Pneumonia: Parasitic

Parasites are eukaryotic organisms that live within another organism or host. They are broadly divided into two groups: single-celled protozoa and multicellular helminths. Most parasites have complex life cycles with multiple stages, often requiring multiple host species to complete their life cycle. Humans acquire infection with parasitic organisms in a number of different ways. Some are ingested through a fecal-oral spread, others transmitted by insect vectors, still others by penetrating through the skin of the host from contaminated soil or water. This article focuses on the major parasitic infections that affect the lungs. Few parasites specifically go to the lungs as their final target organ, with the exception of Paragonimus, the lung fluke. For the majority of the organisms that cause pulmonary disease, either the lungs are secondary sites of infection (e.g., amebiasis and toxoplasmosis), or the parasites migrate through the lung en route to another organ system (e.g., . Strongyloides, . Ascaris). In some infections, pulmonary symptoms are due to a hypersensitivity immune response to parasite antigen as seen in the tropical pulmonary eosinophilia syndrome.