L. Grau-Roma

PCV-2 genotype definition and nomenclature

SIR, — To date, at least three different phylogenetic groups of porcine circo-virus type 2 (pcv-2) have been recognised ([Gagnon and others 2007][1], [Dupont and others 2008][2], [Grau-Roma and others 2008][3], [Timmusk and others 2008][4]). However, the mandate of the International Committee on

Infection, excretion and seroconversion dynamics of porcine circovirus type 2 (PCV2) in pigs from post-weaning multisystemic wasting syndrome (PMWS) affected farms in Spain and Denmark.

Longitudinal case-control studies were performed in post-weaning multisystemic wasting syndrome (PMWS) affected farms from Denmark and Spain using similar designs. Fourteen independent batches of 100-154 pigs per batch were monitored from birth to PMWS outbreak occurrence. Pigs displaying PMWS-like signs and matched healthy cohorts were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. Porcine circovirus type 2 (PCV2) quantitative PCR (qPCR) and serology techniques were applied to analyse longitudinally collected sera and/or nasal and rectal swabs. Results showed that PCV2 load increased in parallel to waning maternal antibody levels, reaching the maximum viral load concurrent with development of clinical signs. PMWS affected pigs had higher PCV2 prevalence and/or viral load than healthy pigs in all collected samples at necropsy (p<0.0001-0.05) and even in sera and nasal swabs at the sampling prior to PMWS outbreak (p<0.01-0.05). Danish farms had a higher PCV2 prevalence in young piglets as well as an earlier PMWS presentation compared to Spanish farms. PMWS diagnoses were confirmed by laboratory tests in only half of pigs clinically suspected to suffer from PMWS. Positive and significant correlations were found among PCV2 viral loads present in sera, nasal swabs, rectal swabs and lymphoid tissues (R=0.289-0.827, p<0.0001-0.01), which indicates that nasal and rectal swabs were suitable indicators of PCV2 excretion. Sensitivity and/or specificity values observed from both tests used separately or combined suggested that qPCR and/or serology tests are not apparently able to substitute histopathology plus detection of PCV2 in tissues for the individual PMWS diagnosis within PMWS affected farms. However, qPCR appears to be a potential reliable technique to diagnose PMWS on a population basis.

Swine torque teno virus (TTV) infection and excretion dynamics in conventional pig farms

Torque teno virus (TTV) is a non-enveloped, single-stranded DNA (ssDNA) virus infecting human and non-primate species. Two genogroups of TTV (TTV1 and TTV2) have been described in swine so far. In the present study, TTV1 and TTV2 prevalences in serum, and nasal as well as rectal swabs of 55 randomly selected piglets from seven Spanish multi-site farms, were monitored from 1 to 15 weeks of age. Also, blood from their dams (n=41) were taken at 1 week post-farrowing. Samples were tested by means of two TTV genogroup specific PCRs. Although prevalence of TTV1 and TTV2 in sows was relatively high (54% and 32%, respectively), it was not directly associated to their prevalence in the offspring. Percentage of viremic pigs for both TTV genogroups followed similar dynamics, increasing progressively over time, with the highest rate of detection at 11 weeks of age for TTV1 and at 15 weeks for TTV2. Forty-two (76%) and 33 (60%) of the 55 studied pigs were TTV1 and TTV2 PCR positive in serum, respectively, in more than one sampling time. TTV1 and TTV2 viremia lasted in a number of animals up to 15 and 8 weeks, respectively. Co-infection with both TTV genogroups in serum was detected at all sampling points, but at 1 week of age. On the contrary, there were animals PCR negative to both genogroups in serum at all sampling times but at 15 weeks of age. During the study period, TTV1 and TTV2 nasal shedding increased also over time and faecal excretion was intermittent and of low percentage (<20%). In conclusion, the present study describes for the first time the infection dynamics of TTV1 and TTV2 as well as the nasal and faecal excretion throughout the life of pigs from conventional, multi-site farms. Moreover, results indicate that both swine TTV genogroups are able to establish persistent infections in a number of pigs.

Inactivated PCV2 one shot vaccine applied in 3-week-old piglets: Improvement of production parameters and interaction with maternally derived immunity

The present study describes the effects of a commercially available vaccine against Porcine circovirus type 2 (PCV2) on clinical, pathological and virological outcomes of 3-week-old piglets from two farms with a clinical history of postweaning multisystemic wasting syndrome (PMWS). The study was a controlled, double-blinded, parallel group (1:1) and randomized trial (with a negative control) involving a total of 1239 animals. The study period comprised from weaning age (time of vaccination or PBS inoculation) until the first shipment of pigs to the slaughterhouse. The vaccine product was able to reduce clinical signs, PCV2 viral load in sera and faeces, and overall mortality in nurseries and fattening units. Moreover, average daily gain was significantly higher in vaccinated versus non-vaccinated piglets during the trial period. On the other hand, it was shown that maternally derived antibodies interfered with the development of an active humoral immune response after PCV2 vaccination.

