Heartworm Disease In Dogs and Cats
Live heartworms in the heart of a dog that died
By Rachele Baker, DVM -Heartworm disease is a serious disease transmitted by mosquitoes. Heartworms (Dirofilaria immitis) invade the heart, lungs, and blood vessels of affected animals. Heartworm disease can result in severe lung disease, heart failure, and damage to other organs in the body.
Heartworm disease can affect both dogs and cats. Dogs are natural hosts for heartworms. Therefore, heartworms living inside a dog will mature into adults, mate, and produce offspring. Cats are atypical hosts for heartworms.
Mosquitoes are an integral part of the heartworm life cycle. When a mosquito bites an infected dog, fox, coyote, or wolf and takes a blood meal, it picks up baby heartworms (microfilaria) which then mature within the mosquito into larvae over a period of 10 to 14 days. When the infected mosquito bites another susceptible animal, the larvae are deposited onto the animal’s skin and enter the animal through the opening in the skin caused by the mosquito bite.
This table from the American Heartworm Society presents an extremely interesting synopsis of heartworm disease in dogs compared to cats.
The American Heartworm Society has recommended the following guidelines for the use of heartworm preventatives in dogs and cats:
“Puppies and kittens should be started on a heartworm preventive as early as possible – no later than 8 weeks of age. Only use heartworm preventive medications approved for pets and prescribed by your veterinarian.
Give heartworm preventives as directed. Make sure your pet gets the right dose for his or her weight and give the medication on schedule.
Dogs and cats over 6 months of age put on heartworm preventive for the first time should be tested for heartworm disease before the preventative is started. Dogs should be tested a second time six months later and thereafter a minimum of once a year. Early detection provides the best opportunity for treatment success.”
I created the following table to provide information about some commonly prescribed oral and topical heartworm preventatives:
If you live in an area where there are mosquitoes, then your dog or cat is at risk of contracting heartworm disease. The best way to protect your pet is to make sure that your pet receives a heartworm preventative every month.
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Wow, that’s really scary. I remember reading about heartworm when I got my first dog years ago, and it grossed me out so much that I’ve never forgotten to give any of our dogs their meds through the years. I doubt if there’s anyone living anywhere who doesn’t have to worry about mosquitoes during some portion of the year.
That’s great that you are making sure that your dogs get a heartworm preventative every month, RaisingDaisy!
It makes me crazy when people don’t give heartworm preventative to their pets. Living in Louisiana a.k.a. Mosquito Central, it is imperative that dogs and cats are guarded against heartworms. Most dogs have to be treated when they are brought into our local humane society. It is can be expensive, but to not treat them can cost much more, including their life.
Thanks for sharing, M.K.!
The dog vs. cat comparison is interesting. I think I’ve heard that there’s a chance that dogs can still contract heartworms, even if they’re on a monthly preventative. If that’s true, how often or likely would that happen? I’ve always been curious why annual heartworm testing is needed if you give the monthly preventative.
Thanks for your question, ChasingDogTales. Annual heartworm testing is recommended even if you are giving a monthly heartworm preventative because, although heartworm preventatives are very effective, no medication is 100% effective and there is still a chance that pets can become infected. In addition, missing a dose of a monthly preventative or giving it late can result in your pet becoming susceptible to heartworm infection. Even if you faithfully give the heartworm preventative every month as recommended, your pet may spit out or vomit an oral heartworm preventative resulting in one or more missed doses.
Important information here about heartworm. I like the charts – makes it easy to read and learn about heartworm in dogs and cats. Now, the photo – it amazes me that those worms could be that big inside a heart. Gross.
I agree that seeing live heartworms in a dead dog’s heart is gross, Val. I watched a video of live heartworms moving around in a dead dog’s heart and that was even more disgusting. However, seeing what heartworms look like is an important part of learning about heartworm disease.
Very informative. Do you mind if I share this with my Chihuahua group/followers? We are South Suburban Chihuahua. WOOF!
Thanks, Piranha Banana. You are welcome to share a link to my post about Heartworm Disease with your Chihuahua group. I would love to have them visit my blog.
Great article and very informative!! Question, is there an oral one that repels mosquitos, fleas and ticks. I’ve been using BioSpot with great results for years but hate the greasy mess of it.
Thanks, Cathy! I am not aware of an oral product that kills heartworms, fleas, ticks, and mosquitos. Trifexis and Sentinel are given orally and are both are labeled to kill heartworms and fleas. Nexgard is an oral product that protects against fleas and ticks.
Great table on different heartworm preventatives. Thanks for another great article.
Thanks, TravelAnimalDr!
So scary, great post!
Thanks, Talent Hounds!
This is such a no brainer to me! I can’t imagine not giving Harley or Jax everything they need to protect themselves. It’s so cruel. Great post Rachele, will definitely share this one. The table was excellent also.
Thanks, Groovy Goldendoodles!
Thank you for this great post on such a deadly disease. My gang is on year round protection.
That’s great to hear, Sand Spring Chesapeakes!
Are you aware of heartworm incidence maps for other parts of the world? We’ll be sailing in the Caribbean with our golden and I wonder how much more we might need to worry about heartworm there.
Hi SomethingWagging. I am not aware of heartworm incidence maps for other parts of the world. The heartworm incidence maps referred to in my post are generated from heartworm tests performed by a large diagnostics laboratory in the United States. I would recommend that you check with diagnostic laboratories or local veterinary medical associations in the countries nearest to where you will be sailing in the Caribbean for information about the incidence of heartworm disease in their countries.