Human IgG subclass antibodies to the 19 kilodalton carboxy terminal fragment of Plasmodium falciparum merozoite surface protein 1 (MSP1(19)) and predominance of the MAD20 allelic type of MSP1 in Uganda.

OBJECTIVE: To determine the natural human humoral immune responses to the 19 kilodalton carboxy terminal fragment of Plasmodium falciparum merozoite surface protein 1 (MSP1(19)), a malaria candidate vaccine antigen and to determine the prevalence of MAD20 and K1 alleles of P. falciparum MSP1. DESIGN: Community based cross-sectional study. SETTING: Atopi Parish, Apac District, Uganda, 1995. SUBJECTS: Three hundred and seventy four Ugandans between <1 and 70 years old provided serum samples. MAIN OUTCOME MEASURES: IgG subclass antibodies by ELISA; MAD20 and K1 allelic types of MSP1 by PCR. RESULTS: Both the prevalence and the mean concentration of serum IgG1, and to a lesser extent IgG3, antibodies increased with age. IgG2 or IgG4 antibodies were virtually nonexistent. The cross-reactivity between the 4 sequence variants (E-KNG, E-TSR, Q-KNG and Q-TSR) of MSP1(19) was confirmed; however, a minority of sera preferentially recognised the KNG but not the TSR variants. All 33 P. falciparum isolates from different parts of Uganda carried the E-TSR (Mad20) allelic type and 3 isolates were mixed infections with E-TSR (MAD20) and Q-KNG (K1) allelic types, confirming the rarity of the K1 allele in Uganda. CONCLUSION: There is a robust IgG1 antibody response to the malaria vaccine candidate antigen MSP1(19) which begins at an early age. Future cohort studies are necessary to estblish the impact of these antibodies on clinical immunity to malaria. The MAD20 allelic type of MSP1 id predominant in Ugandan P. falciparum isolates.

Plasmodium falciparum malariometric indices in Apac district, northern Uganda.

OBJECTIVE: To establish Plasmodium falciparum malariometric indices in a field study site in Apac district, northern Uganda. DESIGN: A community-based cross sectional survey. SETTINGS: Atopi Parish, Apac district, Uganda, 1995. SUBJECTS: One thousand two hundred and thirty four volunteers aged below one and ninety years. MAIN OUTCOME MEASURES: P. falciparum parasitaemia rates and parasite density, splenomegaly, bednet use and chloroquine consumption. INTERVENTIONS: All subjects with P. falciparum positive smears were treated with chloroquine. RESULTS: The population prevalence of parasitaemia was 62.1% with the predominant species being P. falciparum (100%) and P. malariae in the minority (3.5%); P. ovale was not seen. The prevalence of parasitaemia in subjects older than 20 years and in those under ten years was 36% and 85%, respectively. The geometric mean parasite density started to decline by the age of six years. The splenomegaly rate in subjects over the age of 12 years and in those under nine years was 19.8% and 63.1%, respectively. Bednet use and chloroquine consumption was low. Interestingly, the reported use of chloroquine in the week immediately preceding the study was more frequent in children under two years old than in the rest of the population. CONCLUSION: Malaria transmission in Atopi Parish in northern Uganda is hyperendemic and age-related acquired anti-parasite immunity seems to appear by seven years of age.