A wide variety of parasitic organisms may infect the lungs, although clinical disease is rare in the UK. In general, parasites may cause lung disease by two different mechanisms:
• Hypersensitivity reactions, e.g. Löffler’s syndrome and eosinophilic lung disease, most commonly from helminths such as ascaris, toxocara, and liver flukes
• Direct infection and invasion, e.g. amoebic disease, pulmonary hydatid disease.
Some of the more important examples are noted in this chapter.
Pulmonary hydatid disease
• Hydatidosis is the commonest parasitic lung disease worldwide
• Human infection follows ingestion of parasite eggs, with the adult worm found in dogs, sheep, goats, horses, camels, and moose; infection is common in sheep-raising regions, particularly Central Europe and the Mediterranean, as well as Alaska and Arctic Canada
• Caused by a cestode (tapeworm). Two main forms:
• Echinococcus granulosus, which causes cystic hydatid disease as the larvae grow in the lungs. Common. Symptoms include cough (sometimes productive of cyst contents, ‘hydatidoptysis’), haemoptysis, and chest pain. CXR shows rounded cysts, sometimes with calcified walls, most commonly in lower lobes; CT may show ‘daughter cysts’. Cyst rupture may occur, with wheeze, eosinophilia, and bronchial or pleural spread
• Echinococcus multilocularis, which leads to alveolar hydatid disease following tissue invasion. Rare. Lung masses are less clearly delineated on CT than in cystic disease
• Diagnose from serology or sputum analysis. Serology is insensitive for the diagnosis of pulmonary disease (around 50%). Demonstration of liver cysts supports the diagnosis. Avoid needle aspiration of cysts, which may result in hypersensitivity or dissemination
• Treatment is with surgical excision in most cases. Medical treatment with albendazole if the patient is unfit for surgery or following cyst rupture and dissemination.
• Caused by the protozoa Entamoeba histolytica
• Intestinal and liver infection are common, with lung involvement in a minority
• Lung disease can develop either directly via transdiaphragmatic spread from the liver or via the bloodstream or lymphatics
• Pulmonary manifestations include right lower lobe consolidation, empyema, lung abscess, or hepatobronchial fistulae (resulting in large volumes of brown or ‘anchovy’ sputum). May be associated pericardial disease
• Diagnose using serology (sensitivity >90%) or following identification of trophozoites in stool, sputum, or pleural fluid
• Treatment is with metronidazole plus diloxanide.
• An intestinal nematode (roundworm) distributed worldwide
• Following oral ingestion of Ascaris lumbricoides eggs, larvae haematogenously migrate to lungs where they mature over 1–2 weeks
• Clinically presents as a hypersensitivity reaction, with cough, wheeze, fever, retrosternal discomfort, CXR infiltrates, and peripheral eosinophilia (Löffler’s syndrome)
• Examination of gastric aspirates or respiratory secretions for larvae is required to definitively diagnose. Stool for eggs may confirm the diagnosis although often not detectable for ~2 months
• Usually resolves spontaneously after 1–2 weeks. Consider treatment with albendazole/mebendazole for GI infection once larvae have reached maturity.
• Caused by the nematode (roundworm) Strongyloides stercoralis, found in Central and South America and Africa. Filariform larvae (in faecally contaminated soil) migrate through skin and travel to lungs haematogenously
• Pulmonary involvement may lead to a Löffler-type syndrome, with wheeze, skin rash, eosinophilia, and CXR infiltrate. In the setting of immunocompromise, disseminated autoinfection may occur, leading to the ‘hyperinfection syndrome’. ARDS may develop, and 2° bacterial sepsis is common
• Diagnose using serology (sensitivity ~85%; false negatives in immunosuppression) or following microbiological analysis of stool (relatively low sensitivity) or duodenal fluid. In disseminated strongyloidiasis, larvae may be found in sputum, BAL fluid, and pleural fluid
• Treatment is with ivermectin or albendazole.
• Caused by roundworm Toxocara canis, distributed worldwide in dogs (T. cati from cats also causes disease)
• Ingestion of eggs from contaminated soil/food may result in visceral larva migrans. Migration of larvae through the lungs results in an immune response, with wheeze, cough, and eosinophilia. Heavy ingestion causes fever, anorexia, hepatomegaly, and urticarial rashes
• Diagnosis may be made from serology (sensitivity ~80%)
• Treatment often not required; moderate/severe cases are given albendazole; steroids may be beneficial in severe cases.
• Nematode (roundworm) found in USA, Japan, South America
• Infection is caused by Dirofilaria immitis following mosquito transfer from animals, especially dogs. Worms lodge in the pulmonary arteries and elicit an inflammatory response, leading to a necrotic nodule
• Presentation is classically asymptomatic, with a single peripheral nodule on CXR mimicking cancer. Patients may present with cough, chest pain, and haemoptysis, presumably due to pulmonary infarction
• Definitive diagnosis requires lung biopsy. Serology lacks sensitivity and specificity
• Treatment is not usually required.
• Found in the Middle East, South America, South-East Asia, Africa, and the Caribbean
• Schistosoma species are trematodes (flukes) carried by snails, and infection follows skin penetration, often during swimming
• Pulmonary involvement may reflect acute tissue migration, causing cough, wheeze, and CXR infiltrates. Chronic infection can lead to interstitial infiltrates or AV fistulae. In some, portal hypertension opens up portosystemic collaterals, and eggs then embolize into the pulmonary circulation. A granulomatous pulmonary endarteritis develops, causing PHT and cor pulmonale
• Diagnosis from observation of ova in sputum, BAL, urine, or stool, or from lung biopsy. Serology testing is possible, but such tests are not standardized
• Treatment is with praziquantel.
• Caused by Paragonimus spp., particularly P. westermani (oriental lung fluke), a trematode (fluke) distributed in West Africa, the Far East, India, and Central and South America
• Following ingestion of undercooked seafood, flukes migrate to the lung or pleura and become encapsulated, developing into adults in ~6 weeks
• Clinical features may be acute or chronic and include chest pain, pneumothorax, pleural effusion, Löffler’s syndrome, and recurrent haemoptysis. Serum eosinophilia is common
• Diagnose with serology (sensitivity ~90%) or observation of eggs (late phase of infection) in sputum, TBB, BAL, pleural fluid, or stool
• Treatment is with praziquantel.
Tropical (filarial) pulmonary eosinophilia
• Follows infection with Wuchereria bancrofti, Brugia malayi, or Brugia timori in the tropics
• These roundworms reside in the lymphatics and bloodstream
• Pulmonary involvement is common and represents a hypersensitivity reaction to the organism trapped in the lung, with cough, wheeze, CXR infiltrates, peripheral eosinophilia, and raised serum IgE. See pp. [link]–[link]
• Diagnosis is serological (modest sensitivity)
• Treatment is with diethylcarbamazine.