dirofilaria immitis ( the canine heartworm ) is a filarial nematode naturally hosted by dogs , cats , foxes , muskrat , raccoons , and bears . adult worms live in the right heart of these animals and produce a debilitating disease . this filarial nematode is transmited by mosquitoes . when an infected mosquito takes blood from a human , the larvae of d. immitis invade and develop for a time in cutaneous tissues , migrate to the right heart ventricle where they eventually die . the fragments of worms may reach the pulmonary arteries and lodge in a small caliber vessel to cause infarction or embolism events . patients with pulmonary dirofilariasis are usually asymptomatic ; however , occurrence of cough , chest pain , hemoptysis , and wheezing has been described in some patients . eosinophilia , commonly relevant in parasite infections , are present only in 15% of patients with pulmonary dirofilariasis . usually , a non - calcified , peripheral coin lesion or nodule is seen in chest x - ray or computed tomography ( ct ) . pathologically , spherical subpleural infarct with a central thrombosed artery containing the parasite in stage of degeneration is most commonly seen [ 4 - 6 ] . in the republic of korea ( = korea ) , the first case of human pulmonary dirofilariasis was reported in 2000 . in this report a 48-year - old male was referred to seoul national university hospital after a routine check - up at a local hospital due to abnormal findings seen in chest ct . he was an ex - smoker ( quit 10 years ago ) and was a social drinker . he had a pet dog , but the dog died 3 years ago from unidentified parasite infection . complete blood cell count showed a white blood cell count of 6.8610/l ( normal : 4.0 - 10.010/l ) , a hemoglobin concentration of 14.5 g / dl ( normal : 14 - 18 g / dl ) , and a platelet count 26710/l ( normal : 130 - 45010/l ) . the differential count showed neutrophils at 36.1% , lymphocytes at 51.2% , and eosinophils at 1.5% . the c - reactive protein level was 0.02 mg / dl ( normal : 0.5 mg / dl ) . serum sodium , potassium , creatinine , magnesium , calcium , and liver function test were all within normal limits . the spirometry was normal ; fvc 4.95l ( 105% of predicted ) , fev1 3.77l ( 107% of predicted ) , and fev1/fvc ( 76% ) . the chest ct showed a 1.21.0 cm sized subpleural solitary pulmonary nodule at the right lower lobe . although it looked as a benign inflammatory nodule such as cryptococcal infection , malignancy could not be excluded ( fig . on positron emission tomography ( pet ) image , the small subpleural nodule at the right lower lobe showed minimal increased fludeoxyglucose ( fdg ) uptake ( standardized uptake value [ suv ] 1.25 ) ( fig . at first we considered a percutaneous needle biopsy for diagnosis , but biopsy was considered not technically feasible due to the location of the nodule . macroscopic examination of the resected mass revealed a gray , firm , and well - demarcated tumor , measuring 1.21.00.7 cm , with slight pleural indentation and central necrosis , located in the right lower lobe of the lung . microscopically , chronic granulomatous inflammation which was composed of coagulation necrosis with rim of fibrous tissues and granulations was recognized . in the center of the necrotic nodules , the parasite was a nematode larva and had prominent internal cuticular ridges and thick cuticle , a well - developed muscle layer , an intestinal tube , and uterine tubules . the diameter of the worm was approximately 240 m . based on these morphologic features , after surgical resection , the patient was discharged without any complications and is being followed up in healthy conditions . human pulmonary dirofilariasis was first reported in 1887 , when de magalhes documented the discovery of a single male and a single female filarial worm in the left ventricle of a boy from rio de janeiro , brazil . in 1961 , dashiell reported the first case involving the lung . usually d. immitis invades the lungs in human cases , but reports of human dirofilariasis involving other organs like the subconjunctiva , liver , and subcutaneous sites are also available . another case of dirofilariasis in the liver reported in korea   was actually a misdiagnosis of hepatic capillariasis . the chest ct images and pathologic findings of our case were similar to the first korean dirofilariasis case . however , our case is the first to show additional pet imaging . in our case , pet - ct was performed for differential diagnosis of malignancy , and the pet - ct showed a small subpleural nodule at the right lower lobe with minimal increased fdg uptake ( suv 1.25 ) . in the life cycle of d. immitis , the dog is the principal host , though other suitable hosts include cats , wolves , coyotes , and foxes . are the normal vector - intermediate host , but more than 60 species of mosquitoes in 6 genera are capable of propagating the development of d. immitis . in the usual life cycle , the sexually mature female worm resides in the dog 's right ventricle and sheds thousands of microfilariae into the blood stream . when a mosquito bites the dog , it ingests the microfilariae . over the next 10 to 16 days , human are the " dead - end host " since larvae can not develop into adults in humans . in our case , human pulmonary dirofilariasis is usually discovered during routine health examinations because it does not cause notable symptoms . it is seen as a well - circumscribed , non - calcified , peripheral coin lesion or nodule . usually , the pulmonary lesion is a spherical nodule that upon gross examination appears as a well - circumscribed , spherical , grayish - yellow nodule 1 to 3 cm in diameter , surrounded by normal lung parenchyma . on microscopic examinations , there is a central core of necrosis surrounded by a granulomatous zone of tissues . in our case , the nodule was chronic granulomatous inflammation composed of coagulation necrosis with rim of fibrous tissues and granulations . dirofilaria infections can be diagnosed on the basis of worm morphology , such as the thick multilayer cuticle with lateral internal ridges , large lateral cords , and coelomyarian musculature . in cross sections , d. immitis measures 100 - 300 m in diameter and possesses a multilayered curicle with a thickness of 10 - 25 m . the present case showed worm structures such as prominent internal cuticular ridges , no external cuticular ridges , thick cuticle , well - developed muscle layer , and presence of an intestinal tube . the diameter of the worm was 240 m , which was compatible with a d. immitis immature female worm .
dirofilariasis is a rare disease in humans . 
 we report here a case of a 48-year - old male who was diagnosed with pulmonary dirofilariasis in korea . on chest radiographs , 
 a coin lesion of 1 cm in diameter was shown . 
 although it looked like a benign inflammatory nodule , malignancy could not be excluded . 
 so , the nodule was resected by video - assisted thoracic surgery . 
 pathologically , chronic granulomatous inflammation composed of coagulation necrosis with rim of fibrous tissues and granulations was seen . in the center of the necrotic nodules , 
 a degenerating parasitic organism was found . 
 the parasite had prominent internal cuticular ridges and thick cuticle , a well - developed muscle layer , an intestinal tube , and uterine tubules . 
 the parasite was diagnosed as an immature female worm of dirofilaria immitis . 
 this is the second reported case of human pulmonary dirofilariasis in korea .