History and exam
Key diagnostic factors
common
presence of risk factors
Key risk factors include travel to or residence in areas endemic for babesiosis, exposure to Ixodes scapularis ticks, and immunosuppression or asplenia.
Other diagnostic factors
common
constitutional symptoms
Fatigue, fever, chills, myalgias, arthralgias, headache, anorexia, nausea, vomiting, and abdominal pain have all been reported with varying frequency during babesiosis infection.
Not all patients are symptomatic or febrile.
pyrexia
A sustained or intermittent fever may develop within 1 week of symptom onset.
One of the most common findings on physical examination.
uncommon
jaundice
May be found on physical examination.
hepatosplenomegaly
May be found on physical examination.
petechiae, splinter haemorrhages, or ecchymoses
Infrequently found on physical examination and indicate disseminated intravascular coagulation.
dark urine
Infrequently found on physical examination and may indicate haemolysis.
conjunctival injection
Occurs infrequently.
cough
Occurs infrequently.
sore throat
Occurs infrequently.
photophobia
Occurs infrequently.
Risk factors
strong
residence in or travel to an endemic region
The vast majority of cases occur in people who live in or have travelled to areas endemic for babesiosis in the US. Disease is spread through the bite of Ixodes ticks, which have a specific geographic distribution.
Endemic areas include coastal regions of the northeastern US and the northern midwest.[6][14]
Residents of endemic areas can have seroprevalence rates as high as 10%.[15]
exposure to Ixodes scapularis ticks
I scapularis deer ticks transmit Babesia microti, as well as Borrelia burgdorferi and Anaplasma phagocytophilum.
Risk of disease transmission increases with duration of tick attachment, so prompt removal of ticks may help prevent spread of disease.
Approximately one third of patients with evidence of babesiosis recall a preceding tick bite.[5] Thus, a history of preceding tick bite is helpful, but a history of no known preceding tick bite should not be used to rule out disease.
asplenia
People who have had surgical removal of their spleen or who have a non-functional spleen are at higher risk for clinical infections and severe or persistent disease.
Three of 9 (33%) patients who died after transfusion-related babesiosis, and 11 of 34 (32%) patients admitted to hospital with severe babesiosis, had previous splenectomy.[5][18] Another study found that 10 of 14 case patients (71%) with relapsing or persistent disease were asplenic.[29]
immunosuppression
Clinical infections are more common in patients with immunosuppression (either due to HIV or drug induced).
Immunosuppression also increases the risk of severe or persistent disease. Immunosuppressed patients are more likely to experience complications, with higher peak parasitaemia, higher number of babesiosis-related hospital admissions, and higher rates of fatalities.[29]
In one study of immunosuppressed patients, 57% had B-cell lymphoma and had received rituximab alone or with high-dose corticosteroids or further chemotherapy; 10 of the 14 patients were asplenic; and 1 patient had HIV infection and met the case definition for AIDS with a CD4+ cell count <200.[29]
Additionally, a case of severe disease in a patient receiving a tumour necrosis factor (TNF)-alpha inhibitor for rheumatoid arthritis has been reported.[30]
weak
blood transfusion
The risk of transmission through transfusion in endemic areas has been estimated to be 0.17% per unit of packed cells.[17] The US Food and Drug Administration recommends regional testing for Babesia in blood donor samples.[16] Over 70 cases of transfusion-associated disease transmission have been reported over the past 30 years in the US, most occurring in the past 10 years. Many of the donors and recipients were not residents of areas endemic for babesiosis, but donors had travelled to areas of endemicity in the weeks or months preceding donation.[18] Most donors are asymptomatic at the time of donation, and it is common for a single donor or donation to infect multiple patients.[19] This highlights the important impact of prolonged asymptomatic parasitaemia in many infected people.[20][21]
age >50 years
Although all age groups appear to be equally affected, clinical infections are more common in older patients. Most cases of severe disease also occur in those >50 years of age, although severe cases have also been reported in very young patients.
Lyme disease
Clinical infections are more common in patients with concurrent Lyme disease. This is transmitted through the bite of the deer tick (Ixodes scapularis), the same vector as for Babesia microti.
human granulocytic anaplasmosis
Clinical infections are more common in patients with concurrent human granulocytic anaplasmosis disease. This is transmitted through the bite of the deer tick (Ixodes scapularis), the same vector as for Babesia microti.
maternal infection during pregnancy
Congenital infection has been reported, with data suggesting that transplacental infection can occur.[22]
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