Introduction:
Human dirofilariasis is caused by a parasite called Dirofilaria. They are long and slender and spread to humans through mosquitoes. There are many types of Dirofilaria; however, Dirofilaria immitis causes infection in humans. It is also known as heartworm. It is commonly seen in individuals residing in North America and Europe. It mostly affects the lungs, and the condition is known as human pulmonary dirofilariasis. Very rarely, it does affect other parts of the body, like the brain and the eyes.
What Are the Causes of Human Pulmonary Dirofilariasis?
Worms are very minute creatures that enter the body through a mosquito bite. Fortunately, they cannot survive in the tissue present under the skin. Even if they survive, they remain sexually immature. Hence, Dirofilaria immitis cannot multiply or produce larvae. Humans serve as a host for Dirofilaria immitis but cannot transfer the infection to other hosts like dogs, foxes, and wolves. So the infection does not spread through man-to-man contact or man-to-mosquito-to-man contact. But the Dirofilaria worms present in dogs are transmitted to other hosts through mosquitoes. They are sexually active and can produce micro larvae. Hence, mosquitoes serve as intermediate hosts. But the micro larvae produced by Dirofilaria parent worms remain sexually immature. They get attached to the long tubular part of the mosquito’s mouth. Both male and female mosquitoes can transmit human pulmonary dirofilariasis.
What Are the Signs and Symptoms of Human Pulmonary Dirofilariasis?
Many patients with pulmonary dirofilariasis remain asymptomatic for a long period. Very rarely, the following symptoms occur;
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Cough - Several Dirofilaria immitis block the pulmonary artery and produce cough associated with bloody discharge.
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Chills - Since the lung is the major organ affected by dirofilariasis, it causes chills at night.
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Wheezing - Patients with pulmonary dirofilariasis have a high-pitched sound while breathing.
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Exhaustion - Worms weaken the immune system of individuals with pulmonary dirofilariasis. So they became exhausted after a walk or any other physical activity.
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Fainting - The worms destroy the red blood cells and reduce the oxygen supply. It results in fainting.
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Weight Loss - The worms affect the digestive system. It also causes severe dehydration and drastic weight loss.
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Chest Pain - Worms produce small nodules called granulomas in the lungs. It occurs as a result of inflammatory reactions and the production of histiocytes. Also, there is a fluid formation in the pleural (lung) linings which leads to pleural effusion.
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Fever - Worm infection results in high temperature.
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Reduced Ejaculation - Dirofilariasis affects the testicles in males and reduces sperm count. Dirofilariasis infection also causes itching in the male private parts.
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Eye - There is a nodule formation in the skin and conjunctiva of the eye.
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Skin Infection - The area bit by the mosquito appears red and itchy. The inflamed area has a small dot in the center of the bump.
How Is Human Pulmonary Dirofilariasis Diagnosed?
Two to three diagnostic tools are used to diagnose human pulmonary dirofilariasis.
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Chest X-Rays - The dead Dirofilaria worms accumulate together in the pulmonary artery and form a granuloma. They appear as round abnormal lesions on the radiograph. It looks like a coin-sized lesion. Coin lesions are also observed in tuberculosis and lung cancer. Hence, X-rays are not used as a confirmatory diagnosis for human pulmonary dirofilariasis.
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Culture Test - The sputum produced by a pulmonary dirofilariasis patient is obtained and closely examined under the electron microscope for the presence of dead Dirofilaria worms.
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Biopsy - Biopsy is considered a confirmatory diagnostic test for human pulmonary dirofilariasis. Tissue is collected using a special tool from the inflamed lung areas. The inflamed areas of the lungs are identified using computed tomography (CT scan) and X-rays. The biopsy tissue can also be collected from the nodules in the skin and eyes. The fluid is removed from the pleural cavity using a needle biopsy. It is examined in the laboratory for the presence of Dirofilaria. If the result is positive, appropriate measures are taken by the pulmonologist.
Research says blood tests do not prove to be effective for diagnosing human pulmonary dirofilariasis.
How to Prevent Human Pulmonary Dirofilariasis?
Individuals residing in suspected areas of dirofilariasis must stay away from mosquito bites by following the below instructions;
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Individuals should cover their bodies with full sleeves and stockings to prevent exposure to mosquitoes.
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Insect repellants can be used to avoid mosquito bites.
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Sleeping in a bed covered under a mosquito net can prevent mosquito bites.
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Insecticide sprayers can be operated in the streets and play areas by the government to prevent mosquito access to the corners or pits in houses or buildings.
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Pet owners must vaccinate their dogs and keep the surrounding area clean to avoid the proliferation of mosquitoes.
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Avoid staying in camps during humid climates because mosquitoes increase during that season.
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Avoid water retention in sewage and maintain hygiene in the surrounding areas to prevent the proliferation of mosquitoes.
What Are the Different Treatment Methods for Treating Human Pulmonary Dirofilariasis?
Individuals with pulmonary dirofilariasis but asymptomatic do not require any treatment. In the case of symptomatic pulmonary dirofilariasis, the following treatments are done;
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Surgical Excision - The granuloma present in the lungs and the nodules present in the skin and eyes are surgically excised to prevent further complications. The small piece of normal tissue surrounding the nodule is also excised to reduce the inflammation. It is considered the curative method for human pulmonary dirofilariasis. A specialized oncologist or surgeon performs it. The untreated granulomas can transform into cancerous tissue.
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Medication - Fever and productive cough due to dirofilariasis are treated with antibiotics. Bronchodilators help in relieving congested airways due to granuloma.
Conclusion:
In most cases, human pulmonary dirofilariasis was accidentally discovered while diagnosing lung cancer. The first case of human pulmonary dirofilariasis was observed in 1941. After that, until 2005, there were 81 cases reported. Dirofilaria immitis and Dirofilaria repens were found in different parts of the world. The prevalence of pulmonary dirofilariasis in asymptomatic individuals is difficult to predict. Mammals are considered accidental hosts for pulmonary dirofilariasis. The recurrence rate is very low in individuals treated for human pulmonary dirofilariasis. It is not a serious problem in humans unless discomfort or respiratory problems exist.
