Heartworm disease is a serious condition.Caring for a pet is one of the easiest things to do because it’s so fun and rewarding. However, truly taking responsibility for an animal’s health and well-being isn’t without certain challenges or worries. In the case of heartworm disease, there are critical steps that need attention throughout the year.

What Is Heartworm Disease?

Diagnosed in all 50 states, heartworm disease is caused by internal parasites that live in the blood vessels of the lungs and heart. It is potentially life-threatening, and both outdoor and indoor-only pets are at risk.

How It’s Transmitted

The mosquito is responsible for transmitting heartworm disease. When an infected animal is bitten, the mosquito picks up microscopic baby worms (microfilaria) in the bloodstream. Over the next 10-14 days, the microscopic worms develop into infective larvae inside the mosquito. When it bites a vulnerable animal, the mosquito deposits larvae on the skin and the bite wound.

The Life Cycle

Over the next 6 months, the larvae will migrate to the heart and pulmonary wall, and develop into mature adult heartworms that produce their own microfilaria.

Heartworms can live between 5-7 years in dogs (2-3 years in cats) and cause major damage to the heart, lungs, and possibly other internal organs. Some animals present few, if any, clinical signs. Others may have a persistent cough, reluctance to exercise, decreased appetite, and fatigue. Heart failure, cardiovascular collapse, and death are not uncommon outcomes.

Diagnosis of Heartworm Infection

Screening for heartworm disease involves advanced diagnostics to detect:

  •     Adult worms – The Heartworm Antigen Test specifically tests for female, pregnant adult worms, but can be falsely negative if a pet was infected within the previous 6 months, if there are low numbers of worms, or if there are all male or immature worms present.
  •     Microfilaria – The modified Knott’s test uses a centrifuge to quickly spin a small blood sample in order to reveal concentrated microfilaria. The demonstration of heartworm microfilaria also confirms the presence of adult worms.

Heartworms can also be seen on cardiac ultrasound but this is not a very sensitive test. The damage caused by heartworms can be seen on x-rays.

Treating Heartworm Disease

There is no current treatment for heartworm disease in cats. Once the diagnosis of heartworm disease has been confirmed, treatment in dogs typically involves:

  •     Rest – Because physical exertion can increase damage to the heart and lungs during treatment, pets must be kept quiet during and for several weeks after treatment.
  •     Treatment – The only approved and effective treatment for adult heartworms in dogs utilizes the drug Melarsamine. The treatment is carried out in several stages to maximize safety and efficacy. Six months after the treatment the adult test is repeated to assure all the heartworms have been killed.
  •     Monitor and test – Year-round prevention and annual retesting is required after treatment.

The “slow kill” method of simply administering ivermectin-based heartworm preventive medications is not safe, effective or approved. While ivermectin clears the bloodstream of larvae, the adult worms remain intact causing ongoing damage to the heart and lungs of the dog. Lastly, the slow-kill method may end up developing strains of heartworms resistant to heartworm preventive medications which is our greatest weapon to fight this deadly disease.

Best Defense

A monthly oral (vs topical or injectable) heartworm preventive medication is the best defense against heartworm disease and must be given year round to inside and outside pets.

To safeguard your pet’s lifelong health and wellness, we encourage you to contact us at Northpark Animal Hospital with any questions or concerns.