Babesiosis is an infection caused by the protozoan Babesia spp. It is often asymptomatic in immunocompetent individuals or results in a malaria-like illness with a fever and haemolytic anaemia, but can be severe in splenectomised or immunosuppressed patients.
Epidemiology - Etiology
The disease is most prevalent in the United States, where 2,358 cases were reported in 2017. Sporadic cases have also been reported in Europe, Asia, Africa, Australia and South America.Babesiosis is caused by infection with Babesia: B. microti (endemic in North America), B. duncani, B. divergens (more common in Europe), and B. venatorum. Rodents are the main natural reservoir of the disease. Ticks become infected when they parasitise infected rodents, and babesiosis is most commonly transmitted to humans by the bite of an infected tick, Ixodes scapularis (in the United States) or Ixodes ricinus (in Europe), between early summer and late autumn. The parasite can also be transmitted to humans through blood transfusion or, rarely, through the placenta.When Babesia parasitises red blood cells, it takes a pear shape, hence the interest of blood smears examined under the light microscope for diagnosis.
Clinical manifestations
Most immunocompetent patients are asymptomatic or have mild to moderate disease. Signs usually begin one to four weeks after a bite from an infected tick, or one week to six months after a transfusion with infected blood. The most common symptoms are fever, sometimes high, malaise and fatigue. Other symptoms include chills, sweating, headache, myalgias, arthralgias, cough, nausea and weight loss.Symptoms usually last one to two weeks, except for fatigue, which may persist for several months.In immunocompromised, splenectomised or elderly individuals, the infection may be more severe and require hospitalisation. Complications include hepatosplenomegaly with jaundice, haemolytic anaemia, thrombocytopenia, and sometimes disseminated intravascular coagulopathy, acute respiratory distress syndrome, and even cardiac, hepatic, or renal failure, which may lead to death.
Diagnosis
The diagnosis of babesiosis should be made in patients with unexplained febrile illness, who reside in or have recently travelled to a Babesia-endemic area, or who have received a blood transfusion within the past six months.Confirmatory diagnosis is based on a blood PCR or the detection of the parasite on a blood smear stained with May Grünwald Giemsa: intra-erythrocytic parasites appear round, oval or pear-shaped, with blue cytoplasm and red chromatin.PCR is particularly useful in cases of low parasitaemia or diagnostic doubt. It allows Babesia to be differentiated from Plasmodium and the species to be identified (or at least to distinguish B. microti from B. divergens/venatorum according to the technique used). Monitoring parasitaemia by PCR is not indicated in asymptomatic immunocompetent patients.Serology uses an immunofluorescence technique. It can be used to suggest contact with the parasite, but is not useful in cases of suspected diagnosis, as antibodies may persist in the blood for a year or more after resolution of the infection, with or without treatment. If a patient is identified by a positive serological test, it is recommended that Babesia infection be confirmed by blood smear or PCR before treatment is considered.
Management and treatment
Treatment of uncomplicated babesiosis is based on atovaquone and azithromycin for seven to 10 days in immunocompetent patients (often prolonged in immunocompromised patients). The alternative is a combination of clindamycin and quinine.Prevention is based on the use of protective clothing and anti-tick repellents.The prognosis is excellent in immunocompetent patients but varies according to the patient’s condition.
The spectrum of tick-borne diseases is increasing with the advancement of knowledge. Lyme disease is the most common tick-borne disease in Europe; however, when faced with “atypical Lyme disease”, other tick-borne pathogens should be considered.
