CIV H3 Comparison

May 27, 2015 / Diagnostic Updates

The canine influenza virus (CIV) subtype H3N8 is the current vaccine virus that originated in equine, which infected canines in 2003/04 and now is considered enzootic among canines in the U.S. The H3N2 strain originated in avian species in Asia and emerged in the U.S. in 2015. The big question everyone has regarding the CIV outbreak is if the vaccine H3N8 strain will offer cross-protection against the newly emerged H3N2 strain. Based on analysis performed at the University of Illinois Veterinary Diagnostic Laboratory (UI VDL) comparing the H3N2 and H3N8 strains, the current vaccine may provide some, but probably not significant cross-protection.

Like all viruses, influenza viruses mutate, that is change the nucleic acid sequences of their various genes during the infection of their host – human and animals. This change is called antigenic drift for influenza viruses, because the resultant viral proteins (antigens) may be altered. A result of the build up of such mutations in its genes is that different looking viral proteins (antigens) are presented to the host immune system.

Both the CIV H3N8 and H3N2 strains have a H3 subtype. The H (hemagglutinin) is a very important protein for the virus as it uses the H protein attach to host cells to initiate an infection in humans or animals. Therefore, antibodies against this viral protein help protect the host against the infection.

However, due to antigenic drift, not all H3’s are alike.

A CIV H3N2 was isolated at the UI VDL from a dog that died of pneumonia. The whole genome was sequenced at the UI W.M. Keck Center and was determined to be 98% identical to the one found in Asia. Subsequently, a comparison was performed at the UI VDL to predict the similarity of its H3 protein to the H3 protein from 16 enzootic CIV H3N8 strains circulating in the U.S. between 2003 and 2013. The H3 protein of the recent isolate was only approximately 85% identical to the H3 proteins from the H3N8 strains. Because of the differences between these proteins, the current H3N8 vaccine may offer some, but it is unlikely to offer significant cross-protection against the Asian H3N2 strain. — Dr. Gail Scherba

  • Pathologist: Dr. Kuldeep Singh
  • VDL staff: Therese Eggett, Debbie Cassout, Lucienne Burrus and Dr. Sara Lanka
  • EMRL: Alvaro G. Hernandez, PhD, Director of DNA Services
  • W.M. Keck Center: Christopher J. Fields, Technical Lead in Genome Informatics, W.M. Keck Center