Heartworm Lifecycle: Deadly Residents
Heartworm disease is caused by the growth of worms that are transmitted to dogs by mosquitoes. Although heartworms can live for as long as 7 years in an infected pet, they often cause no visible symptoms — which is one reason they can potentially be so deadly. And it's also one of the reasons the Companion Animal Parasite Council recommends year-round heartworm protection.
A yearly blood test, performed by your dog's veterinarian, is the only accurate way to detect heartworm infection.
There are four main phases in the lifecycle of a heartworm: microfilaria, larva, juvenile worm and adult worm.
Microfilariae are actually microscopic larvae. They live in the blood of most heartworm-infected dogs. Microfilariae are ingested by a mosquito that feeds on an infected animal, where they molt twice over a period of about 2 weeks and develop into infective larvae.
There are two main phases of growth in the larval stage. In the first, the infective larvae are passed from the mouth parts of the mosquito to your pet's skin, then burrow into your dog's tissue through the bite wound. In about one to three days, the larvae mature into the second phase during which they migrate through your dog's tissue for several weeks.
In about two months after initial infection, the larvae undergo a final molt and become juvenile (sexually immature) worms. Juveniles range from 1 to 3 cm in length. They enter your dog’s vascular system, and move from there to your dog's heart and lungs in as early as 70 days after initial infection. Once arriving, they mature to adulthood.
Heartworms generally mature into mating adults in the pulmonary artery — or the artery responsible for moving blood from the right ventricle of the heart to the lungs. This artery can become clogged with both live and dead worms, resulting in any number of health issues, including but not limited to infection, clogging of the arteries, and various heart malfunctions — even death.
An infected dog will typically be carrying microfilariae within 6 to 7 months after first being infected by the initial mosquito bite. And the cycle continues.
Trifexis® (spinosad + milbemycin oxime) makes heartworm disease prevention simple and convenient: One chewable tablet, once a month, all year round.
If your veterinarian prescribes less than year-round prevention, it is important that you administer Trifexis each month for at least three months after your dog's last exposure to mosquitoes. Untreated heartworm disease can be debilitating, even deadly, for your dog. Year-round heartworm prevention with Trifexis can stop this deadly cycle, before it begins. Read more about ways you can help control heartworm.