The ONLY national non-profit organization for professional pet sitters.

Heartworm Disease (HWD)

Members of the National Association of Professional Pets Sitters (NAPPS) and pet parents must know about heartworm disease. 

Heartworm disease (HWD) occurs in all fifty states and is spreading to new regions of the country each year. HWD is described as a serious, potentially fatal disease that affects both dogs and cats, wolves, coyotes, and other mammals.  Both indoor and outdoor animals may be affected.  HWD is transmitted by mosquitoes.  When an infected mosquito bites an animal, a form of the HWD organism is injected into the animal and undergoes changes which result in the juvenile heartworm, which enters a vein, from whence it is carried to the heart and lungs. Some juvenile worms turn into adults, reproduce and multiply.  In dogs, the adult worms can live in the heart and lungs for five to seven years. .   After all worms have been killed, dogs can suffer lasting damage to the heart, lungs and arteries, which leads to diminished quality of life.           Signs of HWD include mild, persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite and weight loss.  Signs of heart disease may manifest as swelling of the abdomen.  Dogs with large numbers of worms may develop sudden blockage of blood flow within the heart.  Without surgical removal of the heartworms, few dogs survive.

Preventive medication should be administered as soon as possible.  Prior to treatment, the veterinarian administers a heartworm test and confirms the diagnosis with further tests Annual testing is necessary.  Heartworm medications are highly effective, but protection may be lost if even one dose is missed.  Treatment also includes restriction of exercise, stabilization of the animal’s disease and medication.  The American Heartworm Society has guidelines for treatment, which must be given year-round for the rest of the dog’s life.
Heartworm disease can be transmitted from one pet to another by mosquitos. Female heartworms that live in an infected mammal produce microscopic baby worms called microfilari.  When a mosquito draws blood from a mammal such as a wolf, it also takes the microfilari, which grow into “infective stage” larvae over a period of 10 to 14 days.  When a mosquito then bites a pet, the infective larvae enter the pets bloodstream via the mosquito bite.  Once inside a new host, it takes 6 months for the larvae to mature into adult heart worms and once they are mature, they can live for 5-7 years in dogs and up to 2-3 years in cats.

As mentioned above, heartworm disease is different in dogs and cats, so symptoms can be different as well.  Dogs that are in early stages of the diseases show few symptoms or sometimes none at all.  Once the disease progresses, symptoms may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.  As the disease progresses, dogs may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen.  In cats the signs can be either very subtle or very dramatic including a coughing, asthma-like attacks, periodic vomiting, lack of appetite, weight loss, difficulty walking or seizures.  Unfortunately, the first sign in some cases is a collapse of the cat, or sudden death.

Even though a pet owner cannot entirely control the risk factors of their pet contracting the disease, the AHS recommends to “think 12,” meaning (1) get a pet tested every 12 months for heartworm and (2) give a pet heartworm preventive 12 months a year.