Genetic complexity and gametocyte production of Plasmodium falciparum in Fulani and Mossi communities in Burkina Faso

We have examined Plasmodium falciparum gametocyte prevalence, density and their genetic complexity among children of 2 sympatric ethnic groups (Mossi and Fulani) in villages in Burkina Faso. The 2 groups are known to have distinct differences in their Susceptibility and immune responses to malaria. We used RT-PCR and sequence-specific probes to detect and type RNA of the gametocyte-specific protein Pfs48/45. There were no differences in detection rates of asexual forms and gametocytes among the 2 groups, using PCR and RT-l'CR, respectively. However, there were significant differences in densities of asexual forms and gametocytes, which were both higher among Mossi than Fulani. Both asexual forms and gametocyte densities were influenced by age and ethnicity. Multiple-clone infections with more than 1 gametocyte genotype were equally prevalent among Fulani and Mossi. These differences can most probably be attributed to genetic differences in malaria susceptibility in the 2 ethnic groups

Human IgG response to the Anopheles gambiae salivary protein gSG6: an indicator of exposure to anopheline mosquito bites.

The ability to estimate the risk of malaria infection is crucial for the development and evaluation of control programmes and currently relies on both entomological and parasitological methods. The availability of rapid and sensitive tools to measure the exposure to Anopheles mosquito bites would be extremely valuable in this context. Human antibody response to Anopheles saliva may represent such an indicator (Remoue F et al, 2006, Trans R Soc Trop Med Hyg). However, mosquito saliva is a complex cocktail of bioactive factors and cross-reactivity with other antigens (i.e. salivary proteins from blood-feeders other than anophelines) may be misleading

Human IgG response to the Anopheles gambiae salivary protein gSG6: an indicator of exposure to anopheline mosquito bites.

The ability to estimate the risk of malaria infection is crucial for the development and evaluation of control programmes and currently relies on both entomological and parasitological methods. The availability of rapid and sensitive tools to measure the exposure to Anopheles mosquito bites would be extremely valuable in this context. Human antibody response to Anopheles saliva may represent such an indicator (Remoue F et al, 2006, Trans R Soc Trop Med Hyg). However, mosquito saliva is a complex cocktail of bioactive factors and cross-reactivity with other antigens (i.e. salivary proteins from blood-feeders other than anophelines) may be misleading. In the attempt to identify immunogenic and anopheline-specific proteins to be used as serological indicators of exposure to malaria vectors we focused our attention on the Anopheles gambiae gSG6. This is a small, female salivary gland-specific protein involved in blood feeding (Lombardo F et al, 2009, Insect Biochem Mol Biol). So far, gSG6 has been found only in anopheline species (An. gambiae complex, An. stephensi, An. funestus and An. freeborni) whereas it is absent in culicine mosquitoes and in other blood feeding arthropods. Previous studies suggested that gSG6 is immunogenic (Poinsignon A et al, 2008, PLoS One) and, therefore, we expressed the protein in recombinant form and measured the humoral immune response to gSG6 in human sera collected during three consecutive years in rural malaria hyperendemic areas of Burkina Faso. gSG6 was confirmed to be immunogenic and to elicit an IgG response that varies according to malaria transmission intensity. Interestingly, a significant decrease in the IgG levels was observed during the dry season, suggesting that this response is short-lived. Moreover, anti-gSG6 IgG levels differed significantly in the two sympatric ethnic groups, Mossi and Fulani, already known for their differential response to several P. falciparum antigens (Modiano D et al, 1996, Proc Natl Acad Sci USA). Finally, the IgG response varied with age, being higher in children and progressively decreasing in older people. This decline suggests the possible involvement of a mechanism of tolerance developed as consequence of a continued exposure to the antigen. The high level of anti-gSG6 IgG4 found in the sera of exposed individuals appears compatible with the implication of a desensitization mechanism. Overall, our study provides a solid indication that individual recombinant salivary proteins may represent useful tools for epidemiological studies, evaluation of vector-control campaigns and perhaps for the development of risk maps. (*equal contribution)

Distinct interethnic differences in immunoglobulin G class/subclass and immunoglobulin M antibody responses to malaria antigens but not in immunoglobulin G responses to nonmalarial antigens in sympatric tribes living in West Africa

The well-established relative resistance to malaria observed in the Fulani as compared with other sympatric tribes in West Africa has been attributed to their higher levels of serum immunoglobulin (Ig) G antibodies to malarial antigens. In this study, we confirm and extend the previous findings by analyses of the levels of IgM, IgG and IgG subclasses of anti-malarial antibodies in asymptomatic individuals of different sympatric tribes in Burkina Faso (Fulani/Mossi) and Mali (Fulani/Dogon). The Fulani showed significantly higher median concentrations of anti-malarial IgG and IgM antibodies than the sympatric tribes at both locations. Although the overall subclass pattern of antibodies did not differ between the tribes, with IgG1 and IgG3 as dominant, the Fulani showed consistently significantly higher levels of these subclasses as compared with those of the non-Fulani individuals. No significant differences were seen in the levels of total IgG between the tribes, but the Fulani showed significantly higher levels of total IgM than their neighbours in both countries. While the antibody levels to some nonmalarial antigens showed the same pattern of differences seen for antibody levels to malaria antigens, no significant such differences were seen with antibodies to other nonmalarial antigens. In conclusion, our results show that the Fulani in two different countries show higher levels of anti-malarial antibodies than sympatric tribes, and this appears not to be a reflection of a general hyper-reactivity in the Fulani