Torque teno virus (TTV) infection in sows and suckling piglets

Torque teno virus (TTV) is a single-stranded DNA virus that has been detected in serum of primate and non-primate species including swine. Little information on swine TTV infection and transmission dynamics is nowadays available. The goal of this study was to gain insight into the potential role of the sow in transmitting TTV to piglets and the infection dynamics of both swine TTV genogroups (TTV1 and TTV2) during the lactation period. Serum samples from 44 sows at 1-week post-farrowing and 215 piglets at 1 and 3 weeks of age were tested using TTV1 and TTV2 PCR methods. Sow parity distribution and the number of delivered piglets (liveborn, stillborn and mummified) per each studied sow were recorded. TTV1 was detected in higher percentages than TTV2 in both sows (75% vs. 43%, respectively) and piglets at 1 (17% vs. 7%, respectively) and 3 (32% vs. 12%, respectively) weeks of age. TTV1 and TTV2 co-infections were observed in higher percentages in sows (34%) than in piglets (2% and 4% at 1 and 3 weeks of age, respectively). Detection of swine TTV genogroups in sows was not associated with their detection in piglets. Moreover, there were piglets infected at 1 week of age with a swine TTV genogroup different from the one detected in their dam. The number of sows delivering stillborns and the mean number of stillborns per sow tended to be higher in the TTV2 infected sows; this value was significantly higher when co-infected sows (TTV1 and TTV2) were compared with non-co-infected ones. Old parity sows had a higher percentage of TTV1 infected 1-week-old piglets. Results of the present study showed that the TTV infection occurs early in the production system and that these viruses may be transmitted from sow-to-piglet but also from piglet-to-piglet in farrowing facilities.

Pig-major acute phase protein and haptoglobin serum concentrations correlate with PCV2 viremia and the clinical course of postweaning multisystemic wasting syndrome.

The aim of the present longitudinal study was to assess the evolution of two acute phase proteins (APPs), pig-major acute phase protein (pig-MAP) and haptoglobin (HPT), in serum from pigs that developed postweaning multisystemic wasting syndrome (PMWS) in comparison to healthy and wasted non-PMWS affected pigs. In addition, evidence of infection with other pathogens and its relation with variations in APPs concentrations was also assessed. Fourteen independent batches of 100-154 pigs were monitored from birth to PMWS outbreak occurrence in 11 PMWS affected farms. Pigs displaying PMWS-like signs and age-matched healthy controls were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. At the moment of PMWS occurrence, pig-MAP and HPT concentration in PMWS affected pigs were higher than in healthy ones (p<0.0001). No differences in APPs serum concentrations between subclinically PCV2-infected pigs and healthy non-PCV2-infected pigs (based on quantitative PCR on serum results) were detected. Results showed a significant correlation between PCV2 loads and both pig-MAP (R=0.487-0.602, p<0.0001) and HPT (R=0.326-0.550, p<0.05-0.0001) concentrations in serum of PMWS affected pigs, indicating that the acute phase response in PMWS affected pigs occurred concomitantly to PCV2 viremia. No other pathogen, apart from PCV2, was consistently related with variations in APPs concentrations. A ROC analysis, made to determine the capacity of discrimination of both APPs between PMWS affected and non-affected pigs, showed higher sensitivity and specificity values using pig-MAP compared to HPT. These results suggest that pig-MAP might be a better indicator of PMWS status than HPT. Moreover, the fact that APR occurred some weeks before the start of clinical signs suggests that APPs could provide valuable prognostic information for PMWS development.

Inter-laboratory and inter-assay comparison on two real-time PCR techniques for quantification of PCV2 nucleic acid extracted from field samples.

