Parasites have a eukaryotic cell structure similar to that of human cells and are divided into two types: helminths and protozoa.
Helminths are flatworms and roundworms that can be seen with the naked eye. Some helminths mature from larvae into adults in the GI tract (making humans the definitive host) and usually cause mild disease. In contrast, the larval stage of some helminths penetrates the intestine; migrates through tissue; invades organs, where larvae mature into adults (making humans an intermediate host); and may cause severe disease.
– Except for Strongyloides and Capillaria, all helminths require stages in other hosts to complete their life cycle. Thus increases in the burden of infection require repeated exogenous infections (e.g., residence in an endemic region).
Protozoa are microscopic single-celled organisms that, similar to bacteria, multiply within the human body and cause overwhelming infections.
Table 109-1 breaks down the symptoms of major parasitic infections by organ system and geographic distribution, with comments on clinical and epidemiologic associations.
TABLE 109-1Parasitic Infections, by Organ System and Signs/Symptoms ||Download (.pdf) TABLE 109-1 Parasitic Infections, by Organ System and Signs/Symptoms
|ORGAN SYSTEM, MAJOR SIGN(S)/SYMPTOM(S) ||PARASITE(S) ||GEOGRAPHIC DISTRIBUTION ||COMMENTS |
|Serpentine rash ||Hookworm ||Worldwide ||Can cause anemia in heavy infections |
| ||Strongyloides ||Moist tropics and subtropics ||Disseminated infection in immunocompromise |
| ||Toxocara (animal roundworm) ||Tropical and temperate zones ||Cutaneous or visceral larva migrans |
|Itchy skin rash ||Onchocerca ||Mexico, Central/South America, Africa ||Larvae detectable in skin snips and nodules |
|Painless ulcers ||Leishmania ||Tropics and subtropics ||Amastigotes detectable in biopsies; may cause destructive mucocutaneous infection; AIDS-defining infection |
|Skin nodules ||Onchocerca ||Mexico, South America, Africa ||Large nodules of adult worms |
| ||Loa loa (African eye worm) ||Western and central Africa ||Migratory nodules |
| ||Gnathostoma ||Southeast Asia and China ||Migratory nodules with eosinophilia |
|Painful nodules, especially involving feet ||Dracunculus (Guinea worm) ||Africa ||Nearly eradicated |
|Central nervous system |
|Somnolence, seizures, coma ||Plasmodium falciparum ||Subtropics and tropics ||Cerebral malaria, especially in children |
| ||Trypanosoma brucei rhodesiense ||Sub-Saharan eastern Africa ||Painful chancre from tsetse fly bite; death in weeks to months |
|Space-occupying lesions, seizures ||Acanthamoeba ||Worldwide ||Immunocompromised individuals |
| ||Balamuthia ||Americas ||Indolent meningoencephalitis with brain mass |
| ||Toxoplasma ||Worldwide ||Reactivation disease in immunocompromise; ring-enhancing lesions; AIDS-defining infection |
| ||Taenia solium ||Mexico, Central/South America, Africa ||Cysticercosis; variable sized or calcified larval cysts on CT |
| ||Schistosoma japonicum ||Far East ||Aberrant eggs can form brain or spinal cord masses. |
| ||Schistosoma mansoni ||Africa, Central/South America ||Aberrant eggs can form brain or spinal cord masses. |
|Pyogenic meningitis ||Naegleria ||Worldwide ||Motile trophozoites in fresh cerebrospinal fluid; rapid death |
|Eosinophilic meningitis ||Angiostrongylus (rat lung worm) ||Southeast Asia, Pacific, Caribbean ||Most common cause globally; spontaneous resolution |
| ||Gnathostoma ||Southeast Asia and China ||Migratory nodules |
|Painful corneal ulcers ||Acanthamoeba ||Worldwide ||Freshwater and brackish ...|