In the very large universe of microorganisms, viruses are particularly crafty. For example, during the two-to four-day incubation period before dogs show any signs of illness, the Type A influenza virus that causes dog flu, or CI, can spread through such commonplace activities as being patted on the head, sharing a tennis ball or a water bowl, or a nose-to-nose greeting. And unlike those that cause human flu, the CI virus is active year-round.
As is the case with all microbes, the CI virus can only be seen with an electron microscope. Zoom in, and the hemagglutinin (HA) and neuraminidase (NA) proteins that spike up from its round surface are immediately visible. Influenza viruses are named for the way HA and NA combine, and CI comes in two forms, or strains: H3N8 and H3N2. Only 80 percent of affected dogs show flu-like signs, and the fatality rate is less than 10 percent.
via Whisker Therapy