Heartworm Disease: Know The Facts!


By Dr. Christine Calvert
Calvert Veterinary Center

Heartworm disease is serious and potentially fatal in pets. It is caused by heartworms that live in the heart, lungs and blood vessels of affected pets, causing severe lung disease, heart failure and damage to other body organs. Heartworm disease affects dogs, cats and ferrets, but heartworms also live in other animals. Because wild species such as foxes live in proximity to many urban areas, they are considered important carriers of the disease.

The dog is a natural host for heartworms, which means that heartworms that live inside the dog mature into adults and can reproduce, thereby increasing the number of worms living in your dog. If left untreated, heartworms will increase. Dogs have been known to harbor several hundred worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries. This can affect the dog’s health and quality of life long after the parasites are gone. For this reason, heartworm prevention for dogs is by far the best option, and treatment — when needed — should be administered as early in the course of the disease as possible. With the recent hurricanes affecting southern states such as Louisiana, Texas and Mississippi, the incidence of heartworm disease has increased sharply in these areas. Many rescue groups have helped relocate pets that were stranded after severe flooding led to evacuations. Many of the pets from the flooded areas contracted heartworm disease due to the presence of standing water. Often, these pets were transported to other states, including Maryland, unfortunately bringing heartworm disease with them to their new home.

How is heartworm disease transmitted from one pet to another?

The mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog or fox produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites an infected animal, it picks up these baby worms from the infected pet’s blood. These baby worms will mature inside the mosquito; then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are transferred through the skin. Once mature, heartworms can live for five to seven years in dogs and up to two or three years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet. With Pasadena’s close proximity to water, it is not surprising that we see heartworm disease in our area. Even small amounts of standing water, such as in empty flower pots or other containers and objects that collect rainwater, can serve as a breeding ground for mosquitos.

What are the signs of heartworm disease in dogs?

Many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced signs:

  • Mild, persistent cough
  • Exercise intolerance or fatigue after moderate activity
  • Decreased appetite and weight loss
  • Advanced cases leading to heart failure and the appearance of a swollen belly due to excess fluid
  • Sudden unset of labored breathing, pale gums, death

Do cats get heartworm disease?

Heartworm disease in cats is different from heartworm disease in dogs. The cat is an atypical host for heartworms, and most worms in cats do not survive to the adult stage. Cats with adult heartworms typically have just one or a few worms and many cats affected by heartworms have no adult worms. While this means heartworm disease often goes undiagnosed in cats, it’s important to understand that even immature worms cause real damage in the form of a condition known as heartworm-associated respiratory disease (HARD). Signs of heartworm disease in cats can be subtle or dramatic. Symptoms may include coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss. Occasionally, an affected cat may have difficulty walking, experience fainting or seizures, or suffer from fluid accumulation in the abdomen. Unfortunately, the first sign in some cases is sudden collapse or sudden death.

Moreover, the medication used to treat heartworm infections in dogs cannot be used in cats, so heartworm prevention is the only means of protecting cats from the effects of heartworm disease.

Because of Pasadena’s proximity to water, it is especially important to protect your pets from this deadly disease in our community. Several medications prevent heartworm disease, including monthly oral chews, topical applications, and an injectable form that lasts for six months. Ask your veterinarian which preventative is best for your pet!

For more information on heartworm disease, visit www.heartwormsociety.org.

Calvert Veterinary Center has been serving Pasadena and surrounding communities for 15 years. The office is conveniently located at 4100 Mountain Road in Pasadena. Call 410-360-7297 or visit www.calvertvet.com to schedule an appointment.


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