Heartworm At High Elevations

Reader Contribution by Bruce Mcelmurray

We are multiple dog parents that live remotely at high elevation. When it comes to canine disease we are  lay people with no specific training other than years of accumulated experience. We have been told by several veterinarians that heartworm is pretty much non-existent in our area because of our location and weather conditions. It is usually not even considered much of a possibility in our locale. 

One of our four German Shepherd Dogs recently developed a dry cough and we took her to our vet for diagnosis and treatment. An x-ray was taken and all her vitals were good except it appeared she either had bronchitis or ‘possibly’ heartworm. Heartworm was discounted somewhat in favor of bronchitis since our area is not known for being heartworm infected. She is on treatment for bronchitis; however if she does not clear up soon she will be tested for heartworm even though our area has such low exposure for heartworm. As I studied her x-rays I was concerned from what I saw so I did some research on the parasite.  

Heartworm Transmitters 

Mosquitoes are the primary transmitter of heartworm in dogs and cats. An adult male mosquito has a lifespan of 10 days. A female adult mosquito has a  lifespan of 42-56 days. In everything I have read and experienced pertaining to mosquitoes I have not discovered one single redeeming quality in the pest. I discovered that the males buzz to attract females but the males do not bite. The females are the ones who bite and suck blood. 

How Heartworm Is Transmitted 

Adult heartworm living in an infected animal produces microscopic baby worms called microfilaria that circulate in the animal’s bloodstream. When that infected animal is then bitten by a mosquito the insect picks up the baby worms that within 10-14 days develop into an infectious larvae stage. When that mosquito then bites another host animal the larvae are deposited on the skin and enter the animal via the wound left by the mosquito. Then they travel to the blood stream as they further develop into the adult stage and end up in the heart and lungs where they develop into adults up to 10-12” long. They continue to reproduce inside the animal generating even more worms. Adults can live in an animal up to 7 years.  


Mild persistent dry cough, loss of appetite or weight loss, lethargy, rapid or difficult breathing, and reluctance to exercise are all heartworm symptoms. There are other illnesses that also have some or all of these symptoms so a blood test needs to be conducted by a veterinarian to rule out or diagnose heartworm. Heartworm is a life threatening disease that will ultimately kill the pet therefore early detection through testing is imperative.  

Risk Areas

Different areas of our country carry different elements of risk. Some subtropical  areas have high risk and other areas like ours may not have measurable risk. Our winters are long and our summers are mild which makes a mosquito’s lifespan less prolific. Through what I have researched I realized that because heartworm is minimal or nonexistent in our area that it may still pose a potential danger.

Heartworm can inadvertently be brought into our area from other high risk areas. Many people travel from different parts of the country to our area and the mosquitoes can come in vehicles or campers. I learned that mosquitoes can be blown vast distances by the wind or carried in by other infected non-domestic animals like wolves, coyote, or fox. Those who travel with pets which may have been previously infected, and not treated, can be bitten by local mosquitoes and hence the baby heartworm can be transferred to other susceptible animals. In summary our area is not at risk but is not immune to importation of the dangerous heartworm from other sources.     

Testing For Heartworm 

Dogs and cats should be tested on an annual basis for heartworm. The test for heartworm is a quick easy blood test. Our dogs have been tested but since there is no heartworm activity in our area and the tests were negative they were not re-tested. They stay with us on our homestead and we did not consider the potential of invasion from the outside.They are not exposed to areas where heartworm is even slightly prevalent.   

Changing Weather Patterns

Additionally, weather patterns have greatly changed so the parasite could have been introduced from an outside source and mutated or now finds our area more compatible to its lifecycle. At our elevation I have been bitten in both February and March this year by mosquitoes. Highly unusual for our area especially with 2’ of snow still on the ground. If you have lived in an area that was similar to ours where heartworm was virtually non-existent it may be wise to rethink taking precautions against heartworm. It is my personal opinion that climate change should be a quantified scientific fact and not a political agenda. Clearly our weather patterns are visibly changing or I would not get mosquito bites in February.    


We try to take sensible precautions to keep our pets free from parasite infestation. When the conditions warrant we apply a recommended spray to keep the pests off them. If we need to apply deterrent against mosquitos ourselves then our pets need some also. We had used heartworm preventative in the past but since our immediate area was not considered at risk for heartworm we discontinued this preventative treatment.  

We are hopeful our sweet girl’s (see photo) current condition is bronchitis and will respond well to treatment and is not heartworm which is a far more serious condition. We hope we do not regret taking our fur family off preventive treatment because we live in an area where it has not been a factor in the past.  

Environmental Changes 

With changing weather patterns and the prospect that mosquitoes can be carried on the wind for vast distances or brought into our area inadvertently on other hosts – we now are thinking much differently. We now think it is best to use preventive measures and not take any risk of infection by heartworm parasites. It only takes one bite from a mosquito that is carrying the parasite to infect a family fur member. It should be a conversation to be discussed with your veterinarian as to applicability and risk.     

Bruce and Carol McElmurray and their four German Shepherd Dogs live at 9,800 feet elevation in  a small cabin which they heat with a wood stove in S. Colorado. For more about them and their four German Shepherd family members go to:www.brucecarolcabin.blogspot.com.

Resource: www.heartwormsociety.org