General Facts

Influenza Change






Clinical Signs in Pigs1,2,3
  • Sudden onset of fever
  • Lethargy
  • Sneezing
  • Coughing
  • Mucous discharge from nose and eyes
  • Inflammation of eyes
  • Loss of appetite
  • Weight loss
  • Dyspnea
  • Reduced fertility or abortion
  • Rapid spread through herd (24-72 hours)
Presumptive Diagnosis

The clinical signs and/or pathological findings, in conjunction with the elimination of differentials, can be used to make a presumptive diagnosis. Possible differentials include pasteurellosis, pseudorabies, porcine reproductive and respiratory syndrome, chlamydial and Haemophilus infection.1 The clinician can also use an antigen-detection test for a rapid stall-side result. This test does not prove that the virus is the 2009 H1N1subtype, however, because it cannot differentiate it from the seasonal H1N1.4

Confirmed Diagnosis

Infection of the 2009 H1N1 sub-type can be confirmed by one or both of the following methods2,4:
  1. RT-PCR - This method is sensitive and able to distinguish between H1N1 subtypes
  2. Virus isolation 
Retrospective Diagnosis
Serology can be used to make a diagnosis even after clinical signs have resolved. Hemagglutinin inhibition that illustrates an increase in virus-specific antibodies using acute and convalescent serum samples indicates exposure to H1N1.1 This is can be used to bolster a presumptive diagnosis.


  1. 'H1N1'. The Merck Veterinary Manual. (Accessed September 15, 2009)
  2. '2009 H1N1 Flu (Swine Flu)'. Centers for Disease Control and Prevention. (Accessed September 15, 2009)
  3. 'H1N1 Flu Virus - Advice for Veterinarians and Swine Producers'. Canadian Food Inspection Agency. (Accessed September 15, 2009)
  4. 'WHO Information for Laboratory Diagnosis of New Influenza A (H1N1) Virus in Humans'. World Health Organization. (Accessed September 20, 2009)
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