Article featured in the American Heartworm Society
What is heartworm disease?
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 foot-long worms (heartworms) 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, 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.
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 harbor several hundred worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s health 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 (HARD). 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, fox, coyote, or wolf 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 dog, cat, or susceptible wild animal, 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 for 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 in an infected pet.
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.
How significant is my cat’s risk for heartworm infection?
Many factors must be considered, even if heartworms do not seem to be a problem in your local area. Your community may have a greater incidence of heartworm disease than you realize—or you may unknowingly travel with your pet to an area where heartworms are more common. Heartworm disease is also spreading to new regions of the country each year. Stray and neglected dogs and certain wildlife such as coyotes, wolves, and foxes can be carriers of heartworms. Mosquitoes blown great distances by the wind and the relocation of infected pets to previously uninfected areas also contribute to the spread of heartworm disease (this happened following Hurricane Katrina when 250,000 pets, many of them infected with heartworms, were “adopted” and shipped throughout the country).
The fact is that heartworm disease has been diagnosed in all 50 states, and risk factors are impossible to predict. Multiple variables, from climate variations to the presence of wildlife carriers, cause rates of infections to vary dramatically from year to year—even within communities. And because infected mosquitoes can come inside, both outdoor and indoor pets are at risk.
For that reason, the American Heartworm Society recommends that you “think 12:” (1) get your pet tested every 12 months for heartworm and (2) give your pet heartworm preventive 12 months a year.
What do I need to know about heartworm testing?
Heartworm disease is a serious, progressive disease. 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 veterinarian is important. The test requires just a small blood sample from your pet, and it works by detecting the presence of heartworm proteins. Some veterinarians process heartworm tests right in their hospitals while others send the samples to a diagnostic laboratory. In either case, results are obtained quickly. If your pet tests positive, further tests may be ordered.
When should my cat be tested?
Heartworm infection in cats is harder to detect than in dogs, because cats are much less likely than dogs to have adult heartworms. The preferred method for screening cats includes the use of both an antigen and an antibody test (the “antibody” test detects exposure to heartworm larvae). Your veterinarian may also use x-rays or ultrasound to look for heartworm infection. Cats should be tested before being put on prevention and re-tested as the veterinarian deems appropriate to document continued exposure and risk. Because there is no approved treatment for heartworm infection in cats, prevention is critical.
Oregon Veterinary Specialty Hospital (OVSH) has been serving the Portland and Beaverton area community since 1979. Drs. Steven F. Skinner (Neurology, Neurosurgery) and Robert T. Franklin (Internal medicine.) We welcome referrals from veterinarians all over the Pacific Northwest. Our goal is to help your pet regain health and live a long and happy life.
Oregon Veterinary Specialty Hospital
9339 SW Beaverton Hillsdale Hwy,
Beaverton, OR 97005.
Email: [email protected]