How Do Animals Get Infected?
Heartworm disease is spread by mosquitoes that become infected with microfilariae, the prelarval stage of heartworm, while taking a blood meal from an infected animal. The microfilariae mature into the infective larval stage within the mosquito. When the mosquito then bites an animal, it passes the larvae into the animal’s bloodstream resulting in a heartworm infection. It takes a little over six months for the infective larvae to mature into adult worms which can reproduce. It is thought that adult heartworms live for 5 to 7 years in the dogs and 2 to 3 years in cats.
What Are the Clinical Signs and
Symptoms of Heartworm Disease?
Clinical signs depend on the number of worms present, the duration of infection, and the animal’s immune response.
In dogs, recently infected animals may exhibit no signs of the disease while heavily infected animals may display the following clinical signs: mild to severe cough, reluctance to exercise, labored breathing, and weight loss.
Listening to the chest with a stethoscope will often reveal abnormal lung and heart sounds. In advanced cases, congestive heart failure may be apparent and the abdomen and legs will swell from fluid accumulation.
Clinical signs of heartworm disease in cats include rapid breathing, coughing, vomiting, and weight loss. There are no mild infections in cats as even one worm can cause serious disease and sudden death.
How Do You Diagnose Heartworm Disease?
Diagnosis of heartworm infection is usually made with blood tests that detect either microfilariae circulating in the bloodstream or antigens (proteins) produced by adult female heartworms. These tests are very specific and sensitive in dogs. Heartworm disease in cats, however, is more difficult to diagnose because of the low number of worms usually present. A blood test looking for antibodies against heartworm is more useful in cats.
Heartworm infection may also be detected through x-ray and/or ultrasound images of the heart and lungs. The heart and pulmonary arteries may be enlarged on x-rays and worms can be visualized on an ultrasound.
What Is the Treatment for Heartworm Disease?
In dogs, most cases of heartworm disease can be successfully treated with an adulticide (melarsomine) that kills the adult heartworms. A series of injections is administered after the dog has received a thorough examination to assess the risk of the treatment. Hospitalization is usually recommended during treatment, but treatment can also be performed on an outpatient basis. During the recovery period of one to two months, it is recommended that exercise for the pet be severely limited to decrease the risk of partial or complete blockage of blood flow through the lungs by the dead worms.
Approximately six weeks after the adulticide therapy, treatment with an oral monthly tablet is begun to eliminate the microfilariae and prevent reinfection.
Currently, there are no products in the United States approved for the treatment of heartworm infection in cats. Adulticidal therapy is of greater risk for cats than dogs and is generally avoided. In severe cases of the disease, veterinarians will treat an infected cat with supportive therapeutic measures.
How Can I Prevent Heartworm Disease?
Because heartworm disease is completely preventable, the Animal Humane Society (AHS) recommends that pet owners take steps to talk to their veterinarian about how to best protect their pets from this disease. According to the AHS, heartworm prevention is safe, easy and inexpensive compared to treating a dog or cat after worms have matured into adults. While treatment for heartworm disease is possible, it is a complicated and expensive process, taking weeks for infected animals to recover.
There are a variety of options for the prevention of heartworm infection, including monthly tablets and monthly topicals. All of these methods are extremely effective and when administered properly on a timely schedule, heartworm infection can be completely prevented.
