Etiology:

All Babesia spp. are intraerythrocytic protozoa, or "piroplasms." 

ado-Image3.jpg (29072 bytes) In order to understand babesiosis, it is helpful to understand the life cycle, which involves stages in the mammalian host as well as stages within the tick vector.

 

From GARDINER CH, FAYER R, and DUBEY JP, An Atlas of Protozoan Parasites in Animal Tissues.  Armed Forces Institute of Pathology, Washington, DC, 1998,  p. 71.

After inoculation by a tick vector, Babesia spp. enter the bloodstream and multiply asexually by schizogony in red blood cells (RBC's).  The babesia cause the RBC's to lyse, resulting in severe anemia and other effects due to circulating free hemoglobin.

Babesia bigemina is a "large" babesia which in blood smears typically appears as pear-shaped bodies joined at an acute angle within the red blood cell. bigeminablsmear.jpg (33170 bytes)
bloodsmear.jpg (24342 bytes) Babesia bovis is a "small" babesia usually seen as a single body or as small round bodies within the RBC's.   Occasionally, they pair at an obtuse angle.
Bovine babesiosis in this hemisphere is due principally to Babesia bovis or Babesia bigemina. 

The tick vector is esssential for maintaining the organism.  After ingestion of a blood meal, the organisms eventually infect eggs within the tick, multiply in the yolk, and continue to multiply in tissues of the larvae.  They settle in the cells of the salivary glands, preparing for inoculation of the next bovine host.

tickpic.jpg (14291 bytes) At the left are engorged female Boophilus ticks.  They have just been removed from a cow infected with Babesia.  
  • The Babesia move through the hemolymph and into the ovaries where they enter the eggs.
  • Within a day or two, these females will lay eggs.
  • The eggs hatch, with Babesia undergoing further development in the larvae.  Specifically, they migrate to the salivary glands to reproduce there.
  • The larvae will crawl up grass stalks, watiting to attach to a cow that walks by.
  • Then the tick will feed on the cow, dispensing Babesia from their salivary glands into the mammal's bloodstream.  

Specific tick species are responsible for propagation of the various species of Babesia (see table 1).

Boophilus ticks are "one-host" ticks.  That is, larvae, nymphs and adults are all found on only one type of host - large ruminants, primarily cattle.

Epidemiology

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