Thursday, September 10, 2009


This is essentially the same post I wrote for the Dogs on Thursday blog (I'm helping them out by writing a veterinary article once a month) but I thought I would share it here too-it has some good website links in it anyway.

Heartworms are a serious parasite that all dog owners need to be aware of. Heartworms, in contrast to many intestinal parasites, are spread by the bite of an infected mosquito. The larval stages are injected into your pet and mature over the next 4-6 months into adult worms that live in the heart and larger blood vessels leading to the heart. Heartworms can go undetected for long periods of time before your dog starts showing clinical signs-the most common of which are cough, weight loss, and exercise intolerance. Heartworms, left untreated, can be fatal. However, they are easily prevented with one of several monthly preventatives which we will discuss in more detail later. But first lets go over a few more important facts about heartworms.

Heartworms are not contagious from dog to dog, however an infected dog can serve as a reservoir to infect more mosquitoes which can infect more dogs.

Heartworms can’t be detected in a stool/fecal sample like other worms. A simple blood test is needed to check for heartworms. This test is ideally performed annually to make sure that your preventative is working as it should. Although all of the drugs used as preventatives are very, very effective there can be rare cases of failure. This test is also important in case your dog has spit out or vomited up a pill without you knowing or if you have forgotten to give a pill or were late giving it. It’s also important to test new dogs (6 months of age or older) before starting them on a preventative because some of the medications can cause bad reactions in a dog that is already infected.

Heartworms have been diagnosed in all 50 states but are much more common in some areas such as the midwest and southeast-where there is warm humid weather that favors mosquitoes. Although some states may feel it’s safe to not use heartworm prevention or to go off prevention in the winter months I feel the safest thing to do is to use prevention all year round. Many preventatives are very cost effective, protect against other common parasites and give you peace of mind-especially if you travel with your pet to parts of the country you are not familiar with.

If your dog is infected with heartworms it can be treated. It is expensive, painful, and there will be some dogs that don’t survive treatment-especially in the later stages of the disease. Treatment generally consists of some tests (blood, urine, radiographs) to determine how advanced the disease is. Then your pet will receive two injections to kill the adult worms-these injections can make your pet quite sore. There is then a 30-day period of crate rest while the worms die and are destroyed by the dog’s immune system. Then the dog is given a second treatment-sometimes by injection or orally to kill the baby worms and rested another 4 weeks before testing for heartworms. If the test is negative the dog can begin prevention and go on with normal doggie activities.

More information about heartworms and heartworm disease can be found at The American Heartworm Society.

Now, about prevention-the easy way to manage heartworm disease. Heartworm preventatives come in both chewable tablets and topical spot-on products. All are given or applied monthly. I’ll be going over the most common products today. Which product you choose is based on your preference and what other parasites are a concern to your dog.

Heartgard Plus from Merial is beefy chewable that also protects against roundworms and hookworms (3 varieties).

Interceptor from Novartis is also a monthly chewable that protects against roundworms, the most common species of hookworms, and whipworms. Interceptor and Heartgard are often similar in cost with the difference in the two products being Heartgard covers more species of hookworms and Interceptor protects against only one hookworm but eliminates whipworms.

Sentinel is also from Novartis and is the same as Interceptor except it also contains an insect growth regulator or IGR. This compound sterilizes flea eggs to help prevent flea infestations. Adding the IGR nearly doubles the cost of the product, however it does not kill live adult fleas. For this reason I recommend using Interceptor and a separate flea product if needed.

Revolution from Pfizer is topical product and also protects against fleas, ticks, ear mites, and sarcoptic mange mites. It is not labeled for control of roundworms and hookworms because it did not eliminate a high enough percentage of them to meet FDA standards but it does control them well enough in cases where there is not a high level of exposure and risk of reinfection.

Advantage Multi from Bayer is another topical product. I have not used this one personally but it sounds like a promising product that would be worth trying. It protects against fleas, roundworms, two kinds of hookworms, and whipworms.


TC said...

I'm going to ask my vet about the one that protects against heart worms and kills flea eggs. Currently Dis isn't on anything for fleas but he does have one on him on occasion and I just use a little flea shampoo.

Sara said...

Thanks for all the info. My vet lent me a real heart infected with heartworms in a jar, that I brought to school with me for a biology lesson. That was enough for me to always remember to give my dogs their preventative meds.

Paint Girl said...

Excellent info about heartworms!! Thanks for sharing!

Rohan Shelties said...

And dont forget that if you own a Collie-type dog (collies and shelties mostly), you probably want to stay away from any heartworm med that contains ivermectin (i.e. Heartgard) as your fluffy friend may be a carrier for the MDR1 gene that causes the dog to have a severe reaction to ivermectin (even death). There is a genetic test that will test if you dog is a carrier for it (especially helpful if your dog HAS HW and needs to be treated), but in terms of prevention, it is probably easier to stick with interceptor, or another ivermectin-free option =0)

Nicki said...

That's a good point Rowan but one where there is a lot of confusion. The dose of Ivermectin in Heartgard is safe for even the sensitive breeds but the higher doses, like those for treating Demodex are not safe for those dogs with the mutation. But with so many options many people just choose whatever product gives them peace of mind!

Nicki said...

Whoops, sorry-I meant Rohan!