Greg Wideman from Southwest Ontario Veterinary Service, Choosing An IAV Test Depends On Objectives

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Influenza A virus (IAV) is one of the most frequently   identified   primary   respiratory disease  pathogens  in  respiratory  diseases cases   at   the   Animal   Health   Laboratory (AHL).  IAV  continues  to  be  an  area  of  concern  in the  public  health  arena  because  of  the  potential  for zoonotic  transmission  of  IAV  from  pigs  to  people. Much  more  common, however,  is “Reverse  Zoonoses”  with transmission    from    people    to    pigs    occurring. Sometimes  all  we  need  to  know  about   IAV  is whether  or  not  pigs  have  been  infected.  In  some cases  we  need  more  detailed  information  such  as specific  gene  sequencing  and  /  or  virus  isolation  in order  to  design  effective  prevention  programs  such as   vaccination. Based  on  gene  sequencing,  farms  in  Ontario  have been  getting  hit  with  strains  of  IAV  that  are  not usually well-covered by the commercial vaccines. In these  cases  we  design  prevention  programs  using autogenous   vaccines   made   specifically   for   a farm,    system    or    region.

 

US  researchers  compared  various  virus  sampling approaches  in  order  to  detect,  isolate  and  sequence IAV  using  individual  samples  such  as  nasal  swabs, nasal    wipes    and    oropharyngeal    swabs,    group samples  such  as  oral  fluids,  surface  wipes  and  sow udder  skin  wipes  and  environmental  samples  such as  airborne  particles  deposited  on  surfaces  and  air samples. All samples were tested by  IAV rRT-PCR and  a  subset  was  used  for  virus  isolation  and  direct sequencing.

 

The researchers found that in general:

  • Environmental  and  group  samples  resulted  in higher  odd  ratios  (range  =  3.87-16.5,  p-value  < 0.05)  of  detecting  a  positive  sample  by  rRT-PCR  compared  to  individual  pooled  samples, except  for  oropharyngeal  swabs  (OR  =  8.07,  p-value < 0.05).
  • Individual  samples  were  most  likely  to  yield  an actual  viral  isolate  by  cell  culture  that  could  be used  for  gene  sequencing  or  preparation  of  an autogenous vaccine.

⇒Oropharyngeal    swabs    in    suckling    pigs (78.4%)

⇒Nasal  swabs  (47.6%)  or  nasal  wipes  (45%) in growing pigs

⇒Udder  wipes  in  lactating  sows  (75%)  were the preferred samples to obtain an isolate.

 

Take Home Message

Environmental and group sampling strategies are the  preferred  diagnostic  direction  if  the  goal  is just to detect infection.

Individual  samples  are  more  likely  to  yield  live virus

Udder   wipes   from   lactating   sows   appears   to offer  a  convenient,  cheap  and  sensitive  method to monitor IAV in litters prior to weaning.

 

Submitted by Greg Wideman, DVM

Ref: Garrido-Mantilla   J,   Alvarez   J,   Culhane   M,   Nirmala   J,   Cano   JP, Torremorell M.Comparison of individual, group and environmental sampling strategies to conduct influenza surveillance in pigs. BMC Vet Res. 2019 Feb 14;15(1):61. doi: 10.1186/s12917-019-1805-0.

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