How Do Dogs and Cats Get Heartworm Disease?

Heartworm disease can be transmitted through one method alone: the bite of a mosquito. Whether the new host is a dog, cat, or in rare cases, a human, the parasite’s only means of spreading into the bloodstream is through these pests.

Heartworms in Mosquitoes

Mosquitos contract heartworm microfilaria when they bite infected dogs. The microfilaria then undergo an incubation period inside the mosquito for up to two weeks. During this time, the infected mosquito cannot spread heartworm disease. But when the microfilaria have developed into infective larvae, they move back into position by the mosquito’s mouth so that when the mosquito bites another dog, the larvae can move into the next dog’s tissue. There is no way to tell if a mosquito is carrying heartworm disease, or if they are prime to pass on infective larvae.

Transmitting Heartworm Disease to a Host

Once the larvae pass through the dog’s skin under the mosquito bite, they grow for up to two weeks under the tissue. After they have developed to the next larval stage, they move to the dog’s chest and abdomen muscles until they molt once again, up to two months after the initial bite. Finally, the larvae enter the bloodstream and molt and grow as they travel to the heart and surrounding vessels. These mature heartworms have been in your dog’s system for up to four months.

If one pet has heartworm disease, it doesn’t mean your other pets will become infected with the parasite. Because heartworms can only be transmitted through an infected mosquito bite, dogs and cats that share a common space will not transmit the disease to each other. Even if a mosquito bites the infected pet and then an uninfected pet, the microfilia will not have enough time to incubate and pass along to its next host. Only a mosquito previously infected with incubated heartworm disease will be able to transmit it.

Are Dogs in States With Lower Mosquito Populations at Risk for Heartworm Disease?

Though areas with smaller mosquito populations may seem safe from this disease, cases of heartworm in pets have been found in all 50 states, including Alaska. Giving your pets heartworm prevention medication, like Revolution or Iverhart Max for dogs, is the best way to make sure your pets avoid contracting it no matter where you reside.