Certain breeds such as Dobermans, Rottweilers and German Sheperds are more likely to become infected. Season is also a predisposing factor. From July to September a dog is 3 times as likely to become infected with parvo. Also, intact dogs are 4 times more likely to become infected that dogs that have been spayed or neutered, because they have a tendency to roam and will be more likely to come in contact with other infected dogs. Most importantly, unvaccinated dogs are 13 times more likely to becomes infected than vaccinated dogs.
Prevention is the best cure.