Case Study Analysis: Heartworm Disease Hits Home

Meet Alfred, a 2-year-old Norfolk Terrier.  Alfred first visited us at the end of August after he was recently adopted.  Alfred’s owners adopted him knowing that he was positive for heartworm disease but were committed to providing the treatment necessary to rid him of this debilitating disease.

Alfred, a 2-year old Norfolk Terrier. Recently adopted, Alfred's owners knew he had heartworm disease, but are diligently working with us. So far his treatments are going well!

Alfred, is a 2-year old Norfolk Terrier with heartworm disease. Recently adopted, Alfred’s owners knew he was heartworm positive, but are very dedicated; so far his treatments are going well!

Heartworm disease is a very serious and potentially fatal condition caused by parasitic worms that live in the pulmonary vessels (the vessels which carry blood from the heart to the lungs), causing severe lung disease, heart failure, and damage to other organs in the body. Dogs and cats of any age, breed, or living condition (indoors or outdoors) are at risk in our area.

Heartworm disease is transmitted by mosquitos.  Looking at the map below, you can see that our area ranks in the mid-to-high levels of heartworm incidence compared to the rest of the country.

This map shows the regional incidence of heartworm disease in the United States. It only takes one bite from an infected mosiquot to transfer heartworms to your pet. Image source: American Heartworm Society.

This map shows the regional incidence of heartworm disease in the United States. Testing data from thousands of veterinary practices and shelters is used to create a detailed map showing the average number of heartworm-positive cases per clinic.

How are heartworms transmitted from pet to pet?

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 takes a blood meal from an infected animal, they pick up the microfilaria.  In the mosquito, the microfilaria will develop into “infective stage” larvae. When the infected mosquito takes a bite on another animal, the larvae are deposited onto the animal’s skin and enter the bloodstream through the bite wound.  Once inside the new host, the larvae develop into adult heartworms.  It takes about six months for the larvae to mature into adult heartworms.

Here you can see microfilaria that were living inside Alfred.  This is a video of his blood spun down in a small tube while our doctors are looking at it under a microscope.

You can see that Alfred had a significant and dangerous load of microfilaria circulating, but he has done very well so far with his treatment regimen.

The medical workup and treatment plan in dogs is very expensive, painful, and requires strictly resting the pet for several months to limit the risks of complications.  Alfred’s veterinarian, Dr. Jennifer Boyle, provided a brief synopsis of Alfred’s treatment plan:

Once Alfred was confirmed heartworm positive, his level of disease was staged with chest X-rays and blood work.  Next, he started a course of doxycycline and received his first monthly heartworm preventative. He was monitored in-hospital for this since he had such a high microfilaria load.  Next, he will be scheduled for immiticide injections, be on a low-dose of steroids, pain medication when needed, and strict rest.

For more detailed information on heartworm disease treatment plans for dogs, see this handout from the American Heartworm Society.

Luckily, heartworm disease is preventable!  We recommend routine annual heartworm screening (a simple blood test) for all of our dog patients, and monthly heartworm prevention for all of our dog and cat patients (and ferrets too!).   The diagnosis is much more complex in cats; currently, there is no feline treatment and medical management is very expensive and challenging.

Alfred is from a rescue in Virginia, which is a reminder of the importance of year-round monthly heartworm prevention for our pets in this area.

Are preventatives really needed year round or if my pet is mainly indoors?

Preventatives work by killing the immature larval stages of the heartworm parasite.  Once the larvae become adults, they cannot effectively be eliminated by preventatives. As mentioned earlier, it takes about six months for the larvae to mature to adult heartworms – because of this, it is very important that preventatives be administered strictly on schedule every month without interruption.  Administering late, or skipping a month can allow the immature larvae to molt into the adult stage.

Heartworm Prevention

To get more information about heartworm disease and to see which preventatives we recommend for your pet, visit our blog article here.

*Featured Header Image: American Heartworm Society’s 2013 Incidence Map

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