Differential susceptibility of Onchocerca volvulus microfilaria to ivermectin in two areas of contrasting history of mass drug administration in Cameroon: relevance of microscopy and molecular techniques for the monitoring of skin microfilarial repopulation within six months of direct observed treatment

• Published in: BMC infectious diseases Vol. 20; no. 1; p. 726
• Main Authors: Abong, Raphael Awah, Amambo, Glory N, Chounna Ndongmo, Patrick W, Njouendou, Abdel Jelil, Ritter, Manuel, Beng, Amuam Andrew, Esum, Mathias Eyong, Deribe, Kebede, Fru-Cho, Jerome, Fombad, Fanny F, Nji, Theobald Mue, Enyong, Peter Ivo, Poole, Catherine B, Pfarr, Kenneth, Hoerauf, Achim, Carlow, Clotilde K S, Wanji, Samuel
• Format: Journal Article
• Language: English
• Published: England BioMed Central 02-10-2020; BMC
• Subjects: Actin; Adolescent; Animals; Antiparasitic Agents - therapeutic use; Biopsy; Cameroon; Child; Child, Preschool; Deoxyribonucleic acid; Diagnostic systems; DNA; Drug dosages; Female; Humans; Immunology; Infections; Infectious diseases; Ivermectin; Ivermectin - therapeutic use; Male; Mass Drug Administration; Microfilaridemia; Microscopy; Monitoring; O. volvulus; Onchocerca volvulus; Onchocerca volvulus - physiology; Onchocerciasis - drug therapy; Parasites; Real time; Real-time PCR; Real-Time Polymerase Chain Reaction; Repopulation; Sensitivity; Skin; Skin - pathology; Susceptibility; Worms; Young Adult; Cameroon; Microfilaricides; Microscopy; Real-time PCR; Susceptibility; Microfilaridemia; LAMP; O. volvulus; Monitoring
• ISSN: 1471-2334; 1471-2334
• DOI: 10.1186/s12879-020-05444-2

Ivermectin is an excellent microfilaricide against Onchocerca volvulus. However, in some regions, long term use of ivermectin has resulted in sub-optimal responses to the treatment. More data to properly document the phenomenon in various contexts of ivermectin mass drug administration (IVM-MDA) is needed. Also, there is a need to accurately monitor a possible repopulation of skin by microfilariae following treatment. Skin snip microscopy is known to have a low sensitivity in individuals with light infections, which can be the case following treatment. This study was designed with two complementary objectives: (i) to assess the susceptibility of O. volvulus microfilariae to ivermectin in two areas undergoing IVM-MDA for different lengths of time, and (ii) to document the repopulation of skin by the O. volvulus microfilariae following treatment, using 3 independent diagnostic techniques.
Identified microfilaridermic individuals were treated with ivermectin and re-examined after 1, 3, and 6 months using microscopy, actin real-time PCR (actin-qPCR) and O-150 LAMP assays. Susceptibility to ivermectin and trends in detecting reappearance of skin microfilariae were determined using three techniques. Microscopy was used as an imperfect gold standard to determine the performance of actin-qPCR and LAMP.
In Bafia with over 20 years of IVM-MDA, 11/51 (21.6%) direct observe treated microfilaridemic participants were still positive for skin microfilariae after 1 month. In Melong, with 10 years of IVM-MDA, 2/29 (6.9%) treated participants were still positive. The microfilarial density reduction per skin biopsy within one month following treatment was significantly lower in participants from Bafia. In both study sites, the molecular techniques detected higher proportions of infected individuals than microscopy at all monitoring time points. LAMP demonstrated the highest levels of sensitivity and real-time PCR was found to have the highest specificity.
Patterns in skin mirofilariae clearance and repopulation were established. O. volvulus worms from Bafia with higher number of annual MDA displayed a lower clearance and higher repopulation rate after treatment with ivermectin. Molecular assays displayed higher sensitivity in monitoring O. volvulus microfilaridemia within six months following treatment.