Encyclopedia of Parasitology

2016 Edition
| Editors: Heinz Mehlhorn

Opportunistic Agents

Reference work entry
DOI: https://doi.org/10.1007/978-3-662-43978-4_2234

Those parasites which reach their full pathogenicity only in immunocompromied hosts (e.g.,  AIDS patients, cortisone drug users), while the same parasites lead to no or only to mild clinical symptoms in immunocompetent hosts were considered as opportunists. However, with respect to life cycle only those parasites which have an endogenous reproduction phase in humans, which may give rise to uncontrolled endoautoinvasions, may become opportunists. The most important opportunists in AIDS patients are   Pneumocystis carinii, Cryptosporidium parvum, and   Toxoplasma gondii , which are the main “killers” in American and European AIDS patients comprising of up to 70 % of the cases. Other spp., like the following are also found (often together and in large numbers) in such patients: the protozoans   Giardia lamblia ,   Blastocystis hominis , Naegleria spp., Acanthamoeba spp.,   Entamoeba histolytica ,   Isospora belli ,   Cyclospora cayetanensis , many microsporidian species ( Microsporidia),   Balantidium coli , the nematode   Strongyloides stercoralis , and the  mange mites  Sarcoptes scabei and   Demodex folliculorum . For more details see  Opportunistic Agents, Man,  Encephalitozoonosis.

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