World Health Organization (WHO) criterion for severe anaemia is haemoglobin below 5 g/dL in children and under 7 g/dL in adults. However the clinical manifestations due to anaemia per se are not known and to what extent it contributes to the respiratory distress associated with the hyperdynamic status of the febrile syndrome. There is scarce literature on malarial anaemia in population-based studies in Latin America, as reviewed elsewhere [95] . On top of that, major differences in Latin America are seen when the same methodology is applied. That is probably related to distinct genetic background and environmental factors, e.g. in the Amazon Basin (intense racial mixture) and in the Colombian Pacific Coast (nonmixed black population) [96] . It is not known if anaemia is as frequent among patients from Brazil as in Southeast Asian patients, where P. vivax is considered to be a disease of children because the acquisition of immunity against this species occurs much faster than for P. falciparum, in highly endemic areas [97] . In Brazil only 25% of vivax disease affects children 0-14 years of age, however severe anaemia was reported in hospitalized children and adults, needing red blood cell (RBC) transfusions [45] . A key description of anaemia in vivax malaria children in Latin America was published in Venezuela in 2006 [98] . The 'congenital malaria' in newborns from the present series of reports with severe anaemia confirms previous findings that vivax malaria has an important clinical impact in children under 3 months [99] . Non-severe anaemia, however, seems to be as frequent as 25.8% among the population of a recent occupation area in Rondônia, where hydroelectric power plants are being built [100] . The cut-off of haemoglobin under 12 g/dL as a criterion of anaemia however should be seen with scepticism because of age ranges and the lack of baseline levels of haemoglobin validated to specific populations, which makes meta-analyses susceptible to misclassification. Major confounding factors in the global analysis of anaemia are the local contributors to this haematological complication such as iron-deficiency anaemia, which was found to occur in 5.6% of a rural Amazonian population, mostly among school children and women [101] . Another important associated condition, which may interfere in the comparison between distinct populations, is the prevalence of intestinal helminthic infection. In a study performed with anaemic children, the presence of hookworms and malnutrition was cited [30] . However some controversy exists regarding this influence since in a cohort study, children with any intestinal helminth were protected from anaemia triggered by acute vivax infection [47] . In fact anti-helminthic treatment and iron supplementation reduced the haematological indexes in the population from an endemic area for malaria [102] .