Heartworms can be found in about several dozen animal species, including cats, foxes, ferrets, coyotes, sea lions and even humans. However, they are most common in dogs. They occur when a mosquito carrying heartworm larvae bites a dog. The infection is transmitted into the dog’s blood. The larvae grow and become male and female worms over a period of several months. The worms eventually mate and their larvae also enter the bloodstream.
Dog heartworms are fully grown after one year. They can be up to a foot long and live inside a dog for up to seven years. A dog can have anywhere from one to 250 worms. These worms affect the dog’s lung, heart and blood vessels.
Every dog is susceptible to heartworms, no matter its age, breed or gender. However, 45% of cases occur in dogs located along the Mississippi River and along the Gulf of Mexico to New Jersey. In addition, male dogs that live primarily outdoors are at the highest risk.
The heart and lungs are most commonly affected by dog heartworms. A dog with very few heartworms may never exhibit any signs of them. Dogs with many heartworms and that exercise often will experience the most severe symptoms.
There may be no signs of disease in the early stages. If the disease is mild, the dog may have a cough. As the disease worsens, the owner may hear unusual sounds in the lungs. The dog may be unable to exercise. In severe cases, the dog may have difficulty breathing, periodic lapses of unconsciousness, abnormal sounds in the heart, an enlarged liver and an accumulation of fluid in the abdomen.
The vet will do a thorough physical examination of the dog. Several blood tests may be performed to look for heartworm larva and study the antigens in the blood serum to see if adult heartworms are present. The vet may perform X-rays and ultrasounds. An angiography may also be done to see if any heartworms are located in the dog’s blood vessels. An echocardiogram can help the vet see if there are any worms in the heart.
Most cases of heartworm can be treated, especially if detected early. However, some severe cases can lead to death. The goal is to kill all the adult heartworms and larvae. The vet will prescribe a medication to accomplish this goal.
Only one drug is approved by the Food and Drug Administration (FDA) for treatment of adult heartworms. Merial (also known as Imiticide) is an organic compound that is proven to be very safe and effective. It is injected into the lumbar muscles. Dogs are often hospitalized during this course of treatment.
To kill any heartworm larvae in the dog, the vet will use macrocyclic lactone (ML) anthelmintics, which contain the same ingredients as heartworm preventative medications. Because dogs can suffer severe side effects from the larvae dying too quickly, a vet will usually administer the drug so the larvae clears out within nine months.
Dog owners should use heartworm prevention medications on their dogs to avoid having to treat the heartworms, which can be costly and painful to the dog. Heartgard, Revolution, Sentinel and Interceptor are common brands of medication. It can be bought from the vet or can often be obtained cheaper at various online pet stores.
The American Heartworm Society has some informational videos about how heartworms affect dogs and what you can do to protect them.