In 2004, it was observed that PMWS in Quebec had a significantly higher mortality rate than had been previously reported. Researchers, veterinarians and diagnosticians began to explore the possibilities that a second pathogen could be exacerbating the PCV2 infection, or that a more virulent strain of PCV2 could be infecting swine.
Researchers, led by Gagnon, identified swine Torque Teno Virus (swTTV) in almost 70% of the animals tested. Although often isolated, swTTV, a virus in the same family as PCV2, has not been associated with any known disease.
Recent reports at the 20th International Pig Veterinary Society (IPVS) meeting dealt with swTTV infection and its potential connection to PCV2 and its related diseases. Krakowka et al. reported on disease models where gnotobiotic pigs were infected with PCV2, swTTV or both. In some of their experiments, half of the pigs that were infected with swTTV followed by PCV2 developed PMWS. Yet, if they were infected with PCV2 followed by swTTV, they did not develop any illness.
In other experiments, pigs were infected with the PRRS virus, swTTV or a combination of the two. Only animals infected with both developed Porcine Dermatitis and Nephropathy Syndrome (PDNS). These studies support the idea that swTTV, while not a primary pathogen, may play a significant role in the presentation of other diseases.
In another IPVS report, the work by Valls et. al came to similar conclusions. His team studied the prevalence of different types of swTTV in tissues from pigs that had Porcine Circovirus Associated Diseases (PCVAD) (described as Post-weaning Multisystemic Wasting Syndrome (PMWS)), PDNS or that were healthy. They used a technique called in situ hybridization to test the tissues for the presence of swTTV2 DNA. DNA from swTTV2 was found extensively in the tissues of animals suffering from PWMS, but not in tissues from healthy animals.
These recent reports continue to raise questions about the potential role of swTTV in the presentation of PMWS. Although the link between swTTV, PCV2 and PCVAD has not yet been defined, it is clear that this needs further research.
Information for this article was taken from, "The emergence of porcine circovirus 2b genotype (PCV-2b) in swine in Canada" by Gagnon et al., published in Canadian Veterinary Journal, volume 48, August 2007; "Porcine genogroup 1 torque teno virus (G1-TTV) potentiates both PCV2 and PRRSV infections in gnotobiotic swine" by Krakowka et al., published in the proceedings of the 20th IPVS Congress, June 2008.; and, "Torque teno virus tissue distribution in healthy, postweaning multisystemic wasting syndrome and porcine dermatitis and nephropathy syndrome affected pigs by in situ hybridization" by Martin-Valls et al., also published in the proceedings of the 20th IPVS Congress, June 2008.
[Thanks to Angela DeMirjyn at the National Pork Board for providing this article. For more information visit the Pork Board’s PCVAD web site.]