Human babesiosis in Rhode Island: Epizootiological, epidemiological, and vector competency studies

Renjie Hu, University of Rhode Island


Epizootiological and epidemiological evidence for the risk of acquiring an infection of Babesia microti in Rhode Island is provided. The presence of B. microti was detected in Peromyscus leucopus populations at eight sites (n = 34) where Ixodes scapularis was at least moderately abundant ($>$20 nymphs/hr). Risk factors for human B. microti infection were evaluated by conducting a serosurvey. Among 589 human subjects, 24 (4.1%) subjects exhibited antibody titers ranging from 1:64 to 1:256. The prevalence of anti-B. microti antibodies was significantly greater for subjects also seropositive for Borrelia burgdorferi (9.7%, n = 154) than for either B. burgdorferi seronegative subjects (3.2%, n = 185) or individuals whose sera was taken for reasons unrelated to tick-borne infections (1.8%, n = 166) (p $<$ 0.05). A subject's age and sex appeared not to constitute risk factors.^ Effects of B. microti on feeding, the body weight of engorged ticks, and the molting success of immature I. scapularis were determined. An infection of B. microti in hamsters (Mesocricetus auratus) delayed engorgement of both larvae and nymphs. However, the presence of B. microti has no adverse effect on the body weight of engorged ticks. Ticks which fed on infected hamsters generally molted more successfully than those from uninfected hamsters, suggesting that there is a mutualistic relationship between B. microti and I. scapularis.^ Finally, parasitemias, hematological changes, and humoral immune response developed by hamsters during eight weeks of experimental B. microti infection were described. Hamsters generally reached their peak parasitemia at four weeks post inoculation with a mean ($\pm$ SD) of 21.9 $\pm$ 9.4% (range = 20-35%). Measurements of red blood cell count, packed cell volume, and hemoglobin level as hematological parameters for monitoring the hemolytic anemia in hamsters corresponded inversely to the parasitemia. Individual animals typically attained peak antibody levels ($\ge$1:8192) one week after the peak parasitemia and remained at a high level ($\ge$1:4096) while parasitemias fell dramatically. This study suggests that humoral immunity may, in part, serve to down-regulate the B. microti parasitemia protecting these animals from prolonged severe hemolytic anemia. ^

Subject Area

Biology, Entomology|Biology, Zoology|Health Sciences, Public Health|Health Sciences, Immunology

Recommended Citation

Renjie Hu, "Human babesiosis in Rhode Island: Epizootiological, epidemiological, and vector competency studies" (1996). Dissertations and Master's Theses (Campus Access). Paper AAI9702090.