Molecular characterization of isosporoid coccidia (Isospora and Atoxoplasma spp.) in passerine birds.

Prevalence and disease caused by isosporoid coccidia in passerine birds are well recognized, but confusion about the life cycles of the parasites has led to taxonomic inconsistencies. In this study, we characterized segments of the chromosomal small and large-subunit ribosomal RNA (rRNA) genes of coccidial parasites from 23 species of passerine birds, as well as heat shock protein 70, apicoplast rRNA, and chromosomal 5.8s rRNA genes from a subgroup of these animals, and we correlated genetic data with morphologic findings for different parasite developmental stages, host phylogeny, and overall taxonomic relations within the phylum Apicomplexa. Our findings indicate that isosporoid coccidia of passerine birds are monophyletic but exhibit substantial diversity, with most avian species having one or several unique parasite lineages that underwent synchronous speciation with their hosts, interrupted by sporadic episodes of lateral transmission across species and families. Molecular analyses support a homoxenous life cycle, with sexual forms occurring chiefly in the intestines and asexual merozoites present systemically. Rarely, extraintestinal sexual stages can occur. The passerine coccidia are genetically most closely related to species of Eimeria rather than Isospora. We suggest that these parasites, whether identified from blood merozoite stages or fecal oocysts, be provisionally grouped as a homogeneous clade of individual species in a single taxon and formally named when reliable criteria allowing reclassification of related genera in the suborder Eimeriina are clarified.

Molecular characterization of malarial parasites in captive passerine birds.

Seven of 28 passerine birds that died in captivity were positive for malarial parasites by polymerase chain reaction targeting the mitochondrial cytochrome b (cytB) and apicoplast ribosomal RNA (rRNA) genes. Each bird was infected with a single parasite lineage having a unique genotype. Apicoplast rRNA sequences were present both in Haemoproteus spp. and Plasmodium spp. and had typically high adenosine + thymidine content. Phylogenies for cytB and apicoplast rRNA sequences were largely congruent and supported previous studies that suggest that Plasmodium-Haemoproteus spp. underwent synchronous speciation with their avian hosts, interrupted by sporadic episodes of host switching. Apicoplast phylogeny further indicated that Haemoproteus spp. are ancestral to Plasmodium spp. All the 7 infected passerine birds had histologic lesions of malaria, and malarial parasites may have contributed to the death of at least 4 animals. These findings provide new genetic data on passerine hematozoa, including initial sequences of apicoplast DNA, and emphasize the relevance of parasite prevalence, evolutionary relationships, and host switching to modern management and husbandry practices of captive birds.