Systematic Veterinary Virology

TRANSMISSION

• Infected dogs shed the virus through body secretions and excretions, especially respiratory secretions.
• The main mode of transmission is airborne. Normal animals get the infection by breathing the viral particles. Dogs in recovery may continue to shed the virus for several weeks after symptoms disappear and act as source for contamination.
• Once the virus enters the normal host, it is engulfed by macrophages. Viruses are not killed by the macrophages and the virus uses the macrophage as a means of transportation inside host’s body.
• Within 24 hours, the virus reaches the lymph nodes of the lung. By the 6th day, the virus migrates to the spleen, stomach, small intestine, and liver and results in production of fever.
• After the host’s immune system clears the virus from the different visceral organs, the virus still continues to remain in CNS and skin causing seizures for a long time and hardening of the skin. Though the virus spreads very rapidly inside the body their stability outside the body is questionable.
• The lipid envelope is easily disrupted in the environment, which makes it impossible for infectious virus to persist in the environment. Because an intact fatty envelope is required for infection, virus transmission must involve dog-to-dog contact or at least contact with extremely fresh (less than 30 minutes old) infected body secretions.
• As with other viruses, living virus happily freezes and can survive for years if kept frozen and protected from light. The initial disease in dogs appears quite, but the severity of the symptoms steadily increases despite treatment until the dog is often destroyed on humane grounds.
• CDV infection can take a month to show all of its worst characteristics, and things can still deteriorate from then on. There is no vector involvement in the transmission. In utero infection is rare.