Question

1. Name the protozoan species that is responsible for causing the most serious and even fatal malerial disease.     [0.5]
2. Name the host in which the parasite completes its sexual stages and explain the changes taking place.     [2]
3. How does the parasite damage the human body after entering the blood stream?     [1.5]
4. Suggest two effective preventive measures to control the spread of this disease in endemic regions.     [1]

Answer 1

1. Plasmodium falciparum.
2. The female Anopheles mosquito
   Changes that take place:
   
   • Gametocytes (from infected human blood) develop into male (micro-) and female (macro-) gametes in the mosquito midgut.
   • Microgametogenesis (exflagellation) produces motile microgametes; macrogametocytes become macrogametes.
   • Fertilization of micro- and macrogametes produces a diploid zygote, which becomes a motile ookinete.
   • Ookinete penetrates the gut wall and forms an oocyst on the outer gut surface; sporogony in the oocyst produces many sporozoites.
   • Sporozoites are released and migrate to the mosquito’s salivary glands, ready to infect the next human.
3. After entering the bloodstream, the merozoites invade red blood cells (RBCs) and undergo asexual development (trophozoite → schizont). Rupture of infected RBCs releases new merozoites and parasite-derived toxins, causing periodic fever and chills and loss of RBCs (hemolytic anaemia). Infected RBCs express parasite proteins that mediate cytoadherence and sequestration in capillaries, blocking microcirculation and causing tissue ischemia, a key mechanism behind severe complications such as cerebral malaria.
4. Effective preventive measures-
   • Use of long‑lasting insecticide‑treated bed nets (LLINs) to prevent mosquito bites at night.
   • Vector control indoor residual spraying (IRS) and removal/management of mosquito breeding sites (stagnant water) to reduce the mosquito population.