Heartworm Information For Your Pets: Causes, Treatment & Prevention

In this heartworm information overview, we cover the causes, treatment & prevention of heartworm. According to the American Heartworm Society (www.heartwormsociety.org), “Canine heartworm infection is widely distributed throughout the United States. Heartworm infection has been found in dogs native to all 50 states. All dogs, regardless of their age, sex, or habitat, are susceptible to heartworm infection.” Heartworms are extremely prevalent in the Southeast, and it’s important that pet owners take precautions to protect their dogs, cats, and ferrets, as all these species are susceptible to heartworm-associated disease.

How are Heartworms Spread?

 These parasites are transmitted by mosquitoes. Infected mosquitoes transmit stage 3 larvae when they bite. After several months and a series of molts, the adult heartworm then takes up residence in the pulmonary arteries between the right ventricle of the heart and the lungs. Adult heartworms reproduce, creating stage 1 larvae called microfilariae. The microfilariae are, in turn, picked up by mosquitoes when they feed on an infected animal and then undergo molting to the infective stage 3 form, starting the cycle all over again.

 What Kind of Disease do Heartworms Cause?

 In heartworm-infected dogs, the presence of adult worms in the pulmonary arteries causes inflammation and narrowing of those blood vessels. This, in turn, causes an increase in blood pressure. This is called pulmonary hypertension. The first signs of heartworm disease in a dog are often coughing and tiring out more easily during exercise. Over time, pulmonary hypertension puts stress on the right side of the heart, eventually leading to congestive heart failure. Right-sided congestive heart failure patients often develop fluid accumulation in the abdominal cavity (ascites). The most severe form of heartworm disease is called caval syndrome. In this form of the disease, there are so many heartworms present that they are no longer confined to the pulmonary arteries: they are present in the right side of the heart and in the large vein that brings blood to the heart, the vena cava. Both congestive heart failure and caval syndrome can be fatal.

Disease in cats tends to take a different course. Cats are not the intended host for heartworms, and their immune systems tend to be on high alert when a larval heartworm arrives. This usually results in the larval worm being killed by the immune system as it migrates through the lung. The dead or dying worm then causes an inflammatory reaction that’s something like an asthma attack. Coughing, wheezing, and respiratory distress can be seen in cats with heartworm-associated respiratory disease (HARD).

Can Heartworm Infection be Treated?

 Yes! At Alford Avenue Veterinary Hospital, we follow the treatment guidelines published by the American Heartworm Society. Annual testing for heartworms is strongly recommended, as early recognition of heartworm infection helps us eliminate these parasites before they can cause severe disease.

In dogs, treatment is accomplished through a combination of (1) heartworm prevention to keep infected patients from getting more heartworms, (2) pre-treatment with an antibiotic to eliminate bacteria that live inside and provide benefits for the heartworms, and (3) a series of injections of a drug called Melarsomine that kills the adult heartworms. When a dog tests positive for heartworms, we provide a detailed typed treatment plan so that our pet owners know what to expect during treatment.

Treatment for heartworm-associated disease in cats is typically aimed at reducing inflammation in the lungs. Rarely, a heartworm develops to adulthood in a cat. We do NOT give Melarsomine to cats and, instead, focus on reducing the potential for severe lung inflammation once that adult worm dies.

With Heartworm, An Ounce of Prevention is Worth a Pound of Cure

While we work to make heartworm treatment safe and effective, it’s a long, costly process that requires dogs’ activity to be restricted, and worms may cause damage to the cardiovascular system before a diagnosis is made; therefore, it’s far better to be proactive and prevent heartworm infection.

There are a lot of options for heartworm prevention. Alford’s veterinarians will help you determine which product is right for your pet. Our most popular preventives for dogs include the following:

• Heartgard Plus – This is a monthly, beef-flavored chewable that protects against heartworms and deworms for roundworms and hookworms. Dogs tend to like this product because it tastes good and their owners like the product because it is easy to administer.
• Simparica Trio – This is a monthly, pork-flavored tablet that protects against heartworm infection, flea and tick infestation, and also deworms against hookworms and roundworms. The advantage of this product is that it, essentially, provides all-in-one protection against parasites.
• ProHeart 12 – This is an injection that provides one year of protection against heartworm infection. ProHeart 12’s biggest advantage is that it eliminates the potential for missed doses of oral heartworm prevention.

For cats, we generally recommend monthly topical Revolution Plus. This product provides protection against heartworms, fleas and ticks, ear mites, roundworms, and hookworms.

For ferrets, we recommend monthly topical Revolution.

Questions About This Heartworm Information?

If you’ve got questions about heartworms, heartworm testing, prevention, or treatment, please make an appointment so we can answer them!