Babesia life cycle

Babesias are malaria-like protozoans that live and reproduce inside red blood cells and organs of the circulatory system of its vertebrate host where it reproduces asexually. It often exists in pairs and is sometimes referred to as bigemina.

Pair of Babesia canis merozoites in a red blood cell	Dog tick

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Most occur in wild and domestic mammals like opossums, deer, rodents, bats, cattle, sheep, or dogs. Intermediate hosts are ticks, often belonging to the deer tick of the genus Ixodes. Except for the Babesias of veterinary importance, vectors are largely unknown.

The disease which is transmitted by ticks, strongly resembles malaria: the Babesia parasites which belongs to the the phylum Apicomplexa to which also belong the Plasmodia and the Theileria, develop also inside erythrocytes.

Tick Vectors

Transmission of Babesia microti from one host to another generally takes place through direct tick-host contact. In the northeastern United States, the enzootic cycle is maintained principally by the interactions between immature blacklegged ticks and white-footed mice. In general, larvae acquire the infection when feeding on Babesia microti-infected mice. Engorged larvae overwinter and pass the parasites transstadially to the next developmental stage, the nymph, in the following spring. Nymphs infected in the larval stage pass the infection to susceptible animals upon feeding. In areas where Babesia microti is endemic, infection rates of nymphal ticks with the pathogen typically range from 5 to 40%.

Reservoir Hosts

Plasmodium (Malaria) and Babesia species are the most ubiquitous intraerythrocytic parasites that affect humans and animals. The infection occurs wherever certain hosts are parasitized by ticks. Babesia microti, in particular, has been recognized as the zoonotic agent infecting rodents in various regions of the world. This parasite has been detected in animals including the white-footed mouse, the meadow vole, the eastern chipmunk, the Norway rat, the cottontail rabbit, and the short-tailed shrew. However, the white-footed mouse appears to serve as the primary reservoir host for the infection. In areas endemic for Babesia microti, the infection rates in mouse populations can reach as high as 60%. Laboratory experiments also demonstrated that nearly all mice with the infection produce Babesia microti-infected ticks, suggesting that transmission of Babesia microti between mice and ticks can be intensive in endemic foci.

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