2.6 Economic Roles of Protozoa
1. Pathogenic Protozoa (Harmful)
A. Plasmodium (e.g., Plasmodium vivax, Plasmodium falciparum)
Disease Caused: Malaria in humans.
Vector: Transmitted by the bite of an infected female Anopheles mosquito.
Pathology:
Plasmodium infects human liver parenchymal cells (hepatic schizogony) and then invades Red Blood Cells (erythrocytic schizogony).
Multiplication inside RBCs leads to cell rupture, releasing parasites and a metabolic waste toxin called hemozoin.
Hemozoin causes recurring bouts of high fever, intense chills, profuse sweating, severe anemia, splenomegaly (enlarged spleen), and potential liver dysfunction. P. falciparum can block brain capillaries, causing fatal cerebral malaria.
B. Entamoeba histolytica
Disease Caused: Amoebiasis (Amoebic Dysentery).
Transmission: Ingestion of food or water contaminated with tetranucleate cysts.
Pathology:
Parasitizes the mucosa and submucosa of the human large intestine (colon).
Secretes a proteolytic enzyme called histolysin, which dissolves intestinal tissue, creating characteristic flask-shaped ulcers.
Causes severe abdominal cramps, frequent loose motions containing blood and mucus, and potential secondary liver abscesses if parasites enter the hepatic portal system.
2. Beneficial Protozoa
Trichonympha
Biological Role: Obligate mutualistic symbiont inhabiting the lumen of the hindgut of wood-eating termites (Mastotermes) and wood roaches.
Ecological Importance:
Termites consume large amounts of wood (cellulose) but lack the digestive enzymes required to break down cellulose.
Trichonympha secretes the enzyme cellulase (and glucosidase), which hydrolyzes complex insoluble cellulose into simple fermentable carbohydrates (like glucose and short-chain fatty acids).
Both organisms benefit: the termite gets usable nutrients from wood, while Trichonympha receives a protected environment and a continuous supply of food.
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