A deadly outbreak of psittacosis, also known as parrot fever, has affected several European countries, leading to the deaths of five people, the World Health Organization reported on Tuesday. The outbreak, which was first noted in 2023, has continued into the current year.

Parrot fever is caused by a bacterial infection in the Chlamydia family, commonly found in wild and pet birds as well as poultry. Infected birds may not show signs of illness but can shed the bacteria through breathing or excretion.

Humans typically contract parrot fever by inhaling dust from an infected bird’s secretions or through direct contact, such as bites or beak-to-mouth contact. The disease is not transmitted through consuming infected animals. While human-to-human transmission is possible, it is rare, with most recent cases linked to exposure to infected domesticated or wild birds.

The symptoms of parrot fever in humans usually appear five to 14 days after exposure and can include headache, muscle pain, dry cough, fever, and chills. The infection can be treated with antibiotics and is rarely fatal for humans.

Austria, which usually records two cases of the disease annually, reported 14 confirmed cases in 2023 and an additional four cases as of March 4 this year. The cases are unrelated, and none of the individuals reported traveling abroad or coming into contact with wild birds.

Denmark, on the other hand, typically sees 15 to 30 human cases per year, mainly stemming from exposure to pet birds or hobby birds like racing pigeons. However, the country has reported 23 confirmed cases in the current outbreak as of February 27, with 17 hospitalizations, 15 cases of pneumonia, and four deaths. Public health officials suspect the actual case count to be much higher.

In Germany, there were 14 confirmed cases of parrot fever in 2023 and an additional five cases this year, with almost all patients developing pneumonia and 16 requiring hospitalization. Five of the cases reported exposure to sick pet birds or chickens.