Abstract: Objective  To observe the symptom, disease course of Cryptosporidium-infected mice, and the therapeutic effect of spiramycin on infected mice.  Methods  Seventy Kunming mice were randomly divided into normal control group（A, n=10） and 3 experimental groups（B, C, and D）. Mice in groups B, C, and D（n=20） were immunosuppressed with 5, 7.5, and 10 mg/L dexamethasone in drinking water for two weeks, respectively. The mice were observed and the number of oocysts in fecal sample was counted daily after immunosuppression. Two weeks post immunosuppression, 50% of mice in each group were sacrificed, and small intestine was removed for observation of parasitic site. The pathological changes of mucous membrane were observed under microscope, and sIgA level in intestinal fluid was determined. Immunosuppression was withdrawn in the rest mice, and after two weeks unrecovered mice were divided into treatment group（n=6） and control group（n=7）. Mice in treatment group were each given 2 mg/d spiramycin for 10 d. Each mouse in control group was given same amount of normal saline. The mice were observed and the oocysts shedding in fecal pellets were counted after treatment.  Results  On the 6th day post immunosuppression, Cryptosporidium sp. positive fecal samples were found in the experimental groups. The number of oocysts per gram of feces in groups D（70.3±4.0） and B（31.9±2.4）reached a peak on the 12th day and 10th day post immunosuppression, respectively（P＜0.05）. The conspicuous enteron symptom was observed in each experimental group. Cryptosporidium parasitized mainly in upper jejunum. Pathological examination of intestinal mucous membrane showed that swollen mucous membrane and hemorrhages were observed in group D, and less inflammatory cell occurred in groups B and C. sIgA level in intestinal fluid of experiment mice descended, there was a statistical significance between groups D  [（2.7±0.6）μg/ml], C  [（3.2±0.8） μg/ml], B [（4.9±1.3）μg/ml] and A [（6.1±1.2）μg/ml] （P＜0.05）. After withdrawal of immunosuppression, out of 30 positive mice, symptoms including diarrhea and loose stools improved in 17 mice. After treated with spiramycin, status of the mice got improved, and there was statistical significance in the level of oocyst shedding between treatment group（0）and control group（11.3±8.1）（P＜0.05）.  Conclusion  The level of oocyst shedding, disease course, and  pathological change of intestinal mucosa membrane are closely related to immune status of Cryptosporidium-infected mice. Spiramycin is effective in treating of Cryptosporidium infection.

Key words: Cryptosporidium, Mouse, Pathology, Therapy