Avian influenza (H5N1 influenza) is a type of influenza virus that affects birds and can be transmitted from birds to humans.
H5N1 influenza is transmitted primarily through the fecal-oral route (excreted in the feces of a sick person, and then enters the body of another person through the mouth, infecting him).
Bird flu is accompanied by fever, severe intoxication and catarrhal syndromes.
The first case of human infection with the H5N1 influenza virus was recorded in 1997 in Hong Kong.
The mortality rate from bird flu reaches 50-80%.
The H5N1 influenza subtype is considered the most dangerous for humans. The reasons for this are:
- this subtype can directly infect humans;
- the infectiousness of these microorganisms to humans is very high;
- Avian influenza virus causes severe lung damage;
- this disease can be complicated by multiorgan failure, including damage to the liver, kidneys, and brain;
- the H5N1 subtype is not sensitive to the antiviral drug rimantadine and is resistant to interferon;
- the H5N1 subtype is highly prone to mutations and can become even more dangerous.
Characteristics of the avian influenza virus
This virus is more persistent in the environment than the seasonal influenza virus. At a temperature of 60°C it dies only after 30 minutes, and when boiled it dies instantly. This virus tolerates freezing very well. Can be stored for a long time in water and bird droppings. The virus can remain active in bird carcasses for up to a year. Regular disinfectants can destroy this virus.
The reservoir of the virus in nature is wild ducks, geese, and herons.
Poultry infected with the avian influenza virus become severely ill. The mortality rate among poultry reaches 90%.
The avian influenza virus can also infect mammals: seals, whales, pigs, horses.
Common features of bird flu and coronavirus
Both diseases are transmitted by airborne droplets and through surfaces not treated with disinfectants.
Similarities between COVID-19 and bird flu:
- infections live on the surface: coronavirus - up to 9 days, influenza - up to 3 days;
- Infection can be avoided by maintaining a distance of 1.5–2 meters from a sick person;
- infection occurs even if the infected person is asymptomatic.
Coronavirus enters the human body through the eyes. In this case, the symptoms of COVID-19 differ from the clinical picture of the flu in the following way: red eyes that are watery, swollen and itchy.
Clinical picture of the disease
The incubation period (the period from the moment the virus enters the body until symptoms appear) ranges from 1 to 7 days. On average it lasts 2-3 days.
The disease begins acutely. Chills, muscle and joint pain appear. Body temperature rises to 38°C and above. Fever persists for 10-12 days, in severe cases it lasts until the last hours of life.
On the 2-3rd day of the disease, catarrhal syndrome occurs. It appears in the form of laryngitis and bronchitis. Patients complain of a severe “flaming” sore throat. Rhinitis may occur.
Viral pneumonia can also develop at the same time. In this case, shortness of breath and a wet cough occur.
Along with intoxication and catarrhal syndromes, damage to the gastrointestinal tract is often observed. Patients experience vomiting, diarrhea, and abdominal pain.
Incubation period of avian influenza
From the onset of infection to the first symptoms, it usually takes from 30 hours to 2 days. This period depends on the state of the immune system. In some patients, from the moment of contact with infected birds to the first clinical manifestations, the incubation period reached 17 days.
Symptoms in humans
Symptoms of the disease can be divided into three main groups:
- with damage to the respiratory tract;
- with intestinal damage;
- symptoms of general intoxication.
In the first case, signs of damage to the respiratory tract and lung tissue predominate. By multiplying in the epithelial cells of the larynx, trachea and bronchi, the virus causes acute catarrhal inflammation. This is accompanied by a sore throat and painful sensations behind the sternum in the projection of the trachea. Symptoms intensify as the disease progresses. After 1-2 days, a cough with mucous sputum appears. Over time, the serous form of inflammation of the respiratory tract becomes purulent. The sputum becomes grayish or greenish in color and becomes more viscous.
Symptoms your doctor will detect
Auscultation of the lungs in case of pneumonia development will reveal hard breathing, moist rales of various sizes, and crepitus.
An X-ray of the chest organs can reveal infiltration (clumps of cells), which quickly spreads, and individual foci tend to merge.
