Clint Lichty from Southwest Ontario Veterinary Services, PCV3: Disease Agent Or “Innocent Bystander”?

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PCV2  is  associated  with  a  wide  variety  of combinations    of    clinical    disease    that include     reproductive     failure,     porcine dermatitis    and    nephropathy    syndrome (PDNS),   respiratory   and   systemic   disease.   The discovery   of   PCV3   virus   in   cases   that clinically resembled   PCV2   has   lead   to   some   widespread surveillance  activity.  One  of  the  findings  has  been that  the  PCV3  virus  is  much  more  widespread  than first suspected.  The  virus  was  found  in  many  herds  that have not had evidence of circovirus disease. In order to  truly  say  that  PCV3  is  causing  clinical  disease and   is   not   just   an “innocent   bystander” it   is necessary  to  demonstrate  that  the  affected  pig  is showing    clinical    signs    of    the    disease,    the pathological lesions are present microscopically and that  the  virus  can  be  identified  within  the  affected tissues.

The investigators in this study documented thirty-six field   cases   that   were   submitted   from   multiple production   systems,   numerous   sites   and   varied geographic locations. They were able to demonstrate  PCV3  virus  within  affected  tissues  by using  an “in  situ  hybridization” test  in  fetuses  with myocarditis,    weak-born    neonatal    piglets    with encephalitis  and  myocarditis,  from  cases  of  porcine dermatitis   and   nephropathy   syndrome,   and   in weaned  pigs  with  systemic  periarteritis.  PCV3  was detected  by  PCR  in  numerous  fetuses  and  perinatal piglets at high viral loads. Samples from all cases in this  study were  assayed  and  found  negative  for PCV2   by   PCR.   Metagenomic   sequencing   was performed   on   a   subset   of   reproductive   cases, consisting   of   sixteen   fetuses/fetal   sample   pools. PCV3 was identified in all pools and it was the only virus identified in fourteen pools.

Take Home Message

These particular clinical cases appear to be associated with PCV3 infection.

Thankfully, clinical disease associated with PCV3 is not occurring on a frequent basis. We will however need to monitor this closely as PCV2 started with a “wimper and not a bang!”

Submitted by Clint Lichty, DVM

Ref: Arruda B, Piñeyro P, Derscheid R, Hause B, Byers E, Dion K, Long  D,  Sievers  C,  Tangen  J,  Williams  T,  Schwartz  K.PCV3-associated  disease  in  the  United States  swine  herd.Emerg  Microbes Infect. 2019;8(1):684-698. doi: 10.1080/22221751.2019.1613176.

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