Search

Wildlife-associated Cryptosporidium are an emerging cause of cryptosporidiosis in humans. The present study was undertaken to determine the extent to which North American tree squirrels and ground squirrels host zoonotic Cryptosporidium species and genotypes. Fragments of the Cryptosporidium 18S rRNA and actin genes were amplified and sequenced from fecal samples obtained from three tree squirrel and three ground squirrel species. In tree squirrels, Cryptosporidium was identified in 40.5% (17/42) of American red squirrels (Tamiasciurus hudsonicus), 40.4% (55/136) of eastern gray squirrels (Sciurus carolinensis), and 28.6% (2/7) of fox squirrels (Sciurus niger). Human-pathogenic Cryptosporidium ubiquitum and Cryptosporidium skunk genotype were the most prevalent species/genotypes in tree squirrels. Because tree squirrels live in close proximity to humans and are frequently infected with potentially zoonotic Cryptosporidium species/genotypes, they may be a significant reservoir of infection in humans. In ground squirrels, Cryptosporidium was detected in 70.2% (33/47) of 13-lined ground squirrels (Ictidomys tridecemlineatus), 35.1% (27/77) of black-tailed prairie dogs (Cynomys ludovicianus), and the only golden-mantled ground squirrel (Callospermophilus lateralis) that was sampled. Cryptosporidium rubeyi and ground squirrel genotypes I, II, and III were identified in isolates from these ground squirrel species. In contrast to the Cryptosporidium infecting tree squirrels, these species/genotypes appear to be specific for ground squirrels and are not associated with human disease., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Cryptosporidium is an apicomplexan parasite that causes the disease cryptosporidiosis in humans, livestock, and other vertebrates. Much of the knowledge on Cryptosporidium diversity is derived from 18S rRNA gene (18S rDNA) phylogenies. Eukaryote genomes generally have multiple 18S rDNA copies that evolve in concert, which is necessary for the accurate inference of phylogenetic relationships. However, 18S rDNA copies in some genomes evolve by a birth-and-death process that can result in sequence divergence among copies. Most notably, divergent 18S rDNA paralogs in the apicomplexan Plasmodium share only 89-95% sequence similarity, encode structurally distinct rRNA molecules, and are expressed at different life cycle stages. In the present study, Cryptosporidium 18S rDNA was amplified from 28/72 (38.9%) eastern chipmunks (Tamias striatus). Phylogenetic analyses showed the co-occurrence of two 18S rDNA types, Type A and Type B, in 26 chipmunks, and Type B clustered with a sequence previously identified as Cryptosporidium chipmunk genotype II. Types A and B had a sister group relationship but shared less than 93% sequence similarity. In contrast, actin and heat shock protein 70 gene sequences were homogeneous in samples with both Types A and B present. It was therefore concluded that Types A and B are divergent 18S rDNA paralogs in Cryptosporidium chipmunk genotype II. Substitution patterns in Types A and B were consistent with functionally constrained evolution; however, Type B evolved more rapidly than Type A and had a higher G+C content (46.3% versus 41.0%). Oocysts of Cryptosporidium chipmunk genotype II measured 4.17 μm (3.73-5.04 μm) × 3.94 μm (3.50-4.98 μm) with a length-to-width ratio of 1.06 ± 0.06 μm, and infection occurred naturally in the jejunum, cecum, and colon of eastern chipmunks. The findings of this study have implications for the use of 18S rDNA sequences to infer phylogenetic relationships., (Copyright © 2015 Elsevier B.V. All rights reserved.)