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Plasmodium vivax is the most widespread human malaria, putting 2.5 billion people at risk of infection. Its unique biological and epidemiological characteristics pose challenges to control strategies that have been principally targeted against Plasmodium falciparum Unlike P. falciparum, P. vivax infections have typically low blood-stage parasitemia with gametocytes emerging before illness manifests, and dormant liver stages causing relapses. These traits affect both its geographic distribution and transmission patterns. Asymptomatic infections, high-risk groups, and resulting case burdens are described in this review. Despite relatively low prevalence measurements and parasitemia levels, along with high proportions of asymptomatic cases, this parasite is not benign. Plasmodium vivax can be associated with severe and even fatal illness. Spreading resistance to chloroquine against the acute attack, and the operational inadequacy of primaquine against the multiple attacks of relapse, exacerbates the risk of poor outcomes among the tens of millions suffering from infection each year. Without strategies accounting for these P. vivax-specific characteristics, progress toward elimination of endemic malaria transmission will be substantially impeded., (© The American Society of Tropical Medicine and Hygiene.)

National disease burdens are often not estimated at all or are estimated using inaccurate methods, partly because the data sources for assessing disease burden-nationally representative household surveys, demographic surveillance sites, and routine health information systems-each have their limitations. An important step forward would be a more consistent quantification of the population at risk of malaria. This is most likely to be achieved by delimiting the geographical distribution of malaria transmission using routinely collected data on confirmed cases of disease. However, before routinely collected data can be used to assess trends in the incidence of clinical cases and deaths, the incompleteness of reporting and variation in the utilization of the health system must be taken into account. In the future, sentinel surveillance from public and private health facilities, selected according to risk stratification, combined with occasional household surveys and other population-based methods of surveillance, may provide better assessments of malaria trends.