Torque Teno suus virus: Importance and neuro-clinical meaning in pigs (2017)

med.vet. master thesis by Deborah Peltzer

Torque teno viruses (TTV) can be found on a global scale and with very high prevalence ranging from 40 – 100 % in the most diverse species, such as humans, dogs or pigs. Since their discovery, it is being researched if these viruses are of pathogenic nature, whether they only favor the outbreak of certain diseases or if they are even part of the normal microflora. TTSuV1 (porcine TTV) are known to be able to establish persistent infections and long-lasting viremia and it is currently debated, if they promote the outbreak of PMWS (Postweaning Multisystemic Wasting Syndrome) and PDNS (Porcine Dermatitis and Nephropathy Syndrome) in pigs which are simultaneously infected with porcine circovirus type 2 (PCV2).
Background for this master thesis was the finding of a remarkably high viral load of TTSuV1 by means of Next Generation Sequencing in brain material from a pig, which suffered from a presumed viral polioencephalitis, with the causal infectious agent being unknown. This raised the question, how frequently TTSuV could be found in pig brains and what the neuro - clinical meaning was. Furthermore, it was of interest, whether an association could be made between age, the geographical occurrence, or certain other diseases and the presence of TTSuV1. Therefore, post - mortem reports were included in the evaluation. Additionally, sequencing and a phylogenetic analysis of the viruses that were detected was carried out, to find out which species of TTSuV1 exist in Switzerland and if any of them are specifically associated with disease.
Samples of a hundred brains from Swiss pigs were examined retrospectively, whereby 25 brain samples showed macroscopic and/or histological lesions and 75 brain samples without macroscopic and histological lesions served as control group.
TTSuV1 was detected in 42 out of the hundred brains by quantitative Real Time PCR. Against expectation, no significant difference in prevalence between the group of interest and the control group could be detected (44 % and 41.3 % respectively). A primary pathogenic influence of TTSuV1 with regard to encephalopathies can thus be ruled out with high probability.
Interestingly, the prevalence of TTSuV1 increased with increasing age of the pigs, with piglets showing the lowest prevalence. Moreover, the virus - positive brains of piglets had a significantly lower viral load than any other age group. Older animals carried a higher amount of virus.
Additionally, pigs with pathological findings in the respiratory tract were infected with TTSuV1 more often than animals with a healthy respiratory tract. A connection with other illnesses was not seen. The evaluation of data also showed that animals treated with antibiotics beforehand presented with a higher TTSuV1 prevalence.
The sequencing and the following phylogenetic analysis showed that all the species (1a-d) of the genus Iotatorquevirus circulate in the Swiss pig population without any specific geographic distribution pattern or association with disease.