Field-Based Evidence of Single and Few Doses of Annual Ivermectin Treatment Efficacy in Eliminating Skin Microfilaria Load after a Decade of Intervention

Abstract

BACKGROUND: Impact assessment of community-basedivermectin treatment control of onchocerciasis is required todetermine its effectiveness. This study was conducted to evaluategeographic coverage and demographic ivermectin treatmentcompliance.METHODS: The number of village dosage were obtained from thecommunity based distributors. Bioclinical data of participantscomprising gender, age, number of treatment received frominception and dosage were obtained. Each participant wassubjected to physical examination for palpable nodule and otherskin clinical signs and symptoms of onchocerciasis. Visual acuitytest was done using the Snellen illiterate E-chart. Eye examinationwas performed using touch loop and handheld ophthalmoscope.Skin snips from both iliac crests were incubated overnight at 28-32oC and emerged micrifilaria enumerated under an invertedmicroscope. The changes in epidemiological indices at post-decadeof mass drug administration were compared with baseline data.RESULTS: Village annual ivermectin treatment doses averaged62%, ranging between 10-100%. Individual treatment compliancerate was generally low with an average of 4 treatments and a rangebetween 0-10. Despite variations in treatment compliance, therewere significant improvements in some onchocercal morbidities.These include reduced number and severity of itching, visualimpairment, papular onchodermatitis, onchocercomata (palpablenodules) and leopard skin. Ivermectin treatment halteddevelopment of new blind cases, except the case of a man who hadoptic nerve disease and became blind 2 years after ivermectintreatment had commenced. There was a significant overallreduction in parasite burden with very low mean skin microfilariaload of 1.7mf per skin snip and 3.7% skin mf prevalence, comparedto baseline data of 17.7mf and 37.9% respectively. The palpablenodule was also drastically reduced from 14.5% to 6.4%. Outcomeof this study has practically demonstrated that even a single doseivermectin treatment is capable of clearing skin mf load on a long-term basis. This assertion is exemplified by the result obtained fromBomjock village that had taken treatment only at inception, and theprevalence rate was reduced from 70% to about 9.0% at post-decade of intervention.CONCLUSION: It can be inferred that highdemographic coverage with annual treatmentdoses, it is feasible to attain a shorter time(within a decade) contrary to the anticipatedlonger-term projection.