Canine influenza virus (CIV) is highly infectious.

Modes of transmission and timing of viral shedding and clinical signs contribute to the highly contagious nature of CIV.

Shedding Period

Based on data from experimentally infected dogs, peak viral shedding from the upper respiratory tract occurs 2 to 4 days following infection. CIV may continue to be shed for up to 7 days in most dogs, and even up to 10 days in some dogs.²

As shown in the figure below, because the shedding period, particularly the time of peak shedding, overlaps with the incubation period, infected dogs are likely the most contagious before they show obvious clinical signs.²