Reproductive status of Onchocerca volvulus after Ivermectin treatment in an Ivermectin-naive and a frequently treated population from Cameroon

2014

Article référencé dans le Web of Science WOS:000335342400018

Nana-Djeunga H. C., Bourguinat C., Pion Sébastien, Bopda J., Kengne-Ouafo J. A., Njiokou F., Prichard R. K., Wanji S., Kamgno J., Boussinesq Michel

Plos Neglected Tropical Diseases, 2014, 8 (4), p. e2824 ISSN 1935-2735

Author Summary Onchocerciasis, also known as river blindness, is a parasitic disease due to the filarial nematode Onchocerca volvulus. It affects more than 37 million people worldwide, most of them (99%) living in Africa. The control of river blindness is, up to now, based on annual or six-monthly mass treatment with ivermectin. This drug kills O. volvulus microfilariae (mf) present in the skin and the eyes and prevents for 3-4 months the release of new mf by female worms (embryostatic effect). In Ghana, after 10-19 years of repeated treatments, the emergence of adult parasite populations not responding as expected to ivermectin was postulated. In this study, the reproductive status of female worms was compared, just before and 80 days after ivermectin treatment, between frequently treated and ivermectin-naive cohorts from Cameroon. In both groups, embryogenesis of O. volvulus was not affected by ivermectin. However, the accumulation of microfilariae (mf) in the females uteri expected after ivermectin was less marked in the frequently treated population, suggesting that the temporary sequestration of mf following treatment may have been weakened in this group. After 13 years of repeated annual treatments, the embryostatic effect of ivermectin on O. volvulus still occurs but the present findings, associated with observations of higher rates of skin repopulation by mf in the same individuals, suggest that this effect has been decreased. Background For two decades, onchocerciasis control has been based on mass treatment with ivermectin (IVM), repeated annually or six-monthly. This drug kills Onchocerca volvulus microfilariae (mf) present in the skin and the eyes (microfilaricidal effect) and prevents for 3-4 months the release of new mf by adult female worms (embryostatic effect). In some Ghanaian communities, the long-term use of IVM was associated with a more rapid than expected skin repopulation by mf after treatment. Here, we assessed whether the embryostatic effect of IVM on O. volvulus has been altered following frequent treatment in Cameroonian patients. Methodology Onchocercal nodules were surgically removed just before (D0) and 80 days (D80) after a standard dose of IVM in two cohorts with different treatment histories: a group who had received repeated doses of IVM over 13 years, and a control group with no history of large-scale treatments. Excised nodules were digested with collagenase to isolate adult worms. Embryograms were prepared with females for the evaluation of their reproductive capacities. Principal Findings Oocyte production was not affected by IVM. The mean number of intermediate embryos (morulae and coiled mf) decreased similarly in the two groups between D0 and D80. In contrast, an accumulation of stretched mf, either viable or degenerating, was observed at D80. However, it was observed that the increase in number of degenerating mf between D0 and D80 was much lower in the frequently treated group than in the control one (Incidence Rate Ratio: 0.25; 95% CI: 0.10-0.63; p = 0.003), which may indicate a reduced sequestration of mf in the worms from the frequently treated group. Conclusion/Significance IVM still had an embryostatic effect on O. volvulus, but the effect was reduced in the frequently treated cohort compared with the control population.

Santé : généralités [050] ; Entomologie médicale / Parasitologie / Virologie [052]

CAMEROUN

Fonds IRD [F B010061996]

fdi:010061996