Eimeria tenella: characterization of a 5S ribosomal RNA repeat unit and its use as a species-specific probe.

The oocysts of Eimeria tenella, one of the most pathogenic of several species causing chicken coccidiosis, are difficult to distinguish microscopically from several other infective Eimeria species. One copy of a gene coding for 5S ribosomal RNA has been cloned from E. tenella and sequenced. A coding region of 120 nucleotides and an intergenic region of 608 nucleotides together make up a 5S rRNA repeat unit, of which there are many copies tandemly repeated in the genome. The intergenic region is species-specific and sequences derived from it can be used for species identification by polymerase chain reaction (PCR). The PCR procedure described here is particularly sensitive, with fewer than 10 oocysts sufficing to give a positive result. This method may also be useful for the identification by PCR of other cyst-forming parasites.