Canine distemper is a highly contagious virus that can be treated but not cured. Unfortunately, puppies are particularly susceptible to contracting it. You can have a puppy vaccinated when he is 6 weeks old, but before then he is at high risk, especially if his mother was not vaccinated. If his mother had the virus while pregnant, he may already be infected at birth.
Dogs often contract distemper by coming into contact with the bodily fluids of an infected dog, like blood, saliva or urine. The disease is extremely contagious. Even sharing food and water bowls increase dogs' risk -- especially young puppies, who have undeveloped immune systems. Early symptoms of the virus affect the respiratory system, and include coughing, sneezing and the discharge of eye and nasal mucus.
Because distemper can be treated but not eliminated, it's critical that you take any dog or puppy whom you suspect carries the virus to your veterinarian for testing. This is especially important if you suspect a dog who has recently had puppies has the virus, because she may have passed it to her pups in utero. Puppies who are born with distemper are even more immuno-compromised, and thus susceptible to other conditions such as pneumonia.