A study on the severity and relevance of porcine circovirus type 2 infections in Dutch fattening pigs with respiratory diseases.

Abstract

This study was set up to get more insights in the severity and relevance of porcine circovirus type 2 (PCV2) infections in Dutch fattening farms in an endemic PCV2-situation with no clinical signs of post-weaning multisystemic wasting syndrome (PMWS). In part A of the study, in total 29 commercial fattening farms with varying percentages of pneumonia and pleurisy at slaughter were examined. Blood samples were collected at random by cross-sectional sampling; 10 in the age of 10-12 weeks, 10 at the age of 16 weeks and 10 blood samples at the end of the finishing period (20-22 weeks of age). Serum samples were examined for the presence of PCV2 IgM and IgG antibodies and for antibodies against other porcine lung pathogens. In part B, 8 "high" and 8 "low" herds were selected. The 8 "high" herds were defined as herds having high percentages of lung lesions (pneumonia) at slaughter, and the 8 "low" herds had low percentages of pneumonia at slaughter. For both the "high" and "low" herds, 3 pigs showing signs of respiratory distress were selected for necropsy (n=48). Lung tissue samples were examined post-mortem for macroscopic and histopathological lesions, and for the presence of bacteria and viruses. The results of part A showed that, pigs at 16 weeks of age with IgM antibodies against PCV2 had a lower probability of having pleuritis at slaughter (OR 0.34, P<0.000). Pigs in the age category of 20-22 weeks, and with IgM antibodies against PCV2, also had a lower probability of having pneumonia at slaughter (OR 0.29, P=0.032). In part B lobus apicalis pneumonia, PCV2 in macroscopically unaffected lungs, Pasteurella multocida, Mycoplasma hyopneumoniae, and swine influenza viruses were all found significantly more often in "high" than in "low" pigs at autopsy. High PCV2 DNA loads (>10(4) PCV2 DNA copies/mg) were found in lungs of 14 (58%) "high", and in 7 (29%) of the "low" pigs (P=0.13). In 11 of the 19 affected lungs from "high" pigs, high PCV2 DNA loads were found in combination with one or more other lung pathogens, while this was found only in 5 of the 17 affected lungs from "low" pigs (P=0.02). This study confirms the hypothesis that PCV2 plays a role in pneumonia and pleurisy in 10-24 weeks old fattening pigs, not only in herds with a high prevalence of PMWS, but also in herds with no clinical signs of PMWS.

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Accepted Manuscript
Title: A study on the severity and relevance of porcine
circovirus type 2 infections in Dutch fattening pigs with
respiratory diseases
Authors: G.J. Wellenberg, F.T. Bouwkamp, P.J. v.d. Wolf, W.
A.J.M. Swart, M.J. Mombarg, A.L.W. de Gee
PII:
DOI:
Reference:
S0378-1135(09)00496-9
doi:10.1016/j.vetmic.2009.10.003
VETMIC 4620
To appear in:
VETMIC
Received date:
Revised date:
Accepted date:
7-4-2009
27-9-2009
2-10-2009
Please cite this article as: Wellenberg, G.J., Bouwkamp, F.T., Wolf, P.Jv.d., Swart,
W.A.J.M., Mombarg, M.J., de Gee, A.L.W., A study on the severity and relevance of
porcine circovirus type 2 infections in Dutch fattening pigs with respiratory diseases,
Veterinary Microbiology (2008), doi:10.1016/j.vetmic.2009.10.003
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Accepted Manuscript

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A study on the severity and relevance of porcine circovirus type 2 infections
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in Dutch fattening pigs with respiratory diseases.
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G.J. Wellenberg1, F.T. Bouwkamp¹, P.J. v.d. Wolf¹, W. A.J.M. Swart¹, M.J. Mombarg2, A.L.W. de
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Gee¹.
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1 Animal Health Service (GD), Deventer, The Netherlands.
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2Fort Dodge Veterinaria, Vall de Bianya, Girona, Spain.
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* Address for correspondence and reprints:
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G.J. Wellenberg, Animal Health Service (GD-Deventer), PO Box 9, NL-7400 AA Deventer, The
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Netherlands. Tel: +31 570 660172. E-mail: g.wellenberg@gddeventer.com
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Running head: Role PCV2 in porcine respiratory diseases
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*Manuscript

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Accepted Manuscript
other lung pathogens, while this was found only in 5 of the 17 affected lungs from “low” pigs

