the reason all those breeds are seemingly more at risk is because they’re the most popular, bred by serial breeders and kept in less than ideal settings.
parvo generally (always?) attacks puppies. I don’t recall ever really seeing it strike an adult dog.
Parvo is a single stranded DNA virus that requires a fast growing cell to replicate. Certain breeds have a susceptibility to the virus. It was first identified the Summer of 78’ when it mutated at a Collie show in Mobile, Alabama. Older dogs are rarely infected and younger dogs with the fastest growing cells most susceptible. The virus replicates in such numbers it is highly infective in an environment as it takes as few as eight virions to cause disease. It is now endemic in the canine world so vaccinate your pups and live with it. The Summer of 78’ was an exciting time for me as I was in veterinary microbiolgy and the growing of the virus in vitro was difficult until we found that it grew on Feline kidney cells which gave us a hint as to its origin. I fully expected it to mutate into the human population by now as it mutates into another species about every twenty to forty years.