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by Dr Andrew Reekie, 23 Oct 98
Most days I see someone with a high fever and usually, whether expressed or not, there is anxiety about malaria. This is entirely reasonable and right, although in the great majority of cases, there is an obvious cause for the fever, such as sore throat, gastroenteritis, or perhaps a virus simultaneously affecting family, colleagues or other members of a school class.
Astonishingly all the experts agree that there is no malaria in Dhaka and little in most of Bangladesh, though there are small pockets with significant transmission here and there. Possibly the only area in which malaria is a major problem is the Chittagong Hill Tracts.
Apparently the mosquito Anopheles stephensi, the main vector of malaria in the Indian subcontinent, is absent from Dhaka. I use the word astonishing because malaria is a considerable problem next door in West Bengal and in Calcutta itself.
As the malaria parasite becomes increasingly multidrug resistant, personal protection against mosquitos becomes increasingly important. Something approaching 25% of malaria in this reglon is chioroquine resistant. If you still wish to take prophylaxis, the standard weekly chioroquine and daily proquanil (paludrine) is still probably the best. They are unpleasant tasting drugs and should spend the minimum time on your tongue and are best taken after food with plenty of water (always take any pill with lots of water). It has long been known that alloroquine in high dosage may damage the retina, but there is no evidence that this occurs with the very low dosage used in malaria prophylaxis, however long you take it. But those of you with children need to know that it is very toxic in overdose.
Malaria vectors, all mosquitos of the genus Anopheles, almost exclusively bite around dusk and at night. The risk of malaria is therefore, as with many other illnesses, lifestyle related. What matters is your behaviour at biting times: those of you who are safely indoors in well screened houses, or under a mosquito net or well protected by mosquito repellents and suitable clothing are at a very much lower risk. Those of you who wander around outside semi naked in the middle of the night . . .
DEET is the most effective repellant, but there is some suggestion that it is toxic in high concentration in small children. On children under five, do not use DEET preparations stronger than 10% and wash it off if at all possible before they go to bed. Citronella oil, a natural insect repellant, is non-toxic but not quite as effective. (We have stocks in Elizabeth House.)
When dressing to avoid mosquitos, wear sleeves and trousers where possible. Remember that mosquitos are attracted by dark colours and will bite through loosely woven cloth. Always put repellant on your ankles and feet as well as on other exposed places.
However, even in the worst areas for malaria in the Indian subcontinent, the transmission rate is well below that of sub-Saharan Africa - perhaps more than a hundred fold. I personally take prophylactic drugs in the malarial areas of Africa. Here I depend on protection from bites.
The fever of malaria is generally dramatic. A period of intense shivering called a rigor, typically lasting about an hour, is followed by a longer hot phase after which the patient feels exhausted if better. Early diagnosis is important. With the more severe falciparum malaria, the mortality rises sharply with delay.
One final very important point: the incubation period of malaria is very variable. The minimum is a few days in non-immune individuals but 5% of cases are over a year from possible exposure and the record is over 3 years. (These longer periods may be especially associated with partially suppressed malaria through taking prophylactic drugs.)
It is therefore necessary to consider malaria in any severe fever long after you have left the tropics and this is not always understood by doctors in temperate climates.