Psittacosis Outbreak Across the European Region


In early 2024, a significant uptick in cases of psittacosis, a respiratory infection transmitted from birds to humans, was reported across various countries in the European region. This alarming increase, especially pronounced from November to December 2023, triggered responses from national health authorities and the World Health Organization (WHO) to address the outbreak and mitigate further spread. This article delves into the situation, exploring the geographical distribution of the cases, the investigative measures undertaken, and the potential implications for public health.

Psittacosis: Understanding the Avian Disease and Its Implications

Psittacosis, also known as parrot fever or ornithosis, is a rare but potentially severe zoonotic disease caused by the bacterium Chlamydia psittaci. The name “psittacosis” is derived from the Greek word “psittakos,” meaning parrot. While parrots were initially thought to be the primary carriers, various species of birds, including pigeons, can transmit the infection to humans.

The history of psittacosis dates back to the early 20th century, with documented outbreaks occurring sporadically worldwide. One notable incident was the Manchester outbreak in 1929, where numerous cases were linked to pet shops and the handling of infected birds. Since then, public health measures have been implemented to control the spread of the disease, including regulations on the importation and sale of birds.

Psittacosis primarily affects individuals who come into close contact with infected birds or their droppings. Transmission typically occurs through inhalation of aerosolized particles containing the bacterium, although rare cases of transmission through bites or scratches have been reported. Symptoms of psittacosis can vary widely, ranging from mild flu-like symptoms to severe pneumonia. Diagnosis often relies on clinical presentation, laboratory tests, and serological assays.

Recent research has shed light on the genomic diversity of Chlamydia psittaci strains, highlighting the complexity of the pathogen and its potential for host adaptation. Studies have identified various genetic markers associated with virulence and antibiotic resistance, underscoring the importance of surveillance and molecular epidemiology in managing outbreaks.

The global prevalence of psittacosis remains challenging to determine due to underreporting and misdiagnosis. However, outbreaks continue to occur, particularly in occupational settings such as poultry farms, pet stores, and aviaries. Enhanced surveillance and awareness campaigns are essential for early detection and prevention of transmission.

Veterinary professionals play a crucial role in psittacosis control efforts through surveillance, diagnosis, and education. Proper hygiene practices, including handwashing and personal protective equipment, are essential when handling birds or cleaning aviaries. Avian veterinarians also advocate for regular health screenings and vaccinations to reduce the risk of infection in both birds and humans.

In addition to its impact on public health, psittacosis poses economic challenges for the poultry and pet industries. Outbreaks can result in significant losses due to bird mortality, trade restrictions, and public fear of avian products. Effective biosecurity measures and rapid response strategies are necessary to mitigate the spread of the disease and minimize its socio-economic consequences.

The One Health approach, which emphasizes the interconnectedness of human, animal, and environmental health, is instrumental in addressing emerging infectious diseases like psittacosis. Collaboration between public health agencies, veterinary professionals, researchers, and policymakers is essential for effective surveillance, outbreak response, and risk communication.

The Outbreak: A Regional Overview

In February 2024, Austria, Denmark, Germany, Sweden, and The Netherlands reported through the Early Warning and Response System (EWRS) of the European Union a noticeable increase in psittacosis cases observed throughout 2023 and into the beginning of 2024. This period, especially from November to December 2023, saw a worrying spike in infections, along with five fatalities attributed to the disease. The cases primarily involved exposure to wild and/or domestic birds, underlining the zoonotic nature of the infection caused by Chlamydophila psittaci (C. psittaci).

Country-Specific Insights


In Austria, 14 confirmed cases were reported across five of the nine federal states in 2023, a significant jump from the median of two cases per year over the previous eight years. By 4 March 2024, Austria had already seen four cases, with no reported travel abroad or specific mention of wild birds as the infection source. The steady diagnostic approach, utilizing reverse transcription polymerase chain reaction (RT-PCR), suggests the increase in cases is not due to changes in detection methods.


Denmark’s situation escalated from late 2023 to mid-January 2024, with 23 individuals testing positive for C. psittaci. The majority of these cases emerged from the North Denmark Region, Zealand Region, and the Capital Region, with a significant number requiring hospitalization. Epidemiological investigations link a portion of these cases to domestic birds, though wild birds, primarily via bird feeders, have been implicated in the majority. The Statens Serum Institute in Denmark is probing the role of wild birds further, suggesting a possibly higher than reported infection rate.


