Heartworm (Dirofilaria immitis) is a parasitic worm that is responsible for the so-called heartworm disease, a very serious condition that affects both dogs and cats. Also relatively common in wolves, foxes, coyotes and other mammals, the worm is endemic to all 50 states. It lives and reproduces in the heart, lung and respective vessels of the infected animal. If left untreated, it can cause serious health complications and even death due to heart failure or damage to other inner organs.
Heartworms are transmitted by infected mosquitoes. When a mosquito bites the infected animal, it contracts microfilaria or tiny baby worms that live in the blood system. However, it doesn’t become the carrier of the infection immediately. The mosquito transmits the infection only when microfilaria develop into larvae, which takes a few days. Heartworm cannot be transmitted directly from one animal to another.
Symptoms of Heartworm Disease
In the early stage of the disease, infected dogs and cats usually have no symptoms. But as the worms increase in size or/and number, they begin to cause damage to the heart, lungs, blood vessels or/and other inner organs. Symptoms in this stage may include coughing, vomiting, loss of appetite, weight loss and abdominal swelling in both dogs and cats. Both can also experience heart failure and death without any prior warning signs.
Signs of heartworm disease in dogs may also include the so-called caval syndrome, a life-threatening condition that is caused by the worms blocking blood flow through the right side of the heart. This complication often affects dogs with no prior symptoms of infestation and requires surgical removal of the worms to prevent death. Cats, on the other hand, may develop the so-called heartworm associated respiratory disease (HARD) causing asthma/bronchitis like symptoms.
Tests and Diagnosis
Heartworm disease in both dogs and cats is diagnosed with blood tests although a slightly different procedure is used to detect the presence of the worms in cats. In addition to taking a small blood sample, the veterinarian may also use ultrasound or x-ray to confirm or rule out heartworm infection.
Treatment of Heartworm Disease
Heartworm infection in dogs can be successfully treated, especially if detected early. Unfortunately, there is no approved treatment for cats (that used to kill the worms in dogs isn’t appropriate for feline pets). Otherwise healthy cats with mild to moderate symptoms are usually only monitored. Severe infections require intervention either in the form of corticosteroids or surgical removal of the worms to prevent complications.
Prevention of Heartworm Infection
Prevention is the best (and the cheapest) heartworm treatment for both dogs and cats. Several types of drugs are available to protect your pet from heartworms (and some other parasites as well): pills, topicals and injections. Ask your veterinarian for advice on the selection of preventive medication and have your pet tested for the disease. Dogs should be tested once a year even if being on a year-round preventive treatment. Cats should be tested for heartworm infection before starting the preventive therapy and re-tested as recommended by your veterinarian.