I know we touched on parasites in another entry, however, heartworm infestation is a real problem in dogs, is potentially deadly and is worthy of an in-depth article.

Heartworm (Dirofilaria immitis) is a parasitic roundworm that is spread from host to host through the bites of mosquitoes. The heartworm is a type of filaria, a small thread-like worm that causes filariasis.

The definitive host is the dog, but it can also infect cats, wolves, coyotes, foxes and other animals, such as ferrets, sea lions and even, under very rare circumstances, humans.The parasite is commonly called “heartworm”; however, adults often reside in the pulmonary arterial system (lung arteries) as well as the heart, and a major effect on the health of the animal is a manifestation of damage to the lung vessels and tissues. Occasionally, adult heartworms migrate to the right heart and even the great veins in heavy infections. Heartworm infection may result in serious disease for the host, with death typically, as the result of congestive heart failure.

A German Shepherd Dog heart infested with heartworm.

The parasite is commonly called “heartworm”; however, adults often reside in the pulmonary arterial system (lung arteries) as well as the heart, and a major effect on the health of the animal is a manifestation of damage to the lung vessels and tissues. Occasionally, adult heartworms migrate to the right heart and even the great veins in heavy infections. Heartworm infection may result in serious disease for the host, with death typically, as the result of congestive heart failure. 

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?

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, cat, 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 and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Prevention Vs Treatment

Treatment of heartworm infestation is significantly more expensive than prevention.

Preventing heartworms is available in two different ways, a monthly chewable or an injectable given every six months. Both methods are available at your Veterinary office and require a negative heartworm test prior to administration. Typically, both treatments are low-dose Ivermectin which can completely prevent heartworm microfilaria from maturing.

Treatment for an active heartworm infestation is generally done in hospital because it requires strict cage confinement if the fast kill method is used. Many Veterinarians are moving away from the fast kill method and are now utilizing the slow kill method; this is less costly but may not be used in every case. Circumstances and pets vary so you will need your Veterinarian to evaluate your pet and decide which method is recommended for your pet.