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The Heartworm Parasite

The mosquito serves as the intermediate host for the larval stage of the heartworm. The mosquito ingests the larva when it bites an infected dog and deposits its cargo in an uninfected dog when seeking another blood meal.

The larva burrows into the dog and undergo several changes to reach adult form, then travel to the right side of the heart through a vein and await the opportunity to reproduce. Adult heartworms can reach 12 inches in length and can remain in the dog’s heart for several years.

Dogs can have some larva in their blood and worms in their lungs without manifesting the disease. Once the number of worms exceeds a certain number based on the size and activity level of the dog, however, the adult worms move to the heart and symptoms begin to occur. Very active dogs may experience symptoms with lower numbers of worms than couch-potato dogs.

The time lag between the initial infestation of larva and reproduction by adult worms living in the heart is six-to-seven months in dogs.

Female heartworms bear live young – thousands of them in a day. These young circulate in the bloodstream for as long as three years, waiting to hitch a ride in a bloodsucking mosquito. They undergo changes in the mosquito that prepare them to infect a dog, and they transfer back to the original host species the next time the mosquito bites. The process of change in the mosquito takes about 10 days in warm climates, but can take six weeks in colder temperatures.

The worms grow and multiply, infesting the chambers on the right side of the heart and the arteries in the lungs. They can also lodge in the veins of the liver and the veins entering the heart. The first sign of heartworm infestation may not manifest for a year after infection, and even then the soft cough that increases with exercise may be dismissed as unimportant by the owner.

But the cough worsens and the dog may actually faint from exertion; he tires easily, is weak and listless, loses weight and condition, and may cough up blood. Breathing becomes more difficult as the disease progresses. The progression is traumatic: the dog’s quality of life diminishes drastically and he can no longer retrieve a Frisbee or take a long walk in the park without respiratory distress. Congestive heart failure ensues, and the once-active, outgoing pet is in grave danger.

Testing

Heartworms can be detected by blood test.

Treatment

If a blood test or the onset of symptoms alert owner and veterinarian to the presence of this devastating parasite, treatment is possible and successful if the disease has not progressed too far.

Surgical removal of the adult heartworms is possible and may be indicated in advanced cases with heart involvement.

Prevention

Preventive doses come in oral and topical versions and are only available from a veterinarian.

This entry was written by Dakota Sawbridge, she is a contributor to Idle tymes and CoffeePop. Dakota is fast becoming an authority on omnilux. Read her online journal here.