RESUMEN

OBJECTIVE: Given the magnitude of the HIV epidemic infection, many viral and human factors were analyzed, and the most decisive was the variant CCR5-Δ32. The presence of a low HIV prevalence (1.8%) in Gabon in the 1990s, compared to neighboring countries, represents a paradox that led us to search for viral and human genetic variants in this country. In this study, only variants of coreceptors and chemokines were investigated. METHODS: Variants of the coding region of the CCR5 gene were analyzed by denaturing gradient gel electrophoresis, and then variants of SDF1 and CCR2b were determined by polymerase chain reaction-restriction fragment length polymorphism. RESULTS: Four rare variants of the CCR5 coreceptor were found, while CCR5-Δ32 and CCR5m303 variants were not found. No association with CCR2b-V64I (17%) and SDF1-3'A (2%) variants was determined in relation to HIV-1 infection in Gabonese patients. CONCLUSION: The paradox of HIV seroprevalence in Gabon, which ended in the 2000s, was not caused by human genetic variants but rather by environmental factors.

Asunto(s)

Quimiocina CXCL12/genética , Variación Genética , Infecciones por VIH/epidemiología , VIH-1 , Receptores CCR2/genética , Receptores CCR5/genética , Electroforesis en Gel de Gradiente Desnaturalizante , Ambiente , Gabón/epidemiología , Genotipo , Infecciones por VIH/genética , Seroprevalencia de VIH , VIH-1/inmunología , Humanos , Sistemas de Lectura Abierta , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Prevalencia

RESUMEN

Sickle Cell Disease (SCD) is an important cause of death in young children in Africa, which the World Health Organization has declared a public health priority. Although SCD has been studied at the continental scale and at the local scale, a picture of its distribution at the scale of an African country has never been given. The aim of this study is to provide such a picture for the Republic of Gabon, a country where precisely the epidemiology of SCD has been poorly investigated. To this effect, 4250 blood samples from persons older than 15 were collected between June 2005 and September 2008 in 210 randomly selected villages from the nine administrative provinces of Gabon. Two methods were used to screen Sickle Cell Trait (SCT) carriers: isoelectric focusing (IEF) and high-performance liquid chromatography (HPLC). SCT prevalence in Gabon was 21.1% (895/4249). SCT prevalence was significantly larger for the Bantu population (21.7%, n=860/3959) than for the Pygmy population (12.1%, n=35/290), (p=0.00013). In addition, the presence of Plasmodium sp. was assessed via thick blood examination. Age was positively associated with SCT prevalence (odds-ratio for an increase of 10 years in age=1.063, p=0.020). Sex was not associated with SCT prevalence. The study reveals the absence of homozygous sickle-cell patients, and marked differences in SCT prevalence between the Gabonese provinces, and also between population groups (Bantu vs Pygmy). These findings could be used by the public health authorities to allocate medical resources and target prevention campaigns.

Asunto(s)

Población Negra/etnología , Malaria/sangre , Plasmodium/aislamiento & purificación , Rasgo Drepanocítico/epidemiología , Adolescente , Adulto , Factores de Edad , Anciano , Femenino , Gabón/epidemiología , Gabón/etnología , Hemoglobina Falciforme/metabolismo , Humanos , Malaria/etnología , Malaria/parasitología , Masculino , Persona de Mediana Edad , Plasmodium/clasificación , Rasgo Drepanocítico/sangre , Rasgo Drepanocítico/etnología , Rasgo Drepanocítico/parasitología , Adulto Joven

RESUMEN

Determining the biogeographical histories of rainforests is central to our understanding of the present distribution of tropical biodiversity. Ice age fragmentation of central African rainforests strongly influenced species distributions. Elevated areas characterized by higher species richness and endemism have been postulated to be Pleistocene forest refugia. However, it is often difficult to separate the effects of history and of present-day ecological conditions on diversity patterns at the interspecific level. Intraspecific genetic variation could yield new insights into history, because refugia hypotheses predict patterns not expected on the basis of contemporary environmental dynamics. Here, we test geographically explicit hypotheses of vicariance associated with the presence of putative refugia and provide clues about their location. We intensively sampled populations of Aucoumea klaineana, a forest tree sensitive to forest fragmentation, throughout its geographical range. Characterizing variation at 10 nuclear microsatellite loci, we were able to obtain phylogeographic data of unprecedented detail for this region. Using Bayesian clustering approaches, we demonstrated the presence of four differentiated genetic units. Their distribution matched that of forest refugia postulated from patterns of species richness and endemism. Our data also show differences in diversity dynamics at leading and trailing edges of the species' shifting distribution. Our results confirm predictions based on refugia hypotheses and cannot be explained on the basis of present-day ecological conditions.

