Canine heartworm disease

In my recent visit to the Best Friends Animal Society sanctuary, I fell in love with a little dog that I would have loved to adopt.   I learned that she had heartworm disease and was scheduled to undergo further treatment.

I’m not familiar with this disease because I live in New Zealand, where the disease doesn’t exist (and so our authorities would not allow her into the country, which was news I was not prepared to hear).  Here’s some information on the condition:

Heartworm disease is widespread in the United States but particularly prevalent in the southern states around the Gulf of Mexico (including Texas, where my little dog was picked up).  

Mosquitoes help to transmit the infection.  The mosquito ingests microfilariae that circulate in the blood of an infected animal and then these microfilariae develop inside the mosquito.  When the mosquito bites another dog, the larvae are transferred to the new host and travel through the connective tissues into veins and then travel to the heart where they attach themselves in the arteries and pulmonary blood vessels to feed off the nutrient-rich blood.

Within 3-4 months, the heartworms begin reproducing, releasing microfilariae into the bloodstream, where again they can be picked up by mosquitoes to infect other dogs or re-infect the same dog that is bitten again.

Heartworms can grow up to a foot in length and damage the blood vessels as well as inhibiting the flow of blood.   Many dogs with heartworm will not show symptoms but in more serious cases the dogs may have a mild, persistent cough, be reluctant to exercise, show fatigue after only moderate exercise, or have reduced appetite and weight loss.  Dogs can die from the effects of a severe heartworm infestation.

There is a drug that can be injected into a dog for treatment of heartworm, but administration of drugs to prevent heartworm is essential in all dogs.  Dogs are tested for an antigen to confirm presence of heartworms. 

Dogs that are treated for heartworm are injected with a special drug under close veterinary supervision.  Dogs must be kept quiet because as the worms die off, their bodies can become lodged in the lungs causing pulmonary embolism.  This condition can also kill the dog.   Treatment for heartworm is not a full-proof process and comes with risks.

Heartworm disease can affect animals other than dogs.  It has been found in coyotes, wolves, cats, foxes and ferrets – but is the dog that is considered the definitive and ideal host.

Dog owners in the US should ensure that they are giving their dog an approved heartworm prevention drug. 

You can learn more about canine heartworm disease by visiting the American Heartworm Society website.

A canine heart showing severe heartworm infestation

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