Heartworm is a term that is probably familiar to most pet owners but not many people know what it really is. We know that veterinarians seem to want to have all cats and dogs on a heartworm preventative and that treating the disease can be costly and very hard on the effected animal, but not much else.
With the help of folks at the American Heartworm Society, hopefully we can shed some light on this terrible disease and save a life or two.
As most pet owners already know, heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by Dirofilaria Immitis — a parasitic roundworm that lives 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, but heartworms also live in other mammal species, including wolves, coyotes, foxes, sea lions and—in rare instances—humans. Because wild species such as foxes and coyotes live in proximity to many urban areas, they are considered important carriers of the disease.
The mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected animal produce microscopic baby worms called microfilaria 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 animal — mainly your dog or cat — the infective larvae are deposited onto the surface of your animal’s skin and enter the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately six months for the larvae to mature into adult heartworms.
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 animal.
In the early stages of the disease a dog may show no symptoms at all. As the disease persists, 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, your pet may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen.
Dogs with large numbers of heartworms can develop 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 a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.
As the disease progresses in your cat, 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. So testing and the use of a heartworm preventative are very important.
No one wants hear that their pet has tested positive for heartworm but it happens and 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 keeping the side effects of treatment to a minimum.
Like dogs, cats can be infected with heartworms. There are differences, however, in the nature of the disease and how it is diagnosed and managed. Because a cat is not an ideal host for heartworms, some infections resolve on their own, although these infections can leave cats with respiratory system damage. Heartworms in the circulatory system also affect the cat’s immune system and cause symptoms such as coughing, wheezing and difficulty breathing. Heartworms in cats may even migrate to other parts of the body, such as the brain, eye and spinal cord. Severe complications such as blood clots in the lungs and lung inflammation can result when the adult worms die in the cat’s body.
The key to a successful recovery is getting your pet veterinarian care as soon as possible.