The mildly pathogenic strain of bird flu (avian influenza) primarily affects wild birds. Highly pathogenic strains can affect both wild birds and poultry. Infections in humans are rare but can be serious.
At a glance
- Bird flu is triggered by infection with certain influenza A viruses.
- In poultry and wild birds, it can lead to mass deaths.
- The virus is only transmitted to humans on rare occasions but can be fatal.
- Infections in humans can cause a high temperature and respiratory symptoms. Severe pneumonia may occur.
- Bird flu is primarily contracted by people who work in the poultry industry or come into contact with infected birds.
- Hygiene measures can prevent the transmission of the disease and are particularly important for people whose jobs bring them into close contact with poultry.
Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.
What is bird flu?
Bird flu is a viral infection that primarily affects birds. Specialists also refer to the disease as avian influenza. The pathogens are certain influenza A viruses, which can also be transmitted to humans in rare cases. Those affected tend to have close contact with poultry, for example due to working on poultry farms, breeding and fattening farms or in slaughterhouses.
There are two variants of bird flu that differ in terms of the level of disease they cause in poultry. Infections with one variant only cause mild symptoms. The other, highly pathogenic variant causes serious illness in poultry and many wild bird species coupled with mass deaths. As a result, this severe form is also known as fowl plague. Both virus variants can be transmitted to humans.
Influenza viruses affect several animal species, such as pigs and horses, and also cause seasonal flu in humans. Normally, transmission only occurs within one species. If a human contracts a flu virus from an animal, this is known as a zoonotic influenza. Bird flu viruses can cause very serious illness in humans.
Bird flu in humans is a notifiable disease: even suspected cases have to be reported to the public health authorities. The genetic information of influenza viruses is able to mutate and new variants can emerge that can sometimes trigger a worldwide influenza pandemic.
What are the symptoms of bird flu?
The outlook of bird flu can differ greatly: both asymptomatic and fatal forms exist. The initial symptoms generally appear 1 to 5 days after infection, but sometimes only 14 days later.
People who have been infected usually develop a high temperature and respiratory symptoms such as coughing and a shortness of breath. Nausea, vomiting and diarrhea are also possible. Other flu-like symptoms such as a sore throat, headache and achy limbs are rarer with bird flu than with seasonal flu.
Which pathogens cause bird flu?
Bird flu is caused by influenza A viruses, various subtypes of which are found in both animals and humans. Influenza viruses are classified based on two groups of proteins: hemagglutinin (H proteins) and neuraminidase (N proteins). Bird flu viruses that can currently be transmitted to humans largely fall into subtypes H5N1, H5N6, H7N9 and H9N2.
In nature, influenza A viruses are primarily found in wild waterfowl. As birds become infected via droppings, the viruses can also be transmitted to domestic poultry. Mildly pathogenic virus types spread rapidly without the birds developing clear symptoms of an infection. However, there are also highly pathogenic variants within the subtypes H5 and H7, which can lead to mass deaths in poultry farms and among some wild bird species.
Both virus variants can cause serious illness in humans, who primarily contract the disease through close contact with infected birds and their droppings – by inhaling virus-containing dust particles or through direct contact with the hands (smear infection). Most cases affect people outside Europe who work on poultry farms, in poultry markets or in slaughterhouses. Very few cases of human-to-human transmission have been recorded to date.
How common is bird flu?
To date, there have been no recorded cases of bird flu in humans in Germany. Despite this, repeated cases of highly pathogenic, subtype H5 influenza A viruses have been recorded in poultry and wild birds over the last five years. Accordingly, infection is also possible in Germany as wild birds can introduce the viruses at any time.
There is also an increased risk of contracting bird flu when coming into contact with poultry while traveling, especially in South East Asia, the Middle East and North Africa where there are regions in which bird flu is seen in humans more frequently. The main major outbreaks to date occurred from 2006 to 2014 (subtype H5N1) and from 2013 to 2018 (subtype H7N9). Around 850 people worldwide contracted the H5N1 subtype, 450 of whom consequently died. The subtype H7N9 caused over 1,500 cases of bird flu in humans by 2018 with at least 600 deaths.
As people with mild flu symptoms are not usually closely examined, the actual number of people who contracted bird flu may actually be higher than that recorded. The mortality figures refer to patients with severe symptoms who had to be treated in a hospital.
What is the outlook for bird flu?
