Pathology of acute fatal babesiosis in hamsters experimentally infected with the WA-1 strain of Babesia.

A strain of Babesia (strain WA-1), recently isolated from a human in Washington State, was found to be unusually virulent for hamsters; it caused acute infection and death in a large proportion of animals 5 to 7 days after inoculation. To assess the basic pathologic lesions associated with this infection, 30 male Syrian hamsters (Mesocricetus auratus) were inoculated intraperitoneally with the WA-1 strain. Twelve animals (40%) died within 5 to 6 days. The other 18 animals, all infected and clinically ill, were killed on the sixth or seventh day for biochemical study. All 12 animals that died from the infection showed high parasitemia, heavy intravascular hemolysis, and pronounced vascular stasis with red-cell sequestration in the spleen, liver, lungs, kidneys, and brain. Serologic study revealed severe anemia (mean hematocrit, 29) with hemolyzed serum and marked elevation of the serum transaminases. The mechanism of death was thought to be diffuse anoxic tissue damage secondary to vascular stasis, which led to multiorgan failure.