Parasitic helminths are a distinct group of infectious agents that are among the most prevalent causes of morbidity and mortality in humans worldwide. Billions of people harbor parasitic worms. People with helminthic infections of the lungs often seek medical advice because of one or more common chest complaints—cough, pain, or breathlessness. They may also have unexplained laboratory abnormalities, including eosinophilia or pulmonary nodules. They can pose a diagnostic challenge, particularly in areas where helminthic infections are not endemic. More common causes of chest complaints have to be excluded, a history of residence in certain geographic locations or of dietary or other exposures has to be elicited, and the proper procedures for making the diagnosis of helminthiasis selected.
The helminths that parasitize humans include the nematodes (roundworms) and the platyhelminthes (flatworms), with the flatworms divided into the cestodes (tapeworms) and the trematodes (schistosomes and other flukes). The biology of each of these groups is distinct. Ectoparasites (e.g., the Annelida, such as leeches, ragworms, or earthworms) are uncommonly associated with lung disease and are not discussed here.
In humans, worms produce a variety of pulmonary parenchymal and vascular diseases (Table 137-1). Familiarity with the biologic behavior of each organism is essential for proper diagnosis and treatment because several stages in the life cycle of the parasite are typically found in humans, and pulmonary lesions can occur at different stages, depending on the infecting parasite.
Table 137-1Pulmonary Parenchymal and Vascular Diseases Produced by Worms ||Download (.pdf) Table 137-1Pulmonary Parenchymal and Vascular Diseases Produced by Worms
|Major Pulmonary Presentation ||Infection ||Causative Organism ||Infective Stage ||Pathogenic Stage |
|Loeffler-like syndrome ||Ascariasis ||Ascaris lumbricoides ||Embryonated eggs in soil ||Migrating larvae |
| ||Hookworms ||Ancylostoma duodenale, Necator americanus ||Larvae in soil ||Migrating larvae |
| ||Strongyloidiasis rhabditiform ||Strongyloides stercoralis ||Larvae in soil ||Migrating larvae |
| ||Hyperinfection with filariform ||S. stercoralis ||Larvae in bowel ||Migrating larvae |
|Pulmonary eosinophilia ||Lymphatic filariasis ||Wuchereria bancrofti, Brugia malayi ||Larvae in mosquito ||Microfilariae |
|Eosinophilia, cough ||Visceral larva migrans ||Toxocara canis, T. cati ||Egg ingestion ||Larvae |
|Space-occupying lesions ||Echinococcosis ||Echinococcus granulosus ||Eggs in soil ||Hydatid cysts |
| ||Paragonimiasis ||Paragonimus westermani ||Metacercariae ||Adult worms |
| ||Schistosomiasis ||Schistosoma mansoni, S. japonicum, S. haematobium ||Cercariae in fresh water ||Eggs |
Worms are multicellular organisms that vary substantially in size—from a few millimeters to several meters. They are covered by a tegument cuticle that protects them from the environment. Reproductive organs – both sexual and hermaphroditic – take up a large portion of the body. They are among the most developed and elaborate of human parasites, and their parasitic capabilities are such that they often inhabit more than one host and survive different hostile environments. Despite their relatively large adult size, the infective stages of the worms invade human tissues by ingestion, penetration of skin, or the bite of insect vectors. Furthermore, parasitic helminths have developed a ...