Response to the Letter to the Editor by Eberhard et al.

In a Letter to the Editor, Eberhard et al. question the validity of our model of skin snip sensitivity and argue against the use of skin snips to evaluate onchocerciasis elimination by mass drug administration. Here we discuss their arguments and compare model predictions with observed data to assess the validity of our model

Modelling Neglected Tropical Diseases diagnostics: the sensitivity of skin snips for Onchocerca volvulus in near elimination and surveillance settings.

BACKGROUND: The African Programme for Onchocerciasis Control has proposed provisional thresholds for the prevalence of microfilariae in humans and of L3 larvae in blackflies, below which mass drug administration (MDA) with ivermectin can be stopped and surveillance started. Skin snips are currently the gold standard test for detecting patent Onchocerca volvulus infection, and the World Health Organization recommends their use to monitor progress of treatment programmes (but not to verify elimination). However, if they are used (in transition and in parallel to Ov-16 serology), sampling protocols should be designed to demonstrate that programmatic goals have been reached. The sensitivity of skin snips is key to the design of such protocols. METHODS: We develop a mathematical model for the number of microfilariae in a skin snip and parameterise it using data from Guatemala, Venezuela, Ghana and Cameroon collected before the start of ivermectin treatment programmes. We use the model to estimate sensitivity as a function of time since last treatment, number of snips taken, microfilarial aggregation and female worm fertility after exposure to 10 annual rounds of ivermectin treatment. RESULTS: The sensitivity of the skin snip method increases with time after treatment, with most of the increase occurring between 0 and 5 years. One year after the last treatment, the sensitivity of two skin snips taken from an individual infected with a single fertile female worm is 31 % if there is no permanent effect of multiple ivermectin treatments on fertility; 18 % if there is a 7 % reduction per treatment, and 0.6 % if there is a 35 % reduction. At 5 years, the corresponding sensitivities are 76 %, 62 % and 4.7 %. The sensitivity improves significantly if 4 skin snips are taken: in the absence of a permanent effect of ivermectin, the sensitivity of 4 skin snips is 53 % 1 year and 94 % 5 years after the last treatment. CONCLUSIONS: Our model supports the timelines proposed by APOC for post-MDA follow-up and surveillance surveys every 3-5 years. Two skin snips from the iliac region have reasonable sensitivity to detect residual infection, but the sensitivity can be significantly improved by taking 4 snips. The costs and benefits of using four versus two snips should be evaluated

Phenotypic Evidence of Emerging Ivermectin Resistance in Onchocerca volvulus

Onchocerciasis, commonly known as river blindness, is caused by the filarial nematode Onchocerca volvulus and is transmitted by a blackfly vector. Over 37 million people are thought to be infected, with over 90 million at risk. Infection predominantly occurs in sub-Saharan Africa. Foci also exist in the Arabian Peninsula and Central and South America. Ivermectin, the sole pharmaceutical available for mass chemotherapy, has been used on a community basis for annual or semi-annual treatment since 1987. Multiple treatments with ivermectin kill the microfilariae that are responsible for the pathology of onchocerciasis. More importantly, ivermectin suppresses the reproductive activity of the adult female worms, thus delaying or preventing the repopulation of the skin with new microfilariae and thereby reducing transmission. This study extends earlier reports of sub-optimal responses to ivermectin by examining repopulation levels of microfilaria one year after treatment, worm burdens per nodule, the age structure of adult female worms recovered from nodules, and the reproductive status of adult female worms 90 days after ivermectin treatment. In some communities which have shown a pattern of sub-optimal response to treatment, the data is consistent with an emergence of ivermectin non response or resistance manifested by a loss of the effect of ivermectin on the suppression of parasite reproduction

Diagnosis of O. volvulus infection via skin exposure to diethylcarbamazine: clinical evaluation of a transdermal delivery technology-based patch

Abstract Background Elimination of onchocerciasis in Africa is now regarded as an achievable goal in many areas. This makes monitoring changes in infection prevalence a key component of control programmes. Monitoring is currently based on determining the presence of O. volvulus microfilariae in skin snips, an invasive, labour-intensive method. The Onchocerciasis Control Programme (OCP) had established procedures to detect O. volvulus infections via the localized skin reaction induced by killing of microfilariae upon skin exposure to diethylcarbamazine via a patch (OCP-patch). Large scale OCP - patch use is difficult due to labour-intensive patch preparation. At the request of TDR, a manufacturer specialized in transdermal-delivery systems developed a ready-to-use diethylcarbamazine (DEC) containing patch (LTS-2 patch). To qualify this patch for large scale studies of its sensitivity and specificity, this study evaluated its ease of application, ability to detect infection and DEC exposure related adverse reactions compared to the OCP-patch in 30 infected individuals. Methods Each participant with 0.2–36.8 O. volvulus microfilariae/mg skin received the OCP-patch and 4 days later the LTS-2 patch at the left and right iliac crest, respectively, for 24 h. Presence and characteristics of local skin reactions were assessed at patch removal and 6 h later. Skin reaction and Mazzotti reaction rates were compared with Fisher’s exact and a paired t-test, respectively. Results The LTS-2 patch could be applied within 10 s. Mild itching occured at 63.3 % of OCP-patch (duration 8.9 ± 11.8 h) and 26.7 % of LTS-2 patch sites (duration 1.0 ± 2.5 h) and was the most frequent Mazzotti reaction. At patch removal after 24 h, a diagnostic local skin reaction was present under 90 % of OCP-patches and 83 % of LTS-2 patches; 6 h later, it was present at 93 % of OCP-patch and 100 % of LTS-2 patch sites. Conclusions The data suggest that safety, tolerability and ability to detect infections of the LTS-2 patch are comparable to those of the OCP-patch. They qualify the LTS-2 patch for field studies to determine LTS-2 patch sensitivity, specificity and utility during large scale use and thus to inform use of the LTS-2 patch by onchocerciasis control programmes to determine prevalence of infection. Trial registration Current controlled Trials ISRCTN76875372

