Heartworm kills: Test your dog and use preventative medicine

Heartworms are serious and dangerous canine parasites spread by mosquitoes. When these insects bite your dog they can transmit this parasite which can cause suffering and death. These worms travel to the heart and when mature can be a foot long. Adult heartworms are difficult to treat, so a good prevention program is necessary.

Dogs and cats in the Southeastern US are far more likely to contract this deadly parasite than pets in North Dakota or Montana. If you have not already done so you should get your pets screened. Don’t procrastinate just because mosquito season has passed. Your dog might already be infected.

Dogs get heartworms from female mosquitoes and mosquitoes get them from infected dogs. The parasite can’t complete its life-cycle without both animals. Young larvae called microfilaria live in the bloodstream. There are a total of six developmental stages. L1, L2 develop in infected dogs which become L3 larvae in mosquitoes. This process in mosquitoes takes about 10-14 days.

When an infected mosquito bites a dog it can transmit the L3 larvae into the new host canine. These can now become L4, then developing adults (L5) and finally mature adults (L6). Mature adults reside primarily in the right atrium of the heart. The entire lifecycle can take as long as seven years.

Most dogs with heartworm will be anemic, lack energy or be prone to coughing. They may also have high blood pressure, difficulty breathing and extremely rapid heart rate. Once the disease has reached this stage it is difficult and often dangerous to treat.

Your veterinarian can give you heartworm preventative. This will kill the L3 and L4 larvae and keep them from reaching later stages. This medicine must be administered monthly at regular intervals or L3 and L4 larvae will become adults. Once the next developmental stage is reached the preventative is ineffective.

At this point all is not lost. Your veterinarian can often still treat the problem but it’s tougher. Usually multiple treatments are necessary. Medications required to treat adults come with precautions. Activity should be reduced, for example.

Infected dogs are classed 1-4 with 4 being the worst. These dogs show serious heart problems and killing the adult worms too quickly could hasten death rather than prevent it. Globs of dead heartworms could clog the heart and lungs. Immature larvae are usually attacked first. Your veterinarian can give you more specific information, but this disease is nothing to ignore.

Mosquito season has passed, but heartworm larvae can live in your dog for a long time. However, there’s no need to be paranoid either. If your dog is receiving regular treatments he is safe even if you have another animal with heartworms. They can’t directly pass the parasite. It must go through a mosquito first and regular treatment will combat reinfection.

If some of this confuses you, talk to your veterinarian. That’s always the best policy. Cats and ferrets can also get the disease. Keep that in mind. Heartworm can infect people, but it is rare and the parasites can’t complete their life-cycle in humans, so you don’t have to worry about that.


Ted Manzer teaches agriculture at Northeastern High School.

About tedmanzer

I grew up in Old Town Maine and got a B.S. at the University of Maine in Plant Sciences/ minor in Botany. From there I moved to West Virginia and earned a M.S. in Agronomy at WVU. I also met my wife there. She grew up in rural WV as the daughter of tenant farmers who raised cattle and hogs. Their lifestyle at times was one of subsistence and I learned a lot from them. I've always been a foraging buff, but combining my formal botanical knowledge with their practical 'Foxfire-type' background opened up my eyes a little more. I recently retired from teaching high school agriculture after 25 years teaching with my wife. Until recently I wrote a weekly nature/foraging column for the local paper (dailyadvance.com). I also have written several Christian nature/adventure novels that can be purchased on Amazon in Kindle format. One is a five book family saga I call the 'Forgotten Virtues' series. In the first book, Never Alone (presently out of print), a young boy comes of age after his father dies in a plane crash, and he has to make it alone. The second book, Strange Courage, takes Carl from his High School graduation to his recovery from a nasty divorce. The third book, Second Chances, takes Carl from his ex-wife's death and the custody of his son to his heroic death at age 59. The fourth book, Promises Kept, depicts how his grandchildren react and adjust to his death (this one is not yet published). In the final book, Grandfather's Way, his youngest and most timid granddaughter emerges from the shadow of her overachieving family and accomplishes more in four months than most do in a lifetime. I use many foraging references with a lot of the plants I profile in these articles in those books. I also wrote a romance novel titled Virginia. It is available on Amazon and is a different type of romance from a man's perspective.
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