Avian influenza is an infectious viral disease of birds, some strains of the pathogen of which are pathogenic to humans, causing severe disease with high mortality. Avian flu is accompanied by high fever, diarrhea, vomiting, catarrhal syndrome, bleeding from the nose and gums, chest pain, pneumonia, acute respiratory failure, pulmonary edema. The diagnosis can be confirmed by ELISA, PCR, virological studies, chest radiography. Treatment includes hospitalization, the appointment of antiviral and symptomatic agents.
General information
Avian influenza is an acute viral disease occurring in a person with infectious–toxic, gastrointestinal and respiratory syndromes. Human infection with avian influenza virus first became known in 1997 during an outbreak of infection in Hong Kong. In the following years, disease spread from Asia to Europe and Africa, causing millions of infections of wild and domestic birds and hundreds of cases of the disease among humans. The urgency of the fight against avian influenza is due to the high economic losses associated with the forced destruction of poultry, as well as the pandemic potential of the disease in the human population. Avian influenza has an extremely aggressive course: mortality from pulmonary complications reaches 60-70%.
Causes
The RNA-containing virus that causes avian influenza belongs to type A influenza viruses, the family Ortomyxoviridae. Depending on the type of proteins (hemagglutinin and neuraminidase) contained in its outer shell, various antigenic types of virus are isolated. H5N1 and H7N7 strains are the most dangerous for humans, since they are able to mutate quickly and cause severe forms of the disease with a lightning course and high mortality. These strains are especially dangerous in combination with seasonal and swine flu viruses. There are also known cases of avian influenza in humans caused by a low-pathogenic subtype of the H7N9 virus, mainly affecting people with concomitant pathology. The avian influenza virus can persist for a long time at low temperatures, but it dies after 2-3 minutes when boiled.
The source of the spread of infection are wild waterfowl (geese, ducks, swans) and poultry (chickens, turkeys), in which the avian influenza virus is located in the intestines and is released into the external environment with feces. Due to seasonal migration, wild birds are able to carry the virus over vast distances. Human infection is carried out by airborne droplets and fecal-oral route in contact with an infected or dead bird from avian influenza. Cases of human-to-human transmission of the virus have not been reported. Poultry farm workers, animal technicians, and veterinarians are at increased occupational risk of contracting avian influenza.
Birds infected with avian influenza virus are inhibited, rush badly, drink water greedily, are disheveled, make croaking sounds. They have redness of the eyes and mucous membranes, the release of exudate from the nasal passages; diarrhea occurs, gait disorders, convulsions. Before death, cyanosis of the earrings and comb is observed. When opening a dead bird, attention is paid to multiple hemorrhages in the mucous membrane of the respiratory tract, gastrointestinal tract, kidneys and liver. Due to the mass death of poultry, avian influenza is often referred to as “chicken plague” and “chicken Ebola fever”.
Avian influenza symptoms
When a person is infected with avian influenza virus, the incubation period lasts 2-3 days (rarely up to 2 weeks). Infectious-toxic, gastrointestinal and respiratory syndromes develop at the stage of clinical manifestations of avian influenza. The manifestation of the infection is acute – from a high temperature to 38-40 ° C, terrific chills, muscle and headaches. It is possible to develop a runny nose, conjunctivitis, mild catarrhal syndrome (pharyngitis), bleeding from the nose and gums. In about half of the cases, abdominal pain, repeated vomiting and watery diarrhea occur. A third of patients develop acute renal failure.
After 2-3 days from the beginning of the manifestations of avian flu, respiratory syndrome joins. Interstitial viral pneumonia develops, accompanied by a cough with the release of clear sputum, hemoptysis, shortness of breath, tachypnea, cyanosis. Rapid progression of inflammatory changes in the lungs leads to the development of acute respiratory distress syndrome. The death of patients with this virus usually occurs in the second week of the disease from pulmonary edema, acute respiratory failure, multiple organ failure or secondary bacterial and fungal infection that has joined. Disease is most severe in early childhood. Features of the disease in children are characterized by the development of meningoencephalitis, accompanied by severe headache with vomiting, impaired consciousness.
Diagnostics
In the initial period of the disease, the symptoms of avian flu are similar to the manifestations of the usual seasonal flu, which makes it difficult to diagnose. In addition, disease requires differentiation from parainfluenza, adenovirus, rhinovirus, respiratory syncytial infection. The main signs of avian influenza are the presence of an outbreak of infection in the region, previous contact with infected poultry, high fever, diarrheal syndrome, progressive pneumonia. During the radiography of the lungs, already in the early period of the disease, multiple inflammatory infiltrates are detected, prone to fusion and rapid spread through the lung tissue. Confirmation of disease is carried out by immunological (ELISA), molecular genetic (PCR), virological methods.
Treatment
Patients with suspected or diagnosed avian influenza are hospitalized in infectious hospitals. Etiotropic therapy of infection is carried out with antiviral drugs that reduce the replication of the virus and improve the prospects of survival. Among them, oseltamivir, zanamivir, rimantadine, umifenovir showed the greatest effectiveness. At high temperatures, antipyretic drugs (paracetamol, ibuprofen) are used. Acetylsalicylic acid and sodium metamizole are categorically contraindicated for the treatment of avian influenza. The appointment of antibacterial drugs is justified only in the case of bacterial complications.
Prognosis and prevention
Immunity after bird flu is short-term and type-specific. This means that the possibility of re-infection in another season is not excluded. In outbreaks of infection caused by the most pathogenic strains of avian influenza, the mortality rate is 50-70%. According to the most pessimistic forecasts, the A(H5N1) virus is capable of causing a pandemic of avian influenza around the globe and leading to the death of 150 million people.
The number of birds infected with avian influenza virus is subject to destruction. Poultry vaccination is used as a means of controlling the epizootic of infection. Prevention of avian influenza in humans is aimed at strengthening the immune system, taking antiviral drugs according to preventive schemes. If possible, close contact with domestic and wild poultry should be avoided, and precautions should be taken when preparing poultry meat and chicken eggs. Vaccination against influenza with seasonal vaccines can reduce the risk of complications, as well as prevent possible mutations of the avian influenza virus and its ability to be transmitted from person to person.