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Eclipsed by the debates about malaria incidence and severity in individual patients, malaria transmission in helminth-infected persons has so far received very little attention. Studies in humans have shown increased malaria incidence and prevalence, and a trend for a reduction of symptoms in patients with malaria. This suggests that such patients could possibly be less likely to seek treatment thus carrying malaria parasites and their gametocytes for longer durations, therefore, being a greater potential source of transmission. In addition, in humans, a study showed increased gametocyte carriage, and in an animal model of helminth-malaria co-infection, there was increased malaria transmission. These elements converge towards the hypothesis that patients co-infected with worms and malaria may represent a hub of malaria transmission. The test of this hypothesis requires verifying, in different epidemiological settings, that helminth-infected patients have more gametocytes, that they have less symptomatic malaria and longer-lasting infections, and that they are more attractive for the vectors. The negative outcome in one setting of one of the above aspects does not necessarily mean that the other two aspects may suffice to increase transmission. If it is verified that patients co-infected by worms and malaria could be a transmission hub, this would be an interesting piece of strategic information in the context of the spread of anti-malarial resistance and the malaria eradication attempts.

For thousands of years the deadliest human parasite, Plasmodium falciparum, has been evolving in populations also infected by the most prevalent parasites, worms. This is likely to have shaped the genome of all 3 protagonists--man, worms and malaria. Observational studies in Thailand have shown that although P. falciparum malaria incidence increased two-fold in helminth-infected patients, there was a 64% reduction of cerebral malaria and an 84% reduction of acute renal failure in helminth-infected patients relative to those without helminths. In addition, it was suggested that mixed infections, anaemia and gametocyte carriage were more frequent in helminth-infected patients. On the contrary, fever was lower in helminth-infected patients. The present hypotheses, their implications and the limitations of the results described and of those from studies in Africa are discussed.