Abstract
BackgroundPostweaning Multisystemic Wasting Syndrome (PMWS) is an emerging disease in pigs of multifactorial origin, but associated to porcine circovirus type 2 (PCV2) infection. PMWS was first diagnosed in Sweden at a progeny test station that received pigs aged five weeks from 19 different nucleus herds on the day after weaning. The objective of this study was to examine, for the first time in an index outbreak of PMWS, the relationship between PCV2 virus, antibodies to PCV2 and serum amyloid a (SAA) in sequentially collected serum samples from pigs with and without signs of PMWS.MethodsForty pigs of the last batch that entered the station at a mean age of 37.5 days were monitored for signs of PMWS during the first 55 days after arrival. Serum was collected on six occasions and analysed for presence of PCV2 DNA and antibodies to PCV2, as well as for levels of SAA.ResultsFour of the pigs (10%) were concluded to have developed PMWS, with necropsy confirmation in three of them. These pigs displayed low levels of maternal antibodies to PCV2, more than 107 PCV2 viral DNA copies per ml serum and failed to mount a serological response to the virus. Starting between day 23 and 34 after arrival, an increase in PCV2 viral load was seen in all pigs, but PCV2 did not induce any SAA-response. Pigs that remained healthy seroconverted to PCV2 as the viral load was increased, regardless of initially having low or high levels of PCV2-antibodies.ConclusionIn this index case of PMWS in Sweden, pigs affected by PMWS were not able to mount a relevant serum antibody response which contributed to the disease progression. The maximal PCV2 virus load was significantly higher and was also detected at an earlier stage in PMWS-affected pigs than in healthy pigs. However, a viral load above 107 PCV2 DNA copies per ml serum was also recorded in 18 out of 34 pigs without any clinical signs of PMWS, suggesting that these pigs were able to initiate a protective immune response to PCV2.
Highlights
Postweaning multisystemic wasting syndrome (PMWS) is a disease of pigs first recognised in Canada in 1991 that now is a global epizootic [1,2,3]
Experimental studies in colostrum deprived piglets have demonstrated that such factors can include co-infection with other microbes such as porcine parvovirus [9,10,13], porcine reproductive and respiratory syndrome virus [14,15] or Mycoplasma hyopneumoniae [16], but Postweaning Multisystemic Wasting Syndrome (PMWS) could be induced by porcine circovirus type 2 (PCV2) in combinations with either immunsostimulators [17] or immunosuppressors [18]
Initial health status of the animals Pigs in Sweden are free from all diseases listed by the Office International des Epizooties (OIE), including Aujeszky's disease (AD), porcine reproductive and respiratory syndrome (PRRS), and from porcine endemic diarrhoea (PED) and transmissible gastro-enteritis (TGE)
Summary
Postweaning multisystemic wasting syndrome (PMWS) is a disease of pigs first recognised in Canada in 1991 that now is a global epizootic [1,2,3]. Experimental studies in colostrum deprived piglets have demonstrated that such factors can include co-infection with other microbes such as porcine parvovirus [9,10,13], porcine reproductive and respiratory syndrome virus [14,15] or Mycoplasma hyopneumoniae [16], but PMWS could be induced by PCV2 in combinations with either immunsostimulators [17] or immunosuppressors [18] Experimental infections in both conventional and specific pathogen-free (SPF) pigs with tissue homogenates from PMWS-affected weaners have induced mild PMWS [19,20]. The objective of this study was to examine, for the first time in an index outbreak of PMWS, the relationship between PCV2 virus, antibodies to PCV2 and serum amyloid a (SAA) in sequentially collected serum samples from pigs with and without signs of PMWS
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