A general blood test will show a decrease in the number of leukocytes, lymphocytes and platelets.
Enlargement of the liver may occur, with increased levels of liver enzymes (alanine aminotransferase and aspartate aminotransferase).
With the development of renal failure, creatinine levels increase.
Diagnostics
At the first symptoms of a viral disease affecting the respiratory tract or gastrointestinal tract, it is necessary to carefully study possible routes of infection. It must be remembered that the H7N9 influenza strain is transmitted to humans only from sick birds or through objects contaminated with their secretions.
Of the instrumental methods, chest X-ray is used. In cases of viral pneumonia, areas of inflammatory hemorrhagic infiltration of the lung tissue are clearly visible in the images.
Laboratory diagnostic methods are aimed at identifying specific antibodies in the blood using ELISA (enzyme-linked immunosorbent assay).
Another method, PCR, allows you to identify the RNA virus and, based on this, draw conclusions about the strain that affected the sick person. A virological method of diagnosis is also used with the propagation of the pathogen under special conditions and its further study.
Complications
- Viral pneumonia;
- renal, liver failure;
- encephalitis;
- damage to the hematopoietic organs;
Complications are the leading cause of death. Most often, people die from H5N1 influenza in the second week of the disease.
There are a number of factors that contribute to the severe development of avian influenza in humans:
- delay from hospitalization (the later the patient seeks medical help and is hospitalized, the higher the risk of developing a severe form);
- the presence of a low level of leukocytes;
- presence of concomitant diseases.
In children under 5 years of age, flu symptoms are mild.
How the virus is transmitted
The main carriers of the virus are migratory birds. They have natural immunity to the avian influenza pathogen, unlike poultry. When unprepared poultry is infected, the disease is fatal. When a virus enters the human body, it mutates and interferes with life.
The first cases of human infection with the H5N1 virus were recorded in Hong Kong in 1997. As a result of the epidemic, 60% of those infected died. A total of 18 cases of the disease were observed, which coincided with the intensification of the avian influenza epidemic among poultry. Medical studies showed that all patients had direct contact with poultry before becoming infected. The research also revealed that family members of the sick and medical workers involved in localizing the outbreak were not harmed. They showed no symptoms of the disease. Thus, it was possible to diagnose that the virus is transmitted only from animals to people. When a sick person comes into contact with another person, infection does not occur. Emergency measures were developed and implemented to destroy the poultry population. Thus, it was possible to avoid the spread of infection and save some of the sick people.
The virus could manifest itself with minor symptoms. Perhaps some people simply did not seek medical help.
Bird flu is transmitted only from birds to humans, so epidemics are localized to small outbreaks, unlike regular flu. But if we take into account the high level of virulence of this disease, the possibility of an epidemic with transmission of the virus from person to person cannot be ruled out.
Diagnosis of avian influenza in humans
A timely diagnosis of bird flu not only improves the prognosis of the disease, it is also responsible for the epidemiological situation in the region and helps prevent the spread of the disease.
A preliminary diagnosis of H5N1 influenza can be made if the following data are available:
- if there is evidence of H5N1 influenza diseases in a given region among birds and animals;
- if there was contact with a person sick with H5N1 influenza;
- in case of travel to a region where cases of H5N1 influenza have been reported;
- in the presence of high body temperature, difficulty breathing, diarrhea.
The final diagnosis of H5N1 influenza is made only after laboratory confirmation by virological, serological methods, immunofluorescence analysis or polymerase chain reaction.
Diagnosis and analysis for avian influenza
The prognosis for the recovery of a patient suffering from avian influenza directly depends on the timeliness of verification of the diagnosis, the adequacy of treatment measures, as well as further preventive measures. The main difficulty in early diagnosis of the disease lies in the clinical symptoms common to avian influenza and most acute respiratory viral diseases. Infectious disease specialists initially establish a diagnosis of avian influenza in humans in a situation where there is official data on the patient’s epidemiological history and information on the presence of avian influenza outbreaks among the bird population. In addition, cases of contact with a person sick with avian influenza whose diagnosis is laboratory confirmed should be suspicious.
