HEARTWORMS IN CATS

What is it?
• Heartworms are parasites that live in your animal’s lungs
• The primarily infest the lungs of dogs and wild canines, however cats are also susceptible to this condition
• The changes that result from these parasites are different in cats than in dogs

What causes it?
• Heartworms molt in mosquitos and are spread between animals as such
• The heartworms molt in the cat, and spread to the lungs where they develop into adults
• Some of the parasites will die and irritate the lungs about 2-5 months after the cat is infected
• Adult heartworms release substances that irritate the lungs and possibly other organs
• In cats, heartworm disease is only a respiratory problem
• Symptoms include coughing, heavy breathing, weight loss, sporadic vomiting, and lethargy
• Sudden death may result from heartworms dying in the lungs and blocking major air pathways

What tests are needed?
• Chest x-rays, routine lab tests, and testing for heartworm antigens and antibodies are typical for diagnosis
• Sometimes the diagnosis of heartworm disease can be difficult in cats (false negatives or positives), an heart ultrasounds (echocardiogram) and a radiologic contrast study of the lungs may be necessary

How is it treated?
• Treatment is tricky, because if too many of the heartworms die at once, it could potentially kill the cat
• Surgical removal of the heartworms has proven only slightly successful, so often the recommendation is to treat the cat’s symptoms and allow 1-3 years for the heartworms to die on their own
• Steroids may be prescribed to reduce lung irritation and vomiting and bronchodilators have proven effective in relieving respiratory signs

What follow up care is needed?
• Periodic monitoring of the cat is necessary to evaluate any changes in their condition
• Until the problem resolves, regular chest x-rays may be recommended to track progress once the cat has stabilized
• Few cats continue to have chronic respiratory disease

HEARTWORMS IN DOGS

What is it?
• Heartworms are parasites that reside in the lungs of dogs and wild canines, and occasionally cats
• They live in the pulmonary arteries, causing elevated pressure and thus strain on the right side of the heart
• Eventually this may cause the right side of the heart to fail
• The changes that result from these parasites are different in dogs than in cats 

What causes it?
• Heartworms are spread by mosquitos, in which the heartworms molt
• They are passed on to dogs and cats in their infected form
• Adult heartworms produce larvae which spread to different areas of the body
• Heartworms take about 6 months to mature in the dog’s lungs
• They produce a substance that irritates the lungs, and the presence of these parasites causes the lining of the pulmonary arteries to become thickened and stiff
• If heartworms exist in the vena cava (large vein that carries blood back to the heart) it is called caval syndrome, in which a large mass of heartworms alters blood flow and damages red blood cells
• Caval syndrome is very time sensitive, and if it goes untreated for too long can lead to death
• Spreading of the larvae can cause irritation in other organs such as the kidneys and can lead to hypertensions in the lungs
• Many dogs show no signs, but the disease can be detected with routine heartworm blood tests
• However, lethargy, heavy breathing, coughing, and decreased activity may result

What tests are needed?
• A Knott’s test will look for the presence of larvae in the dog’s blood
• A heartworm blood test will determine the amount of heartworm antibodies and antigens
• Chest x-rays may be done to look for heart and lung changes
• A heart ultrasound (echocardiogram) may be performed to rule out other causes of heart trouble

How is it treated?
• If heart failure, kidney or liver disease is present, they must be treated first to avoid problems with heartworm medication
• Adulticide drugs will kill the heartworms, and are administered in one of two ways depending on the severity of the dog’s condition
• Once the issue has been resolved, the dog will be treated with heartworm-preventative drugs
• Any shock resulting from caval syndrome is treated aggressively with intravenous fluids and supportive care
• Once the dog is stable, they will undergo surgery to remove the heartworms

What follow up care is needed?
• When the adult heartworms die, they break up and can get lodged in smaller pulmonary arteries
• Typically, the dead heartworms cause no significant problems, but sudden death may occur if a major artery gets blocked
• Four to six months after treatment, a blood test should be performed to ensure all the heartworms have died
• Preventative therapy should be given year-round • Asymptomatic dogs have a very good prognosis
• Dogs with right heart failure have a poor prognosis because significant lung changes may not reverse after treatment, but may improve with therapy