Protozoan Pathogens: Identification

Abstract

Abstract The 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 Concepts Of the around 100 protozoan species that can infect humans, some are of prime importance for human health, including the causative agents of malaria , amoebiasis , Chagas , leishmaniasis and sleeping sickness . Several protozoan infections show a more severe progression in the immunocompromised host , important examples being toxoplasmosis, cryptosporidiosis and visceral leishmaniasis. See also: Protozoan Pathogens of Humans The size of protozoan pathogens varies from ∼2 μm (amastigote Leishmania spp.) to ∼150 μm ( Balantioides coli ). See also: Protozoan Pathogens of Humans As parasite density in stool or body fluids may vary, the collection of repeated samples is often essential. Proper collection, storage and transport of clinical specimens are of crucial importance for reliable laboratory diagnostics. Accurate diagnosis includes both parasite detection and species identification (in some cases: genotype/serotype). In the past years, molecular methods have 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 demonstration of the causative agent in native material or stained smears remains the gold standard , for example in malaria or in active amoebic dysentery, giardiasis or also trichomoniasis. Good microscopic expertise is 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 for identification on or below the species level , which is today mostly based on molecular biological methods.