Avian influenza - Causes, symptoms and treatment. MF.

Avian influenza is a viral infection of birds with high infectiousness, which can occur among them both asymptomatically and cause death. In recent years, one of the strains of avian influenza has become pathogenic for humans. The carriers of the infection are mostly wild birds( waterfowl - geese, ducks), which practically do not fall ill, but they have the ability to migrate from place to place and thereby carry the virus over long distances. Domestic species of birds, susceptible to infection with the avian influenza virus, are chickens, turkeys.

About bird flu for the first time it became known in 1997, when the outbreak of the disease among people was recorded in Hong Kong with a fatal outcome of up to 60%.Further, the H5N1 virus spread from Asia to Europe and Africa. In Russia, avian influenza A( H5N1) in birds in previous years was recorded in the Novosibirsk, Kurgan, Chelyabinsk, Tambov, Tula oblasts and in the Altai. Several years ago, from a dangerous disease, more than 200 swans died in the Astrakhan region. Previously, avian influenza circulated periodically in Western Europe. In 2003, the Netherlands registered an outbreak of avian influenza A( H7N7), during which 89 people fell ill, one with a fatal outcome from a pulmonary complication.

The epidemiological situation in 2013: In April 2013, an outbreak of avian influenza A( H7N9) was registered in China, which affected about 130 people( 32 people died).According to WHO in August-September 2013, cases of avian influenza have been registered among poultry in Italian farms, which have identified a highly pathogenic strain of H7N7.Several hundred thousand birds are slaughtered because of an outbreak of avian flu. This strain of the virus with a certain mutation may well become pathogenic for humans. Also at this time, a case of bird flu from one farm employee was recorded. In this regard, the Chief State Sanitary Doctor G.G.Onishchenko instructed epidemiologists to inform the population about this epidemic situation, and medical workers to be more attentive to patients with ARVI from Italy. Recently, a highly pathogenic strain of the influenza A( H7N9) virus has appeared in China.

Causes of avian influenza

The bird flu virus belongs to the family Ortomyxoviridae, to influenza viruses type A. The structure of the virus is complex. It is an RNA-containing virus, two proteins are known in the outer shell - hemagglutinin( the function of attachment of the virus to the target cell of the host, as well as the production of antibodies, including protective ones, that is, the development of immunity) and neuraminidase( the function of penetration of the virus into the target celland multiplication of the virus within the cell).To date, several subtypes of hemagglutinin and neuraminidase have been studied, thereby distinguishing different antigenic types of the avian influenza virus. Antigenic type H7N7 is able to cause the so-called "chicken plague", and H5N1 - the total death of chickens. These two types are highly pathogenic for poultry( 100% bird mortality within 48 hours).There are also low pathogenic strains( birds either carry the infection, or carry it in mild form).

Bird flu virus

What is the pathogenicity of the avian influenza virus for humans? Previous 10-12 years showed that the viruses H5N1 and H7N7 mutate rapidly, which significantly affected their properties. Now they easily go beyond the bird population, passing through the pig's body and spread among people who are increasingly diagnosed with severe forms of infection, as well as lightning with lethal outcome.

Source of infection - wild waterfowl( ducks, geese) and poultry( chickens, turkeys).The virus is in the intestine and is excreted with feces.

Poultry mortality from avian influenza

Infection mechanism - aerogenic( path - airborne).Most cases of avian influenza in humans are associated with actual contact with a sick bird( live or dead).Human-to-human transmission of the virus was not recorded.

Symptoms of avian influenza in humans

The duration of the incubation period( from the moment of infection before the onset of symptoms) for influenza A( H5N1) is usually 2-3 days, but it can vary from 1 to 8 days, and in rare cases up to 2 weeks.

Symptoms of the disease can be combined in several clinical syndromes:
1) infectious-toxic;2) respiratory;3) gastrointestinal.

The onset of avian influenza is always acute, which is due to its high pathogenicity for humans. There is a tremendous chill, a discharge from the nose, a sore throat, muscle aches. Often, patients are disturbed by stool dysfunction up to watery, often repeated vomiting. The most constant symptom is an increase in body temperature to 38-40º, and from the first day of illness it is immediately high. After 2-3 days, respiratory syndrome occurs: often the primary viral pneumonia develops( the patient has a pronounced cough with transparent sputum, sometimes with a trace of blood, and shortness of breath quickly joins).When listening - hard breathing and wet rattles.

When carrying out the X-ray of the of the chest, already at the onset of the disease, there are multiple, sometimes extensive, inflammatory infiltrates, the feature of which is in rapid fusion and spread beyond the primary inflammation focus;sometimes fractional compaction.

