[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/) › Babesia spp.

[Microbiology](https://durgical.com/en/microbiology/) · [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/)

# Babesia spp.

- Parasite
- For completeness

A red-cell parasite spread by ticks. It mimics malaria and is severe in people without a spleen or with weak immunity.

Updated 2026-11-01

Also called: Babesia microti, Babesia divergens

## Key points

- Ixodes tick; white-footed mouse; northeastern United States.
- Maltese-cross tetrads and pigment-free rings: separate it from P. falciparum.
- Severe in asplenia, the elderly and the immunocompromised.
- Atovaquone plus azithromycin.

## At a glance

**Shape**
Small rings, pear shapes and Maltese-cross tetrads

**Family**
Babesiidae

**Type**
Intraerythrocytic apicomplexan protozoan (piroplasm)

**Stain**
Giemsa on thick and thin films

**Size**
Small intraerythrocytic forms

## Morphology

- Small rings, sometimes several per cell, resembling P. falciparum.
- Tetrads (four parasites in a Maltese cross), highly characteristic.
- No malaria pigment and no gametocytes in the blood.
- Extracellular forms may be seen.

## Transmission

- Bite of Ixodes ticks (in the United States, I. scapularis; in Europe, I. ricinus).
- Transfusion of blood from infected donors.
- Rarely transplacental.

**Reservoir:** White-footed mouse (B. microti); Cattle (B. divergens)

**Vector:** Ticks of the genus Ixodes, the same ones that transmit Lyme disease.

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- An infected tick injects sporozoites while feeding.
- Sporozoites invade red cells directly; there is no liver stage.
- Inside the red cell they divide by budding, forming rings and tetrads.
- Rupture of the cell releases merozoites that infect other red cells.
- A tick takes up parasites from an infected rodent; the sexual phase occurs in the tick.
- Humans are accidental hosts with no role in the natural cycle.

## Virulence factors

- Invasion and lysis of red cells: hemolytic anemia.
- The spleen is key for clearance; asplenia allows high parasitemia.
- Systemic inflammation with risk of multi-organ failure.

## Diseases it causes

- Babesiosis: fever and hemolytic anemia, mild to severe, potentially fatal in people without a spleen, the elderly or the immunocompromised. [Babesiosis →](https://durgical.com/en/conditions/babesiosis/)

## Clinical picture

- Many cases are silent.
- Fever, chills, sweats, myalgia and fatigue one to several weeks after the bite.
- Hemolytic anemia, jaundice, dark urine and low platelets.
- Severe forms: respiratory distress, kidney failure, disseminated intravascular coagulation.

## Diagnosis

- Giemsa blood smear: rings without pigment and tetrads.
- PCR to confirm, identify the species and detect low parasitemia.
- Serology (immunofluorescence) as support.
- Checking for coinfection with other Ixodes-borne infections.

## Treatment

Atovaquone plus azithromycin in most cases; in severe disease clindamycin with quinine and exchange transfusion have been used in specialized centers.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)

## Prevention

- Avoiding tick bites: long clothing, repellents and skin checks after time in the woods.
- Prompt removal of attached ticks.
- Blood-donor screening in endemic areas.

**Vaccine:** There is no human vaccine.

## In Colombia

Human babesiosis is exceptional in Colombia; Babesia is better known in the country as a parasite of cattle and dogs. In humans it matters mostly for USMLE and in travelers.

## Memory aid

«Babesia draws a cross in the red cell»: the Maltese cross of four parasites, no pigment; dangerous for anyone who has lost their spleen.

## Test yourself

Think of the answer, then tap the question to see it.

## Which smear form is typical of Babesia?

The tetrad or Maltese cross: four parasites joined inside one red cell.

## Which patients are at highest risk of severe babesiosis?

People without a spleen, the elderly and the immunocompromised, for example with HIV or on rituximab.

## Which vector transmits Babesia microti?

The Ixodes scapularis tick, which also transmits Lyme disease.

## Which findings help separate Babesia from Plasmodium falciparum on the smear?

Babesia makes no pigment or gametocytes and can form tetrads; a history of ticks or transfusion also helps.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/babesia-spp/)

## Related

- [Plasmodium falciparum](https://durgical.com/en/microbiology/plasmodium-falciparum/)

## Related conditions

- [Babesiosis](https://durgical.com/en/conditions/babesiosis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Babesiosis](https://www.cdc.gov/dpdx/babesiosis/index.html) (CDC (DPDx), 2024); [Clinical Overview of Babesiosis | Babesiosis | CDC](https://www.cdc.gov/babesiosis/hcp/clinical-overview/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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