DEVELOPMENT OF DNA PROBES FOR THE OVINE EIMERIA SPECIES E-CRANDALLIS AND E-OVINOIDALIS

As an alternative to morphological speciation, DNA probes have been de veloped to identify Eimeria crandallis and E. ovinoidalis, the species associated with ovine coccidiosis. Coccidia-free lambs were infected with pure cultures of E. crandallis and E. ovinoidalis. Oocysts separa ted from faeces were sporulated and treated to release sporozoites fro m which DNA was purified. Repetitive DNA sequences were identified by hybridisation and cloned. The specificity of selected clones was teste d by hybridisation with dot blots of four other ovine Eimeria species, a mixture of caprine Eimeria species and E. acervulina of the chicken . The probes allowed the detection of DNA equivalent to that present i n approximately 1,500 oocysts. To increase the sensitivity of the test , a polymerase chain reaction (PCR) approach was adopted, using oligon ucleotide primers specific for the cloned repeats. By this method, les s than 10 oocysts of E. ovinoidalis could be reliably detected. In add ition to the species-specific probes, other highly repetitive DNA sequ ences from E. crandallis and E. ovinoidalis were cloned and sequenced; these repeats hybridised to all ovine, caprine and avian Eimeria spec ies tested and contained tandem CGA and putative telomeric repeats.