Relationships between Plasmodium falciparum infection and morbidity in a highly endemic area

Abstract

SUMMARYA total of 736 outpatients diagnosed as having malaria using clinical criteria at a health centre in a highly endemic area of Papua New Guinea were investigated parasitologically. Plasmodium falciparum-attributable fractions were determined using a logistic regression model to compare parasite densities in cases with those of healthy individuals in community surveys. Thirty-seven percent of presumptive cases were found to have raised P. falciparum parasitaemia. This corresponds to an average reporting rate for the population of 053 attributable episodes per annum. Whilst the maximum prevalence of parasitaemia in the community was in children aged 5-9 years, the maximum age-specific incidence of attributable cases at the outpatient clinic was 2 cases per annum in the 2-to 4-year-old age group. The procedure for estimating attributable fractions makes it possible to compare morbidity rates between age groups, and to examine how the relationship between morbidity risk and parasite density changes with age, without diagnosing individual episodes. The average tolerance of parasites in an age group was measured by considering the level of parasitaemia associated with a given risk of malaria-attributable morbidity. In contrast to anti-parasite immunity, tolerance of parasites declines with age since at parasite isodensity the probability of being symptomatic increases with age.

Reduced risk of clinical malaria in children infected with multiple clones of Plasmodium falciparum in a highly endemic area: a prospective community study

“…The incidence of morbidity showed a strong age dependence similar to that found in previous studies in the same area (SMITH et al, 1994;GENTON et al, 1995b). Therefore analyses of the risk of clinical malaria in relation to parasitological status (Table) were adjusted for age effects.…”

Effects of age and parasitemia on nitric oxide production/leukocyte nitric oxide synthase type 2 expression in asymptomatic, malaria-exposed children.

“…Although the age distribution varies with intensity of malaria transmission, morbidity and mortality attributable to malaria in coastal subSaharan Africa is low in early infancy, peaks in early childhood, and then decreases in older children. [26][27][28][29] In coastal Tanzania, we also found this age-related pattern of morbidity/mortality following further analysis of our previously described group of children with cerebral malaria (mean age FIGURE 5. Age-related frequency of cerebral malaria in children recruited at the same time and same study site in Dar es Salaam, Tanzania (mean age ϭ 3.9 years).…”

11. Premunition in Plasmodium falciparum infection: insights from the epidemiology of multiple infections

“…When tolerance is assessed epidemiologically, it is found that the age dependence of tolerance differs from that of the control of density. Adults have less tolerance of high parasitaemia than have all but the youngest children (SMITH et al, 1994;ROGIER et al, 1996). Chronic infection will itself induce immune responses, which in turn might influence any of several malariological outcome measures: (i) the risk or rate of reinfection;…”