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.
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 system. 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.