A malariometric survey in a rural community in the Muheza District, Tanzania: age profiles in the development of humoral immune responses

Abstract

A malariometric survey was carried out in a rural community situated in a malaria holoendemic endemic area of Tanzania. A random sample ( n=228) of different age groups was taken to elucidate the association between anti-Pf155/RESA and anti-Pf332 antibody responses and classical malaria indices. Parasitaemia, fever, splenomegaly, haematocrit and antimalarial consumption were assessed. Antibody responses against Pf155/RESA and Pf332 peptides were determined by ELISA. The age profiles of parasite density, splenomegaly, fever, haematocrit values and prevalence of antibody responses indicated intensive malaria exposure and the highest impact of malaria in small children. Forty-five percent of the study population had detectable chloroquine and desethyl-chloroquine blood levels, and the highest frequency and concentrations were recorded in the 12–23 months old. There was no significant association between the presence of drug and parasite density in the different age groups, although in the <15 years old there was lower parasite prevalence among the children positive for drug in their blood ( P<0.05). High prevalence of antibody responses to all antigens was observed already at an early age, but the mean anti-Pf155/RESA and anti-Pf332 antibody levels increased significantly only in the adult group ( P<0.01). Significantly lower mean parasite densities were observed in high responders to Pf155/RESA and Pf332 peptides for the ≥10 years old. For the 1–9 years, a similar difference was only observed in the high responders to Pf332. For the whole material, anti-Pf155/RESA and anti-Pf332 antibody levels correlated positively with age. When the effect of age was allowed for in analysing the relationship between parasite density and antibody level against the different antigens, a significant negative correlation was found only with regard to Pf332 in the ≥10 years age group. These results suggest that anti-Pf332 antibodies appear to be a better indicator for antiparasitic immunity, but both antigens are important for immune protection.