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ABSTRACT
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This study was set up to get more insights in the severity and relevance of porcine circovirus type 2
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(PCV2) infections in Dutch fattening farms in an endemic PCV2-situation with no clinical signs of
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post-weaning multisystemic wasting syndrome (PMWS). In part A of the study, in total 29
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commercial fattening farms with varying percentages of pneumonia and pleurisy at slaughter were
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examined. Blood samples were collected at random by cross-sectional sampling; 10 in the age of 10-
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12 weeks, 10 at the age of 16 weeks and 10 blood samples at the end of the finishing period (20 - 22
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weeks of age). Serum samples were examined for the presence of PCV2 IgM and IgG antibodies and
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for antibodies against other porcine lung pathogens. In part B, 8 “high”- and 8 “low” herds were
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selected. The 8 “high” herds were defined as herds having high percentages of lung lesions
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(pneumonia) at slaughter, and the 8 “low” herds had low percentages of pneumonia at slaughter.
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For both the “high” and “low” herds, 3 pigs showing signs of respiratory distress were selected for
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necropsy (n=48). Lung tissue samples were examined post-mortem for macroscopic and
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histopathological lesions, and for the presence of bacteria and viruses. The results of part A showed
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that, pigs at 16 weeks of age with IgM antibodies against PCV2 had a lower probability of having
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pleuritis at slaughter (OR 0.34, P<0.000). Pigs in the age category of 20 – 22 weeks, and with IgM
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antibodies against PCV2, also had a lower probability of having pneumonia at slaughter (OR 0.29,
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P=0.032). In part B lobus apicalis pneumonia, PCV2 in macroscopically unaffected lungs, Pasteurella
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multocida, M. hyopneumoniae, and swine influenza viruses were all found significantly more often in
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“high” than in “low” pigs at autopsy. High PCV2 DNA loads (>104 PCV2 DNA copies/mg) were
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found in lungs of 14 (58%) “high”, and in 7 (29%) of the “low’ pigs (P=0.13). In 11 of the 19
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affected lungs from “high” pigs, high PCV2 DNA loads were found in combination with one or more
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(P=0.02). This study confirms the hypothesis that PCV2 plays a role in pneumonia and pleurisy in 10 -
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24 weeks old fattening pigs, not only in herds with a high prevalence of PMWS, but also in herds with
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no clinical signs of PMWS.
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Keywords: Porcine circovirus type 2, respiratory disease, lungs, swine
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Accepted Manuscript
infections and respiratory disease, the role of other concurrent co-infections can not be excluded and

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1. INTRODUCTION
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Porcine circovirus type-2 associated diseases (PCVAD) are an important concern to swine producers
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around the world. In addition to post-weaning multisystemic wasting syndrome (PMWS), porcine
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circovirus type 2 (PCV2) has also been associated with porcine dermatitis and nephropathy syndrome
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(PDNS), porcine respiratory disease complex (PRDC) and proliferative and necrotizing pneumonia
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(PNP) (Allan et al., 1999; Opriessnig et al., 2004; Wellenberg et al., 2004; Opriessnig et al., 2006;
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Grau-Roma and Segalés, 2007; Opriessnig et al., 2007). In the US, PCV2 associated pneumonia was
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the most common presentation of PCV2 associated diseases (Opriessnig et al., 2007).
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PCV2 has often been associated with lung lesions in pigs co-infected with PRRSV, swine influenza
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viruses (SIV) or Mycoplasma hyopneumoniae. These agents appeared to create a synergistic
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environment that resulted in increased amounts of PCV2 and unusual severe respiratory disease
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outbreaks. However, there have also been reports on uncomplicated PCV2 pneumonia cases in
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western Canada (Opriessnig et al., 2007). These lesions included necrotizing and ulcerative
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bronchiolitis, granulomatous inflammation in the alveolar septa and mixed inflammation and
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fibroplasias in the lamina propria and peribronchiolar areas.
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More insight is warranted on the role of PCV2 as etiological agent in porcine respiratory diseases such
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as PRDC and PNP in endemic situations. In addition, little or no information is available about
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whether PCV2 can be associated with pneumonia in pigs from Dutch swine herds, as described for US
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and western Canada.
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The purpose of this study was to get more insight in the severity and relevance of PCV2 infections in
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Dutch pigs with symptoms of respiratory distress in an endemic situation (situation with no or low
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prevalence of PMWS: Wellenberg and Segalés, 2006). In studies on the association between PCV2
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therefore, this study was not only focused on the detection of PCV2 infections, but also on the
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presence of other infectious agents associated to respiratory diseases in swine.
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The results of this study may be used to gather more evidence on the hypothesis that PCV2 plays a
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role as etiological agent in respiratory diseases such as PRDC and PNP.
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done to correct for the “slaughterhouse effect” during our statistical calculations, as differences

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2. MATERIALS EN METHODS
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This study was divided in two parts: A and B. In part A, blood samples were examined for the
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presence of antibodies directed against pathogens associated with porcine lung lesions. In part B, pigs
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from 8 herds, with high percentages of lung lesions (pneumonia) at slaughter (“high”), and pigs from
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8 herds, having low percentages of pneumonia at slaughter, were examined. These pigs, from both
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groups of herds, were selected on showings signs of respiratory distress, and further examined
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post mortem.
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2.1 Part A
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2.1.1 Herds
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In total, 29 commercial fattening farms, with no signs of PMWS and with varying percentages of
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pneumonia and pleurisy at slaughter, were involved in this part of the study. The farms were
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recruited all over The Netherlands, and not from certain districts. In the selection of herds we
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did not take into consideration management systems, herd size, hygiene, breeding lines, feed and
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medications. For each herd, the following technical data of 2006 were recorded (mean values); the
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number of slaughtered pigs, growth rate (grams/day), feed conversion (feed to gain; kg/kg), mortality
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percentage, percentage of slaughter pigs showing macroscopic lung lesions and pleuritis at slaughter.
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In addition, the “2006 over-all slaughterhouse percentage” on recorded pneumonia and pleuritis in
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slaughtered pigs were recorded for each slaughterhouse. The relative pneumonia and pleuritis scores
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of each herd were calculated by dividing the percentages of pneumonia and pleuritis found at slaughter
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with the “2006 overall slaughterhouse percentage” of the corresponding slaughterhouse. This was
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between slaughterhouses in determining and registering abnormalities in lungs and pleura were
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considerable.
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2.1.2 Animals and blood samples (cross-sectional)
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