What was a disease primarily in the Southeast now can be seen in all 50 states, particularly in the lower 48 and Hawaii. Increased human mobility, especially into rural and natural habitats, and increased suburbanization has increased breeding grounds for vector species, and potential contact between wildlife vectors and domestic pets. Increased dog density Adaptation to additional vector species by D. immitis . Adaptation to a wider temperature range for development of larval stages in the mosquito by D. immitis . Finally, there are some features which place some dogs at higher risk than others for heartworm disease.
Risk is increased with increased age, size, and exposure to the outdoors.
In addition, sporting breeds tend to be at higher risk than other dogs, since they are also more likely to be outdoors during the transmission season. However, there seems to be no increased risk associated with gender or hair coat length.