EXPERIMENTAL-INFECTION OF SWINE BY ISOSPORA-SUIS BIESTER 1934 FOR SPECIES CONFIRMATION

A survey of Isospora suis performed in 177 faecal samples from 30 swin e farms detected thin wall type I. suis oocysts in seven samples. This type of oocyst measuring 23.9 by 20.7 mu m had a retracted thin wall similar to that of the genus Sarcocystis. This type of oocysts, isolat ed from four different faecal samples, was inoculated in four-five-day s-old piglets free of contamination in order to verify the life cycle and pathogenicity of the species. The pigs were kept in individual met al cages and fed with cow milk. Daily faecal collections and examinati ons were performed until the 21st day after infection. MacMaster and S heather's methods were used for oocyst counting and identification. In fected piglets produced yellowish-pasty diarrhoea with slight dehydrat ion. The prepatent and patent periods were respectively from 6 to 9 an d 3 to 10 days after infection. Oocyst elimination was interrupted on the 10th and 11th days after infection with biphasic cycles. Thin and thick wall oocysts were detected in the same faecal samples. Thin wall s were not observed in unsporulated oocysts. The observations suggest that this type of oocysts could appear in specific strains which occur in the later stages of their development. These oocysts seem to be re sponsible for clinical and pathogenic signs of neonatal isosporosis in pigs.