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Protozoa are considered to be zoonotic, eukaryotic, single-celled organisms. They possess a cellular membrane and, in contrast to bacteria, a nucleus. Many protozoa have different proliferative stages and undergo substantial changes during their life cycle. As a consequence of their size, which ranges from 10 μm to greater than 50 μm, they can very often easily be found in various tissues (eg, stool, other body fluids). Protozoa are widely distributed throughout the world.

A number of protozoan pathogens are human parasites and can induce severe courses of disease, especially as inducers of opportunistic disease (eg, in patients with HIV/AIDS). Treatment of protozoan infections is often difficult and prophylaxis through vaccination, for example, does not exist yet.

Among the protozoan infections (Table 176-1), leishmaniasis, trichomoniasis, and (rarely) amebiasis, as well as rhinosporidiosis, primarily manifest in the skin. The other protozoan infections are associated with (transient) skin affection and are only briefly mentioned in this chapter.

TABLE 176-1Protozoan Infections Important for Humans



  • Leishmaniasis is a complex of diseases caused by the protozoa Leishmania and transmitted by the bite of infected phlebotomine sandflies.

  • Four major human diseases: (a) localized cutaneous leishmaniasis, (b) diffuse cutaneous leishmaniasis, (c) mucocutaneous leishmaniasis, and (d) visceral leishmaniasis.

  • Which of the 4 diseases results depends mainly on the interaction between Leishmania species and the immunologic status of the host.

  • Diagnosis is by organism isolation or serology, but species identification is only possible with isoenzyme analysis and new molecular techniques.

  • Management ranges from observation to systemic therapy, primarily with antimonials, and vaccines in development.


Together with malaria and dengue, leishmaniasis is the third most frequent infectious disease transmitted by a vector. Annually, approximately 1.6 million new cases are reported; among these, it is estimated that approximately 200,000 to 400,000 cases represent visceral leishmaniasis, and 700,000 to 1.2 million cases represent cutaneous leishmaniasis. Around 12 million individuals are currently infected worldwide.1-3

The World Health Organization (WHO) considers leishmaniasis to belong among the so-called neglected tropical diseases. Neglected tropical diseases are poverty-associated infectious diseases that are primarily prevalent in subtropical and tropical regions, and for which there is little to no public interest, little research activity, high morbidity and mortality, ...

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