Germany reported an increase in psittacosis cases in December 2023, continuing into 2024. Unlike Austria and Denmark, there’s no reported geographical clustering, except for cases around Hannover. Notably, most cases had pneumonia, and a fraction reported exposure to domesticated birds, with no mention of wild birds as a potential source.


Sweden witnessed a marked rise in cases towards the end of 2023, with a notable number of cases reported in November and December. This surge represents a doubling of the cases compared to previous years for the same months. While the number of cases in early 2024 decreased, it still remains above the average. Most cases were linked to exposure to bird droppings, highlighting the disease’s transmission route.

The Netherlands

The Netherlands saw a doubling in psittacosis cases since late December 2023, with a geographic spread across the country and no identified common source of infection. The demographic affected primarily comprised older adults, with a significant proportion requiring hospitalization. The exposure varied between wild and domestic birds, with a notable portion of cases lacking direct contact with birds.

Response and Risk Assessment

The affected countries have embarked on epidemiological investigations to pinpoint potential exposures and case clusters. Additionally, the analysis of wild bird samples for avian influenza has been expanded to include checks for C. psittaci prevalence. The WHO, monitoring the situation closely, currently assesses the risk to public health as low, albeit with ongoing vigilance for any escalation.

Psittacosis Outbreak: Epidemiological Insights and Public Health Response

Chlamydophila psittaci, a bacterium responsible for psittacosis, has garnered attention due to its zoonotic potential, particularly affecting individuals working with birds or in close proximity to them. This bacterium is versatile, affecting a wide range of avian and mammalian species, although it primarily infects psittacine birds, finches, canaries, and pigeons. Psittacosis typically spreads through inhalation of contaminated particles from bird respiratory secretions, dried feces, or feather dust, highlighting its significance in occupational and domestic settings.

Symptoms of psittacosis in humans are generally mild, including fever, chills, headache, muscle aches, and dry cough, usually manifesting within 5 to 14 days post-exposure. However, timely antibiotic treatment is crucial to prevent complications such as pneumonia, with mortality rates remaining low with appropriate intervention.

In response to the emergence of psittacosis cases, affected countries have initiated rigorous epidemiological investigations and implemented national surveillance systems. These efforts aim to identify potential exposure sources and clusters of cases, facilitating targeted interventions and resource allocation.

The World Health Organization (WHO) has conducted risk assessments to evaluate the global implications of the outbreak. Notably, a surge in psittacosis cases has been observed in five countries within the WHO European region, with some cases progressing to severe pneumonia requiring hospitalization and, in rare instances, resulting in fatalities.

Sweden’s experience highlights the importance of diagnostic advancements, particularly the utilization of more sensitive polymerase chain reaction (PCR) panels, which may contribute to the observed increase in reported cases since 2017. However, distinguishing between genuine rises in cases and enhanced surveillance capabilities remains a challenge, warranting further investigation.

Despite concerns regarding international spread through avian carriers, current evidence suggests minimal human-to-human transmission of C. psittaci. Consequently, WHO assesses the overall risk posed by the outbreak as low, emphasizing the importance of accurate diagnosis and prompt antibiotic therapy in mitigating the spread and impact of psittacosis.

WHO Advice

WHO recommends the following measures for the prevention and control of psittacosis:

  • increasing the awareness of clinicians to test suspected cases of C. psittaci for diagnosis using RT-PCR.
  • increasing awareness among caged or domestic bird owners, especially psittacines, that the pathogen can be carried without apparent illness.
  • quarantining newly acquired birds. If any bird is sick, contact the veterinarian for an examination and treatment.
  • conducting surveillance of C. psittaci in wild birds, potentially including existing specimens collected for other reasons.
  • encouraging people with pet birds to keep cages clean, position cages so that droppings cannot spread among them and avoid over-crowded cages.
  • promoting good hygiene, including frequent hand washing, when handling birds, their faeces, and their environments.
  • standard infection-control practices and droplet transmission precautions should be implemented for hospitalized patients.

The psittacosis outbreak in the European region underscores the intricate relationship between human and animal health, especially in a world where interactions between wild and domestic birds and humans are frequent. The increase in cases across Austria, Denmark, Germany, Sweden, and The Netherlands highlights the need for enhanced surveillance, public awareness, and preventive measures to curb the spread of this zoonotic infection. As investigations continue, the insights gained will be crucial in formulating strategies to address current and future outbreaks, ensuring the health and safety of populations across Europe and beyond.


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