|The American Heartworm Society is now recommending year-round avoidance, even in seasonal locations. 1 reason for this can be compliance ” to make certain that the medicine has been given properly by the pet owner. Additionally, most monthly heartworm preventives have action against intestinal parasites. A number of these exact same intestinal parasites that infect dogs can also infect people, with projected infections occurring in three to six million people each year. So this extra plus of monthly deworming makes great sense.Before beginning a preventive program, all dogs which may possibly be infected with older heartworms should be tested.