Why model malaria?

The past 30 years have seen little tangible progress in alleviating the worldwide burden of malaria. Ellis McKenzie here discusses some of the history, problems and prospects of mathematical models of malaria, and the contributions that models might make towards progress. He argues that models can be powerful tools for integrating information from different disciplines, and that advances in computer modeling can complement and extend classic approaches.     

Can fungal biopesticides control malaria?

Recent research has raised the prospect of using insect fungal pathogens for the control of vector-borne diseases such as malaria. In the past, microbial control of insect pests in both medical and agricultural sectors has generally had limited success. We propose that it might now be possible to produce a cheap, safe and green tool for the control of malaria, which, in contrast to most chemical insecticides, will not eventually be rendered useless by evolution of resistance. Realizing this potential will require lateral thinking by biologists, technologists and development agencies.     

What can the residents of malaria endemic countries do to protect themselves against malaria?

The incidence of malaria may vary substantially between adjacent communities and within an individual community, even in areas of high malaria transmission. Analysis of the factors responsible for these local variations in the incidence of malaria may identify potential control measures. Factors shown to be associated with local protection against malaria in some situations include house position, house design, the use of insect repellents and mechanical barriers such as bednets and curtains. The efficacy of insecticide treated nets and curtains in preventing mortality and morbidity from malaria, at least in the short-term, has been demonstrated convincingly. However, other measures of personal protection have not been evaluated in large trials which have clinical malaria as their endpoint. Such trials are needed to see if new malaria control tools can be identified that will assist current international efforts to improve malaria control, especially in Africa. The millions of non-immune travellers who visit malaria endemic areas each year need to protect themselves against malaria and the ways in which they can do this most effectively have been studied extensively. However, less attention has been paid to the local population of malaria endemic areas. What steps can they adopt to provide personal protection against malaria and how effective are these measures? Clues to which measures might be effective can come from study of the reasons for local variations in the incidence of malaria.     

Have malaria parasites three genomes?

Recent efforts to define the mitochondrial genome of malaria parasites have uncovered an unexpected complexity: there are two almost totally dissimilar organellar DNA molecules. lain Wilson, Malcolm Gardner, Jean Feagin and Donald Williamson discuss the surprising possibility that Plasmodium may have, in addition to the nuclear genome, two unrelated organellar genomes, one evidently mitochondrial and the other of unknown function.     

Could malaria return to Britain?

With predicted global warming, the mosquito fauna of Britain is certain to change. How will this effect our native Anopheles mosquitoes and the development of malarial parasites within them? Will exotic species become established, and act as more effective vectors of malaria?     

Is the malaria diagnosis expensive?

Malaria remains the most important of the tropical diseases, widespread throughout the tropics, but also occurring in many temperate regions. The disease causes a heavy toll of illness and death, especially among children in endemic areas. It also poses a risk to business travellers, tourists and inmigrants and imported cases of malaria are increasingly seen in non-endemic areas. We discuss here how microscopical diagnosis is essential for identifyingPlasmodium species responsible of the infection and discarding possible mixed infections. Thus, a correct treatment can be administered in 30 min, avoiding secondary stays and saving important amounts of money. Problems of drug resistance have to be distinguished from those arising due to erroneous diagnosis.     

Is immunity to malaria really short-lived?

Protection against Plasmodium falciparum malaria is usually considered to be the cumulative product of repeated exposure to parasites, and thus a function of age, in endemic areas. The recent outbreak of malaria in the central highlands of Madagascar gave Philippe Deloron and Claire Chougnet the opportunity to compare the incidence of malaria in children and young adults exposed to malaria for the first time, with that in older adults who spent their childhood in the study area before malaria control was introduced. Protection, as well as immune responses to two major P. falciparum antigens, was not related to age. Individuals older than 40 years were more protected than were younger adults. This increased protection was probably due to immunological memory.     

Thrombocytopenia in malaria: who cares?

Despite not being a criterion for severe malaria, thrombocytopenia is one of the most common complications of both Plasmodium vivax and Plasmodium falciparum malaria. In a systematic review of the literature, platelet counts under 150,000/mm3 ranged from 24-94% in patients with acute malaria and this frequency was not different between the two major species that affected humans. Minor bleeding is mentioned in case reports of patients with P. vivax infection and may be explained by medullary compensation with the release of mega platelets in the peripheral circulation by megakaryocytes, thus maintaining a good primary haemostasis. The speculated mechanisms leading to thrombocytopenia are: coagulation disturbances, splenomegaly, bone marrow alterations, antibody-mediated platelet destruction, oxidative stress and the role of platelets as cofactors in triggering severe malaria. Data from experimental models are presented and, despite not being rare, there is no clear recommendation on the adequate management of this haematological complication. In most cases, a conservative approach is adopted and platelet counts usually revert to normal ranges a few days after efficacious antimalarial treatment. More studies are needed to specifically clarify if thrombocytopenia is the cause or consequence of the clinical disease spectrum.