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Babesia are protozoa transferred by a tick-vector and are acquired most frequently (though not exclusively) in the Americas.

Summary of simple forms

Babesia simple.jpg

The particular challenge of babesia is their resemblance to the trophozoites of malaria (most specifically P.falciparum). This is important since babesia may be a severe diease and treatment differs Click here for further information

  • The most common species in humans (Babesia microti) has the appearance of a “ring”
  • May involve fewer than 1% of erythrocytes or up to 80%
  • Rings resemble P. falciparum: small and fine with accolé forms and multiple parasites within a single cell

Distinguishing babesia trophozoites from malaria

  • Typically, size and form vary more significantly than in malaria
  • Pigment is not seen at any developmental stage
  • Extra-erythrocytic forms (single or clumped) are often present

Summary of complex forms

Babesia complex.jpg

Babesia is frequently associated with complex parasite forms within cells. These may include:

Extracellular forms

  • Single free parasites
  • Masses of parasites clumped together

Asexual forms

Asexual replication (similar to schizonts of malaria) with two division cycles forming up to four separate daughter parasites:

  • Tetrads of merozoites arranged in the form of a ‘Maltese Cross’ (characteristic but rare)
  • More often a complex of fine elongated or ring forms occurs within a single cell
  • These may be difficult to distinguish from cells infected by multiple parasites
  • In contrast to malaria, pigment is not seen

Sexual forms

  • Gametocytes remain intra-erythrocytic, becoming more solid and larger than typical rings, these forms are often infrequent.


click for gallery of forms