Virus shedding occurs by 7 days post infection. The virus is most abundant in the respiratory exudates, and transmission is
most commonly via a aerosol or droplet route. This said, the virus has been isolated form most other tissues and secretions.  Virus shedding can continue up to 90 days after infection, but two weeks is more typical. Most recovered dogs will clear the virus, but a few may maintain the infection in their CNS (2,6,8). It is estimated that between 25 and 75% of susceptible animals that become infected will be sub clinical and will clear the virus but may still go through a period during which they shed the virus. (2).  Canine distemper virus is very resistant to cold, and the majority of cases in domestic dogs are seen in the fall or winter.  (6)


Lack of vaccination is the number one factor contributing to an animal developing clinical canine distemper. One study in Indianna showed that 93.8% of cases of clinical canine distemper were attributed to lack of vaccination, that is to say, there is a 350 fold increased risk in unvaccinated animals.  (11)

The greatest prevalence of spontaneous distemper in cosmopolitan dongs is in animals between 3 and 6 months of age, corresponding to the waning of passive maternal immunity gained from colostrum consumed shortly after birth.  However, in naïve isolated populations, outbreaks affect all ages.  Variation in the susceptibility of different breeds or sexes has never been proven, although brachiocephalic breeds have been reported to have lower prevalence of disease, mortality, and sequelae of the disease than do dolichocephalic breeds.  (2)

More cases occur in the fall and winter than do in other seasons due to the viruses high resistance to cold.  (6)

Viral Characteristics
Clinical Signs
Transmission and Risk
Other Species
Treatment and Prognosis
Medical Dictionary