This article is a review of recently published papers dealing with the possible participation of TT viruses in the multifactorial etiology of disease syndromes, particularly in postweaning multisystemic wasting syndrome (PMWS) of swine. The information concerning the taxonomy of these viruses is presented. The virus strain of this group was demonstrated for the first time in 1997 in a human in Japan and was called TTV in reference to the initials of his name. Recently the International Committee of Taxonomy of Viruses has established a new meaning of TT, namely Torque teno virus, deriving from the Latin terms “torque” meaning “necklace” and “tenuis” meaning “thin”. These terms were chosen to reflect the shape of the TTV genome. TTV was classified to the Anellovirus genus of the Circoviridae family. It was stated that there is no evidence of a link between TTV infection of humans and specific diseases. The same was true in relation to infection of cattle, sheep, chickens, dogs, cats and swine infected by other TTV strains, specific in its replication for a particular species of animals. The following text deals particularly with the last mentioned species. Globally TTV infection is widely spread in pigs. Animals, among them pigs, remain infected and even viremic for years without any apparent negative effects. However, in coinfection with porcine circovirus type 2 (PCV2), being the main etiological factor of PMWS, TTV may possibly contribute to the development of the clinical course of the disease. This is more evident in gnotobiotic pigs. In case of an infection exclusively with TTV in gnotobiotic pigs no clinical symptoms occur. However post mortem pathological changes including thymic atrophy, glomerulonephropathy and modest lymphocytic to histiocytic infiltrates in the liver are found. Summarizing, research concerning the role of TTV in the multifactorial etiology of disease syndromes needs to be continued.
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