The influence of intestinal parasites on Plasmodium vivax-specific antibody responses to MSP-119 and AMA-1 in rural populations of the Brazilian Amazon.

BACKGROUND: Polyparasitism is a common condition in humans but its impact on the host immune system and clinical diseases is still poorly understood. There are few studies of the prevalence and the effect of malaria-intestinal parasite co-infections in the immune response to malaria vaccine candidates. The present study determines whether the presence of malaria and intestinal parasites co-infection is associated with impaired IgG responses to Plasmodium vivax AMA-1 and MSP-119 in a rural population of the Brazilian Amazon.

METHODS: A cross-sectional survey was performed in a rural area of Rondonia State and 279 individuals were included in the present study. At recruitment, whole blood was collected and Plasmodium and intestinal parasites were detected by microscopy and molecular tests. Blood cell count and haemoglobin were also tested and antibody response specific to P. vivax AMA-1 and MSP-119 was measured in plasma by ELISA. The participants were grouped according to their infection status: singly infected with Plasmodium (M); co-infected with Plasmodium and intestinal parasites (CI); singly infected with intestinal parasites (IP) and negative (N) for both malaria and intestinal parasites.

RESULTS: The prevalence of intestinal parasites was significantly higher in individuals with malaria and protozoan infections were more prevalent. IgG antibodies to PvAMA-1 and/or PvMSP-119 were detected in 74 % of the population. The prevalence of specific IgG was similar for both proteins in all four groups and among the groups the lowest prevalence was in IP group. The cytophilic sub-classes IgG1 and IgG3 were predominant in all groups for PvAMA-1 and IgG1, IgG3 and IgG4 for PvMSP-119. In the case of non-cytophilic antibodies to PvAMA-1, IgG2 was significantly higher in IP and N group when compared to M and CI while IgG4 was higher in IP group.

CONCLUSIONS: The presence of intestinal parasites, mainly protozoans, in malaria co-infected individuals does not seem to alter the antibody immune responses to P. vivax AMA-1 and MSP-119. However, IgG response to both AMA1 and MSP1 were lower in individuals with intestinal parasites.