Heartworm DiseaseWhat is Heartworm disease?
Why do you need to worry about it?
What can you do about it?

Heartworm disease is a disease of dog (and rarely cats) caused by a parasite (Dirofilaria immitis) which lives in the large pulmonary blood vessels just outside the heart. These worms grow and reproduce in the blood vessels and, over time clog the blood vessels causing the dog to die of heart failure or a stroke.

Heartworms are transmitted from dog to dog by mosquitoes. The young heartworm larvae actually has to spend some time developing in the mosquito before a dog can be infected, so your dog is not going to get heartworm disease directly from being around an infected dog.

Although the mosquito population is not great in the Santa Fe area, they do exist. The Espanola Valley, the Rio Grande Valley of Albuquerque and the Pecos River Valley all have a high incidence of heartworm disease. In these areas, we have all of the necessary ingredients to continue to transmit heartworm disease- standing water from irrigation for the mosquitoes to breed in and numerous infected dogs to act as a reservior of infection.

Traveling to these areas with your dog, going hiking, fishing or playing in the water increases your dog’s heartworm exposure risk.

In the four years that we have had the clinic open, we have diagnosed three cases of heartworm disease. One was in a newly adopted dog whose previous life history was not known. Another was in a dog who has lived in Santa Fe for 5 years, moving from southern New Mexico. The dog had not been on heartworm preventative or had a heartworm test run since moving to Santa Fe.


Heartworm prevention

Heartworm disease can be prevented safely, easily and inexpensively. Preventing heartworm disease is done by giving your dog a monthly medication that kills young heartworm larvae shortly after the dog has been infected.

The early larval stages of heartworm in the dog are susceptible to medication, but as the worms mature, they become resistant to the preventative medications. The larvae are succeptible during the first 30-40 days after introduction into the dog from the bite of an infected mosquitoe.

This timing is the reason for giving heartworm preventative every 30 days. Forgetting a month’s preventative dose, or your dog spitting out the medication or vomiting it up before absorbing it could lead to an infection developing despite being on preventative. This is one of the reasons that it is important to test for heartworm annually even when giving the preventative medication.

There are also injectable, timed-release medications available if remembering a monthly medication is challenging.

We recommend preventative use from June through November for dogs living in and around Santa Fe. If you travel to more temparate areas in the winter months, we may recommend additional preventative medication. We will discuss this with you when running your dog’s heartworm test and during your dog’s annual physical examination.

Preventatives are drugs like ivermectin, milbemycin oxime, moxidectin and selemectin that are oral or topical 30-day preventatives. Starting this year we will use and recommend Interceptor Plus, which also treats dogs for intestinal worms including tapeworms. 

Some breeds of dog (austrailian shepherd, border collies, etc.) may be more succeptible to adverse effects of the medication due to a genetic difference in a portion of their nervous system. The preventative medications are generally at such a low concentration that this is not an issue. If you are concerned about this or the effects of other medications, there is a test available to see if your dog carries the genes that make them at greater risk. This test is available through our clinic or you can submit your own dog’s sample. If you submit the sample, please make sure that we recieve the results.

Heartworm testing

Heartworm testing is simple, inexpensive and quick. We draw a small blood sample from your dog and run the test in the clinic. Results are received in about ten minutes. The test is inexpensive, costing $25.00.

Timing of the test is important. The heartworm test can identify the mature adult heartworm. From the time that a dog becomes infected with young larvae to the adult stage that we can pick up on the test takes 6 months.

The mosquitoes that can transmit heartworm disease are generally around this area from May- October.

Because of this, we recommend that the heartworm test be done in April in the Santa Fe area. If we test your dog in April, we can be more certain that an infection picked up the preceeding year (May- October) will be picked up by the test.

There are other scenarios where we may recommend additional testing. We will discuss these with you as we talk about your dog’s history.

We recommend testing your dog annually, even when they are on preventative medication, based on recommendations from the American Heartworm Society.

Heartworm treatment

Heartworm treatment is much more difficult and hard on the patient than is prevention. Treatment entails giving a medication that will kill the adult worms in the blood vessels and giving the dog’s cardiovascular and immune systems time to dissolve the dead adult worms. This means keeping the dog confined and inactive for a period of months during and after the treatments to lessen the risk of fatal side effects from.