Have you heard of heartworms? Unfortunately, I still have clients who have not heard of heartworm disease and do not know that it’s spread via mosquitoes. Heartworm disease was primarily found in the southeast and southern coastal states in what would be called epidemic areas. As of late, with the mobile U.S. populations, it has spread through the movement of infected dogs to areas that have mosquito seasons. San Juan County would now be called an endemic area, meaning we have an infected population of dogs, a seasonal climate and mosquitos. 

Heartworms are blood-borne parasites called Dirofilaria Immunitis that reside in the heart or adjacent blood vessels of infected dogs and cats. They develop to an infective stage in the mosquito, and, when that mosquito takes a blood meal of a new uninfected dog or cat, it injects the infective larva into the blood system. It takes approximately six months for larva to develop into the adult stage in the heart and lungs of the newly infected host. I describe heartworms as 12-inch, spaghetti sized worms. Many dogs will not develop symptoms for one to two years, and, by the time they are diagnosed, they have damage to the heart, lungs and liver. The most obvious initial signs are a soft dry cough, shortness of breath and weakness, which are most noticeable after exercise.  

The diagnosis of heartworms can be made by a 10-minute blood test that can be run in a veterinary hospital that recognizes the adult heartworms in the heart. People often ask why it is recommended that dogs be tested annually for heartworm disease. The answer is so an early diagnosis and treatment can be made before too much damage is done by the adult heartworm. Recently, there is evidence that resistance is occurring in epidemic areas to some older heartworm preventatives. Combine that with human error, such as forgetting to give a monthly dose of prevention, and pet error, such as a dog vomiting a pill, and we can see why we want to test yearly. Be sure and give the pill at night when your pet is indoors. And no medication is 100 percent effective. 

Heartworm disease can be treated in dogs, but it is expensive, costing $600 to $1,200 dollars, depending on the size of the dog. The best solution to heartworm is to prevent this disease by giving a monthly medication year-round. This medication prevents the larva stages from developing into the heart. The newer preventatives have medications for intestinal parasites, such as roundworms, hookworms and tapeworms, as well as some with flea control. The Companion Animal Parasite Council, www.petsandparasites.org, recommends all dogs and cats be on monthly intestinal parasite prevention medication, not only for your pets benefit but as to decrease the total roundworm and hookworm zoonotic potential nationwide.


In regards to cats, it has been recommended to put cats on a monthly preventative, too. Cats are more resistant to heartworm infection and typically do not show specific signs. The most common sign are a sudden onset of coughing and rapid breathing or even sudden death. Diagnosis in cats is more difficult, and, unlike dogs, there is no safe treatment if infected. 

In summary, annual testing and year-round prevention is recommended for dogs, and, in cats, year-round prevention is recommended as well. Heartworm disease is definitely a situation where an ounce of prevention is better than a pound or care. Follow recommendations by your veterinarian and to learn more go the American Heartworm Society, www.heartwormsociety.org. 

Dr. Darren Woodson has practiced veterinary medicine in the Farmington area for more than 28 years and has a passion for educating pet owners. If you have a question you would like him to address, email dwoodson@valleyvetpet.com. Please understand Dr. Woodson will choose the questions that are most relevant to our readers.