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MCQs in Tropical Medicine

Rob Skelly DTM+H FRCP

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Answer 10

Plasmodium falciparum

True a. causes more severe disease in pregnancy
False b. is associated with recurrent relapses after initial treatment because of liver hypnozoites
True c. is the only malarial parasite causing greater than 20% parasitaemia
True d. infection is typically associated with thrombocytopaenia
True e. is the only cause of cerebral malaria

Falciparum malaria (malignant tertian malaria) is the most serious of the malarias. This is in part because P.falciparum has the potential to invade red blood cells of any age, resulting in high parasitaemias. Furthermore, the schizonts are sequestered in organ capillaries causing local obstruction to blood flow with local acidosis and tissue hypoxia.

TNF-alpha is grossly elevated and this is most likely to be significant in the pathogenesis.

Raised intracranial pressure has occurred in children with cerebral malaria but rarely in adults and dexamethasone has been shown to be of no benefit.

P.falciparum does not form hypnozoites so true relapses do not occur after successful treatment. Recrudescence of infection may occur if treatment is incomplete but this usually occurs soon after initial therapy or at latest within 3-6months. This is not the case with the other malarial parasites. All the other malarial parasites have hypnozoite liver stages. Apparently successful therapy may be followed by relapse even 20 years later. Treatment for non-falciparum malaria should usually be followed by primaquine which will kill the liver hypnozoites.

Clinical malaria is usually accompanied by some fall in the platelet count. Indeed thrombocytopaenia helps to differentiate malaria from other causes of fever in regions where asymptomatic carriage of malarial parasites is common.

Copyright: Rob Skelly 2006