By: Dr. Hilary Slaven
I saw two mosquitoes in my house last night as I was vegging out in front of the TV.
For the record, it is the middle of March in central Indiana. What the heck.
(Yes, I am a veterinarian.)
All of us vets have seen and treated dogs that have had heartworm disease, watched animals suffer and folks have to spend a lot of money to treat it and I think that I can speak for all of us when we say:
We hate it.
Here’s how it works.
As soon as the days start to warm, the mosquitoes start feeding and laying eggs. We know that female mosquitoes can over winter in homes, sheds, holes in trees, etc. (See Purdue University’s Mosquito Information Page).
These mosquitoes take blood meals from mammals, including coyotes, dogs and cats. They act as carriers for many diseases, including heartworms.
Mosquitoes carry the heartworm parasite from infected animals to uninfected animals. They carry the super-small larvae form of the worm (sort of a ‘baby’ heartworm). Infected animals could be dogs, cats, coyotes, or other wild animals.
(Here is a great three minute video on the life cycle of heartworms)
Heartworms live as an adult worm 4-12 inches long within blood vessels of mammals. They lodge inside vessels of the lung and within the heart itself.
Adult worms feed off of nutrition from the blood and start reproducing within the animal. The female worm produces a smaller larval stage of heartworm that moves throughout the vessels of the body.
Now imagine that a mosquito feeds on this infected animal. When it takes a blood meal, it also takes in the heartworm larvae. Then the mosquito moves to another dog, an uninfected furry friend, and takes another meal. The tiny heartworm larvae then move from the infected mosquito into the bloodstream of the uninfected dog. Now our furry friend is infected with the larval stage of heartworm. In 6-8 months’ time, the heart will be full of these worms, causing inflammation and blockage of the vessels, death of lung tissue, and eventually death of the animal.
See what I mean? I hate heartworms.
The good news is that dogs that take heartworm prevention medications stop the heartworm larvae in his tracks. It kills the larvae before it develops into an adult worm. Because adults develop 40-70 days after the dog is infected, that gives us a two month window in which to stop the larvae before they continue to grow into adults. This is important because heartworm prevention products don’t kill adult worms. Once they develop, a new protocol for treatment is necessary.
The complex life cycle of this worm makes it difficult to treat. There is no drug available that kills both heartworm larvae and adult worms. Only one drug kills adult heartworms; it is a parasiticide that has to be injected into the muscle. It is expensive and it has to be given in a very specific protocol in the clinic, as it can have many potential side effects (including shock).
We treated 18 dogs for heartworm disease in 2014 in the Veedersburg clinic. This does not include the many dogs out there aren’t tested and their heartworm status is unknown.
Veterinarians recommend a yearly blood test for heartworm disease (it’s a quick, 10 minute test that we run in the clinic) and year-round heartworm prevention.
Prevention comes in a couple of different forms: a monthly chewable treat or an injection given every 6 months.
The chewable ‘treats’ come in a few different flavors and sizes. Most of them also deworm for intestinal parasites and some kill fleas for 30 days, too.
Cats can get heartworm infections too! They can be given a monthly preventive too, just like dogs — often we use a liquid that is applied monthly to the back of the neck. (The one that we use kills ear mites and intestinal parasites too, it’s great.) There is a chewable tablet for kitties too.
One thing to remember is that all heartworm prevention is prescription only. However, most folks are surprised at how affordable the products are in the clinic. Treatment for heartworms is always more expensive than prevention.
Come and see us, we can help find the product that works best for you and your furry friend.
Check out this website for more information about heartworms, it’s a wonderful resource: