Human babesiosis is a rare zoonosis in Europe caused by protozoa of the genus Babesia, transmitted to humans mainly by ticks of the genus Ixodes. The infection mainly affects individuals who have undergone splenectomy, are immunocompromised, or are elderly, which correspond to the risk factors for the disease. The infection is often underdiagnosed due to its rarity and its often nonspecific clinical presentation (asthenia, fever, flu-like syndrome).

In these high-risk patients in particular, the infection can progress to severe forms, with a mortality rate of up to 20-40%. The clinical picture is then that of a severe infection with multiple organ failure: multifactorial renal failure, respiratory distress due to lesion edema, and disseminated intravascular coagulation. One of the main obstacles to understanding human babesiosis in France and Europe is the low number of cases recorded and published. This situation limits knowledge about the epidemiology of the disease, its clinical presentations, its potential severity, and the effectiveness of the treatments used.

The aim of this study is to describe the epidemiological, clinical, biological, therapeutic, and prognostic characteristics of human babesiosis cases diagnosed in metropolitan France.

Inclusion Criteria:

• Adult subjects (≥18 years old)
• With a diagnosis of babesiosis confirmed by blood smear or PCR
• Treated in associated centers during the period from January 1, 2000, to December 31, 2024

Exclusion Criteria:

- Refusal to participate in the study

Adult subjects with a diagnosis of babesiosis confirmed by blood smear or PCR