Analysis of anti-Plasmodium IgG profiles among Fulani nomadic pastoralists in northern Senegal to assess malaria exposure.

BACKGROUND: Northern Senegal is a zone of very low malaria transmission, with an annual incidence of < 5/1000 inhabitants. This area, where the Senegal National Malaria Control Programme has initiated elimination activities, hosts Fulani, nomadic, pastoralists that spend the dry season in the south where malaria incidence is higher (150-450/1000 inhabitants) and return to the north with the first rains. Previous research demonstrated parasite prevalence of < 1% in this Fulani population upon return from the south, similar to that documented in the north in cross-sectional surveys. METHODS: A modified snowball sampling survey of nomadic pastoralists was conducted in five districts in northern Senegal during September and October 2014. Demographic information and dried blood spots were collected. Multiplex bead-based assays were used to assess antibody responses to merozoite surface protein (MSP-119) antigen of the four primary Plasmodium species, as well as circumsporozoite protein (CSP) and liver stage antigen (LSA-1) of Plasmodium falciparum. RESULTS: In the five study districts, 1472 individuals were enrolled, with a median age of 22 years (range 1 to 80 years). Thirty-two percent of subjects were under 14 years and 57% were male. The overall seroprevalence of P. falciparum MSP-119, CSP and LSA-1 antibodies were 45, 12 and 5%, respectively. Plasmodium falciparum MSP-119 antibody responses increased significantly with age in all study areas, and were significantly higher among males. The highest seroprevalence to P. falciparum antigens was observed in the Kanel district (63%) and the lowest observed in Podor (28%). Low seroprevalence was observed for non-falciparum species in all the study sites: 0.4, 0.7 and 1.8%, respectively, for Plasmodium ovale, Plasmodium vivax and Plasmodium malariae MSP-1. Antibody responses to P. vivax were observed in all study sites except Kanel. CONCLUSION: Prevalence of P. falciparum MSP-119 antibodies and increases by study participant age provided data for low levels of exposure among this transient nomadic population. In addition, antibody responses to P. falciparum short half-life markers (CSP and LSA-1) and non-falciparum species were low. Further investigations are needed to understand the exposure of the Fulani population to P. vivax.

SEROPREVALENCE TO SCHISTOSOMA SOLUBLE EGG ANTIGEN AMONG NOMADIC PASTORALISTS RESIDING IN NORTHERN SENEGAL.

Urinary and intestinal schistosomiasis are endemic in Senegal, with prevalence heterogeneous throughout the country. Because of their way of life, nomadic pastoralists are not typically included in epidemiological surveys, and data on the prevalence of schistosomiasis in Senegalese nomadic populations are largely non-existent. The purpose of this study was to determine the seroprevalence of schistosomiasis in Senegalese nomadic pastoralists. A modified snowball sampling survey was conducted among 1,467 nomadic pastoralists aged 6 mo and older in 5 districts in northern Senegal. Dried blood spots from participants of all ages and data regarding demographics were collected to assess IgG antibody responses against Schistosoma mansoni soluble egg antigen (SEA) using a bead-based multiplex assay. Out of 1,467 study subjects, 1,464 (99.8%) provided IgG serological data that cleared quality assurance. Of the participants with appropriate data, 56.6% were male, the median age was 22 yr, and 31.6% were under 15 yr of age. The overall anti-SEA IgG seroprevalence was 19.1% (95% confidence interval [CI]: 17.1-21.1%) with the highest estimates observed in Dagana (35.9%) and the lowest observed in Podor nomadic groups (3.4%). Antibody responses increased significantly with age except for the oldest age groups (>40 yr of age), which saw lower levels of antibody response compared to younger adults. When controlling for age and location by multivariate regression, the male sex was associated with a 2-fold greater odds of anti-SEA IgG seropositivity (aPOR: 2.0; 95% CI: 1.5-2.7). Serosurveys for anti-SEA IgG among nomadic peoples in northern Senegal found a substantial percentage of individuals with evidence for current or previous Schistosoma spp. infection with the highest levels of exposure in the district adjacent to the Diama dam along the Senegal River. With IgG prevalence increased by age except in the older adults, and the male sex significantly associated with seropositivity, these data point toward sex-associated behavioral practices and human environmental modification as risk factors for Schistosoma exposure.

Serological Data Shows Low Levels of Chikungunya Exposure in Senegalese Nomadic Pastoralists.

The chikungunya virus (CHIKV) is spread by Aedes aegypti and Ae. albopictus mosquitos worldwide; infection can lead to disease including joint pain, fever, and rash, with some convalescent persons experiencing chronic symptoms. Historically, CHIKV transmission has occurred in Africa and Asia, but recent outbreaks have taken place in Europe, Indonesia, and the Americas. From September to October 2014, a survey was undertaken with nomadic pastoralists residing in the northeast departments of Senegal. Blood dried on filter paper (dried blood spots; DBS) were collected from 1465 participants of all ages, and assayed for Immunoglobulin G (IgG) antibodies against CHIKV E1 antigen by a bead-based multiplex assay. The overall seroprevalence of all participants to CHIKV E1 was 2.7%, with no persons under 10 years of age found to be antibody positive. Above 10 years of age, clear increases of seroprevalence and IgG levels were observed with increasing age; 7.6% of participants older than 50 years were found to be positive for anti-CHIKV IgG. Reported net ownership, net usage, and gender were all non-significant explanatory variables of seropositivity. These data show a low-level historical exposure of this pastoralist population to CHIKV, with no evidence of recent CHIKV transmission in the past decade.