RESUMEN
BACKGROUND: Rapid diagnostic test (RDT) positivity is supplanting microscopy as the standard measure of malaria burden at the population level. However, there is currently no standard for externally validating RDT results from field surveys. METHODS: Individuals' blood concentration of the Plasmodium falciparum histidine rich protein 2 (HRP2) protein were compared to results of HRP2-detecting RDTs in participants from field surveys in Angola, Mozambique, Haiti, and Senegal. A logistic regression model was used to estimate the HRP2 concentrations corresponding to the 50 and 90% level of detection (LOD) specific for each survey. RESULTS: There was a sigmoidal dose-response relationship between HRP2 concentration and RDT positivity for all surveys. Variation was noted in estimates for field RDT sensitivity, with the 50% LOD ranging between 0.076 and 6.1 ng/mL and the 90% LOD ranging between 1.1 and 53 ng/mL. Surveys conducted in two different provinces of Angola using the same brand of RDT and same study methodology showed a threefold difference in LOD. CONCLUSIONS: Measures of malaria prevalence estimated using population RDT positivity should be interpreted in the context of potentially large variation in RDT LODs between, and even within, surveys. Surveys based on RDT positivity would benefit from external validation of field RDT results by comparing RDT positivity and antigen concentration.
Asunto(s)
Antígenos de Protozoos/análisis , Pruebas Diagnósticas de Rutina/métodos , Malaria Falciparum/diagnóstico , Plasmodium falciparum/aislamiento & purificación , Proteínas Protozoarias/análisis , Adolescente , Adulto , África del Sur del Sahara/epidemiología , Anciano , Anciano de 80 o más Años , Niño , Preescolar , Femenino , Haití/epidemiología , Humanos , Lactante , Malaria Falciparum/epidemiología , Malaria Falciparum/parasitología , Masculino , Persona de Mediana Edad , Prevalencia , Sensibilidad y Especificidad , Adulto JovenRESUMEN
A major public health question is whether urbanization will transform malaria from a rural to an urban disease. However, differences about definitions of urban settings, urban malaria, and whether malaria control should differ between rural and urban areas complicate both the analysis of available data and the development of intervention strategies. This report examines the approach of the International Centers of Excellence for Malaria Research (ICEMR) to urban malaria in Brazil, Colombia, India (Chennai and Goa), Malawi, Senegal, and Uganda. Its major theme is the need to determine whether cases diagnosed in urban areas were imported from surrounding rural areas or resulted from transmission within the urban area. If infections are being acquired within urban areas, malaria control measures must be targeted within those urban areas to be effective. Conversely, if malaria cases are being imported from rural areas, control measures must be directed at vectors, breeding sites, and infected humans in those rural areas. Similar interventions must be directed differently if infections were acquired within urban areas. The hypothesis underlying the ICEMR approach to urban malaria is that optimal control of urban malaria depends on accurate epidemiologic and entomologic information about transmission.
Asunto(s)
Malaria/epidemiología , Población Urbana , Animales , Anopheles/parasitología , Brasil/epidemiología , Ciudades/epidemiología , Colombia/epidemiología , Ecología , Humanos , India/epidemiología , Insectos Vectores/parasitología , Cooperación Internacional , Malaria/parasitología , Malaria/prevención & control , Malaria/transmisión , Malaria Falciparum/epidemiología , Malaria Falciparum/parasitología , Malaria Falciparum/prevención & control , Malaria Falciparum/transmisión , Malaui/epidemiología , Plasmodium falciparum , Senegal/epidemiología , Viaje , Uganda/epidemiologíaRESUMEN
Genetic variation allows the malaria parasite Plasmodium falciparum to overcome chemotherapeutic agents, vaccines and vector control strategies and remain a leading cause of global morbidity and mortality. Here we describe an initial survey of genetic variation across the P. falciparum genome. We performed extensive sequencing of 16 geographically diverse parasites and identified 46,937 SNPs, demonstrating rich diversity among P. falciparum parasites (pi = 1.16 x 10(-3)) and strong correlation with gene function. We identified multiple regions with signatures of selective sweeps in drug-resistant parasites, including a previously unidentified 160-kb region with extremely low polymorphism in pyrimethamine-resistant parasites. We further characterized 54 worldwide isolates by genotyping SNPs across 20 genomic regions. These data begin to define population structure among African, Asian and American groups and illustrate the degree of linkage disequilibrium, which extends over relatively short distances in African parasites but over longer distances in Asian parasites. We provide an initial map of genetic diversity in P. falciparum and demonstrate its potential utility in identifying genes subject to recent natural selection and in understanding the population genetics of this parasite.