IgG reactivities against recombinant Rhoptry-Associated Protein-1 (rRAP-1)are associated with mixed Plasmodium infections and protection against disease in Tanzanian children

A cross-sectional sero-epidemiological study was performed in Magoda, Tanza nia, an area where malaria is holoendemic. Blood samples were collected fro m children (1-4 years) and tested for IgG antibody reactivity against 2 rec ombinant protein fragments of Plasmodium falciparum Rhoptry-Associated Prot ein-1 (rRAP-1). The data were related to the prevalence of malarial disease and single P. falciparum or mixed Plasmodium infections. Fever (greater th an or equal to 37.5 degrees C) in combination with parasite densities > 500 0/mu l were used to distinguish between children with asymptomatic malaria infections and those with acute clinical disease. Furthermore, C-reactive p rotein (CRP) was applied as a surrogate marker of malaria morbidity. The pr evalence of Plasmodium infections was 96.0%. Eleven children were defined a s clinical malaria cases, all with single P. falciparum infections. The den sity of P. falciparum was significantly lower in children with mixed Plasmo dium infections compared to those with single P.falciparum infections. Chil dren with asymptomatic P. falciparum infections had higher IgG reactivities to rRAP-1, compared to IgG reactivities of children with malarial disease. Children with mixed Plasmodium infections generally showed elevated IgG re activity to rRAP-1, when compared to children with single P. falciparum inf ections. The possible relationship between mixed species infections, clinic al outcome of the disease and antibody responses to RAP-1 is discussed.