Browsing by Autor "Joseph Kamgno"

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Co-infection withOnchocerca volvulusandLoa loamicrofilariae in central Cameroon: are these two species interacting?
(Cambridge University Press, 2006) Sébastien D. S. Pion; Paul Clarke; João A. N. Filipe; Joseph Kamgno; Jacques Gardon; María‐Gloria Basáñez; Michel Boussinesq
Ivermectin treatment may induce severe adverse reactions in some individuals heavily infected with Loa loa. This hampers the implementation of mass ivermectin treatment against onchocerciasis in areas where Onchocerca volvulus and L. loa are co-endemic. In order to identify factors, including co-infections, which may explain the presence of high L. loa microfilaraemia in some individuals, we analysed data collected in 19 villages of central Cameroon. Two standardized skin snips and 30 mul of blood were obtained from each of 3190 participants and the microfilarial (mf) loads of both O. volvulus and L. loa were quantified. The data were analysed using multivariate hierarchical models. Individual-level variables were: age, sex, mf presence, and mf load; village-related variables included the endemicity levels for each infection. The two species show a certain degree of ecological separation in the study area. However, for a given individual host, the presence of microfilariae of one species was positively associated with the presence of microfilariae of the other (OR=1.79, 95% CI [1.43-2.24]). Among individuals harbouring Loa microfilariae, there was a slight positive relationship between the L. loa and O. volvulus mf loads which corresponded to an 11% increase in L. loa mf load per 100 O. volvulus microfilariae. Co-infection with O. volvulus is not sufficient to explain the very high L. loa mf loads harboured by some individuals.
Genetic polymorphism of the β-tubulin gene of Onchocerca volvulus in ivermectin naïve patients from Cameroon, and its relationship with fertility of the worms
(Cambridge University Press, 2005) Catherine Bourguinat; Sébastien D. S. Pion; Joseph Kamgno; Jacques Gardon; N. Gardon-Wendel; B. O. L. Duke; Roger K. Prichard; Michel Boussinesq
Observations of low response of patients infected with Onchocerca volvulus to ivermectin suggest that the parasite may be under a selection process toward potential resistance. To limit the extension of this phenomenon, it is crucial to characterize the genes of O. volvulus that are involved. For this, O. volvulus adult worms collected before the introduction of ivermectin in an onchocerciasis endemic area of central Cameroon were genotyped for beta-tubulin. To derive a baseline to investigate the selective pressure of ivermectin, we analysed (1) the frequency distribution of the beta-tubulin alleles, and (2) the relationship between the different beta-tubulin related genotypes and the fertility status of the female worms. The frequency of allele b of the beta-tubulin gene was very low, as it was observed in West Africa. We observed a deficit of heterozygous female worms leading to Hardy Weinberg disequilibrium, which might be explained by a shorter life-span of these worms compared to the homozygous worms. Unexpectedly, our results also show that the heterozygous female worms were much less fertile than the homozygotes: more than two thirds of the homozygotes were fertile, whereas only 37% of the heterozygotes were fertile. These results will be further considered when analysing post-treatment data.
Genetic Selection of Low Fertile Onchocerca volvulus by Ivermectin Treatment
(Public Library of Science, 2007) Catherine Bourguinat; Sébastien D. S. Pion; Joseph Kamgno; Jacques Gardon; B. O. L. Duke; Michel Boussinesq; Roger K. Prichard
The results indicate that ivermectin is causing genetic selection on O. volvulus. This genetic selection is associated with a lower reproductive rate in the female parasites. We hypothesize that this genetic selection indicates that a population of O. volvulus, which is more tolerant to ivermectin, is being selected. This selection could have implications for the development of ivermectin resistance in O. volvulus and for the ongoing onchocerciasis control programmes.
Microfilarial distribution of Loa loa in the human host: population dynamics and epidemiological implications
(Cambridge University Press, 2006) Sébastien D. S. Pion; João A. N. Filipe; Joseph Kamgno; Jacques Gardon; María‐Gloria Basáñez; Michel Boussinesq
Severe adverse events (SAEs) following ivermectin treatment may occur in people harbouring high Loa loa microfilarial (mf) densities. In the context of mass ivermectin distribution for onchocerciasis control in Africa, it is crucial to define precisely the geographical distribution of L. loa in relation to that of Onchocerca volvulus and predict the prevalence of heavy infections. To this end, we analysed the distribution of mf loads in 4183 individuals living in 36 villages of central Cameroon. Mf loads were assessed quantitatively by calibrated blood smears, collected prior to ivermectin distribution. We explored the pattern of L. loa mf aggregation by fitting the (zero-truncated) negative binomial distribution and estimating its overdispersion parameter k by maximum likelihood. The value of k varied around 0.3 independently of mf intensity, host age, village and endemicity level. Based on these results, we developed a semi-empirical model to predict the prevalence of heavy L. loa mf loads in a community given its overall mf prevalence. If validated at the continental scale and linked to predictive spatial models of loiasis distribution, this approach would be particularly useful for optimizing the identification of areas at risk of SAEs and providing estimates of populations at risk in localities where L. loa and O. volvulus are co-endemic.
P-glycoprotein-like protein, a possible genetic marker for ivermectin resistance selection in Onchocerca volvulus
(Elsevier BV, 2008) Catherine Bourguinat; Bernadette F. Ardelli; Sébastien D. S. Pion; Joseph Kamgno; Jacques Gardon; B. O. L. Duke; Michel Boussinesq; Roger K. Prichard
What are the mechanisms associated with post-ivermectin serious adverse events?
(Elsevier BV, 2006) Michel Boussinesq; Joseph Kamgno; Sébastien D. S. Pion; Jacques Gardon