Protozoan Pathogens: Identification

AbstractThe identification of protozoan pathogens is based on direct detection of the respective causative agents in clinical specimens and/or detection of specific immune reactions of the host. Protozoan diagnostics still relies on microscopy; however, in the past years, molecular methods, particularly PCR‐based techniques, have gained more and more importance. One of the big advantages of molecular techniques is that they usually allow identification below the genus level, which is often impossible by light microscopy. Serological tests are of great value in all tissue parasites and generally in most extraintestinal infections, while they only have limited importance in acute infections with short incubation times and in immunocompromised patients. Rapid and easy‐to‐use test systems are available for several important protozoan parasites and serve particularly well in the field setting.Key ConceptsOf the around 100 protozoan species that can infect humans, some are of prime importance for human health, including the causative agents ofmalaria,amoebiasis,Chagas,leishmaniasisandsleeping sickness.Several protozoan infections show a more severe progression in theimmunocompromised host, important examples being toxoplasmosis, cryptosporidiosis and visceral leishmaniasis.See also:Protozoan Pathogens of HumansThe size of protozoan pathogens varies from∼2 μm(amastigoteLeishmaniaspp.) to∼150 μm(Balantioides coli).See also:Protozoan Pathogens of HumansAs parasite density in stool or body fluids may vary, the collection ofrepeated samplesis often essential.Propercollection, storage and transportof clinical specimens are of crucial importance for reliable laboratory diagnostics.Accurate diagnosis includes both parasitedetectionand speciesidentification(in some cases: genotype/serotype).In the past years,molecular methodshave gained more and more importance in diagnostics of protozoan infections, and also commercial test systems are now available for most protozoan pathogens.In some cases,microscopic demonstrationof the causative agent in native material or stained smears remains thegold standard, for example in malaria or in active amoebic dysentery, giardiasis or also trichomoniasis.Goodmicroscopic expertiseis essential: low parasite density and/or morphologic variability can result in false negative results, while pseudoparasites and artefacts are common causes of false positive results.In many protozoan taxa, morphology alone does not provide enough information foridentification on or below the species level, which is today mostly based on molecular biological methods.