| Isospora(syn.Cystoisospora)suis(I. suis)is the leading cause of neonatal porcine isosporosis. Infections occur by oral ingestion of sporulated oocysts and are characterized by non-hemorrhagic transient diarrhea, resulting in poor weight gain. Pigs in all ages or breeds are susceptible to I. suis, especially for suckling piglet which cause watery diarrhoea while pigs in other growth stage manifest as recessive infection.Toltrazuril was the only registered veterinary drug in China which was appropriate for preventing and curing the porcine coccidian. Due to the tolerance and residue of toltrazuril,a new solution should be developed. In this study, the prevalence of porcine isosporosis in Guangdong province was investigated. Secondly the typical biological characteristics of the I. suis was illustrated. Finally the suitable breed of laboratory pig was selected to establish experimental infection model, which laid the solid foundation for developing new type anticoccidials or vaccine.To determine the prevalence of isosporosis infection of suckling piglets in Guangdong province, 438 fecal samples from 11 pig farms in 6 areas including Huizhou, Shaoguan?Foshan, Zhaoqing, Maoming and Jiangmen were collected. These samples were examined for the presence of I. suis oocysts by standard saturated saline flotation method. According to the research data, the infection rates of different areas were various, the highest prevalence rate was found in Huizhou(55.56%), followed by Jiangmen and Zhaoqing with the prevalence rate of 37.5% and 36.96%, respectively. Compared to other areas, Shaoguan had the lowest prevalence rate, only 13.13%. As expected, the piglets at age between 11~20days had the highest prevalence rate and the youngest piglets(1~10 days)had the lowest prevalence rate. Among the three farm scale in this investigation, the large-scale pig farm has the lowest prevalence rate in the present study.The hybrid-crossed piglets and Wuzhishan piglets at new-born and 2-days-old were chosen to examine their self-adaptability. No deaths occurred in any of the groups. The piglets at 2-days-old made a better performance than new-born one. Meanwhile, the Wuzhishan wild piglets showed excellent adaptability comparing to hybrid piglets. In orderto demonstrate the basic parasitological characteristic, the I. suis oocyst was isolated and pured. The mean size of I. suis Guangdong strain was 30.14×28.67 ?m. There were two sporocysts existed in oocyst and each sporocyst contained 4 sporozoites. Combining the morphology result and special PCR assay, the oocysts could be recognized as I. suis. The latent period of this strain was 144 hours and the shortest sporulated time was 26 hours.For observation the clinical and parasitological outcome of experimental infection, 8Wuzhishan piglets at different ages were divided into 4 groups. The group 1 and group 3 at two-day-old were inoculated with 5×10~4 I. suis oocysts or 2×10~5 I. suis oocysts respectively,and the group 2 and group 4 at five-day-old were inoculated with 5×10~4 I. suis oocysts or2×10~5 I. suis oocysts respectively. Diarrhoea happened in all groups in D.P.I.5, and the use of antibiotics failed to treat. The I. suis oocysts were found in the fecal samples of all groups. These findings indicated the Wuzhishan piglets were artificially infected with I.suis, and the animal model of porcine cystoisosporosis was successfully established.When different doses range from1×10~4 to1×10~5 and 2×10~5 were inoculated to healthy piglets, lesion tissue concentrated on jejunum and ileum. Based on the findings, more oocysts they took, more severe the diarrhea was, and the body weight gain was decreased with the increasing of dose. |
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