ABSTRACT. The present study was conducted to clarify the mechanism underlying the oxidative process in erythrocytes infected with Babesia gibsoni. The parasite B. gibsoni was cultured together with erythrocytes from normal dogs for 7 days. When parasitemia reached 12.0-13.4% at Day 7, the production of superoxide in erythrocytes was significantly higher in the parasitized culture than in the control culture (p<0.005). The concentration of thiobarbituric acid reactive substances (TBARS) in erythrocytes in parasitized culture was also significantly increased compared with the control culture (p<0.005), indicating that lipid peroxidation was greater in infected erythrocytes than in non-infected cells. In addition, the rates of superoxide generation in the blood of B. gibsoni-infected dogs were also significantly higher than in non-infected dogs (p<0.001). These results indicate that superoxide anions are increased in erythrocytes parasitized with B. gibsoni, and suggest that oxidative damage, due to lipid peroxidation, might be caused in host erythrocytes by the parasite. KEY WORDS: Babesia gibsoni, oxidative damage, superoxide.J. Vet. Med. Sci. 63(10): 1077-1081, 2001 Babesia spp. are well-known blood parasites that cause severe hemolytic anemia in domestic animals [4]. In general, Babesia parasites, as well as Theileria and malaria parasites, invade erythrocytes of infected animals, which results in the destruction of the parasitized erythrocytes [3]. However, severe anemia often occurs in animals infected with this parasite in spite of a low percentage of parasitized erythrocytes in their peripheral blood [4,9]. This phenomenon suggests the possibility of non-parasitized erythrocytes also being damaged due to the parasite infection, resulting in enhanced erythrocyte destruction. We previously reported that concentrations of both methemoglobin and malondialdehyde (MDA), an end product of lipid peroxidation, increase in erythrocytes cultured with B. gibsoni, and that B. gibsoni-infected dogs with high parasitemia also show significant increases of both methemoglobin and MDA in erythrocytes compared with those in non-infected dogs [10]. These results indicate that oxidative damage to erythrocytes is induced by B. gibsoni infection and suggest that active oxygen might be generated by the multiplication of the parasites. Furthermore, erythrocytes cultured with B. gibsoni are more susceptible to phagocytosis by bone marrow macrophages from normal dogs than erythrocytes cultured without B. gibsoni. In addition, 89 percent of erythrocytes phagocytized by macrophages were non-parasitized erythrocytes [10]. However, it has not been clarified whether the Babesia parasite is able to generate reactive oxygen species. The present study was carried out to elucidate the mechanisms underlying the oxidative process in erythrocytes infected with B. gibsoni.
MATERIALS AND METHODSThree dogs were inoculated with B. gibsoni-infected blood from other carrier dogs, and used as B. gibsoniinfected dogs in the present study. Five normal do...