Frequency of Mutations Within P-Glycoprotein and Beta-Tubulin Associated With Ivermectin Treatment in Onchocerca volvulus Adult Female Worm Populations in Some Onchocerciasis Endemic Communities in Ghana.

Abstract

Background: Ivermectin is the drug of choice for the control of onchocerciasis because of its potent embryostatic and microfilaricidal effect. However, with long periods of mass drug administration, the effect of ivermectin on the Onchocerca volvulus worms is waning. These suboptimal responses have been linked to genes such as p-glycoprotein (P-gp) and beta-tubulin (B-tub). The purpose of this study was to define the proportion of adult female O. volvulus from some endemic communities in Ghana that have mutations in these genes.

Methods: O. volvulus adult female worms were obtained from 33 participants in four endemic communities. Genomic DNA was isolated from worms and evaluated utilising polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) using DdeI and AluI restriction enzymes to identify genetic mutations within P-gp and B-tub genes. The wild-type and mutant forms of the genes were identified and associations between the frequencies of the mutations and ivermectin treatment were determined.

Results: A total of 45 adult female worms were obtained from 33 participants, and about 40% of these worms were reproductively active. High frequencies of mutant genes observed in parasite population (91.1%) for the B-tub gene and all the samples (100%) for the P-gp gene. Irrespective of these high frequencies in mutation, a Fisher's Exact Test (p = 0.621) and Mann-Whitney U test (p = 1.000) showed no significant relation between mutations and community rounds of ivermectin or individual participant's treatment.

Conclusion: This study shows a high frequency of mutations in both P-gp and B-tub genes in O. volvulus isolates, indicating the possible involvement of genetic changes in suboptimal response of the disease to ivermectin in parasite population. Continuous molecular surveillance to monitor emerging resistance is important to guide future strategies towards elimination.