2. Introduction
Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able
to multiply in humans, which contributes to their survival and also permits serious infections to develop
from just a single organism. Transmission of protozoa that live in a human’s intestine to another human
typically occurs through a fecal-oral route (for example, contaminated food or water or person-to-person
contact). Protozoa that live in the blood or tissue of humans are transmitted to other humans by an
arthropod vector (for example, through the bite of a mosquito or sand fly). Some species of protozoans are
abundantly found in soil. Some protozoans are helpful is keeping water clean but there are also some
protozoans which pollute the water. The disease occur as a result of interaction between the protozoans and
human being under specific environmental conditions. This interaction is referred to as infection, the
manifestation of which is always the infectious disease.
3. Types of parasitic protozoa
1. Ectoparasites- Those parasitic protozoans which are found on the body of the host are called ectoparasite.
Example- hydramoeba
2. Endoparasities- The parasities found within the body of the host are called endoparasites. Example -
Entamoeba , trichomonas.
life cycle
Monogenetic -Many parasites are monogenetic which life cycle completed in a single host. Ex- monocystis.
Digenetic –some parasites are digenetic which life cycle completed in a two host. Ex-plasmodium, trypanosome
Harmful protozoans are the following types-
1. Protozoa found in soil
2. Water polluting protozoans
3. Parasitic protozoans
Common characteristic features-
1.They depend for their existence upon their hosts.
2.All exhibit host specificity.
3.They complete their life cycles in one or more than one host.
4.They secrete toxic substances which cause the particular disease.
4. The disease causing protozoans are called pathogenic protozoans and are met within all the classes of this
phylum. the more important pathogenic protozoan of man cattle and other useful animals along with
their mode of transference from one host to the other and the disease caused by them all given in table
S. No. Name of parasite Host and site of parasite in the body Disease caused Method of transmission
Class Rhizopoda (the ameba)
1 Entamoeba histolytica In the clone of man, sometime in dog
and cat also. It may reach liver spleen
lung and brain.
Amoebic dysentery by contaminated food
and water
2 Entamoeba coli in the clone of man gastrointestinal disturbances by transmitted form the
water
3 Entamoeba gingivalis Blood secret in teeth and gum pyorrhea transmitted by kissing
5. S. No. Name of parasite Host and site of parasite in the body Disease caused Method of transmission
Class Mastigophora (the flagellates)
1 Trypanosoma gambiense in the blood of Africans African sleeping sickness by the bite of the fly glossina
palpalis
2 Trypanosoma cruzi in early stage it is found in the muscles
heart brain spinal cord and go need of
children but in later stages in the blood
Chaga’s disease by a bug
3 Leishmania donovani in the liver, lymph glands and
leucocytes of man dog and cat
Kala-azar fever by sand fly
4 Leishmania tropica in the endothelium of blood capillaries
of skin of man
Oriental shore by sand fly
5 Trichomonas vaginalis in urinogenital tract of women veginitis during sexual intercourse
6 Trichomonas foetus in urine genital system of cattle abortion of foetus during copulation
7 Giardia intestinalis In small intestine of man Diarrhoea by contaminated food
6. S.
No.
Name of parasite Host and site of
parasite in the body
Disease caused Method of transmission
Class sporozoa (organisms whose adult stage is not motile )
1 plasmodium vivax in erythrocytes and
liver of man
different type of malaria
fever
by the bite of female Anopheles
mosquito
2 Plasmodium falciparum - - -
3 Plasmodium malaria - - -
4 Plasmodium oval - - -
Class Ciliata (the ciliates)
1 Balantidium coli in clone of human
beings
ulcers in clone and diarrhoea by spores.
