Since 2001, data from the American Heartworm Society has shown that cases of heartworm disease in pets in the United States have risen by 12%. What’s more, vet clinics in areas that had few to zero cases of heartworm are now starting to see canine patients test positive for this serious disease. Now, heartworm disease is seen in all fifty states and it’s also becoming more prevalent all over the world.

Top States for Heartworm Disease
The American Heartworm Society collects data from about 6000 veterinary clinics every three years. Their latest data available is from 2019. The states with the highest numbers of incidences of heartworm disease in dogs were Mississippi, Louisiana, South Carolina, Arkansas, and Alabama, all states known for their humid climates. Also among the top ten states were Texas, Tennessee, Georgia, North Carolina and Oklahoma.
However, all 50 states saw multiple cases of heartworm disease in 2019 - even Alaska.

Why Heartworm Disease Effects All 50 States
Dogs (and cats, for which data is limited), contract heartworm disease via the bite of a mosquito infected with heartworm larvae. So, as you might expect, heartworm disease is most prevalent in warm, humid, subtropic climates, but exists anywhere mosquitoes live.
Fluctuations in data can be partially attributed to climate change, which has been bringing on milder winters, earlier spring seasons, and more precipitation. Droughts in some areas can cause temporary relief from mosquitoes.
Veterinarians surveyed by the American Heartworm Society also reported that owner compliance also seemed to be a strong factor. In regions where more pet parents started using preventatives, heartworm cases saw a modest decline.
Yet another factor that may be causing fluctuations in heartworm disease data could be the increase of pet adoption across state lines. Heartworm positive pets can pass larvae to local mosquitoes, which then pass on the disease to other animals. As a matter of fact, heartworm cases in Alaska have only been recorded in dogs that have been imported or traveled to other states.

Preventing Heartworm in All 50 States
Veterinarians in areas that saw the greatest increase in heartworm cases reported struggling to get pet owners to give their pets a preventative year-round. While we cannot control the weather, and we cannot eliminate all mosquitoes, we can keep our pets protected by giving them a monthly pill or spot-on treatment.