Babesiosis is an infectious disease caused by Babesia protozoa, transmitted mainly by ticks. Causes mammalian infections and RBC lysis.

Epidemiology

• Primary reservoir = white footed mice or other small mammals. Primary vector = nymphial stage of Ixodes scapularis tick.
• Generally occurs in NE USA, upper Midwest (includes Ontario regions). Increasing incidence rate and a high population seroprevalance rate.

Transmission

• Ticks: May to September, Nymphial stage, feed on deer and small mammals
• Blood transfusion, organ transplantation, transplacental
• Coinfection with other tick-borne illnesses is common:
  • Lyme disease (1/2)
  • Anaplasma
  • Powassan virus
  • Erlichia muris-like agent

Risk Factors

• Endemic area, travel
• Blood transfusion
• Asplenia/hyposplenia, immunosuppression, HIV, malignancy, prematurity, increased age

Pathogenesis

• RBC hemolysis due to release of merozoites from RBCs and loss of cell membrane integrity
• CD4+ t cell function is integral to host immunity, and disease is more severe in HIV+ and in those on cellular immunity antagonists
• • severity depends on risk factors and parasitemia:
  • mild to moderate disease: immunocompetent, parasitemia <4%
  • severe disease: risk factors and parasitemia >4%

Clinical Presentation

• incubation period: 1-4 weeks from a tick bite; 3-7 weeks from blood products
• many patients are completely asymptomatic
• lymphadenopathy is classically ABSENT
• complications can be broad:
  • ARDS (most common)
  • severe anemia
  • renal failure
  • splenic infarct or rupture
  • warm AIHA

System	Manifestations
Hematologic	hemolytic anemia, thrombocytopenia
constitutional	fever, arthralgias
gastrointestinal	hepatosplenomegaly, transaminitis

Diagnosis

• clinical syndrome as above
• laboratory findings of hemolytic anemia, thrombocytopenia, mixed transaminitis
• epidemiologic exposure risk
• Babesia serology as a screening test
• thin blood smears (Maltese cross, trophozoites, parasitemia %)
• PCR for Babesia DNA

Treatment

Per the 2020 IDSA Guidelines:

1. B microti
   1. Azithromycin + atovaquone (first-line)
   2. Clindamycin + quinine (alternative)

2. B divergens

   1. Clindamycin + quinine

3. duration is 7-10 days. If immunocompromised and high risk of relapse, treat for at least 6 consecutive weeks and until at least 2 weeks of consecutive peripheral blood smears are negative.

4. consider exchange transfusion if parasitemia > 10% or for severe hemolysis or organ failure.
5. monitor with peripheral smears
6. Treat relapses with another repeat course of antibiotics (same course OK if tolerated).

References

1. Babesia microti acquired in Canada | CMAJ
2. Babesiosis: Clinical manifestations and diagnosis - UpToDate
3. Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA): 2020 Guideline on Diagnosis and Management of Babesiosis