Torque teno sus virus 1 and 2 viral loads in faeces of porcine circovirus 2-positive pigs

Recently, studies have suggested an association between the Torque teno sus virus (TTSuV) and the Porcine circovirus-2 (PCV2) in PCV2-associated disease cases. The aim of this study was to verify TTSuVs loads in pig faeces from PCV2-positive animals with and without diarrhea from PCVADaffected and PCV2-unvaccinated herds. A total of 80 faecal samples were collected individually from nursery and grow-finish pigs with (n = 40) or without (n = 40) diarrhea. The samples were tested for PCV2 and TTSuVs by using DNA binding dye SYBR Green quantitative polymerase chain reaction (qPCR). Torque teno sus virus k2 (TTSuVk2) load in the faeces was significantly higher in the nursery pigs with diarrhea, and these pigs also exhibited significantly higher PCV2 (P < 0.01) faecal matter loads compared to the non-diarrheic animals from the same age group. Torque teno sus virus 1 (TTSuV1) viral loads were the same regardless of age group and disease condition. There were no correlations between PCV2 and TTSuV1 or TTSuVk2 and TTSuV1 viral loads; however, a weak correlation (r = 0.23, P = 0.03) was found between TTSuVk2 and PCV2 viral loads. In conclusion, TTSuVk2 viral loads were significantly higher in the diarrheic faeces from the nursery pigs. Additionally, the higher loads of PCV2 and TTSuVk2 in the nursery-diarrheic animals revealed that diarrhea might have an important role in the spread of both viruses in herds. Epidemiology, swine virus, diarrhea, disease Torque teno sus virus (TTSuV) is classified within the Anelloviridae family and Iotatorquevirus genus and comprises the following species: Torque teno sus virus 1a (TTSuV1a) and Torque teno sus virus 1b (TTSuV1b) (ICTV 2013). The genus Kapatorquevirus comprises only one species, Torque teno sus virus k2 (TTSuVk2). The TTSuV1 and TSuVk2 are distributed in several countries with frequencies ranging from 24% to 100% (Kekarainen et al. 2006; Taira et al. 2009). The pathogenic role of TTSuV is not clear because this virus infects a relatively high proportion of animals that are apparently healthy (Segalés et al. 2009). The TTSuV has been considered nonpathogenic; however, studies have shown that it can serve as a ‘trigger’ or cofactor for Porcine circovirus 2 (PCV2) in the porcine circovirus 2-associated disease (PCVAD) (Krakowka et al. 2000). This association between TTSuVs and PCV2 infection has been suggested because TTSuVk2 prevalence is significantly higher in post-weaning multi-systemic wasting syndrome (PMWS) affected animals than in healthy domestic swine (Kekarainen et al. 2006). However, no differences between TTSuV loads in PCVAD-affected and non-affected pigs were found in another study (Lee et al. 2010). Coinfections with PCV2 and TTSuVs in reproductive organs, semen and ovarian follicular fluid exhibit no correlation between TTSuVs and reproductive failure (Ritterbusch et al. 2012). Additionally, in a double-blinded, randomized trial included in a PCV2 vaccination study, the vaccination of PCV2 sub-clinically infected pigs did not modify the outcome ACTA VET. BRNO 2015, 84: 91–95; doi:10.2754/avb201584020091 Address for correspondence: Dr. Alessandra M.M.G. de Castro Complexo Educacional Faculdade Metropolitanas Unidas Faculdade de Medicina Veterinária Rua Ministro Nélson Hungria, 541 Real Parque, São Paulo, SP, Brazil Phone: +55 11 30917704; 24 E-mail: [email protected] http://actavet.vfu.cz/ of TTSuVk2 infection (Nieto et al. 2012). The role of TTSuVs co-infections in PCV2 faecal shedding is unknown, and even less is known about this role in PCV2-unvaccinated PCV2-positive swine. The aim of this study was to verify TTSuVs loads in pig faeces with and without diarrhea from PCV2-positive animals from PCVAD-affected and PCV2unvaccinated herds. Materials and Methods A total of 80 faecal samples were individually collected without environmental contamination from pigs from two PCVAD-affected and PCV2-unvaccinated herds in the State of São Paulo, Brazil between July 2008 and July 2009. PCVAD was defined as a significant increase in post-weaning mortality and ‘wasting’ rates and by the detection of PCV2 nucleic acid by polymerase chain reaction (PCR) in at least 50% of the pigs that died with clinical signs of PCVAD. The wasting rates were determined as the percentages of animals that were delayed in or never reached slaughter weight and were discarded prior to slaughter, relative to the total numbers of animals that were slaughtered during the year-long period. None of herds had been subjected to PCV2-vaccination protocols at the time of the study. In each herd, the same numbers of nursery (± 35–70 days) and grow-finish (± 35–150 days) pigs were randomly selected based on the presence (n = 20) or absence of diarrhea (n = 20) at the moment of sample collection. The faeces were collected by massaging the pig’s abdomen and placed in a sterile bottle that was conditioned in ice during transport to the laboratory. In the laboratory, the samples were homogenized in 20% TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0) and stored at -20 °C until further processing. DNA was extracted from the faecal suspensions using a phenol-chloroform and proteinase K protocol that was previously described by Sambrook et al. (1989). The extracts were subsequently used for the detection and quantification of PCV2, TTSuV1, and TTSuVk2 using primers that were previously described by Yang et al. (2007) and Segalés et al. (2009). Quantitative PCR was performed using SYBR green chemistry and a StepOne Real-Time PCR system (Applied Biosystems, Canada) under universal conditions. The numbers of copies of viral DNA were determined by comparisons with a standard curve, and the viral concentrations are expressed as the log10 PCV2 and TTSuVs DNA per 100 ng of total DNA in the faecal samples. The extracted samples were also tested for β-actin with PCRs as a control as previously described by Hui et al. (2004) to detect possible PCR false-negative results due to failures in DNA extraction or the presence of PCR inhibitors. All samples were positive for β-actin. Shapiro-Wilk’s test was used to evaluate the normalities of data distributions of the examined variables. Nonparametric Mann-Whitney test was used to analyze PCV2, TTSuV1, and TTSuVk2 viral loads within each age group between the diseased and healthy animals. Spearman’s correlations were used to examine the relationships between the viral loads of PCV2, TTSuV1, and TTSuVk2 in the animals. The results were considered significant at P < 0.05.