Although often regarded as causing a benign infection, there is recent increasing evidence that the overall burden, economic impact, and severity of P. vivax have been underestimated, in part due to a bias in the scientific literature which traditionally devoted most of its attention to the more lethal parasite Plasmodium falciparum, probably as a reflection of a more substantial funding [5] . Until 16 October 2011, the search in MED-LINE using P. vivax as keyword retrieved 5,026 indexed abstracts; using P. falciparum, on the other hand, retrieved almost five times more abstracts: 25, 807 . Even in places where P. vivax represents the major local problem to be tackled, clinical research is still focused on P. falciparum [6] . There is robust evidence in the past decade from hospital-based studies in India and Indonesia that P. vivax is able to cause severe disease [7, 8] . Some authors argue that this clinical severity may only now be properly recognized and announced by researchers in the field, but these complications apparently are not new from a historical perspective [9] . Actually, the case fatality rate (CFR) related to malarial infections in the English marshes during the 16th and 17th centuries, corresponding to the Little Ice Age, suggest that P. vivax (a parasite more prone to persist in vectors even under low temperatures) may have killed part of this population already victimized by famine [10] . During the first half of the 20th century, malariotherapy in patients with neurosyphilis, using essentially the 'nonsevere' P. vivax parasite, led to diverse complications, CFR ranging from 3.3 to 30.3% [11] . The major related complications in these co-infected patients were liver damage, ruptured spleen, jaundice, delirium, uncontrolled vomiting and persistent headaches [11] . That reinforces the concept that P. vivax infection may synergize with other co-morbidities resulting in more complicated disease. Added to local geographical and social determinants, wide Annual Parasite Incidence (API) and CFR variations due to this species are seen around the world.