Evaluation of novel and effective chemotherapeutic agents for bovine and equine piroplasmosis is urgently needed because of the toxic side effects of currently available drugs. Heat shock protein 90 (Hsp90) becomes a promising drug target due to its important roles in protecting the cells. In this study, we report the in vitro inhibitory effect of gedunin, an Hsp90 inhibitor, on the growth of Babesia bovis, B. bigemina, B. caballiM, and Theileria equi. The IC₅₀ values of gedunin for four parasites were 21.72 µM, 15.25 µM, 22.1 µM, and 33.21 µM, respectively. Severe morphological changes, such as pyknotic and degenerative change, were also observed in the parasites treated with gedunin. Although further experiments are required to evaluate the in vivo activity of gedunin against Babesia and Theileria parasites, the present study indicated that Hsp90 could be a drug target in bovine and equine piroplasms.

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Previously, we have identified a gene encoding thrombospondin-related anonymous protein of Babesia gibsoni (BgTRAP), and have shown that the antisera raised against recombinant BgTRAP expressed in Escherichia coli inhibited the growth of parasites. In the present study, a recombinant vaccinia virus expressing the BgTRAP (VV/BgTRAP) was constructed. A specific band corresponding to a molecular mass of 80 kDa, which was similar to that of native BgTRAP on the merozoites of B. gibsoni, was detected in the supernatant of VV/BgTRAP-infected RK13 cells. Moreover, mice inoculated with VV/BgTRAP produced antibody that specifically reacted with the native BgTRAP on parasites. These results indicated that the recombinant vaccinia virus expressing BgTRAP might be a vaccine candidate against canine B. gibsoni infection.

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The study aimed to show endocytosis and hemoglobin uptake in Trypanosoma congolense. All the different developmental stages of T. congolense, IL3000 strain were cultured with dextran Alexa Fluor® 568 10,000 MW, dextran fluorescein 70,000 MW and hemoglobin labeled with Alexa Fluor® 488. The trypanosomes were also incubated in Hoechst® 33342 and observed by confocal laser scanning microscopy. The results showed that non-specific endocytosis was up-regulated in metacyclic form (MCF) and bloodstream form (BSF) whereas receptor-mediated hemoglobin endocytosis was highly activated only in the insect stage epimastigote form (EMF). This might indicate that the rapid uptake of surface-bound molecules in MCF and BSF may be important in the survival of the trypanosomes in the mammalian host. However, there was no observed non-specific endocytosis in the two insect stages procyclic form (PCF) and EMF, which might suggest that these stages totally depend on receptor-mediated endocytosis. Furthermore, the results showed uptake of hemoglobin in EMF but not in other stages. This might explain as to why a haptoglobinhemoglobin receptor (TcHpHbR) has been specifically expressed in EMF stage of T. congolense. Therefore, TcHpHbR mediated hemoglobin requirement of the insect stage is probably higher than other stages because of their habitat and fully activated mitochondrial metabolism.

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