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What is heartworm and why it so dangerous for dogs?

Monday March 13, 2017 Written by Published in Local

Heartworm is a parasite of dogs that is found most commonly in hot, humid areas.


It can uncommonly affect other animals, including cats, but the disease is usually much less severe in this species.

Heartworm does not spread dog to dog, but rather it is spread via mosquitoes that are infected with heartworm larvae.

Mosquitoes can more easily bite short-coated dogs making them more susceptible, however long-haired dogs can get bitten too. 

Once the mosquito bites the dog, the heartworm larva enters the skin and starts its lifecycle.

It moves to the bloodstream and reaches the heart and lungs. It takes six months from the time of infection for the heartworm larva to mature and start producing new young larvae.

It often takes several years for worm numbers to accumulate enough to cause signs of disease. For this reason, the actual signs of heartworm disease are usually only seen in dogs two years of age or older.

The early signs of heartworm disease are a low soft cough that gets worse with exercise, shortness of breath and loss of stamina.

If left untreated, the disease progresses as the adult worms block blood flow through the heart and damage blood vessels.

This leads to weight loss, lethargy and a swollen abdomen from fluid accumulation and possibly coughing up blood, before eventual heart failure, organ failure and death.

Heartworm infestation can be diagnosed with a blood test.

A drop of blood can be placed on a glass slide and examined under the microscope to look for heartworm larvae. This test has limitations, though, because it cannot detect low worm burdens, and because there is another type of worm that sometimes lives in dog blood that looks very similar to heartworm but is harmless and it can be very hard to differentiate the two.

For these reasons another test called a Snap test is preferred, as it can detect small heartworm burdens more accurately. These tests can be performed from six months of age.

The good news is that heartworm is very preventable, most often done by giving the dog a monthly tablet.

 It should be given lifelong to ensure complete protection.

The dog should be tested for heartworm before starting on the tablets and then once a year thereafter to ensure that there is no infestation developing.

Limiting contact between mosquitoes and your dog can also help reduce the risk of infection, for instance by avoiding walks at dawn and dusk when mosquitoes are most active.

For dogs already infected and suffering heartworm disease, there is a treatment. Treatment consists of injections of a compound that kills and breaks up the adult worms into tiny pieces.

A dog being treated must be kept confined and very quiet for several weeks because these worm pieces can block blood vessels during strenuous exercise and cause death.

Affected dogs are also treated with steroid and antibiotic tablets to suppress the damage caused by dying heartworms. The dog then needs to come in for the blood test six months after treatment to check that the treatment worked, and then be tested yearly as per usual.

The Esther Honey Foundation is planning to set up heartworm testing stations across the island in the next few weeks so that people can bring their dogs to get checked and so we have an idea of how prevalent the disease is on the island.

The microscope test will cost $20 and the Snap test will cost $40.

Heartworm prevention tablets will also be available to purchase at these stations and cost $5 per tablet.

At the moment we are low on supplies of Snap tests and are waiting for more to arrive from overseas. The Esther Honey Foundation would love to see all the dogs on the island so we can really get a handle on this disease.

            - EHF


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