Heartworm in Dogs and Cats

Heartworm disease is a serious and potentially fatal disease in pets. It is caused by worms that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body. Heartworm disease affects dogs, cats and ferrets.

Dogs

The dog is a natural host for heartworms, which means that heartworms that live inside the dog mature into adults, mate and produce offspring. If untreated, their numbers can increase, and dogs have been known to harbour several worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s heath and quality of life long after the parasites are gone. For this reason, prevention is by far the best option, and treatment, when needed, should be administered as early in the course of the disease as possible.

Cats

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

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 that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into ‘infective stage’ larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog or cat, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound.

Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms.

Once mature, heartworms can live 5 to 7 years in dogs and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms of an infected pet.

What are the signs of heartworm disease in dogs?

In the early stages of the disease, many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs.

Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop a sudden blockages of blood flow within the heart leading to a life threatening form of cardiovascular collapse. This is called caval syndrome, and is marked by sudden onset of laboured breathing, pale gums, and dark bloody or coffee-coloured urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.

What are the signs of heartworm disease in cats?

Signs of heartworm disease in cats can be very subtle or very 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 of the cat, or sudden death.

What can I do to, if I think my pet has heartworm?

The earlier it is detected, the better the chances the pet will recover. There are few, if any, early signs of disease when a dog or cat is infected with heartworms, so detecting their presence with a heartworm test administered by a vet is important. The test requires just a small blood sample from your pet, and it works by detecting the presence of heartworm proteins.

What happens if my dog tests positive for heartworms?

No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated. The goal is to first stabilize your dog if he is showing signs of disease, then kill all adult and immature worms while keep the side effects of treatment to a minimum.

 

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