Babesiosis

Synonym: piroplasmosis, "The malaria of the North East"

Babesiosis is an uncommon but worldwide vector-borne malaria-like parasitic disease caused by protozoan parasites of the genus Babesia.^[1] Babesiosis is an infection of rodents, cattle, wild animals and man and is spread by the bites of ixodid (hard-bodied) ticks which are also the vectors for Lyme disease (25% of babesiosis patients have both diseases).^[2]

Babesial parasites reproduce in red blood cells, forming cross-shaped inclusions (rarely seen). There are over a hundred different Babesia species; human disease is usually caused by B. divergens in Europe and B. microti in the Northeast and Midwest United States. B. divergens infections tend to be more severe (frequently fatal) than those due to B. microti, where clinical recovery is usual. Patients who are immunosuppressed (including HIV-infected patients), splenectomised or elderly are most susceptible to babesial infection. B. microti infection can occur in non-splenectomised individuals and be transmitted by blood transfusion.

Epidemiology

• Babesiosis has some similarities to malaria, but much rarer.
• Seroprevalence estimated at 3-8%.^[3]
• Common in coastal areas in the northeastern United States, especially the offshore islands of New York and Massachusetts.^[2]
• Incidence and prevalence difficult to know as many cases of babesiosis are misdiagnosed as malaria where the latter is endogenous and many cases are self-limiting.^[3]

Presentation

• Is being increasingly recognised in patients who receive blood transfusion.^[3]
• The incubation period is typically 1 to 4 weeks, but may be longer.
• Severe symptoms occur in elderly, immunocompromised or asplenic.

Symptoms and signs

• Most cases are asymptomatic
• Those who are symptomatic may have anorexia, fever, fatigue, myalgia
• Examination may reveal jaundice, hepatosplenomegaly, haemolytic anaemia, haemoglobinuria and renal failure

Investigations and diagnosis

Babesial parasites invade the red cells directly, and multiply there - there is no exo-erythrocytic liver stage as required by human malarial parasites.

• Full blood count may reveal anaemia, thrombocytopenia, atypical lymphocytes and leucopenia.
• Diagnosis depends on microscopy of Giemsa-stained thin and thick films (the intracellular parasite resembles plasmodia). Several smears may be needed before diagnosis is apparent.
• ESR, bilirubin, LDH and transaminases may be elevated.
• Urine may be dark and urinalysis may show haemoglobinuria and proteinuria.^[2]
• Immunofluorescence antibody testing or PCR may confirm diagnosis when blood films are negative.
• ELISA IgM for Lyme disease may also be positive - it is important to treat both conditions where they co-exist.

Differential diagnosis

• Malaria
• Lyme disease
• Q-fever
• Tularaemia
• Other tick-borne infections

Treatment

• Supportive care is the only treatment required if the patient is young and otherwise healthy.
• Elderly, immunocompromised patients, and splenectomised patients should be treated with immediate intravenous clindamycin and oral quinine to avoid acute renal failure.^[2]
• Atovaquone with azithromycin is an alternative treatment used.^[4]
• Azithromycin alone or trimethoprim-sulfamethoxazole may be tried if the above regime is ineffective.^[2]
• Consider exchange transfusion in severe cases - to reduce the level of parasitaemia.^[5]

Complications

• Acute respiratory distress syndrome (ARDS)
• Pulmonary oedema - most frequent lung complication and rarely fatal^[6]
• Renal failure
• Multi-organ failure
• Coma

Prognosis

• Mortality rate estimated at 5%.^[3]
• Poor outcomes are associated with hospitalisation for more than 14 days, an intensive care unit stay more than 2 days, male sex and raised white cell count and alkaline phosphatase. However, this is based on a very small number of patients and thus must be interpreted cautiously.^[3]

Prevention

• No vaccine is available
• When outside wear a hat, long sleeves and long pants to cover legs
• Use insecticides to repel or kill ticks
• Check for and remove ticks using tweezers, eg between the fingers and toes (common areas)
• Use tweezers, and grab as closely to the skin as possible