A bird flu infection with the subtypes H5N1 and H7N9 may cause serious symptoms in humans. About half of the people who are hospitalized with the condition die. This is often as a result of multiple organ failure. In addition, the viral infection damages patients’ immune systems so much that bacteria can cause additional infections (superinfections) and further weaken the body.
People who survive bird flu often suffer from permanent lung damage. Long-term kidney damage is also possible.
How can bird flu be prevented?
To prevent bird flu, people should avoid direct contact with diseased birds (dead or alive). Anyone who finds a dead wild bird should report it to the responsible veterinary office and not touch it.
People who work with poultry should observe the applicable occupational health and safety measures and implement appropriate hygiene measures. Any suspected bird flu infection in poultry must be reported to the competent veterinary office without delay.
Birds are only vaccinated against bird flu in regions of the world where the condition is frequently seen throughout the year. To date, these have not included Germany and Europe.
Anyone planning a trip to South East Asia, the Middle East or North Africa can contact the Foreign Office (Auswärtiges Amt) to find out exactly where and in what situations there is a heightened risk of infection. Whether in high-risk areas or not, it is sensible:
- not to visit animal and poultry markets
- only to eat well-cooked poultry and eggs
- to thoroughly wash the hands with warm water and soap after preparing poultry
Important: Close contacts of people who have contracted bird flu or been in contact with infected poultry can take a flu drug containing the active substance oseltamivir for 7 to 10 days to prevent illness.
How is bird flu diagnosed?
A high temperature and respiratory symptoms are not definitive indications of flu or bird flu. To make a definitive diagnosis, evidence of the viruses is required. In the case of respiratory symptoms, a recent trip to high-risk areas or professional contact with poultry may indicate bird flu.
To diagnose the condition, a doctor takes a nasopharyngeal swab (a swab of the throat and nose). In practice, this material can be directly used to perform a rapid test. However, this will only provide evidence of a general infection with influenza viruses and is relatively insensitive. To determine the existence of bird flu, a PCR test in a laboratory is subsequently performed. This examines the sample material to see if it contains the pathogen’s genetic material.
How is bird flu treated?
Bird flu in humans can be a serious condition. It is therefore useful to prescribe medication that specifically combats the viruses. Treatment with antiviral medication such as oseltamivir or zanamivir should be initiated at an early stage, ideally within the first 48 hours of the suspected contact with the pathogen.
It also helps to take antipyretic (fever-reducing) painkillers and drink plenty of fluids. Patients who are hospitalized are often given fluid intravenously as an infusion.
If pneumonia develops, patients are given additional oxygen. Mechanical ventilation is sometimes necessary. Seriously ill patients must then be monitored in an intensive care unit.
Where can I find further information about bird flu?
The Federal Institute for Risk Assessment (BfR) provides information about recommended food hygiene measures and how consumers can protect themselves against bird flu.
- Auswärtiges Amt. Vogelgrippe – Aviäre Influenza. 05.2013. Aufgerufen am 19.01.2022.
- Robert Koch-Institut (RKI). Infektionskrankheiten A-Z. Influenza-Pandemieplanung. Antworten auf häufig gestellte Fragen. Stand 12.2016. Aufgerufen am 17.02.2022.
- Robert Koch-Institut (RKI). Infektionskrankheiten A-Z. Zoonotische Influenza. Antworten auf häufig gestellte Fragen. Stand 2018. Aufgerufen am 20.01.2022.
- Robert Koch-Institut (RKI). RKI-Ratgeber. Influenza (Teil 1): Erkrankungen durch saisonale Influenzaviren. Aufgerufen am 17.02.2022.
- Robert Koch-Institut (RKI). RKI-Ratgeber. Influenza (Teil 2): Erkrankungen durch zoonotische Influenzaviren. Aufgerufen am 20.01.2022.
- Robert Koch-Institut (RKI). Das RKI zu humanen Erkrankungen mit aviärer Influenza A (H7N9). 05.2018. Aufgerufen am 13.01.2022.
- Robert Koch-Institut (RKI). RKI zu humanen Erkrankungen mit aviärer Influenza (Vogelgrippe). 02.2021. Aufgerufen am 13.01.2022.
- Sendor AB, Weerasuriya D, Sapra A. Avian Influenza. [Updated September 18, 2021]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Aufgerufen am 20.01.2022.
Reviewed by the Society of Virology (Gesellschaft für Virologie e.V. – GfV).As at: