As shared by the County of Los Angeles Veterinary Public Health:
What is Canine Influenza?
Canine influenza (CIV) is a disease in dogs caused by an influenza virus. There are two influenza virus strains that can spread between dogs: H3N8 and H3N2. Both of them cause similar symptoms in dogs. Unlike Leptospirosis, neither of them are known to make people sick, but can affect cats.
Infected dogs start shedding the virus 2 days before the start of symptoms, and for at least 21 days or more afterward, even after they appear healthy.