Avian Influenza (Bird Flu)
Avian Influenza (Bird Flu, Chicken Plague, Bird Flu) is a highly contagious disease caused by type A of the influenza viruses observed as influenza viruses in humans, showing respiratory and digestive symptoms in most domestic and wild birds and mammals, resulting in death.
Influenza A viruses are classified according to hemagglutinin (H) and neurominidase (N) antigens. There are 15 subtypes of the influenza virus that causes disease in birds.
Avian influenza A virus, which infects poultry, is divided into two according to its ability to cause disease.
Those with high virulence lead to avian influenza with high pathogenicity, which can have a mortality rate of 100% in a flock. Birds can even die within the first day of symptoms. Those with low virulence cause a much milder disease. Viruses responsible for both tables are currently H5, H7 and H9 subtypes.
How Is It Transmitted?
Direct contact with the discharge of sick animals and especially feces; contact with food, water, supplies and clothing; Contact with water and seabirds that do not show clinical signs of disease may cause contamination. It is transmitted through respiration and contact, especially to dead or live infected birds and people exposed to the waste of birds.
Avian influenza viruses generally do not infect humans directly and do not circulate between humans. There are very few natural infections in humans that have been reported to occur with avian influenza viruses. Cases in humans are thought to have developed as a result of contact with infected poultry or contaminated surfaces.
Although it is stated by the World Health Organization that there is no human-to-human transmission, suspicious transmission cases have been reported among healthcare workers, poultry workers and family members in the literature. It is understood that some strains of Avian Influenza A (H5N1, H7N7 and H9N2 etc.) can be transmitted from person to person, albeit in a very limited way, in healthcare workers, family members, poultry farmers and those working in chicken disposal teams.
The disease can spread rapidly among farms within the country. They are transported from one place to another by infected vehicles, clothes and shoes.
The most important cause of epidemic is that wild migratory birds infect domestic birds directly or indirectly. Also, live bird markets are important in spreading the epidemic.
It can be transported from one country to another via international live poultry trade and migratory birds.
During the periods of infection, there is a risk of moving to settlements with vehicles and people entering and exiting wetlands. In risky periods, there is the possibility of the disease to be transported to settlements through hunting activities.
Another situation that creates a risk is the spread of the disease by uncontrolled vehicle and human movements from settlements where the disease has occurred.
The disease has been reported to cause outbreaks in Asian countries, including the Republic of South Korea, Vietnam, Thailand, Cambodia, Indonesia, but the World Health Organization does not restrict travel to these countries.
What are the Symptoms?
In patients;
- Cough with fever above 38 ° C
- Throat ache,
- Brokenness,
- Shortness of breath,
- One or more of diarrhea complaints can be seen together.
It is important to have a history of contact with poultry or a known or suspected avian influenza case in a country affected by H5N1 within 10 days prior to the onset of symptoms. Although the incubation period is 2-5 days on average, it has also been reported that the disease develops after 17 days.
The course of the disease:
The incubation period of avian influenza may be longer than the known human flu. In recent data, it is stated that the incubation period is two to five days, however this period may extend up to eight days. However, the upper limit has been reported as 17 days, possibly due to contact with unidentified infected animals or environmental sources.
The main clinical manifestations of avian influenza infection depend on the virus subtype causing the disease. Initial symptoms; Most patients have a high fever (typically higher than 38 ° C) and a flu-like illness with lower respiratory tract symptoms. Sore throat, cough and muscle pain may occur. Upper respiratory symptoms are rarely present. Conjunctivitis is rarely present in infection with avian influenza A / H5N1, unlike infection with H7 or H9 viruses. Diarrhea, vomiting, abdominal pain, pleuritic pain, nose and gum bleeding have been reported in some patients in the early period of the disease.
After the initial symptoms, lower respiratory tract symptoms usually develop and these findings are present at the patient’s visit to the physician. Respiratory distress, tachypnea, and inspiratory rales are common. Sputum production varies and can be bloody at times. Almost all patients have pneumonia clinically. Radiological changes are in the form of diffuse, multifocal patch infiltrations, interstitial infiltrations and segmental or lobular consolidation with air bronchograms. Pleural effusion is uncommon. It is emphasized that radiological findings related to lung damage in surviving patients may continue for a few months after the disease. Mechanical ventilator support may be required in severe cases. Progression of respiratory failure is associated with diffuse bilateral ground glass infiltration and ARDS symptoms. Signs of renal failure, sometimes with cardiac dilatation and supraventricular tachyarrhythmias, are common.
Although children are more susceptible to avian influenza disease, children have been among the cases detected so far. In addition, avian influenza is more severe in children.
Complications such as pneumonia (viral or secondary bacterial), COPD exacerbation, myocarditis, myositis, pericarditis, renal failure, respiratory failure, ventilator-associated pneumonia, pulmonary haemorrhage, pneumothorax, pancytopenia, Reye’s syndrome, and sepsis syndrome without documented bacteremia may develop. H5N1 has a more serious and lethal course compared to other avian influenza A strains.
How is it treated?
Antivirals (Neuraminidase inhibitors: oseltamivir and zanamivir) are used in the treatment of the disease. These medications should be started within the first 48 hours after symptoms start. Supportive care with oxygen and ventilator support forms the basis of treatment.
People with unprotected risky contact will receive prophylaxis. If there are unprotected contacts, prophylaxis is started in coordination with the infectious diseases specialist. Prophylaxis will be started by the Community Health Center where the contact is registered and will be followed up for 10 days.
Prophylaxis should be initiated as soon as possible, within the first 48 hours after initial contact with the confirmed or probable case. If this is not possible, prophylaxis can be started within 7 days after the last contact.
For chemoprophylaxis, oseltamivir should be given instead of standard influenza prophylaxis (1x75mg) at the therapeutic dose (2x75mg) for a short period of 5 days if the contact is not continuing, and for 10 days in intensive and continuous contacts.
Antivirals (Neuraminidase inhibitors: oseltamivir and zanamivir) are used in the treatment of pediatric patients as well as adult patients. These medications should be started within the first 48 hours after symptoms start. Supportive care with oxygen and ventilator support forms the basis of treatment.
