Protozoans are eukaryotic, single celled organisms, which are
predominantly microscopic in size. The majority are between 5 to 250
microns in diameter. Protozoan microbiology is mostly concerned with the
disease aspects in humans. Some well known protozoan diseases in human
beings are the intestinal amoebiasis, African sleeping sickness, and malaria.
Several flagellate protozoans are responsible for diseases in both children
and adults. Giardia intestinalis is associated with diarrhoea in children.
Trichomonads are found in the mouth and cause gingivitis.
A. Plasmodium and Malaria (Protozoan microbiology)
Malaria is a mosquito borne disease caused by the protozoan,
Plasmodium. The life cycle of malarial parasite comprises two phases namely
the asexual phase in man and the sexual phase in the female Anopheles
mosquito (Definitive host).
Four different types of Malaria are recognized on the basis of period
of recurrence of fever. They are 1. Tertian, Benign Tertian or Vivax malaria,
caused by Plasmodium vivax. 2. Quartan Malaria caused by Plasmodium
malariae 3. Mild Tertian or Ovale Malaria caused by Plasmodium ovale
4. Malignant Tertian or Pernicious Malaria caused by Plasmodium
falciparum Of the four, the malignant type is fatal.
In malarial fever, the patient suffers from shaking chills, and
sweating. As the chills subside, the body temperature may rise to 106 o F.
The high fever is induced by the toxic haemozoin granules, which are liberated in plasma when the parasite schizonts burst out from the RBCS.
The patient also suffers from severe anaemia due to destruction of
erythrocytes. Other symptoms are enlargement of spleen, due to massive
increase in the number of phagocytic cells of the lymphoid macrophage
In the case of falciparum infection thrombosis of visceral capillaries
occurs. Death takes place when the capillaries of brain are plugged with
both the parasites and the malarial pigment. Another very serious outcome
of the falciparum infection is black water fever. It is characterized by the
wholesome destruction of patient’s erythrocytes and the excretion of
liberated haemoglobin in the urine.
B. Amoebiasis (Protozoan microbiology)
Amoebiasis in man is due to the infection by the protozoan endoparasite
(Sarcodina) Entamoeba histolytica. It is worldwide in distribution but,
its prevalence is greater in tropics and sub tropics than in temperate zones.
The vegetative trophozoite form is pathogenic. The trophozoites make their
way deep into the sub mucosa of the large intestinal wall by eating through
the intestinal mucosa. The blood and the ulcer contents pour into the lumen
of the intestine and pass out as bloody stool. This characterizes the amoebic
dysentry or amoebiasis.
C. Other pathogenic protozoans (Protozoan microbiology)
1. Trypanosoma gambiens – causes African sleeping sickness
2. Leishmania donovani – causes kala azar
3. Leishmania tropica – skin leishmaniasis
IV. Larval microbiology (Protozoan microbiology)
Larval microbiology deals with human diseases caused by parasitic
larvae. Parasitic infections which man acquires from animals are known as
zoonotic infections or zoonoses. In the zoonoses, human infections are only
accidental events and the parasite is not benefited since the chain of
transmission is usually broken with human infection. The term anthroponoses
means infections with parasites species that are maintained in man alone.
Malaria and filaria are examples. The term Zooanthroponoses refers to
infections in which man is not merely an incidental host but an essential link in
the life cycle of the parasite (eg., Beef and pork tapeworm).
Related Topics in Zoology:
- Microbiology Introduction and History of Medical Microbiology
- Pasteur, Koch, Lister
- Structure of Viruses
- Viral genetics
- Virus Culture
- Viral Diseases
- Bacteria Structure Culture
- Bacterial Genetics
- Bacterial Diseases
- Protozoan microbiology
- Pathogenecity of Microorganisms
- Antimicrobial Resistance
- Antibiotics and Chemotherapy
- AIDS – HIV