Susceptibility of Five Strains of Mice to Babesia microti of Human Origin

Abstract

One outbred (CF1) and four inbred (BALB/c, C57, CBA and C3H) strains of mice were tested for susceptibility to Babesia microti of human origin. Of these, intact C3H mice developed higher parasitemia than all other intact mice, while BALB/c mice developed the highest parasitemia among splenectomized mice. Susceptibility was not related to H-2 haplotype in any obvious way. Because C3H and BALB/c mice developed relatively high initial peak parasitemias, the parasite was serially passaged in both of these mouse strains in an attempt to increase parasite virulence. After 30 passages in BALB/c and 49 passages in C3H mice over a period of 12 months, maximum parasitemias were 50 times higher than those observed initially. After the peak parasitemias of these two mouse-adapted parasites had stabilized, the relationship between onset and level of maximum parasitemia and number of parasites inoculated was determined. With both C3H- and BALB/c-adapted parasites, as inoculum size increased, the time required to reach maximum parasitemia decreased and the level of maximum parasitemia increased. Studies involving infection of either mouse strain with parasites adapted to the heterologous mouse strain indicated that C3H mice were more susceptible than BALB/c mice to homologous or heterologous parasites. These data suggest that the virulence of B. microti to the mouse can be increased by prolonged passage in this host. Once adaptation to this host species has occurred, virulence appears to be more dependent on the innate susceptibility of the mouse strain than on adaptation of the parasites to a particular strain of mouse.

Inhibitory effects of 19 antiprotozoal drugs and antibiotics on Babesia microti infection in BALB/c mice

“…Mice infected with B. microti produced transient high levels of parasitemia, but subsequently recovered from acute infection within 24 to 38 days. A self-limiting course was observed in all strains, whether splenectomized or intact [10].…”

“…microti can infect many species of animals [9] and different strains of mice with different susceptibility to infection [10]. Previous studies compared the susceptibility of one outbred (CF1) and four inbred (BALB/c, C57, CBA, and C3H) strains of mice with human-origin B. microti.…”

Effect of Sex Steroids on Babesia microti Infection in Mice

“…strain WA1, and susceptible mouse models. [23][24][25][26][27][28][29] Aguilar-Delfin and others reported a sex-related influence on resistance to acute Babesia sp. strain WA1 infection in C57BL/6 mice, with males being more resistant than females.…”

Susceptibility of Chinese Hamsters (Cricetulus griseus) to the Infection of Babesia microti

“…However, the hamsters are not suitable to control infection as reservoir rodent hosts showing spontaneous remission with low parasitemia of less than 0.5% infected erythrocytes in the chronic and convalescent stages [8]. Mice are susceptible for mouse-adapted B. microti strains, but not so for the primary infection with the strains maintained in Syrian hamsters [22]. In this study, we confirmed that Chinese hamsters were susceptible to the infection with B. microti and would be useful for the infective examination with the patasite.…”

“…Syrian hamsters (Mesocricetus auratus) have high susceptibility to B. microti infection and are used to isolate and maintain the parasite in laboratories [4,16,21], but the hamsters are not suitable rodent reservoir hosts to control the infection with the parasite, because they show spontaneous remission with low parasitemia [8]. Several species of mice are more commonly used for experimental infections with the parasite, but the mouse-adapted parasites are essential for experimental infections [22]. The rodents are as small as mice and susceptible to B. microti as well as Syrian hamsters, so they will be useful for infection experiments with the parasite.…”