Abstract. The epidemiology of malaria in 2 riverine localities in Rondônia, Brazilian western Amazônia, was assessed by a 1-year study at Portuchuelo, and a cross-sectional survey at riverine communities at Rio Machado ‫ס(‬ Ji-Paraná). Plasmodium spp. infections were diagnosed by light microscopy and by polymerase chain reaction (PCR) amplification of ribosomal DNA. PCR was 6-7 times more efficient than microscopy for detecting plasmodial infections. Both Plasmodium vivax and Plasmodium falciparum infections occurred as asymptomatic and symptomatic forms of the disease. The relation between symptomatic and asymptomatic clinical forms was roughly similar for both species of Plasmodium. Symptomless patients were monitored for 2 months. The prevalence of symptomless infections was 4-5 times higher than the symptomatic ones-respectively, 20% and 4.6% for Portuchuelo and 49.5% and 10% for JiParaná. Symptomatic malaria occurred mostly in patients in younger age groups. In contrast, there was a significant association of symptomless malaria with older age groups (medians of 26.5 and 21 years, respectively, for Portuchuelo and Ji-Paraná), whereas the age medians for symptomatic malaria were 14 and 8 years, respectively, in the 2 regions. Symptomatic malaria also was more prevalent in groups living for shorter times in Amazônia (13 and 4 years, respectively, for Portuchuelo and Ji-Paraná) as compared with symptomless malaria, which was more prevalent in groups living for longer periods in the region (medians of 25.5 and 18 years, respectively, for Portuchuelo and Ji-Paraná). The high prevalence of symptomless malaria may pose new problems for the currently adopted strategy for the control of malaria in the Amazonian region, which is essentially based on the treatment of symptomatic patients.

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We propose a taxonomic revision of the dixenous trypanosomatids currently classified as Endotrypanum and Leishmania, including parasites that do not fall within the subgenera L. (Leishmania) and L. (Viannia) related to human leishmaniasis or L. (Sauroleishmania) formed by leishmanias of lizards: L. colombiensis, L. equatorensis, L. herreri, L. hertigi, L. deanei, L. enriettii and L. martiniquensis. The comparison of these species with newly characterized isolates from sloths, porcupines and phlebotomines from central and South America unveiled new genera and subgenera supported by past (RNA PolII gene) and present (V7V8 SSU rRNA, Hsp70 and gGAPDH) phylogenetic analyses of the organisms. The genus Endotrypanum is restricted to Central and South America, comprising isolates from sloths and transmitted by phlebotomines that sporadically infect humans. This genus is the closest to the new genus Porcisia proposed to accommodate the Neotropical porcupine parasites originally described as L. hertigi and L. deanei. A new subgenus Leishmania (Mundinia) is created for the L. enriettii complex that includes L. martiniquensis. The new genus Zelonia harbours trypanosomatids from Neotropical hemipterans placed at the edge of the Leishmania-Endotrypanum-Porcisia clade. Finally, attention is drawn to the status of L. siamensis and L. australiensis as nomem nudums.

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