Human heartworm disease is extremely rare. You cannot contract heartworms directly from a dog or cat, even if it's suffering from the parasite. Human heartworms are usually spread via mosquito. Heartworms can't complete their life cycle inside the human body the way they can in dogs and cats, but they can become a real problem. In unusual cases, they may even cause amputation of a body part. Treatment of heartworm in humans depends on the individual case.
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Symptoms
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While heartworm symptoms in cats and dogs can include fatigue, coughing, blindness, weight loss, digestive trouble and even death, humans rarely present symptoms that indicate a problem. Instead of classic "disease" signs, humans tend to have an immune reaction. As the worms die off inside an organ, the organ forms nodules. These nodules cause pulmonary dirofilariasis, also known as a parasitic pneumonia. If symptoms are present, they include cough, fever and chest pain, but most people show no signs.
Diagnosis
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Many humans with heartworm or associated problems only find out about their condition as the result of a CT scan or X-ray for another condition. The diagnosis isn't definitive until testing to rule out other problems has been done, though. Human heartworm may look much like cancer or other lesion-causing conditions. If nodules appear on an X-ray, the physician will usually perform a biopsy to determine whether they're cancerous or caused by heartworm.
Likelihood
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The incidence of heartworm in humans is going down as more dogs get preventative treatment. People who live in an area where there is a large population of dogs that don't get this treatment are much more likely to get heartworms than people who don't live near dogs or live near treated dogs. This is because heartworm larvae live in the bloodstream of infected dogs and cats. When a mosquito bites one of these animals, then bites a human, heartworms may be transmitted in the mosquito's saliva. Feral animals can contribute to this increase in risk, as well as untreated pets.
Effects
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Despite the name, human infestations of heartworms do not usually live in the heart. Instead, they often migrate to the lungs, eventually dying and forming cysts. They may also find other areas in the body that have similar conditions. These include the eye and the testicles, though infestations in these areas are much rarer. In serious cases, heartworm may require the removal of the affected body part. The U.S. National Library of Medicine reports one case where orchiectomy -- removal of a testicle -- was required due to heartworm.
Prognosis
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So far, there are no recorded cases of human death from heartworm infestation. Because humans aren't the preferred host for heartworms, they can't complete their life cycle. Once the worms die, doctors simply treat the secondary conditions caused by the parasite. Complete recovery from heartworm infection is possible and expected.
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