When I was in vet school I saw a large 9 year old lab mix by the name of Gator. He came to the school health clinic every year since he was a puppy and every year diligent veterinary students like me tried to convince his owner to put him on heartworm prevention. Every year it was a different reason, but I think the one I got takes the cake. Gator's owner told me that he did not need to be on heartworm prevention because he only went outside into his fenced in backyard. When I asked about the fence (picturing a screened in area), i was told it was a chain-link fence. I breathed a sigh of relief to learn that Gator and his owner lived out in the country, because if the mosquitoes in his area were too big to fit through a chain-link fence then I think heartworms were the least of their concerns.
I hear almost on a daily basis hundreds of different reasons why someone doesn't want to put their dog or cat on heartworm prevention. I want to address the common ones I hear and explain why it is so important, especially in Florida where we have mosquitoes year round.
1) Scenario: "My dog doesn't go outside." says the owner.
"Oh! You have him litterbox trained?" I ask.
"No," replies the owner.
"Then where does he urinate and defecate?"
"Outside," the owner replies. "But, he is on a leash at all times and I am right with him."
I don't know about where you live, but mosquitoes are really common in my backyard. I may be able to protect Fido from another dog, or from being hit by a car by keeping him on a leash, but I can't even protect myself from those tiny little vampires. Even stepping outside long enough to get the mail can be enough for a bite or two. And for those cat owners who's cats never go outside....I just killed a mosquito that landed on my arm, in a closed room, in a closed house where no one has been outside for several hours.
Heartworms have a two host life cycle. A mosquito takes a blood meal from a dog infected with heartworms. With the blood meal the mosquito ingests the microfilariae (baby heartworms). The mosquito then flies happily on its way. Over the next 10 to 14 days the microfilariae mature into L3 stage larvae and migrate to the mosquito's salivary gland. When that mosquito bites another dog or cat the droplet of saliva it leaves behind will contain heartworm larvae. The larvae then burrow into the body of the animal through the mosquito bite wound. Over the next two to four months the larvae travel throughout the body until they finally end up pulmonary vasculature. During this time the larvae are also maturing into L4 and then L5 (adult) heartworms. The adult heartworms then mate and start producing microfilariae in six to nine months after the initial bite. Now they are carriers and start the whole cycle again.
It only takes a single bite from an infected mosquito to give your dog or cat a life threatening disease.
2)Heartworm prevention is too expensive.
If someone told you that for a mere $7 a month (thats $0.23 a day) you could protect yourself from a deadly form of heart disease don't you think you would find a way to do it? I know times are tight and every penny counts, but $7 is one meal at McDonalds, or two Mochas at Starbucks. Considering treatment is anywhere from $300 to $1000+, I think heartworm prevention is VERY affordable.
3)Giving your pet poison: Many people are afraid to give their dog or cat heartworm prevention because they believe they are giving them a cehmical that is staying in their body for the whole month. While there are a few topical medications that do stay around for that length of time, most oral preventions are out of their system in 24 to 48 hours. The medication is a dewormer that kills any susceptible parasites as soon as it is administered. The reason we can get away with only giving it once a month is because the L3 and L4 larvae take at least 50 days to mature to adult heartworms. Once the parasite has matured into the adult stage heartworm preventatives can no longer kill them. Another thing to note is that most heartworm preventatives contain an active ingrediant at such a small dose that the chance of a bad reaction are almost non-exsistant. More pets react to the taste additives than to the active ingredient.
4)Why not just treat if your pet gets heartworms instead of giving a prevention?
First reason is that the medication we use to kill adult heartworms is on manufacturer back-order that is expected to last for at least several months. This means that other than surgically removing the adult heartworms from the heart, there is NO treatment available for adult heartworms. This has always been the case in cats because the available treatments are more likely to kill the cat than the worms.
Second reason is that once treatment becomes available again it is risky. If you want to compare poisons, Melarsomine (the active ingrediant in Immiticide) is a nuclear bomb compared to the vinegar and baking soda bomb that the active ingredients in preventatives. While Ivermectin (the active ingredient in Heargard and Iverhart) can be given at 800 times the dose in heartworm prevention before serious side effects occur (the LD50 is 6500x the dose) just two times the standard dose of melarsomine can be fatal.
The third reason is the actual death of the hearworms can be fatal not only to the heartworms, but to the dog as well. Preventing heartworms provides almost no negative effects to the dog. Its like wearing sunscreen to prevent a sunburn. Once you ahve the sunburn it is painful and can have lasting negative effects such as skin cancer. The same thing is true for heartworms. An adult heartworm can reach a foot in lenght and it lives inside the heart and pulmonary vessels. Not only is it causing damage by existing, but when you kill it where do you think it is going to go? Thats right, right into the lungs. If too many worms break off at the same time or there is too much inflamation you can get a serious pulmonary embolism which can be fatal. Heartworm treatment requires two to three injections with a 1 and a half inch needle into the lower back muscles. Then you MUST keep you dog calm and quiet for six to eight weeks after the last injection because anything that increases his heart rate could lead to a pulmonary emboli and death.
5) Why should cats be on heartworm prevention? Cats are not the preferred host for heartworms and are much more resistent to infection than dogs. According to the American Heartworm Society "When dogs not previously exposed to heartworms are injected with 100 L3 larvae, approximately 75 adult worms develop in almost 100% of the dogs whereas in cats, 3 to 10 adult worms develop in 75% of the cats." Cats will usually only have 1-6 adult worms, but when you take a single foot long worm and place it into the tiny heart and lungs of a cat you can still have major problems. There is NO treatment for adult heartworms in cats except for surgery which in itself is very risky. Common clinical signs of a cat with heartworm disease are asthsma-like symptoms, coughing, collapse, or sudden death. Treatment is supportive with fluids and oxygen.
If you haev any other questions about heartworm disease or any "facts" that you would like verified please ask! Heartworm disease is 100% preventable. We walk our dogs on a leash to keep them from being hit by a car. We vaccinate our cats for Feline Leukemia to protect them from that fatal disease. Lets protect them from heartworms as well.
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