- The peripheral-blood smear shows numerous intracellular organisms in red blood cells.
- Multiple ring forms are seen, as well as rare tetrads (thin arrow).
- These so-called Maltese cross formations are essentially pathognomonic of babesiosis.
- The dark, round body in the right lower quadrant of the red blood cell with the tetrad is a Howell–Jolly body (thick arrow), an erythrocyte inclusion representing an incompletely extruded nucleus.
- Howell–Jolly bodies are seen in patients with functional asplenia, and such patients are particularly susceptible to serious babesial and encapsulated bacterial infections.
Babesiosis is a worldwide tick-borne hemolytic disease that is caused by intraerythrocytic protozoan parasites of the genus Babesia.
The organisms are intraerythrocytic ring forms closely resembling Plasmodium, the organism causing malaria.
Three distinguishing features differentiate the two organisms.
- Babesial organisms usually form tetrads ("Maltese cross"),
- Do not have hemozoin pigments within the affected red blood cells and
- Have extracellular merozoites.
- Atovaquone suspension (Mepron; 750 mg twice daily) plus azithromycin (Zithromax; 500 to 1,000 mg per day) is a very effective treatment.