| Amoeba infecting humans |
| Entamoeba histolytica | causes amoebic dysentery; can cause liver abscesses |
| Intestinal and genital flaggellates |
| Giardia lamblia | causes diarrhea; one of the most common parasites in North America |
| Trichomonas vaginalis | causes inflammation of reproductive organs; very common |
| Haemoflagellates |
| Leshmania donovani | causes visceral leshmaniasis (kala-azal), hepatosplenomegaly |
| L. mexicana | causes fulminating, cutaneous ulcers |
| L. major | causes cutaneous ulcers |
| Trypanosoma brucei sp. | causes sleeping sickness in humans and cattle (African trypanosomiasis) |
| T. cruzi | causes Chagas′ disease (South American trypanosomiasis) |
| Gregarines, coccidia, and related organisms |
| Plasmodium falciparum | major cause of human malaria |
| P. vivax, P. ovale, P. malariae | also causes human malaria |
| Causes of opportunistic infections in immunodeficiency states |
| Toxoplasma gondii | causes muscle and intracellular pain |
| Pneumocystis carinii | causes interstitial cell pneumonia |
| Cryptosporidium parvum | intracellular parasites of intestinal cells resulting in diarrhea |
