Back to Search
Start Over
Phenotypic evidence of emerging ivermectin resistance in Onchocerca volvulus.
- Source :
-
PLoS neglected tropical diseases [PLoS Negl Trop Dis] 2011 Mar 29; Vol. 5 (3), pp. e998. Date of Electronic Publication: 2011 Mar 29. - Publication Year :
- 2011
-
Abstract
- Background: Ivermectin (IVM) has been used in Ghana for over two decades for onchocerciasis control. In recent years there have been reports of persistent microfilaridermias despite multiple treatments. This has necessitated a reexamination of its microfilaricidal and suppressive effects on reproduction in the adult female Onchocerca volvulus. In an initial study, we demonstrated the continued potent microfilaricidal effect of IVM. However, we also found communities in which the skin microfilarial repopulation rates at days 90 and 180 were much higher than expected. In this follow up study we have investigated the reproductive response of female worms to multiple treatments with IVM.<br />Methods and Findings: The parasitological responses to IVM in two hundred and sixty-eight microfilaridermic subjects from nine communities that had received 10 to 19 annual doses of IVM treatment and one pre-study IVM-naïve community were followed. Skin snips were taken 364 days after the initial IVM treatment during the study to determine the microfilaria (mf) recovery rate. Nodules were excised and skin snips taken 90 days following a second study IVM treatment. Nodule and worm density and the reproductive status of female worms were determined. On the basis of skin mf repopulation and skin mf recovery rates we defined three categories of response--good, intermediate and poor--and also determined that approximately 25% of subjects in the study carried adult female worms that responded suboptimally to IVM. Stratification of the female worms by morphological age and microfilarial content showed that almost 90% of the worms were older or middle aged and that most of the mf were produced by the middle aged and older worms previously exposed to multiple treatments with little contribution from young worms derived from ongoing transmission.<br />Conclusions: The results confirm that in some communities adult female worms were non-responsive or resistant to the anti-fecundity effects of multiple treatments with IVM. A scheme of the varied responses of the adult female worm to multiple treatments is proposed.
- Subjects :
- Adolescent
Adult
Aged
Animals
Antiparasitic Agents pharmacology
Female
Ghana
Humans
Ivermectin pharmacology
Male
Middle Aged
Onchocerca volvulus isolation & purification
Treatment Failure
Young Adult
Antiparasitic Agents therapeutic use
Drug Resistance
Ivermectin therapeutic use
Onchocerca volvulus drug effects
Onchocerciasis drug therapy
Subjects
Details
- Language :
- English
- ISSN :
- 1935-2735
- Volume :
- 5
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- PLoS neglected tropical diseases
- Publication Type :
- Academic Journal
- Accession number :
- 21468315
- Full Text :
- https://doi.org/10.1371/journal.pntd.0000998