Malaria

This is endemic in most parts of the developing world and transmitted by the female mosquito. There are four different species of malaria parasites, life threatening plasmodium falciparum (P. falciparum), and the three benign malarias: P. vivax, P. ovale, and P. malariae. A fifth species of malaria, P. knowlesi is being investigated). The majority of cases of malaria amongst travellers are preventable with appropriate education and medication. The most important message to deliver is:

avoid being bitten.

This has to be continually reinforced throughout an expedition.

With the advent of more widespread travel and inappropriate use of antimalarials there has been a recent and rapid emergence of resistant strains of P. falciparum worldwide. Excellent up to date advice on appropriate malaria prophylaxis in the different geographical regions can be found at the Malaria Reference Laboratory and the Travax website (contact details at back of manual).

It is worth remembering that no antimalarial purports to be 100% effective at preventing malaria; they will however reduce the severity of the illness if contracted whilst taking antimalarials.

The recognised treatment for malaria is quinine 600mg tds for 7 days, followed by doxycycline to prevent relapse.

Mefloquine 500mg repeated after 8 hours is an alternative if this was not used as prophylaxis. Fansidar and Malarone are also useful standby treatments.

For uncomplicated malaria in the field the most useful malaria treatment is an artemisinin-based therapy. They are the most parasiticidal of all of the antimalarial drugs against P. falciparum. There are a number available. They are manufactured as mono or combined therapies. The WHO currently recommends that an artemisinin-based combined therapy (ACT) be given as a seven day course. This may be at odds with the information on the drug leaflets which recommend only 5 days, which may be inadequate, and is currently under review. The two main ACT are marketed as Riamet (24 tablet treatment course) or CoArtem (16 tablet treatment course). WHO recommends a 6 dose regime which is 24 tablets. Hence Riamet is probably the preferred treatment choice until the current confusion is concluded.

The benign malarias can establish themselves in the liver despite malaria prophylaxis and may re-emerge to cause relapsing infections even years later. This is eradicated by a 2-4 week course of primaquine 15mg daily. For this reason be suspicious of a pyrexia of unknown origin (PUO) in a person who has travelled in a malaria endemic area even years ago. Understanding the life cycle is useful when deciding on treatment.

On expedition the medical officer should seek expert advice on the risk and type of malaria locally, and appropriate prophylaxis. If possible everyone should be on the same medication. This avoids problems with members of an expedition being on different drugs and questioning their efficacy. It is also prudent to persuade expedition members to bring several weeks of extra medication in case some is lost or damaged.

For larger expeditions it is prudent for the expedition medical team to ensure everyone’s mosquito nets are impregnated with insecticide. Permethrin is the preferred agent, but it is possibly carcinogenic, having been linked to lung tumours, so always wear a face mask and protect your skin against contact with the agent. It is an unpleasant job but preferable to treating malaria, and should be repeated every 4-6 months.

Children may be less compliant with the use of long sleeves and trousers. At dusk and dawn children under 2 should be brought indoors and those over 2 should have repellent applied. 10% DEET is recommended, as stronger solutions have been linked to encephalopathy and seizures in children.

 In the field, on expedition the diagnosis of malaria is difficult, as diagnostic tests are often unavailable. Some test kits are gaining credence, becoming increasingly sensitive and specific. Contact the Malaria Reference Laboratory for guidance on the best RDT for the region you will be working. Various RDTs appear to be gaining respect as good first line indicators of both P. falciparum and the benign malarias. Especially Optimal and Binax NOW. They are cheap and easy to carry, though some concerns have been voiced regarding there enzyme stability. These cannot compare to the gold standard of thick and thin blood films but can be incredibly useful in the field. Any PUO has to be assumed to be malaria until proven otherwise, and treated and evacuated as such. Interestingly any PUO with a rash is NOT malaria, and lymphadenopathy is also rare.