Infection dynamics of Babesia microti in mice in different immune status
CAI Yu-chun, LU Yan, CHEN Shao-hong, GUO Jian, CHEN Mu-xin, TIAN Li-guang, ZHANG Ling-ling, ZHOU Yang, CHEN Jia-xu
National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention / Laboratory of Parasite and Vector Biology, Ministry of Public Health / WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Shanghai 200025, China
Abstract：To observe the infection dynamics of Babesia microti in the mice of different immune status, BALB/c mice, BALB/c mice of immune suppression, SCID mice, and NOD-SCID mice were divided into 4 groups(5 in each). Dexamethasone, one kind of immunosuppressant, was intraperitoneally injected into BALB/c mice for five consecutive times (0.5mg/dose/day) to form BALB/c mice of immune suppression. Of 100 μL BALB/c mice blood (20% RBC infection rate) with Babesia microti was intraperitoneally injected into four of BALB/c mice, BALB/c mice of immune suppression, SCID mice and NOD-SCID mice, respectively, and left one normal control in each group. Tail blood was used to prepare thin blood films and giemsa staining to observe the infection changes. On the third days after infection, Babesia microti were firstly found in RBC of BALB/c mice. The highest infection rate (82.4%) of Babesia microti in BALB/c mice appeared on the seventh day after infection, and the infection rate were higher than 20% for 7 days; on the fifth day after infection, the infection rate of BALB/c mice of immune suppression was up to a peak of 73.18%, and the infection rate were higher than 20% for 14 days; after that, the rate of the Babesia microti in these two kind of mice blood was in a very low state (0%-2%). The peak of infection rates of Babesia microti in NOD-SCID mice group were appeared on the seventh day after infection (72.5%), the 16th day (67.4%) and the 24th day (58.9%), and the rate of Babesia microti in NOD-SCID mice blood was high. The average rate was 41.9% and could not heal by itself. The highest infection rate of Babesia microti in SCID mice was first appeared on the 8th day after infection, and the rate was 86.4%. The second rate peak was appeared on the 18th day, and the rate was 62.23%. The rate of Babesia microti in SCID mice blood was high, and the average rate was 38.2%. From the thin blood films, many form of Babesia microti were observed, such as small point-like body, the Maltese cross, a small circular ring, circular ring, long threadlike body and parasites free outside of red blood cells. In normal and short-term suppression BALB/c mice, insect density of Babesia microti first raised to a higher level, and then dropped to a lower level, which was called host self-limiting phenomenon; while in SCID and NOD-SCID mice, density of Babesia microti appeared more than one peak, and could sustained in a higher level.
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2013, Vol. 29 
