Protozoan infections are caused by a parasite called a protozoa, which are tiny, one-celled organisms that can live and multiply in the body.  

The different types protozoa have evolved to live in different parts of the body and the way you become infected with a protozoa is dependant on where in the body the protozoa lives.

Intestinal protozoa infection is through the fecal-oral route whereby food or water that is contaminated is ingested, or there is person-to person contact with an infected person.  For protozoa that live in blood or tissue these protozoa infections can be transmitted to other people by being bitten by infected insects such as mosquitoes and sandflies. Some protozoa inhabit the genital area and can be sexually transmitted by any form of genital touching.

Examples of protozoa infections in humans:

Intestinal protozoa
Entameoba histolytica causes amoebiasis (amoebic dysentery)
Cryptosporidium causes cryptosporidiosis
Giardia lamblia causes giardiasis

Blood-Tissue protozoa
Plasmodium falciparum  causes malaria
Trypanosoma brucei  causes sleeping sickness
Trypanosoma cruzi  causes Chagas disease

Genital protozoa
Trichomonas vaginalis  causes Trichomoniasis

Drugs used to treat Protozoan Infection