Detection and characterization of group C rotaviruses in asymptomatic piglets in Ireland

Abstract

Group C rotaviruses are important human enteric pathogens that have also been detected in a variety of mammalian species, including pigs. Group C rotaviruses have been identified in piglets with diarrhea, but their ecology remains to be elucidated. By screening of 292 fecal samples collected from 4- to 5-week-old asymptomatic pigs from four herds in Ireland between 2005 and 2007, 13 (4.4%) samples tested positive by reverse transcription-PCR for group C rotavirus. Group A rotaviruses were also detected in 19 samples but not in conjunction with group C viruses. The gene encoding the major group C neutralization antigen, the outer capsid protein VP7, was sequenced. The majority of the strains were very closely related to each other (>99% amino acid [aa] identity) and were characterized as genogroup G1 since they were genetically related to the prototype porcine strain Cowden (92.6% aa identity). Conversely, two strains (1GA/05/Cork/Ire and 281/07/Dublin/Ire) were characterized as genogroup G6 since they displayed the highest identity (89.2 to 94.0% aa) to porcine G6 strains (43/06-22-like). Unexpectedly, one such G6 strain, 1GA/05/Cork/Ire, lacked the 4-aa insertion in the VP7 variable region VR8 found in all the other G6 group C rotaviruses. This study provides evidence that porcine group C rotavirus may be detected not infrequently in asymptomatic piglets. In addition, it provides evidence that, unlike the human viruses, porcine group C rotaviruses display broad genetic heterogeneity, which may pose a challenge for the development of prophylactic tools.

FIG. 1.

Neighbor-joining unrooted tree based on the VP7 amino acid sequences of the following porcine GCRVs described in this study and reference strains: the porcine (Po) strains Cowden, WH, 118-05-4, 118-05-27, and 118-05-18; the bovine (Bo) strains Shintoku and Yamagata; the porcine strain HF; the human (Hu) strains OK450, Preston, Belem, BCN21, Moduganari, and Jajeri; the porcine strain 134-04-18; and the porcine strains 43-06-16, 134-04-2, 43-06-22, and 344-04-7.

FIG. 2.

Comparison of the deduced amino acid VP7 sequences from animal and human GCRVs. The genotypes of GCRVs are also given. Identical amino acids are indicated by dots, and gaps are shown by dashes. The variable regions VR-1 to VR-8 (48) are boxed. Potential N-linked glycosylation sites are underlined. Also, the conserved cysteine residues and the putative signal cleavage site GQ are underlined in the consensus sequence (strain po/Cowden).