Babesiosis

What is babesiosis?

Babesiosis is a parasitic infection caused by protozoa of the genus Babesia. Various species of Babesia cause disease throughout the world. Most reported cases have occurred in the United States, with Babesia microti the main species responsible.

Babesia is transmitted by the bite of ixodid ticks. These ticks are the same vector responsible for the transmission of Lyme disease, and consequently, around 20% of patients with babesiosis are co-infected with Lyme disease. As well as the tick vector, Babesia requires a vertebrate reservoir, most commonly mice or cattle. The ticks are most often found in wooded or grassy areas. Tick transmission usually occurs between the months of May to October.

The prevalence of babesiosis is unknown because most patients are symptom-free. Surveys using serological testing to detect evidence of past infection, have shown around 10% of the population have been infected in highly endemic areas, such as Rhode Island. Other areas of the United States where tickborne transmission occurs include the Northeast and upper Midwest, especially in parts of New England, New York State, New Jersey, Wisconsin, and Minnesota.

While most cases of babesiosis are transmitted by ticks, cases of disease associated with blood transfusions have been reported.

What are the clinical features of babesiosis?

After a bite from an infected tick, Babesia cause lysis (rupture) of the host's red blood cells. Clinical features range from nil or mild symptoms to severe disease and death.

• In healthy individuals, babesiosis is usually symptom-free.
• Some people experience a flu-like illness, with 1-2 weeks of fatigue, malaise, fever, chills, and sweating. The incubation period following a tick bite is around 1-4 weeks.
• The disease is most severe in older patients, have impaired immunity, or who have no spleen. These patients can experience jaundice, congestive heart failure, renal failure, acute respiratory distress syndrome, disseminated intravascular coagulation, or death. Among patients with symptomatic infections, the mortality rate is 10% in the United States and 50% in Europe (mostly in patients with no spleen).

Skin manifestations of babesiosis

• Skin manifestations of babesiosis are rare and difficult to separate out from those of Lyme disease. Co-infection with Babesia may alter the skin manifestations of Lyme disease.
• No consistent skin manifestation of babesiosis has been found.
• Rash has been identified as the presenting symptom in around 12% of patients hospitalised with babesiosis.
• Petechiae (small red or purple spots due to bleeding into the skin) and bruises may occur, most likely due to thrombocytopenia (low platelets, which causes abnormal blood clotting).
• Jaundice has been reported, most likely due to lysis of red blood cells.

How is babesiosis diagnosed?

Consider a diagnosis of babesiosis in:

• Patients with suspected Lyme disease that is resistant to treatment.
• Patients who are elderly, have impaired immunity, or who are asplenic - with an undiagnosed febrile illness, who have been to endemic areas.

The definitive diagnosis of babesiosis can be made by:

• Microscopic examination of blood smears, using Wright or Giemsa stain. This will show the organisms inside the host's red blood cells. A false-negative result may occur in patients who are symptom-free.
• A polymerase chain reaction can detect Babesia genetic material and is useful when there are few circulating parasites (e.g. when symptoms first begin and during convalescence).
• Antibody testing with immunofluorescence.

What is the treatment of babesiosis?

• If the patient is otherwise healthy and symptom-free, no treatment is necessary.
• Patients who are older, have impaired immunity, or who are asplenic are treated with a combination of clindamycin and quinine; or atovaquone and azithromycin.
• In severe cases, whole-blood exchange transfusion (removal of infected blood and replacement by fresh donor blood) may be required to reduce the level of parasites circulating in the blood.

How can babesiosis be prevented?

• Those at risk of severe infection with babesiosis should avoid endemic areas between May and October.
• Long-sleeved clothing and pants should be worn when outdoors, to cover as much skin as possible.
• DEET insect repellent should be applied to skin and clothes.
• Ticks must remain attached for at least 24 hours to transmit Babesia. Therefore early removal of ticks from humans and pets should prevent transmission of disease. Careful daily checks for ticks are important as the tick may be as small as a poppy seed.