All persons who have close contact with a patient who died from an acute respiratory pathology of unknown etiology, as well as tourists who come from countries with an unfavorable epidemiological situation are subject to dynamic observation.
The patient’s clinical manifestations of the disease must be differentiated from similar symptoms of other infectious pathologies affecting the respiratory tract. Thus, parainfluenza is also characterized by high fever, but inflammatory changes rarely affect the pulmonary parenchyma, unlike avian influenza. With respiratory sencitial infection, pronounced catarrhal symptoms are observed, however, unlike bird flu, signs of abdominal syndrome do not develop under any circumstances. For adenovirus infection, inflammatory damage to the proximal parts of the respiratory tract is more typical, and with rhinovirus infection there is no intoxication syndrome at all.
Pathognomonic clinical markers of avian influenza in humans are: hectic type of febrile reaction, cough and progressive respiratory disorders, contact with a person sick with this pathology and an unfavorable epidemiological background.
In most situations, reliable verification of the diagnosis of “bird flu in humans” becomes possible only after obtaining the results of additional methods of examining the patient. The final diagnosis can be made after laboratory confirmation, which is based on such studies as: virological (isolation of a specific virus of the causative agent of the disease and obtaining a positive viral culture), serological (detection of an increase in the titer of specific anti-influenza antibodies in the serum of the person being examined), immunofluorescent (detection of a specific antigenic composition of the causative virus) and PCR diagnostics (detection of RNA virus particles).
As instrumental methods for visualizing the pathomorphological manifestations of avian influenza, radiation diagnostic methods are used in the form of standard radiography of the chest cavity and spiral computed tomography. Pathognomonic skialological criteria for avian influenza at the height of clinical symptoms is the visualization of many extensive inflammatory infiltrates, prone to rapid fusion and spread beyond the primary inflammatory structure with the addition of an inflammatory reaction of the pleura, which is a sign of severe interstitial pneumonia.
If the patient does not take the medicine for avian flu for a long time, the patient experiences progression of the disease and the appearance of respiratory complications in the form of acute respiratory distress syndrome. Diagnostic criteria for respiratory distress syndrome are the detection of total inflammation of the pulmonary parenchyma, an increase in shortness of breath and the appearance of signs of hypoxia. The fundamental analysis, based on the results of which the course of avian influenza complicated by respiratory distress syndrome is established, is the determination of the blood gas composition.
Among the nonspecific laboratory signs of avian influenza, which are also found in other infectious pathologies with similar symptoms, in most situations leukopenia, lymphocytopenia and thrombocytopenia are detected. Severe avian influenza, complicated by renal and hepatic failure, which is observed in the terminal stage of the disease, is diagnosed by a significant increase in creatinine levels in the blood, as well as the activity of ALT and AST.
Prevention measures
Nonspecific
If cases of avian influenza occur on farms, it is necessary to eliminate the entire bird population. At the same time, people destroying birds on an infected farm must work in respirators and special clothing.
In regions affected by the virus, quarantine is imposed on the export of eggs and birds.
It is necessary to disinfect rooms and places where sick birds were located.
Specific
Specific methods of prevention include the introduction of a vaccine. Developments are underway to produce an effective and safe bird flu vaccine that can be used in humans. Some countries are producing limited quantities of vaccine against variants of the virus that can lead to widespread avian influenza illness.
The insidious "Spanish flu" and the Hong Kong killer
The story of the “bird flu” once again testifies to the truth that if you don’t know something, this does not mean that this “something” does not exist.
All of us have repeatedly in our lives encountered a disease that doctors diagnose as influenza. And, as has now been established, most often the primary source of this disease in humans are the descendants of the same “bird flu” viruses that have undergone many years of evolution in the human population, more than once causing epidemics and pandemics.
The first historically recorded pandemic was the infamous “Spanish flu”, whose ancestor was the H1N1 bird flu virus and which caused the death of 20 to 50 million people worldwide. Many people died during the first days of the disease and many more as a result of complications caused by the flu.
1957-1958 “Asian flu”, which claimed about a million lives. First registered in February 1957, it “covered” half the world in just five months, reaching the American continent.
