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Travellers should be advised that it is still possible to contract malaria, regardless of the protective measures employed and the chemoprophylaxis used, even in situations where a low level of risk was anticipated. They should be cautioned that, although malaria is readily treatable in the early stages, delay in diagnosis or the commencement of appropriate therapy may lead to serious or fatal consequences. Travellers and health care providers must therefore consider the diagnosis of malaria in any febrile illness that occurs during or after travel to a malaria-endemic area. If the diagnosis of malaria is considered, a blood slide should be taken and examined without delay.
Chloroquine and proguanil are safe for use in pregnant women travelling to areas with chlor-oquine-sensitive malaria. Non-immune women are advised to postpone travel to areas where there is a significant prevalence of chloroquine-resistant malaria. If this is not possible CDC advises that use of mefloquine ‘‘during second and third trimesters of pregnancy is not associated with adverse fetal pregnancy outcomes’’. Limited data suggest it is safe during first trimester. There is insufficient data about safety
of Malarone® in pregnancy and so it is not currently recommended (Centers for Disease Control and Prevention, 2001). However, one limited study suggested a trend towards an increased rate of spontaneous abortion in women receiving mefloquine, compared with controls (Samuel and Barry, 1998). CDC concludes that mefloquine may be considered for prophylaxis in women who are pregnant or likely to become so, when exposure to chloroquine-resistant P. falciparum is unavoidable. Deoxycycline should not be used. WHO guidelines recommend chloroquine plus proguanil in cases where the risk from malaria is low, especially for those in the first trimester of pregnancy (World Health Organization, 2001). As there is widespread resistance to these drugs, it would also be necessary to carry presumptive therapy, for emergency use if no medical help is immediately available (quinine). Primaquine eradication therapy should not be used in pregnancy because of the rare possibility of severe haemolytic anaemia if the foetus is G-6-PD-deficient (Samuel and Barry, 1998). Instead, weekly prophylaxis can be continued through pregnancy and then primaquine administered to the mother after delivery.
The need for diligence in avoidance of mosquito bites and compliance in taking prophylaxis should be emphasised. The safety of insect repellents containing DEET in pregnancy has not been established and therefore low concentration formulations should be used sparingly and for short periods.
Malaria Presumptive Treatment
Stand-by treatment regimes (Fansidar®, Malarone®, quinine) may be useful in individuals who will be travelling in remote areas without easy access to medical assistance. It is important to advise patients with a febrile illness to seek out medical care, and self-treatment for malaria should be viewed as a temporary measure only. Standby treatment remains controversial because of concerns about the risk of incorrectly treating another disease, and the potential toxicity of the antimalarial drugs. The recent availability of antigen test kits for falciparum malaria may enable more rational self-treatment and allay some of these concerns (Schlagenhauf et al., 1995).
Vaccination against P. falciparum is the intervention that is most likely to reduce malaria-associated severe morbidity and mortality in infants and young children in areas with the most intense transmission and to reduce the risk to non-immune travellers to endemic areas. The rationale for developing a malaria vaccine includes prevention of infection (pre-erythrocytic vaccines), prevention of disease (blood-stage vaccines) and reduction of transmission (transmission blocking vaccines) (Miller and Hoffman, 1998).
The general strategy since the cloning of P. falciparum blood-stage antigens in 1983 (Kemp et al., 1983) has been to develop subunit vaccines composed of defined antigens that can be synthesised chemically or by recombinant technology. As malaria immunity is stage-specific, the main focus in the development of a subunit vaccine has been to identify critical target antigens at each stage of the life-cycle (e.g. Coppel et al., 1984). This has involved the characterisation of components of the parasite that are essential for its survival or development, as well as a detailed investigation of the immunological mechanisms that confer partial protection following natural infection (Anders etal., 1985). A range of different vaccine delivery methods has also been developed. These include malaria antigens linked to strong T-helper epitopes, synthetic malaria peptides or recombinant proteins formulated with adjuvant liposomes (Fries et al., 1992) or other particles, malarial protein gene sequences incorporated into live vectors, such as the attenuated vaccinia virus strain, NYVAC (Tine et al., 1996) and DNA vaccines (Hoffman et al., 1995).