The epidemiology of malaria in a Karen population on the western border of Thailand

Abstract

From November 1991 to November 1992 a prospective, descriptive study of malaria epidemiology was conducted in a Karen population on the western border of Thailand. Two study groups were selected at random and more than 80% of the subjects were followed for one year. In Group 1, comprising 249 schoolchildren (aged 4-15 years), daily surveillance for illness was combined with fortnightly malaria surveys. These children experienced 1.5 parasitaemic infections per child-year (95% confidence interval [CI] 1.3-1.7), of which 68% (193/285) were symptomatic (Plasmodium falciparum 84%, P. vivax 57%). The estimated pyrogenic densities were 1460/microL for P. falciparum and 181/microL for P. vivax. In Group 2, comprising subjects of all age from 428 households, malaria was diagnosed during two-monthly surveys, at weekly home visits, and otherwise by passive case detection. Malaria and splenomegaly prevalence rates were low in all age groups (spleen index 2-9%; P. falciparum prevalence rate 1-4%; P. vivax 1-6%). Group 2 subjects had 1.0 infections per person-year (95% CI 0.9-1.1), most of which were symptomatic (312/357; 87%). Malaria infections clustered in households. Overall, P. vivax caused 53% and P. falciparum 37% of the infections (10% were mixed), but whereas P. vivax was most common in young children, with a decline in incidence with increasing age, P. falciparum incidence rates rose with age to a peak incidence between 20 and 29 years, although the risk of developing a severe malaria decreased with increasing age. There was no death from malaria during the study. P. falciparum infections were more common in males, subjects with a history of malaria before the study, and in those who had travelled outside their village. These findings suggest a higher transmission rate for P. vivax than P. falciparum, although adults still suffered symptomatic malaria due to both species. The 2 malaria parasites found in this area contribute approximately 50% of infections each, but their clinical epidemiology is very different.

Efficacy and effectiveness of dihydroartemisinin-piperaquine versus artesunate-mefloquine in falciparum malaria: an open-label randomised comparison

“…These infections were particularly frequent (40%) in children under 5 years of age. 20 Both health providers and parents in this area need to be informed that there is a high risk of another malaria episode in young children, and parents should be encouraged to bring the children to the clinic if fever reappears.…”

Selection strength and hitchhiking around two anti-malarial resistance genes

“…In southern Laos, where we collected the samples analysed here, a prevalence of P. falciparum of more than 30% has been reported (Toma et al 2001;Vythilingam et al 2003). By comparison, cross-sectional surveys along the Thailand/Burma border revealed prevalences of 1-4% (Luxemburger et al 1996). Similarly, the number of infective mosquito bites has been estimated at between 1.9 and 7.5 per person per month in Sekong (Vythilingam et al 2003).…”

Clinical and laboratory profile of Plasmodium vivax malaria patients hospitalized in Apartadó,

“…La malaria por P. vivax está ampliamente distribuida alrededor del mundo; en las regiones del sur y sureste de Asia, representa 50 % de los casos de paludismo que se presentan (2,3, Tjitra E, Warikar N, Ebsworth EP, Kenangalem E, Sugiarto P, Okoseray MJ, et al Major burden of P.vivax infection in Papua, Indonesia; A region with high levels of chloroquine resistance; 16th IFTM Medicine in the Tropics; Marseille, France. 2005).…”