Paper II — 2014 September (Supplementary) (2010 Scheme) — Q1
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Paper II
2014 September (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
A 45 years old male complaints of intermittent high grade fever which was cyclical and
associated with rigor and chills. On examination he has hepatosplenomegaly. Answer
the following:
(a) What is the probable diagnosis. 1 mark(s)
(b) List the species of organism which can cause this type of disease 2 mark(s)
(c) Discuss briefly the pathogenesis of the condition 3 mark(s)
(d) Discuss in detail the laboratory diagnosis of this disease 4 mark(s)
Q110 marksEssays
Answer
a) Probable diagnosis: Malaria — intermittent, cyclical high-grade fever with rigor/chills and hepatosplenomegaly is classical.
b) Species causing this disease: Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, and Plasmodium ovale (with P. knowlesi as an additional zoonotic species in some geographic regions).
c) Pathogenesis
An infective female Anopheles mosquito injects sporozoites, which travel to the liver and multiply within hepatocytes (exoerythrocytic schizogony), releasing merozoites into the blood, which invade RBCs and mature through ring, trophozoite, and schizont stages. Schizont rupture releases new merozoites (along with pyrogenic parasite antigens/toxins that trigger a cytokine response — TNF-α, IL-1, IL-6) that invade fresh RBCs, repeating the cycle — this synchronized cyclical rupture produces the classical periodic fever pattern (every 48 hours for P. vivax/ovale/falciparum, every 72 hours for P. malariae, giving rise to the terms tertian and quartan malaria respectively). Hepatosplenomegaly results from reticuloendothelial hyperplasia in response to parasitized/destroyed RBCs and parasite antigen clearance. In P. vivax/P. ovale, dormant liver-stage hypnozoites can cause later relapse.
d) Laboratory diagnosis
Peripheral blood smear microscopy — the gold standard; thick smear for screening/detecting low parasitaemia, thin smear for species identification and parasitaemia quantification; Giemsa staining is standard, ideally taken during/soon after a febrile episode when parasitaemia peaks.
Rapid diagnostic tests (RDTs) — immunochromatographic detection of parasite antigens (HRP-2 specific for P. falciparum; pLDH/aldolase for pan-species detection).
QBC (Quantitative Buffy Coat) method — fluorescence-based concentration technique, more sensitive than routine smear but does not allow precise species identification.
PCR — highly sensitive/specific, useful for detecting low-level or mixed infections.
Serology — detects past exposure, not useful for diagnosing acute infection.
