Sg. Yang et al., Infection of immunosuppressed C57BL/6N adult mice with a single oocyst of Cryptosporidium parvum, J PARASITOL, 86(4), 2000, pp. 884-887
The present study was designed to determine the minimum number of Cryptospo
ridium parvum oocysts capable of producing pat ent infections in immunosupp
ressed C57BL/6N adult mice. Sixty-four female mice were divided into 6 grou
ps of 8 mice each, except group 1 that contained 24 mice. Mice in groups 1-
3 were immunosuppressed with dexamethasone and inoculated with 1, 5. and 10
oocysts per mouse, respectively. The accuracy of the inoculum size was mic
roscopically confirmed. Mice in groups 4-6 served as controls: they receive
d either only oocyst inoculation (group 4), or immunosuppression (group 5),
or no treatments (group 6). Fecal oocyst shedding was monitored daily for
each mouse using an indirect immunofluorescent assay. Parasite colonization
in the terminal ileum of each mouse was evaluated histologically. Four of
24 mice in group 1 developed patent infections, with a prepatent period of
approximately 6 days. All mice in groups 2 and 3 developed patent infection
s, with prepatent periods ranging from 4 to 7 days. Mice in groups 4-6 rema
ined uninfected. Parasite colonization was observed in the terminal ilea of
all mice in groups 1-3 that shed fecal oocysts. The present study experime
ntally demonstrates that a single viable oocyst can induce patent C. parvum
infections in immunosuppressed C57BL/6N adult mice and indicates that this
mouse model could be used for the parasite genotype or isolate cloning.