Molecular investigation of Torque teno sus virus in geographically distinct porcine breeding herds of Sichuan, China

Abstract

Background: Torque teno sus virus (TTSuV), infecting domestic swine and wild boar, is a non-enveloped virus with a circular, single-stranded DNA genome. which has been classified into the genera Iotatorquevirus (TTSuV1) and Kappatorquevirus (TTSuV2) of the family Anelloviridae. A molecular study was conducted to detect evidence of a phylogenic relationship between these two porcine TTSuV genogroups from the sera of 244 infected pigs located in 21 subordinate prefectures and/or cities of Sichuan.

Results: Both genogroups of TTSuV were detected in pig sera collected from all 21 regions examined. Of the 244 samples, virus from either genogroup was detected in 203 (83.2%), while 44 animals (18.0%) were co-infected with viruses of both genogroups. Moreover, TTSuV2 (186/244, 76.2%) was more prevalent than TTSuV1 (61/244, 25%). There was statistically significant difference between the prevalence of genogroups 1 infection alone (9.4%, 23/244) and 2 alone (64.8%, 158/244), and between the prevalence of genogroups 2 (76.2%, 186/244) and both genogroups co-infection (18.0%, 44/244). The untranslated region of the swine TTSuV genome was found to be an adequate molecular marker of the virus for detection and surveillance. Phylogenetic analysis indicated that both genogroups 1 and 2 could be further divided into two subtypes, subtype a and b. TTSuV1 subtype b and the two TTSuV2 subtypes are more prevalent in Sichuan Province.

Conclusions: Our study presents detailed geographical evidence of TTSuV infection in China.

Figure 1

Prevalence of torque teno sus virus infection in different breeding herds of Sichuan, China. Prevalence of torque teno sus virus infection in geographically distinct breeding herds of different cities of Sichuan, China. Total prevalence of torque teno sus virus genogroups infection in Sichuan, China (***p < 0.001).

Figure 2

The number of transitions (×) and transversions (∆) versus of the genetic distance calculated with the TN93 among all pairwised strains of TTSuV1 (A) and 2 (B). Solid lines indicate the best fit found in each mutational type. The “s”and “v” represented the number of transitions (×) and transversions (∆), respectively.

Figure 3

Phylogenetic tree generated on a 125 bp overlapping stretch of the UTR of TTSuV isolates in this study and 28 reference strains. Three other Anellovirus from different species were used as outgroups in this study. The neighbor-joining (NJ) method was used to construct this tree, which was evaluated using the interior branch test (Mega 5.0). Only bootstrap support values higher than 50% are shown at each node. ML (Maximum Likelihood), MP (Maximum Parsimony), and BI (Bayesian inference) inference analysis resulted in a very similar branching pattern. GenBank accession number, source and name of isolates are shown in Additional file 1: Appendix 1. Two subtypes, PTTV1a-VA and PTTV2b-VA, are proposed subtypes for TTSuV1 and TTSuV2.