What is heartworm disease?
Heartworm disease is a serious and potentially fatal disease in pets in Canada/US and many other parts of the world. It is caused by foot-long worms (heartworms) that live in the heart, lungs and blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body. Heartworm disease affects dogs, cats andferrets, but heartworms also live in other mammal species, including wolves, coyotes, and foxes.
The dog is a natural host for heartworms, which means that heartworms that live inside the dog mature into adults, mate and produce offspring. If untreated, their numbers can increase, and dogs have been known to harbor several hundred worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s health and quality of life long after the parasites are gone. For this reason, prevention is by far the best option, and treatment—when needed—should be administered as early in the course of the disease as possible.
How is heartworm disease transmitted from one pet to another?
The mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.
How significant is my pet’s risk for heartworm infection?
Many factors must be considered, even if heartworms do not seem to be a problem in your local area. Your community may have a greater incidence of heartworm disease than you realize—or you may unknowingly travel with your pet to an area where heartworms are more common. Heartworm disease is also spreading to new regions of the country each year. Stray and neglected dogs and certain wildlife such as coyotes, wolves, and foxes can be carriers of heartworms. Mosquitoes blown great distances by the wind and the relocation of infected pets to previously uninfected areas also contribute to the spread of heartworm disease (this happened following Hurricane Katrina when 250,000 pets, many of them infected with heartworms, were “adopted” and shipped throughout the country).
When should my pet be tested?
Concerning dogs, all dogs should be tested annually for heartworm infection, and this can usually be done during a routine visit for preventive care. Following are guidelines on testing and timing:
- Puppies under 7 months of age can be started on heartworm prevention without a heartworm
test (it takes at least 6 months for a dog to test positive after it has been infected), but should be
tested 6 months after your initial visit, tested again 6 months later and yearly after that to ensure
they are heartworm-free.
- Adult dogs over 7 months of age and previously not on a preventive need to be tested prior to
starting heartworm prevention. They, too, need to be tested 6 months and 12 months later and
annually after that.
- You need to consult your veterinarian, and immediately re-start your dog on monthly
preventive—then retest your dog 6 months later. The reason for re-testing is that heartworms
must be approximately 7 months old before the infection can be diagnosed.
Annual testing is necessary, even when dogs are on heartworm prevention year-round, to ensure that the prevention program is working. Heartworm medications are highly effective, but dogs can still become infected. If you miss just one dose of a monthly medication—or give it late—it can leave your dog unprotected. Even if you give the medication as recommended, your dog may spit out or vomit a heartworm pill—or rub off a topical medication. Heartworm preventives are highly effective, but not 100 percent effective. If you don’t get your dog test, you won’t know your dog needs treatment.
For more information, please visit: https://www.heartwormsociety.org/