Ticks are important ectoparasites among the blood-feeding arthropods and serve as vectors of many deadly diseases of humans and animals. Of tick-transmitted pathogens, Babesia, an intracellular haemoprotozoan parasite causing a malaria-like disease called babesiosis, is gaining increasing interest due to its zoonotic significance. When vector ticks acquire the protozoa via blood-meals, the protozoa invade midgut and undergo several developmental stages prior to exiting through the salivary glands. The midguts of these ticks have diverse innate immune mechanisms and perform blood digestion critical for tick survival. A cysteine proteinase, longipain, was identified from the babesia parasite vector tick Haemaphysalis longicornis, and it shows potent parasiticidal activity. Longipain is localized in midgut epithelium, and its expression is induced by blood feeding. A series of experiments demonstrated that longipain-knockdown ticks, after feeding on a Babesia -infected dog, exhibited significantly increased numbers of parasites compared with controls. Longipain has been shown to interact on the surface of Babesia parasites in vitro and in vivo, and is thought to mediate direct killing of the parasites, suggesting that longipain may be a potential chemotherapeutic target against babesiosis and ticks themselves.
(Research Team for Zoonosis, TEL +81-29-838-7708)
Tsuji, N., et al. (2008) PLoS Pathog. 4: e1000062.