they should have had injections when they were puppies and a booster shot every year
Shots are not 100% effective. The parvo its self is not harmful but it is very common for parvo infected dogs to get a secondary infection that can be slightly harmful just because pregnant women are immunesupressed (sc). Take the sick dog to the vet for further diagnose, isolate your other dogs and be sure that they get a buster because they can get mildly infected. Disinfectant the house (floors, areas where dogs are mostly and dog dishes with bleach).
Sorry for the needy response lol vet tech student