Paper II — 2013 September (Supplementary) (2010 Scheme) — Q1
4 min read
Paper II
2013 September (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Read the following clinical history and answer the following questions:
A 30 years old man presented with history of fever, chills on and off; O/E patient had
hepatosplenomegaly, pallor++. A peripheral blood smear helped in the diagnosis.
(a) What are the probable diagnosis and the etiologic agent. 2 mark(s)
(b) Describe the life cycle of this agent. 4 mark(s)
(c) How the disease is diagnosed in the laboratory 4 mark(s)
Q110 marksEssays
Answer
a) Probable diagnosis and etiologic agent: Malaria — periodic fever with chills, hepatosplenomegaly, and pallor (anaemia), confirmed by peripheral blood smear, is classical. Etiologic agent: Plasmodium species (P. vivax, P. falciparum, P. malariae, or P. ovale).
b) Life cyclePlasmodium has a life cycle spanning a human (intermediate) host and the female Anopheles mosquito (definitive host, where sexual reproduction occurs).
In the mosquito: an infective female Anopheles injects sporozoites into the human bloodstream while feeding.
Exoerythrocytic (hepatic) cycle: sporozoites travel to the liver and invade hepatocytes, undergoing schizogony to form thousands of merozoites, released into the blood (in P. vivax/P. ovale, some parasites remain dormant in the liver as hypnozoites, causing later relapse).
Erythrocytic cycle: merozoites invade RBCs, maturing through ring → trophozoite → schizont stages; schizont rupture releases new merozoites (and pyrogenic toxins, producing the periodic fever) that invade fresh RBCs, repeating the cycle (~48 hours for P. vivax/ovale/falciparum, ~72 hours for P. malariae).
Gametocytogenesis: some merozoites differentiate into male and female gametocytes within RBCs.
In the mosquito (sexual cycle): gametocytes ingested during a blood meal fuse to form a zygote, which develops into an ookinete, then an oocyst in the mosquito gut wall, ultimately releasing sporozoites that migrate to the salivary glands, completing the cycle.
c) Laboratory diagnosis
Peripheral blood smear microscopy — thick smear for screening, thin smear for species identification and parasitaemia quantification; Giemsa staining is standard.
Rapid diagnostic tests (RDTs) — immunochromatographic detection of parasite antigens (HRP-2 for P. falciparum, pLDH/aldolase).
QBC (Quantitative Buffy Coat) method — fluorescence-based, more sensitive than routine smear.
PCR — highly sensitive/specific, useful for mixed/low-level infections.
Serology — detects past exposure, not useful for acute diagnosis.
