Babesia microti

           The lifecycle of Babesia microti is fairly simple. It is epidemiologically found worldwide wherever ticks with that parasite can be found. There are about 99 species of Babesia so geographically they can be found all over. Various species of ticks are found over the world transmitting B. microti to different hosts. In the United Kingdom, Ixodes trianguliceps is the species of tick that transmits Babesia. Ixodes dammini for example is the tick found in the Northeast United States (Boustani et al., 1996). The lifecycle of I. dammini lasts approximately two years.

            The larval form of the definitive host, I. dammani is produced in the spring when the eggs hatch. The larva feed throughout August and September on a variety of hosts. These hosts contract the babesial infection from the larva. The most common host of Ixodes dammini is the white-footed mouse, Peromyscus leucopus (Boustani et al., 1996). P. leucopus is accounting for 90% of the vector host animals on Nantucket Island, where the first U.S. reported case of Babesia microti was reported is 1969 (Johnson et al., 2009). Other animals such as chipmunks, mice, rabbits, voles, and deer are also common hosts.

            When the Ixodes dammini takes a blood meal from any of its hosts it injects spoorozoites which undergo asexual reproduction and budding in the host. The humans enter the lifecycle by being bitten by an infected tick. Similarly to the animal hosts, when I. dammini takes a blood meal it injects spoorozoites into the human, also undergoing asexual reproduction and budding. Humans are usually the dead end hosts. Babesia microti can only be transmitted from human to human by contaminated blood transfusions (Johnson et al., 2009).

 Babesia is transmitted from the larval phase of the tick to the nymph phase of the tick. The disease acquired by humans is from the nymph phase, rarely the adult phase. The nymph stage is the size of a single poppy seed and is extremely difficult to see even when looking for. The adult phase is host specific usually to white-tailed deer, Odocoileus virginianus (Boustani et al., 1996). The tick lifecycle is complete after depositing the eggs and the death of the tick.

Literature Cited

Boustani, M.R., Gelfand, J.A. 1996. Babesiosis. Clinical Infectious Diseases. 22(4): 611-614

Johnson, S.T., Cable, R.G., Tonnetti, L., Spencer, B., Rios, J., Leiby, D.A. 2009. Seroprevalence of Babesia microti in blood donors from Babesia-endemic areas of the northeastern United States:2000 through 2007. Transfusion. 49(12): 2574-2582