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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.
Insights
This study shows that prolonged passage of Babesia microti in mice increases its virulence. Mouse strain susceptibility, rather than parasite adaptation, ultimately determines virulence levels.
Area of Science:
- Parasitology
- Immunology
- Infectious Diseases
Background:
- Babesia microti is a tick-borne parasite causing babesiosis in humans and animals.
- Understanding host-parasite interactions and factors influencing parasite virulence is crucial for disease management.
Purpose of the Study:
- To investigate the susceptibility of different mouse strains to Babesia microti.
- To determine if prolonged parasite passage in mice can increase Babesia microti virulence.
- To explore the relationship between mouse strain, parasite adaptation, and virulence.
Main Methods:
- Tested susceptibility of outbred (CF1) and inbred (BALB/c, C57, CBA, C3H) mice to human-origin Babesia microti.
- Serially passaged the parasite in susceptible mouse strains (C3H and BALB/c) to enhance virulence.
- Assessed parasitemia levels, time to peak parasitemia, and inoculum size effects.
- Investigated cross-infectivity between homologous and heterologous parasite-adapted strains.
Main Results:
- C3H mice showed higher parasitemia than other intact strains; BALB/c mice had the highest parasitemia among splenectomized mice.
- Serial passage increased Babesia microti maximum parasitemia by 50-fold over 12 months.
- Increased inoculum size decreased time to peak parasitemia and increased its level.
- C3H mice were more susceptible to both homologous and heterologous adapted parasites than BALB/c mice.
Conclusions:
- Babesia microti virulence in mice can be significantly increased through prolonged host passage.
- Innate mouse strain susceptibility plays a more critical role in determining virulence than specific parasite adaptation to a strain.
- Findings highlight the importance of host genetics in the outcome of Babesia infections.