- Amoebiasis (Amoebic dysentery):  caused by Entamoeba histolytica. The infection is by the cysts Entamoeba in the stool of infected person through the agency of houseflies; The parasites pass into blood stream and enter various body organs (liver, spleen, lungs and  brain); It is characterized by abdominal pain, mild diarrhoea alternating with constipation, passing out mucus.
- African sleeping sickness: Caused by Trypanosoma gambiense. Trypanosomes are parasitic protozoans. They inhabit blood and lymph spaces or tissues of their hosts. They are pathogenic to man and domestic animals. It causes a fatal disease known as African sleeping sickness. In the late stage of Infection Trypanosomes migrate to the cerebrospinal fluid of the host manifesting nervous disorders.Â
- Kala azar (Leishmaniasis): caused by Leishmania donovani through the bite of the sand fly Phlebotomus; In man, L donovani lives intercellularly in leucocytes or cells of liver, spleen, bone marrow, lymphatic glands; Early symptoms are swelling, enlargement of spleen and liver, followed by weakness, anemia, peculiar darkening of skin.
- Malaria: caused by digenetic (having two hosts to complete i.e., human and Anopheles mosquito) and tribasic (having three phases of life cycle) protozoan parasite, Plasmodium; The infective stage of parasite in human being is sporozoite. Symptoms: It is characterized by fever at intervals, sudden acute chilliness accompanied by shivering, profuse seating. Drugs like chloroquine and primaquine are administered to treat malaria.
