Bird flu, also known as avian influenza, is an infectious disease caused by influenza A viruses that primarily affects birds but can, in rare cases, be transmitted to mammals and humans. As of April 2025, the global situation remains dynamic, with a particular focus on the H5N1 subtype, which is currently circulating most frequently worldwide. This article examines the current situation based on established medical facts.
Distribution and Affected Species
Since 2021, the world has seen an unprecedented wave of H5N1 outbreaks affecting almost all continents, with the exception of Australia. Infections have been documented in Europe, North America, Asia, and increasingly in Antarctica. Wild birds, particularly waterfowl such as ducks and swans, are considered the natural reservoir for the virus. In Germany, the Friedrich Loeffler Institute (FLI) reported a calming of the situation in March 2025, after numerous outbreaks in poultry and wild birds were registered during the winter of 2024/2025. In Lower Saxony, for example, the last confirmed case was on February 23, 2025.
However, the situation in the USA remains tense. H5N1 has been rampant among dairy cows since April 2024, an unusual development as cattle were not previously considered susceptible. By March 2025, over 70 human infections had been confirmed there, mostly in individuals with direct contact with infected animals, as well as one death in December 2024 in Louisiana. Globally, the virus has also infected other mammals such as cats, foxes, seals, and even a sheep in Great Britain (March 2025).
Transmission and Pathogenicity
The virus is mainly transmitted through direct contact with infected birds, their droppings, saliva, or droplets. In dairy cows in the USA, transmission was found to occur primarily through contaminated milking equipment and milk, with high virus concentrations in the udder. Highly pathogenic subtypes like H5N1 cause mortality rates of up to 100% in poultry, while the course of the disease in mammals and humans varies. Low pathogenic variants (LPAI) may remain asymptomatic or cause mild symptoms.
Human Infections
According to the World Health Organization (WHO), over 2,600 human infections with avian influenza viruses have been registered worldwide since 2003, resulting in approximately 1,100 deaths. The majority are attributed to H5N1 and H7N9, although H7N9 has not occurred since 2019. In June 2024, the WHO reported the first human death from H5N2 in Mexico. In Germany, no human cases have been documented to date, as confirmed by the Robert Koch Institute (RKI). Most infections result from close contact with infected poultry, for example, on farms or at markets. Sustained human-to-human transmission has not yet been proven.
Symptoms in humans range from mild flu-like complaints (fever, cough) to severe cases with pneumonia and high lethality (up to 60% for H5N1). The incubation period is typically 1–5 days. In the US, many infections in 2024/2025 were mild, often only with conjunctivitis.
Risk assessment and measures
The WHO and ECDC currently assess the risk to the general population as low, as the virus is not efficiently transmitted between humans. In the US, the government invested approximately $306 million in January 2025 in surveillance and research. In Germany, avian influenza is a notifiable disease, and mandatory housing of poultry was imposed regionally, for example in Lower Saxony in the winter of 2024/2025. Finland has been offering H5N1 vaccinations to risk groups since 2024, while vaccines approved in Germany are primarily available for exposed professional groups.
Treatment
For human infections, antiviral drugs such as oseltamivir and zanamivir are used, which inhibit viral replication. Early treatment is crucial to prevent severe courses. In addition, symptomatic treatment is provided, for example for pneumonia.
Conclusion
The current situation of avian influenza shows a broad geographical distribution and an increasing diversity of affected hosts. While the risk to humans is currently limited, the virus's high adaptability requires growing vigilance. Continuous monitoring, biosecurity measures, and research remain central pillars for early detection and control of potential risks.
