In children, the Intermittent Preventive Treatment (IPTc), currently called Seasonal Malaria Chemoprevention (SMC), was considered effective on malaria control due to the reduction of its incidence in Papua New Guinea and in some areas with seasonal malaria in Africa. However, the IPT has not been indicated because of its association with drug resistance and for hindering natural immunity development. Thus, we evaluated the alternative IPT impact on malaria incidence in three riverside communities on Madeira River, in the municipality of Porto Velho, RO. We denominate this scheme Selective Intermittent Preventive Treatment (SIPT). The SIPT consists in a weekly dose of two 150？mg chloroquine tablets for 12 weeks, for adults, and an equivalent dose for children, after complete supervised treatment for P. vivax infection. This scheme is recommend by Brazilian Health Ministry to avoid frequent relapses. The clinic parasitological and epidemiological surveillance showed a significant reduction on vivax malaria incidence. The results showed a reduction on relapses and recurrence of malaria after SIPT implementation. The SIPT can be effective on vivax malaria control in localities with high transmission risk in the Brazilian Amazon. 1. Introduction In Brazil 99% of malaria cases occur in Amazon areas. In recent years, the number of cases per year decreased from 500.000 (2006) to 300.000 (2011) [1]. The Artemisin-based Combination Therapy, used by Brazilian Health Ministry decreased the falciparum malaria incidence (i.e., number of total positive thick blood smear/falciparum thick blood smear 100) from 26.5 in 2006 to 12.4 in 2011. These results do not consider Asymptomatic Plasmodium Carriers (APC), found frequently in holoendemic areas of Africa and Papua New Guinea [2, 3], but not in Amazon areas [4, 5]. However, recent studies show the presence of APC in several areas of the Brazilian Amazon [6–11]. Several works showed that residual malaria may resist to conventional treatment [12–15]. Thus, the APC presence, associated with ineffective tools for vector control and population mobility in Amazon, can be regarded as important factors to explain the increase and maintenance of malaria [16]. Frequencies from 10% to 40% APC were found in adults living in different riverside areas of Madeira River, in Rond？nia state [8, 10, 12, 14]. In the same areas, relapses frequency of 6.5% was found after complete treatment with chloroquine (CQ) plus primaquine (PQ) for 14 days, and of 26.7% after the same treatment for 7 days [17]. Previous works were performed to verify
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