Puppies are usually inoculated for parvo virus, but the time after their natural immunity from the mother's colostrum wanes and before the vaccination is particularly dangerous. Puppies between weaning and 6 months of age should be kept away from the feces of other dogs, of from places where dogs congregate.
The symptoms of parvo include depression, vomiting and diarrhea. Vets and vet-techs say that there is a smell to the feces of a parvo infected dog...it is the smell of rotting meat/blood, since the lining of the intestine is shed and blood is often found in the stool. The feces will often be grey or yellow-grey and is often streaked with blood. An infected dog will usually die within 48-72 hours. Some dog breeds, such as dobermans and rottweilers seem to be more susceptible to the disease.
Parvo is particularly deadly, but if treatment to combat dehydration and to prevent secondary infection is started promptly it is possible to save the dog, though there may be other permanent effects, such as loss of the sense of smell, or blindness. I do know one dog who had parvo as a puppy and he is now a happy, healthy, well-loved chocolate lab who is blind in one eye.
The best treatment is prevention. Make sure you never buy a puppy mill puppy (most, if not all puppies, from pet stores come from puppy mills) and when you get your puppy, keep her in your yard, away from places where she might come into contact with adult dogs and/or their feces. The virus can live for many months on a surface unless it is disinfected. One quarter cup of bleach in a gallon of water is sufficient to disinfect a contaminated area. If your dog of any age is vomiting for no apparent reason (it didn't eat, say, a half a fruitcake, or a stick of butter*) you should get it to the vet ASAP.
*Nikki the Schnauzer (deceased) and Molly the Beagle, respectively.