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.
Schrenzel
Mark D
MD
Zoological Society of San Diego, Center for Reproduction of Endangered Species, Department of Pathology, Molecular Diagnostics Laboratory, P.O. Box 120-551, San Diego, California 92112, USA. mschrenzel@sandiegozoo.org
Maalouf
Gabriel A
GA
Gaffney
Patricia M
PM
Tokarz
Debra
D
Keener
Laura L
LL
McClure
Diane
D
Griffey
Stephen
S
McAloose
D
D
Rideout
Bruce A
BA
D000818:Animals; D001483:Base Sequence; D001715:Bird Diseases / Q000469:parasitology*; D003048:Coccidiosis / Q000469:parasitology / Q000662:veterinary*; D016054:DNA, Protozoan / Q000737:chemistry / Q000302:isolation & purification; D021743:Eimeriidae / Q000145:classification / Q000235:genetics* / Q000648:ultrastructure; D005838:Genotype; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D007549:Isospora / Q000145:classification / Q000235:genetics* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D046109:Passeriformes / Q000469:parasitology*; D010802:Phylogeny; D016133:Polymerase Chain Reaction / Q000662:veterinary; D012335:RNA, Ribosomal / Q000235:genetics; D016415:Sequence Alignment
D016054:DNA, Protozoan; D018840:HSP70 Heat-Shock Proteins; D012335:RNA, Ribosomal