It should come as no surprise that puppies (and kittens, and pretty much any type of animal) from pet stores can carry infectious diseases. The same can be said about puppies (and kittens, and pretty much any type of animal) from other sources. It’s really a question of the relative degree of risk.
Do you know where ‘that doggy in the window’ came from?
Nearly 700 dogs were seized in the largest puppy mill raid ever in Tennessee. Puppy mills are large scale breeding operations that produce large numbers of puppies under questionable to horrible conditions. They typically raise dogs under intensive conditions, such as in cages in barns. There may be little attention to the quality