonary hemorrhage, pleural effusion, thrombocytopenia, renal failure, sepsis, shock, and Reye’s syndrome and other complications, and the severe cases may lead to death. If the body temperature continues to exceed 39℃ during treatment, we need to be alert to the tendency of severe disease.H7N7 infected patients have mild symptoms, most of the patients can have conjunctivitis, a few patients with mild flu-like symptoms, H9N2 infected patients only cause transient flu symptoms, and there is no report of fatal cases. Severe patients may have signs of solid changes in the lungs.
Examination
1. Peripheral blood and bone marrow
The total number of leukocytes is generally not high or low, platelets are normal, and the total number of leukocytes and the number of lymphocytes are often decreased in severe cases. Bone marrow cytology shows active cell proliferation, reactive histiocytosis with hemorrhagic phagocytosis.
2. Viral antigen and gene detection
Take respiratory specimens from patients and use immunofluorescence method (or enzyme immunoassay) to detect the nucleoprotein antigen (NP) of influenza A virus and the antigen of avian influenza virus subtype H. RT-PCR can also be used to detect the genes of avian influenza virus subtype-specific H antigen.
3. Virus isolation
Isolation of avian influenza virus from respiratory specimens (e.g., nasopharyngeal secretions, oral gargle, tracheal aspirates, or respiratory epithelial cells).
4. Serologic examination
Collect double serum at the beginning of the disease and during the recovery period, and use hemagglutination inhibition test, complement binding test or enzyme-linked immunosorbent assay to detect anti-avian influenza viral antibodies, if the titer before and after the disease is 4-fold or higher, it can be used as a reference index for retrospective diagnosis.
5. X-ray examination
Chest X-ray of severe patients may show unilateral or bilateral pneumonia, and a few patients have pleural effusion.
Diagnosis
Diagnosis should be made with reference to the Diagnostic and Treatment Program for Human Avian Influenza of the People’s Republic of China (for trial implementation). The diagnosis of human avian influenza can be made based on epidemiologic history, clinical manifestations and laboratory findings, and after excluding other diseases.
1. Cases under medical observation
Clinical manifestations within 1 week, close contact with human avian influenza patients or epidemiologic history.
2. Suspected cases
Patients whose respiratory secretion specimens are positive for influenza A virus and subtype H monoclonal antibody antigen, with relevant clinical manifestations or epidemiologic history.
3. Confirmed cases
Patients with specific viruses isolated from respiratory secretion specimens or avian influenza subtype H viral genes detected by RT-PCR, or with relevant clinical manifestations or epidemiologic history, and with 4-fold or higher double serum anti-avian influenza viral antibody titers during the initial and recovery phases of the disease.
Treatment
1. Isolation
Suspected and confirmed patients should be isolated for treatment to prevent deterioration and spread of the disease.
2. Symptomatic supportive treatment
Antipyretic and analgesic medicines, medicines for relieving nasal mucous membrane congestion, cough expectorants, etc. Children should avoid the use of salicylic acid medicines to reduce fever, so as not to cause Reye’s syndrome, pay attention to rest, drink plenty of fluids, eat a light diet, and take appropriate nutrition and intravenous rehydration.
3. Anti-influenza virus treatment
Anti-influenza virus drugs should be tried within 48 hours of the onset of illness.
(1) Ion channel M2 blockers Inhibit the replication of influenza virus strains by interfering with the activity of viral M2 ion channels.
(2) Neuraminidase inhibitors Inhibit viral replication by inhibiting the neuraminidase enzyme of the influenza virus, and at the same time reduce the viral pathogenicity.
(3) Others In addition to the above conventional treatments, supportive therapy and prevention of various complications are required for severely ill patients.