Several real-time PCR assays for quantification of PCV2 DNA (qPCR) have been described in the literature, and different in-house assays are being used by laboratories around the world. A general threshold of 10(7) copies of PCV2 per millilitre serum for postweaning multisystemic wasting syndrome (PMWS) diagnosis has been suggested. However, neither inter-laboratory nor inter-assay comparisons have been published so far. In the present study, two different qPCR probe assays used routinely in two laboratories were compared on DNA extracted from serum, nasal and rectal swabs. Results showed a significant linear association between the assays (p<0.0001), and a systematic difference of 1.4 log10 copies of PCV2 per millilitre of sample (p<0.0001). This difference indicated that the assay from laboratory 1 yielded a higher output than the one from laboratory 2. Results also showed that there was no linear association between the amount of PCV2 DNA and the amount of total DNA, neither in nasal (p=0.86) nor in rectal (p=0.78) swabs, suggesting that normalizing of PCV2 DNA load in swab samples to total DNA concentration is not suitable. The present exploratory study highlights the need for the performance of ring trials on qPCV2 protocols between laboratories. Meanwhile, the proposed thresholds for PMWS diagnosis should only be considered reliable for each particular laboratory and each particular assay.

Dynamics of Torque teno sus virus 1 (TTSuV1) and 2 (TTSuV2) DNA loads in serum of healthy and postweaning multisystemic wasting syndrome (PMWS) affected pigs

Torque teno viruses (TTVs) are vertebrate infecting, small viruses with circular single stranded DNA, classified in the Anelloviridae family. In pigs, two different TTV species have been described so far, Torque teno sus virus 1 (TTSuV1) and 2 (TTSuV2). TTSuVs have lately been linked to postweaning multisystemic wasting syndrome (PMWS). In the present study, TTSuV1 and TTSuV2 prevalence and DNA loads in longitudinally collected serum samples of healthy and PMWS affected pigs from Spanish conventional, multi-site farms were analyzed. Serum samples were taken at 1, 3, 7, 11 and around 15 weeks of age (age of PMWS outbreak) and viral DNA loads determined by quantitative PCR. For both TTSuV species, percentage of viremic pigs increased progressively over time, with the highest prevalence in animals of about 15 weeks of age. TTSuV1 and TTSuV2 viral DNA loads in healthy and TTSuV1 loads in PMWS affected animals increased until 11 weeks of age declining afterwards. On the contrary, TTSuV2 DNA loads in PMWS affected pigs increased throughout the sampling period. It seems that TTSuV species differ in the in vivo infection dynamics in PMWS affected animals.

Longitudinal serological and virological study on porcine torovirus (PToV) in piglets from Spanish farms.

Abstract A study was performed to evaluate porcine torovirus (PToV) seroprevalence and infection in three multi-site farms from the North-eastern region of Spain. Serum samples from 120 piglets and faecal samples from 36 piglets were longitudinally collected at 1, 3, 7, 11 and 15 weeks of age. Serum samples from their dams (n =30) were also taken 1-week post-farrowing. PToV antibodies in serum were monitored by ELISA, while viral infection was assessed by real-time RT-PCR in faeces. A high seroprevalence (about 100%) was observed in animals older than 11 weeks and in adult sows. Moreover, all 1-week-old animals were seropositive, indicating maternal antibody transference through colostrum. The antibody titers declined to close to or below the ELISA cut-off value by the age of weaning (3 weeks of age). Development of a significant antibody response to PToV occurred before 7 weeks of age in about 50% of piglets, and the remaining animals developed the response by weeks 11 or 15. These results indicate that PToV infection occurred soon after weaning. Although the prevalence of infection in suckling piglets varied among the studied farms, PToV prevalences in 7 and 11-week-old pigs were between 50–67% and 58–75%, respectively, in all farms. Sequencing results indicated that more than one PToV strains were circulating in the studied farms. Present data suggest that PToV was endemic on the studied farms, and provide new insights on the epidemiology of PToV.

Wooden breast lesions in broiler chickens in the UK

A new condition causing significant economic losses due to lesions in the pectoralis major muscle of commercial broiler chickens has been recently reported in Finland. The condition has been named wooden breast and is characterized by its gross and histological appearance. Between October 2014 and April 2015, samples from 5 pectoralis major muscles downgraded in the slaughterhouse were submitted to the Veterinary Pathology Service of the University of Nottingham for histological examination. All the five studied samples showed moderate or severe multifocal polyphasic muscular degeneration and necrosis. All cases showed variable degree of interstitial fibrosis and/or presence of adipose tissue within interstitium, as well as formation of small nodular follicle-like aggregates of lymphocytes adjacent to small blood vessels. These lesions are compatible to wooden breast and overlap with another recently reported condition known as white striping. The present communication provides evidence that wooden breast lesions are present in broiler chickens in the UK and discusses its similarities with white striping. Larger studies assessing the prevalence of wooden breast are needed to determine the relative economic importance of this condition in this country.