Clinical features

Clinical manifestations of babesiosis range from mild to fulminating illness resulting in death.

Patients have usually been in an endemic area between May and September. This is the time when the Ixodes tick is in its infectious nymph stage. Patients often do not recall being bitten by a tick. The incubation period is between 1-4 weeks

• prevalence of B. microti infection in nymphal I. scapularis ticks ranges from 1% in newly endemic areas to 20% in some well-established endemic areas (1)

It is usually asymptomatic in healthy individuals but in the elderly, immunocompromised or splenectomised patients infection may be severe. Infection can lead to haemolytic anaemia, thrombocytopenia, abnormal white cells and changes in red cell adhesion such that some patients can develop adult respiratory distress syndrome.

In moderate illness there may be a gradual onset of fatigue - this is accompanied by fever and one or more of the following: chills, sweats, anorexia, headache, myalgia, nausea, nonproductive cough and arthralgia

Patients may have a fever, rigors, be jaundiced, admit to muscle tenderness and have hepatosplenomegaly

• less common clinical features are mild pharyngeal erythema, jaundice, and retinopathy with splinter hemorrhages and retinal infarcts
• rash is rarely seen - if present should raise the possibility of concurrent Lyme disease

Severe disease:

• especially those who are older than 50 years, are immunocompromised, have comorbidities, or experience B. divergens infection
• complications include adult respiratory distress syndrome, pulmonary edema, DIC, heart failure, renal failure, coma, splenic rupture, or a prolonged relapsing course of illness despite standard antibiotic therapy

Notes:

• the incubation period may be 1 to 9 weeks (but up to 6 months) following transfusion of contaminated blood products

Reference:

• Diuk-Wasser M, Liu L, Steeves T, et al. Monitoring human babesiosis emergence through vector surveillance New England USA. Emerg Infect Dis. 2014;20:225-31