Avian flu: Description
Bird flu is actually a general term used by experts to describe an animal disease caused by avian influenza viruses. It is also known as avian influenza or bird flu and usually affects chickens, turkeys and ducks, but also wild birds that introduce it into fattening farms.
Avian influenza is caused by influenza A viruses, of which there are various subgroups (subtypes). Some of these do not appear to spread to humans at all, while others can cause infection through very close contact with poultry. To date, around 1000 cases of bird flu in humans have been reported worldwide – most of them in Asia. Depending on the pathogen subtype, between 20 and 50 percent of those infected have died.
Subtypes of influenza A viruses
Some of these bird flu subtypes can cause severe illness in the affected birds (e.g. H5N1). They are described as highly pathogenic. Other subtypes cause only mild symptoms or no symptoms at all in the infected animals and are therefore low pathogenic (e.g. H7N7). Subtypes that can also infect humans are called human pathogenic.
Avian influenza: symptoms
Bird flu viruses mainly affect the respiratory tract. Therefore, the symptoms, which usually occur suddenly, are generally flu-like:
- high fever
- cough
- shortness of breath
- sore throat
In around half of cases, patients also complain of gastrointestinal complaints. These include
- diarrhea
- abdominal pain
- nausea, vomiting
Avian flu: causes and risk factors
Avian flu can occur in humans if the pathogens, which otherwise only affect poultry, are transmitted to humans. This usually requires very close contact with the animals, as the bird flu pathogens are not actually well adapted to the conditions in the human organism. In many cases, it is known that sick people lived closely with their farm animals.
During an infection, the viruses mainly attach themselves to cells in the uppermost cell layer that lines the respiratory tract (epithelium). Humans and birds have different epithelia, which is why not every contact with the virus leads to disease in humans. The virus subtypes H7N9 and H5N1 in particular have been transmitted to humans in the past. It cannot be ruled out that the virus may be transmitted from person to person in individual cases.
Avian influenza virus H5N1
The major bird flu epidemic that began in Korea in mid-December 2003 was triggered by the H5N1 subgroup.
Avian influenza virus H7N9
In 2013, the first human cases of a new subtype of bird flu – H7N9 – were reported in China. There are more than 1,500 confirmed cases, of which at least 600 have died (as of 24.02.2021). The average age of onset was 58 years, and more men than women contracted this form of bird flu.
Other subtypes
Individual cases are known in which people fell ill with the bird flu subtypes H5N6, H7N2 and H3N2. Some of those affected died.
In February 2021, it was reported that seven workers at a poultry farm in Russia had contracted the highly pathogenic type A (H5N8) in 2020. The disease was mild and there was no human-to-human transmission.
Risk of illness in Germany
- People who work in the poultry farming or meat processing industry
- Veterinarians and employees of specialized laboratories
- People who handle dead wild birds
- People who eat poultry that has not been cooked properly
- Older people, the chronically ill and pregnant women (they are also more susceptible to “normal” flu)
Avian flu: tests and diagnosis
To make a diagnosis of bird flu, your doctor will first ask you about your medical history. He will ask you the following questions, among others:
- Have you been on vacation recently?
- Have you handled wild birds?
- Have you come into contact with raw poultry meat?
- When did you start feeling ill?
- Did the symptoms come on suddenly?
- Do you suffer from shortness of breath?
This is followed by a physical examination. Among other things, the doctor will listen to your lungs, take your temperature and look at your throat.
Avian flu: Treatment
If bird flu is suspected, the first step is to isolate the patient to prevent possible transmission to other people and thus the spread of the disease. Antiviral drugs (neuraminidase inhibitors such as zanamivir or oseltamivir) can prevent the viruses from spreading in the body. However, they are only effective if they are given within a short time of infection.
If the infection has been present for some time, bird flu can only be treated symptomatically – i.e. with the aim of alleviating the symptoms. The cause itself – the bird flu virus – can then no longer be treated directly. Symptomatic treatment of bird flu includes
- Adequate fluid and salt intake
- oxygen supply
- antipyretic measures (for example by administering paracetamol or calf compresses)
Children should not be given acetylsalicylic acid (ASA) for fever. Otherwise a life-threatening illness, Reye’s syndrome, could develop in connection with the bird flu virus.
Avian flu: course of the disease and prognosis
The time between infection with the bird flu virus and the outbreak of the disease (incubation period) is two to five days on average. However, it can also take up to 14 days. As mentioned above, flu-like symptoms are typical of bird flu. Pneumonia is often a complication – severe shortness of breath, which occurs on average six days after the start of the illness, is a sign of this. Pneumonia can be so severe that those affected die of respiratory failure. This is observed in over half of patients.
Bird flu cases in the 1990s were more likely to kill older people, while many children died from the cases in 2013.
Avian flu: prevention
It is still very unlikely that humans will become infected with bird flu. However, as with other animal diseases that can be transmitted to humans, contact with the pathogen should be avoided wherever possible. Therefore the following tips:
- Fry or boil poultry and eggs – the virus dies quickly when exposed to heat. However, it survives at low temperatures in the freezer.
- Wash your hands after handling raw poultry meat (e.g. when cooking)
- Do not touch live birds – or any surfaces that the animals have been in contact with – in countries where acute bird flu outbreaks are known.
Obligation to report
It is not only a proven case of bird flu in humans or a death from bird flu that must be reported to the responsible health authority by the doctor treating the patient – even a suspected case of bird flu must be reported. In this way, disease control measures can be initiated in good time and the spread of the disease prevented.
If an animal on a poultry farm falls ill with bird flu, the entire bird population is usually killed as a precautionary measure.
