Dogs get distemper primarily by breathing in virus-laden droplets released when an infected animal coughs, sneezes, or barks. This airborne route is the most common way the canine distemper virus (CDV) spreads, but it’s not the only one. Dogs can also pick up the virus through direct contact with an infected animal, contaminated objects, wildlife encounters, and even before birth.
Airborne Droplets Are the Primary Route
When an infected dog or wild animal coughs, sneezes, or barks, it releases tiny droplets containing the virus into the air. A nearby dog that inhales those droplets can become infected. This makes close-quarters environments like shelters, boarding facilities, dog parks, and training classes higher-risk settings, especially when dogs are unvaccinated or only partially vaccinated.
Contaminated Objects and Surfaces
The virus doesn’t have to travel through the air to reach your dog. CDV can also spread through contaminated surfaces: shared water bowls, food dishes, bedding, toys, leashes, and even clothing. If an infected dog drinks from a communal water bowl at a dog park and your dog uses it next, that’s a potential exposure. The good news is that the distemper virus is relatively fragile outside a host. It doesn’t survive long on surfaces, especially in warm or sunny conditions, and standard disinfectants destroy it quickly. Still, in cool, shaded environments or busy shelters where surfaces are constantly re-contaminated, the risk is real.
Wildlife Carriers
Domestic dogs aren’t the only animals that carry distemper. Raccoons, skunks, foxes, coyotes, badgers, and mink all harbor the virus and have been documented spreading it for decades. Raccoons appear to play a particularly important role in maintaining and transmitting the virus, especially in urban and suburban areas where they live at high densities and overlap with pet dogs.
Your dog doesn’t need to get into a fight with a raccoon to be exposed. Sniffing the spot where an infected raccoon recently rested, investigating raccoon droppings, or simply being in an area where a sick raccoon coughed can be enough. Dogs that spend time outdoors unsupervised, live near wooded areas, or encounter wildlife on walks face a higher risk of picking up the virus from these wild reservoirs.
Transmission From Mother to Puppies
A pregnant dog infected with distemper can pass the virus to her unborn puppies through the placenta. Research published in the American Journal of Veterinary Research confirmed transplacental transmission in dogs, with one infected mother delivering three puppies already carrying the virus at birth. In another case, infection triggered an abortion. Puppies infected this way are born with the virus already in their system and are extremely vulnerable, since their immature immune systems struggle to fight it off. This route is uncommon compared to airborne spread, but it underscores why breeding dogs should be fully vaccinated.
The Incubation Period
After exposure, the virus works silently for a while before any symptoms appear. The incubation period is typically one to two weeks but can stretch to four or five weeks or even longer. A mild, transient fever often appears three to six days after infection, sometimes with a dip in appetite, but these early signs are easy to miss entirely. This means a dog can be infected and spreading the virus before anyone realizes something is wrong.
Why Puppies Are Most Vulnerable
Puppies between about 8 and 16 weeks old face the highest risk of infection, and the reason is a frustrating biological catch-22. Newborn puppies receive protective antibodies from their mother’s milk, which shield them in the first weeks of life. But as those maternal antibodies gradually fade, they reach a level that’s too low to actually protect the puppy yet still high enough to interfere with vaccination. This creates what veterinarians call a “window of vulnerability,” a stretch of time when the puppy is neither protected by mom nor fully responsive to vaccines.
This is why the puppy vaccine series requires multiple doses rather than just one shot. Current guidelines from the World Small Animal Veterinary Association recommend starting distemper vaccination at 6 to 8 weeks of age, then repeating it every 2 to 4 weeks until the puppy is at least 16 weeks old. An additional dose at or after 26 weeks is also recommended to catch any puppies whose maternal antibodies blocked earlier vaccines. Until the full series is complete, puppies should avoid high-risk environments where unvaccinated or sick dogs may have been.
Other Dogs at Higher Risk
Puppies get the most attention, but they’re not the only dogs at risk. Adult dogs that were never vaccinated, dogs with lapsed boosters, and immunocompromised dogs are all susceptible. Shelter dogs are disproportionately affected because they’re often unvaccinated, stressed, and housed in close proximity to many other animals. Dogs rescued from stray populations or imported from regions with low vaccination rates also carry higher risk.
For adult dogs that completed their puppy series and received a booster at one year, revaccination is needed no more often than every three years. That schedule provides strong, lasting protection. The distemper vaccine is one of the core vaccines in veterinary medicine precisely because the disease is severe and highly contagious, but also highly preventable.
How to Reduce Your Dog’s Risk
Vaccination is by far the most effective protection. Keeping your dog’s vaccines current, completing the full puppy series on schedule, and maintaining adult boosters every three years covers the vast majority of risk. Beyond vaccination, a few practical steps help:
- Avoid communal water bowls at dog parks and outdoor cafés, especially if you have a puppy or an unvaccinated dog. Bring your own water and a portable bowl instead.
- Limit wildlife contact. Don’t let your dog investigate dead animals, and discourage nose-to-nose encounters with raccoons, skunks, or foxes. Secure outdoor trash cans to reduce wildlife visits to your yard.
- Keep young puppies away from unknown dogs until the vaccine series is complete. Socialization is important, but stick to controlled settings with dogs you know are vaccinated.
- Isolate sick dogs immediately. If a dog in your household or neighborhood shows signs of distemper (nasal discharge, coughing, lethargy, neurological symptoms), keep your dog well away and clean any shared spaces thoroughly.