Eimeria crecis and Eimeria nenei have been detected in association with enteric disease ("coccidiosis") in the corncrake (Crex crex: Family Rallidae, Order Gruiformes). Both parasite species are common in apparently healthy free-living corncrakes, but captive-bred juvenile birds reared for reintroduction appeared particularly susceptible to clinical coccidiosis. We investigated the occurrence and relative pathogenicity of these Eimeria species in this juvenile corncrake population and developed a diagnostic species-specific polymerase chain reaction (PCR) for their identification. PCR amplification and sequencing of 18S rDNA were performed on genomic DNA extracted from samples of corncrake intestine, liver and spleen. Sequences generated were used to design a GeneScan diagnostic PCR assay targeting a species-specific TTA indel located within the 18S rDNA - the results suggested this assay was more sensitive than the 18S rDNA/amplicon sequencing approach. Eimeria sp. DNA (consistent with Eimeria sp. infection) was detected at a high prevalence and E. crecis was the predominant species. Each Eimeria species was detected in cases with and without histological evidence of coccidiosis: parasite detection was not statistically associated with disease. In addition to intestinal tissue, liver and spleen samples were positive for Eimeria sp. DNA. Its detection in tissues other than intestine is unusual and a novel finding in corncrakes, although extra-intestinal infection occurs with closely related Eimeria species in cranes (Family Gruidae, Order Gruiformes). Eimeria sp. infection of corncrakes appears typically to be chronic, and to exhibit extra-intestinal spread: as in cranes, these characteristics may be adaptations to the host's migratory nature.
Keywords: Eimeria sp; Rallidae; coccidiosis; corncrake Crex crex; wild bird.