Discovery of a novel Torque teno sus virus species: genetic characterization, epidemiological assessment and disease association.

The study describes a novel Torque teno sus virus (TTSuV) species, provisionally named Torque teno sus virus k2b (TTSuVk2b), originally found in commercial pig sera by applying the rolling-circle amplification technique. Full-length sequences of TTSuVk2b were obtained, annotated and used in the phylogenetic analyses, which revealed that TTSuVk2b is a novel Anellovirus species within the genus Kappatorquevirus of the family Anelloviridae. Quantitative PCR techniques were developed to determine total TTSuV DNA quantities as well as the prevalence and viral DNA quantities of TTSuV1, TTSuVk2a and TTSuVk2b. The mean total TTSuV load in seven commercial sera was determined at 6.3 log(10) DNA copies ml(-1) of serum, with TTSuVk2b loads being the lowest at 4.5 log(10) DNA copies ml(-1) of serum. Subsequently, prevalence and loads of TTSuVs were determined in pig sera from 17 countries. TTSuVk2b prevalence ranged from 0 to 100 % with viral loads from 3.3 to 4.6 log(10) copies ml(-1) of sera. TTSuVk2a, so far the only species in the genus Kappatorquevirus, has been linked to an economically important swine disease, namely post-weaning multisystemic wasting syndrome (PMWS). Considering the grouping of TTSuVk2b in the same genus as TTSuVk2a, TTSuVk2b prevalence and viral DNA load were determined in PMWS-affected animals and healthy counterparts. This revealed that TTSuVk2a and TTSuVk2b are not only genetically related, but also that their viral loads in serum are elevated in PMWS animals compared with those of healthy pen mates. In summary, the present work describes a novel TTSuV species including its genetic characterization, epidemiological assessment and potential disease association.

Vaccination of pigs reduces Torque teno sus virus viremia during natural infection.

Anelloviruses are a group of single-stranded circular DNA viruses infecting several vertebrate species. Four species have been found to infect swine, namely Torque teno sus virus (TTSuV) 1a and 1b (TTSuV1a, TTSuV1b; genus Iotatorquevirus), TTSuVk2a and TTSuVk2b (genus Kappatorquevirus). TTSuV infection in pigs is distributed worldwide, and is characterized by a persistent viremia. However, the real impact, if any, on the pig health is still under debate. In the present study, the impact of pig immunization on TTSuVk2a loads was evaluated. For this, three-week old conventional pigs were primed with DNA vaccines encoding the ORF2 gene and the ORF1-A, ORF1-B, and ORF1-C splicing variants and boosted with purified ORF1-A and ORF2 Escherichia coli proteins, while another group served as unvaccinated control animals, and the viral load dynamics during natural infection was observed. Immunization led to delayed onset of TTSuVk2a infection and at the end of the study when the animals were 15 weeks of age, a number of animals in the immunized group had cleared the TTSuVk2a viremia, which was not the case in the control group. This study demonstrated for the first time that TTSuV viremia can be controlled by a combined DNA and protein immunization, especially apparent two weeks after the first DNA immunization before seroconversion was observed. Further studies are needed to understand the mechanisms behind this and its impact for pig producers.