As many of us know, heartworm disease is caused by a worm that lives in the heart of dogs and has baby worms that swim in the bloodstream. These baby worms are sucked up by a mosquito and injected into the next victim. My first small animal job had a dog heart in a pickle jar with three-inch worms protruding from the pulmonary artery. In those days, the worm burden was so high that we could see baby worms swirling in a drop of blood. Only sometimes did we need to use a microscope! Preventatives were a daily pill. How successful do you think that was? The advent of monthly preventatives about 35 years ago saved many dogs!
The annual blood test is now more accurate and sensitive and does not rely on baby worms. Furthermore, there is also a blood test that tests for tick disease as well as heartworm disease.
In 2022, CAPC stated that heartworm infected over 200,000 dogs in the US. These are dogs who “never go outside,” dogs who go up north to their cabins and dogs who go for walks in their city neighborhoods. Here at Southfork, a case that I remember clearly was an employee’s dog who always got preventative except for the one year it was missed. It was treated for heartworm disease but died suddenly some months later. Another case was a dog who had the type of heartworm disease that causes liver and kidney failure along with heart failure. That dog died. We have treated some dogs successfully but they need to be kenneled for 8 weeks as the worms die so respiratory arrest is less likely. Clients have commented that the 8-week rest is almost worse than the cost of treatment!
Heartworm disease in cats is less straightforward. The most severe part of the disease is after the mosquito bite. The baby worms migrate through the lungs causing respiratory signs and sudden death. Few worms develop in the heart leading to false negative testing. It is best to put your cat on preventatives as this has been seen in indoor cats as well as outdoor cats.
Spring is coming, really. Please respond to your heartworm reminders and take this disease seriously. A 12-month preventative is recommended since winters, TYPICALLY, have been warmer with less snow cover.
CAPC stands for Companion Animal Parasite Control. Their website has information on all parasites that affect your pet.
This article has been written by Dr. Paula Schanck