1968-1969 The latest pandemic is the “Hong Kong flu”, and again the death of about a million people around the world. The H3N2 virus serotype that caused it still circulates in the human population.
All of these pandemics had several common features. Thus, the first outbreaks of diseases occurred in Southeast Asia. The emergence of the H2N2 and H3N2 viruses was accompanied by the disappearance from the human population of the influenza viruses that had circulated before them (subtypes H1N1 and H2N2, respectively). The reason for the latter phenomenon remains unclear to this day.
Moving from history to modern times, let us return to the already mentioned outbreak of the disease in poultry in Hong Kong in 1997, which was accompanied by infection of people. The age of the patients ranged from 1 year to 60 years, all of them had high fever, gastrointestinal disorders, and hepatitis. The death of six patients occurred from primary viral pneumonia.
And these were just the “first signs”. Thus, from 2003 to the beginning of February 2006, according to WHO, about 170 cases of bird flu among humans were officially registered in the world with a mortality rate of more than 50%. The largest number of cases was recorded in Vietnam (93 people), the highest mortality rate was in Cambodia and Indonesia.
Causes and signs of the disease
The causative agent of bird flu is an RNA virus belonging to the type A strain. There are 15 subtypes, depending on the type of protein contained in the outer shell. The most dangerous species for humans are H5N1 and H7N7. They mutate quickly, the disease progresses at lightning speed and often ends in death.
The danger increases when the virus is combined with the causative agents of colds.
Bird flu can also be caused by H7N9, a subtype of virus with low pathogenicity. It more often affects people with health problems. A special feature of the pathogen is its high resistance in various conditions. It does not die in the cold, even when the temperature drops to -30 degrees Celsius. However, the virus cannot withstand boiling.
The disease spreads through birds, in which the virus lives in the digestive tract and is released into the environment through feces. Seasonal migration contributes to its wear over long distances. Main routes of infection:
- airborne;
- fecal-oral.
The virus enters the human body through contact with sick poultry or through consumption of insufficiently cooked meat. People working on farms and veterinarians are at risk. The disease is not transmitted from person to person.
Some symptoms suggest the presence of the disease in birds. They are lethargic, lay few eggs, and drink a lot of water. When examining them, you can notice changes in the eyes and mucous membranes, which become red and swollen. Fluid flows from the nose. Chickens develop diarrhea and their gait is impaired. In some cases, seizures may occur.
At the end of the disease, the birds' earrings and comb turn blue. During an autopsy, many hemorrhages in various organs can be found. Because the virus infects birds en masse, it is sometimes called chicken plague.
The incubation period is short and amounts to 48-72 hours. In rare cases, it can last up to 14 days. Its duration depends on the subtype of the virus. When infected with H5N1, symptoms appear after 5 days, and when infected with H5N7 after 7-8 days.
After this time, the stage of pronounced clinical signs begins, manifested by infectious-toxic, gastrointestinal and respiratory syndromes. The first symptoms occur acutely. A person’s temperature rises to 39-40 degrees, severe chills and headaches occur, muscles begin to ache and bones break.
Sometimes a runny nose appears, the mucous membrane of the eyes and throat becomes inflamed, and the gums begin to bleed.
Some people experience abdominal pain, vomiting and diarrhea already on the first day of illness. The fulminant course of avian influenza is characterized by the development of renal failure during the first 24 hours. It often causes death.
Respiratory symptoms appear 48-72 after the onset of the disease. A person's lungs become inflamed, which is manifested by a cough that produces clear sputum or blood. The patient experiences shortness of breath and rapid breathing. The skin and mucous membranes acquire a bluish tint. With rapid progression of the disease, acute respiratory distress syndrome develops.
The cause of death is pulmonary edema, acute respiratory or multiple organ failure. It is also possible that a bacterial component or fungal infection may be attached. The most severe course of the disease is observed in children. When the virus enters the brain through the blood, it causes meningoencephalitis. The child appears:
headache;- nausea;
- vomit;
- neurological symptoms;
- consciousness is impaired.
In case of recovery, a person develops short-term immunity and over time he can get sick again.
