Parasites in dogs take many forms, but they all have one thing in common: sooner or later their presence will almost always have an impact on your pet’s health or comfort. They can cause anything from mild irritation to serious illness. The CAPC website has very helpful prevalence maps that provide data of the infection of parasites, from low to moderate to high, across the U.S., broken down by state. Especially useful is that the maps are further broken down into types of parasite, the risk to your pet. There are also separate maps for cats, and there is a glossary of additional parasites and terms.