Further development of the disease leads to the development of complications: respiratory failure and acute respiratory distress syndrome( ARDS).ARDS is accompanied by a pronounced total inflammation of the lung tissue, gross violations of breathing, oxygen deficiency and the development of pulmonary edema. Often the development of such a complication is fatal to the patient.

Respiratory distress syndrome

In the peripheral blood of patients, a decrease in leukocytes( <2.10 × 109 / L), a decrease in lymphocytes and platelets is determined.

Manifestations of avian influenza can be a violation of liver and kidney function, more than a third of patients develop acute renal failure. In the blood, the level of ALT, AST, and also creatinine rises.

Young children ( up to 3 years old) are very ill. Often, the virus overcomes the blood-brain barrier and develops encephalitis( inflammation of the brain substance).To the existing complaints is added a pronounced headache with vomiting, possible violation of consciousness.

Risk factors for severe development: later seeking medical help, initially low blood leukocyte count( immunodeficiency), the presence of concomitant diseases.

The forecast is generally unfavorable. The lethality reaches 50-60%.Lethal outcome is usually observed in the second week of illness.

Immunity after the transferred infection type-specific, short-term. It is possible to re-infection in another season.

Diagnosis of Avian Influenza

Because of the similarity of the symptoms of avian influenza A( H5N1) with symptoms of ordinary flu, it is difficult to put a correct diagnosis at the beginning of the disease. Helps report on outbreaks of influenza A( H5N1) or poultry death in patients' homes;contact with a patient confirmed to be infected with influenza A( H5N1) virus, as well as unknown ARVI 7 days before the appearance of the first clinical signs;arrival from a country where outbreaks of avian influenza in poultry are recorded;and also professional infection - veterinarians, workers of poultry farms.

Symptoms for suspected avian influenza:

1. Heat, cough and difficulty breathing from the first days of illness;
2. Stool disorder( in the absence of mucus and blood in the feces);
3. Rapid increase in the severity of symptoms.
The final confirmation of avian influenza A( H5N1) can occur by the following methods:
- by immunological methods( immunofluorescence analysis for H5-antigen using H5-monoclonal antibodies or determination of specific H5 antibodies in the patient's paired sera),
- molecular genetic( PCRon A / H5) methods,
- virological methods - virus isolation( positive viral culture on A / H5).

Treatment of avian influenza

1) Regimens: all patients with suspected bird flu are hospitalized in a hospital. The extract is carried out only after the temperature is normalized within 7 days.
2) Specific treatment includes broad-spectrum antiviral drugs:
oseltamivir or Tamiflu, zanamivir or relenza, arbidol, algirem.
3) Symptomatic treatment: with a high temperature reaction, antipyretic drugs( paracetamol, nise, ibuprofen) are used. They have an intensifying effect of antiviral therapy.

Drugs not used in the treatment of influenza A( H5N1): salicylates( aspirin), analgin. Analgin and antigrippins are strictly contraindicated for the treatment of avian influenza.

Antibiotics are prescribed only if there is a suspicion of a mixed pattern of pneumonia( i.e., viral-bacterial).With severe inflammation of the lungs with the threat of complications, hormonal preparations are prescribed.

Preventative treatment or emergency prophylaxis. As a means of emergency prevention, the drug Amiksin, Cycloferon and other inducers of interferon is recommended. The effectiveness of interferon inducers is higher the earlier they are administered. They are recommended for risk groups and medical personnel in infectious hospitals for the care and treatment of patients with influenza pneumonia.

Avian Influenza Prevention

WHO recommends the vaccination of a routine influenza vaccine in avian influenza-endemic areas. This is done so that two pathogenic strains of the influenza A virus do not get to one person, which, of course, will cause a lightning-fast flow of avian flu.

The groups at risk for vaccination are:

1. Contact persons with poultry or poultry farms suspected of being infected with avian influenza( H5N1).
2. Health workers working with influenza H5N1.

A specific vaccine against avian influenza has not yet been received for widespread use among the general population.
Chemoprophylaxis of avian influenza is carried out by the appointment of inducers of interferon( cycloferon and amixin), algism, remantadine, arbidol and oseltamivir( Tamiflu) as antiviral drugs. All contacts in the outbreak of avian influenza, as well as farm workers, are subject to prevention.
Currently, the main concern is the possibility of transmission of the virus from person to person. This will lead to the development of a severe and extensive pandemic of avian influenza, exciting in scale for many countries and continents.

The doctor infektsionist Bykova N.I.