Asunto(s)

Variación Genética , Filogenia , Árboles , África Central , Genética de Población , Genotipo , Geografía , Guinea , Repeticiones de Microsatélite/genética

RESUMEN

Under the isolation-by-distance model, the strength of spatial genetic structure (SGS) depends on seed and pollen dispersal and genetic drift, which in turn depends on local demographic structure. SGS can also be influenced by historical events such as admixture of differentiated gene pools. We analysed the fine-scale SGS in six populations of a pioneer tree species endemic to Central Africa, Aucoumea klaineana. To infer the impacts of limited gene dispersal, population history and habitat fragmentation on isolation by distance, we followed a stepwise approach consisting of a Bayesian clustering method to detect differentiated gene pools followed by the analysis of kinship-distance curves. Interestingly, despite considerable variation in density, the five populations situated under continuous forest cover displayed very similar extent of SGS. This is likely due to an increase in dispersal distance with decreased tree density. Admixture between two gene pools was detected in one of these five populations creating a distinctive pattern of SGS. In the last population sampled in open habitat, the genetic diversity was in the same range as in the other populations despite a recent habitat fragmentation. This result may due to the increase of gene dispersal compensating the effect of the disturbance as suggested by the reduced extent of SGS estimated in this population. Thus, in A. klaineana, the balance between drift and dispersal may facilitate the maintenance of genetic diversity. Finally, from the strength of the SGS and population density, an indirect estimate of gene dispersal distances was obtained for one site: the quadratic mean parent-offspring distance, sigma(g), ranged between 210 m and 570 m.

Asunto(s)

Ecosistema , Flujo Génico , Magnoliopsida/genética , Árboles/genética , Teorema de Bayes , Análisis por Conglomerados , ADN de Plantas/química , ADN de Plantas/genética , Gabón , Variación Genética , Genética de Población , Genotipo , Repeticiones de Microsatélite , Reacción en Cadena de la Polimerasa

RESUMEN

Several studies have focused their attention on the relationship between host genetic factors and susceptibility/resistance to severe malaria. However, there is a paucity of information concerning the role of host genetic factors in asymptomatic malaria, a form of low-grade Plasmodium falciparum infection without clinical symptoms. We investigated in this study the potential relationship between the host (human) genetic polymorphisms (glucose-6-phosphate dehydrogenase [G6PD], mannose binding lectin [MBL], tumor necrosis factor alpha [TNFalpha](-308) and (-238), and nitric oxide synthase 2 [NOS2](-954)) and the prevalence and profile of asymptomatic P. falciparum infection in 158 Gabonese schoolchildren. We found that G6PD A- heterozygous females (18 of 74) have a low prevalence of asymptomatic malaria (38.9% versus 67.3%; P = 0.03, by chi-square test). Children heterozygous for TNFalpha(-238) (25 of 156) carry high number of diverse infecting parasite genotypes (2.5 versus 1.99; variance F = 3.05). No statistically significant association was found between MBL, TNFalpha(-308), or NOS2 polymorphisms and asymptomatic malaria. Upon combining our data on asymptomatic forms with those from the literature for others forms, we conclude that G6PD A- heterozygous females are protected against all forms of P. falciparum malaria, and that the TNFalpha(-238A) allele confers protection against clinical malaria.

Asunto(s)

Predisposición Genética a la Enfermedad , Malaria Falciparum/epidemiología , Malaria Falciparum/genética , Adolescente , Adulto , Alelos , Animales , Antígenos de Protozoos/genética , Niño , Estudios Transversales , Cartilla de ADN , Enfermedades Endémicas , Femenino , Gabón/epidemiología , Glucosafosfato Deshidrogenasa/genética , Humanos , Malaria Falciparum/patología , Masculino , Lectina de Unión a Manosa/genética , Óxido Nítrico Sintasa/genética , Óxido Nítrico Sintasa de Tipo II , Plasmodium falciparum/genética , Plasmodium falciparum/aislamiento & purificación , Reacción en Cadena de la Polimerasa , Polimorfismo Genético , Prevalencia , Proteínas Protozoarias/genética , Factor de Necrosis Tumoral alfa/genética