A Randomized, Single-Ascending-Dose, Ivermectin-Controlled, Double-Blind Study of Moxidectin in <i>Onchocerca volvulus</i> Infection

<div><p>Background</p><p>Control of onchocerciasis as a public health problem in Africa relies on annual mass ivermectin distribution. New tools are needed to achieve elimination of infection. This study determined in a small number of <i>Onchocerca volvulus</i> infected individuals whether moxidectin, a veterinary anthelminthic, is safe enough to administer it in a future large study to further characterize moxidectin's safety and efficacy. Effects on the parasite were also assessed.</p><p>Methodology/Principal Findings</p><p>Men and women from a forest area in South-eastern Ghana without ivermectin mass distribution received a single oral dose of 2 mg (N = 44), 4 mg (N = 45) or 8 mg (N = 38) moxidectin or 150 µg/kg ivermectin (N = 45) with 18 months follow up. All ivermectin and 97%–100% of moxidectin treated participants had Mazzotti reactions. Statistically significantly higher percentages of participants treated with 8 mg moxidectin than participants treated with ivermectin experienced pruritus (87% vs. 56%), rash (63% vs. 42%), increased pulse rate (61% vs. 36%) and decreased mean arterial pressure upon 2 minutes standing still after ≥5 minutes supine relative to pre-treatment (61% vs. 27%). These reactions resolved without treatment. In the 8 mg moxidectin and ivermectin arms, the mean±SD number of microfilariae/mg skin were 22.9±21.1 and 21.2±16.4 pre-treatment and 0.0±0.0 and 1.1±4.2 at nadir reached 1 and 3 months after treatment, respectively. At 6 months, values were 0.0±0.0 and 1.6±4.5, at 12 months 0.4±0.9 and 3.4±4.4 and at 18 months 1.8±3.3 and 4.0±4.8, respectively, in the 8 mg moxidectin and ivermectin arm. The reduction from pre-treatment values was significantly higher after 8 mg moxidectin than after ivermectin treatment throughout follow up (p<0.01).</p><p>Conclusions/Significance</p><p>The 8 mg dose of moxidectin was safe enough to initiate the large study. Provided its results confirm those from this study, availability of moxidectin to control programmes could help them achieve onchocerciasis elimination objectives.</p><p>Trial Registration</p><p>ClinicalTrails.gov <a href="http://www.clinicaltrials.gov/ct2/show/NCT00300768" target="_blank">NCT00300768</a></p></div

Map of Ghana showing the location of some towns/villages in the area from which participants were recruited.

<p>The boundaries and names shown and the designations used in this map do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.</p

Number of live female macrofilaria, live young female macrofilaria and live male macrofilaria in excised nodules vs skin mf density 18 months after treatment by treatment.

<p>A. Ivermectin, B. 2×axis maximum was set to 7. The data for one participant treated with 2 mg moxidectin who had 13 live female macrofilaria and a skin mf density of 8.2 mf/mg are thus not displayed. Participants with 0 macrofilaria in excised nodules either had no palpable nodules or all excised nodules were non-onchocercal based on histological evaluation. Abbreviations: LI FM – live female macrofilariae, Y FM – live young female macrofilariae, LI MW – live male macrofilariae.</p

Overview of assessment of treatment effects.

<p>D: Day, M: Month. X indicates examination at each time point indicated in the top row, numbers indicate the day or alternative days for performing the examination.</p>1<p>PE: Physical examination including neurological examination and subcutaneous nodule palpation.</p>2<p>VS: Vital signs including temperature, respiratory rate, pulse rate (PR) and blood pressure (BP) after at least 5 minutes supine.</p><p>PR and BP were repeated after 2 minutes standing following ≥5 minutes supine.</p><p>Day 1: once before and 3 times after drug administration PR and BP after ≥5 minutes supine and subsequent 2 minutes standing still, Days 2–8: 5 times, PR and BP after ≥5 minutes supine and subsequent 2 minutes standing still, Days 9–17: twice, supine only, M1–M18: once, supine only.</p>3<p>12 lead ECG on day 1 approximately 4 hours after drug administration.</p>4<p>OE: Ocular Examination included visual acuity, visual fields (calibrated Goldman perimeter), colour vision, intraocular pressure, examination of the fundus, slit lamp examination of anterior segment, counting of microfilariae in anterior chamber, living and dead microfilariae in cornea and punctate opacities.</p><p>Colour fundus photography and fluorescein angiography to month 3, thereafter as per protocol only in participants with lesions or visual defects on OE (which was not applicable).</p>5<p>LE: Laboratory evaluations included: serum biochemistry (Na⁺, K⁺, Cl⁻, bicarbonate, glucose, total protein, albumin, urea, creatinine, alkaline phosphatase, lactic dehydrogenase, total bilirubin, gamma-glutamyl transpeptidase, aspartate aminotransferase, and alanine aminotransferase), hematology (prothrombin time, a complete blood cell count, hematocrit, hemoglobin, 5-part differential white blood cell count, platelet count), dipstick semiquantitative urinalysis microscopic urine evaluation, urine and blood microfilariae quantitation after nucleopore membrane filtration and Giemsa staining.</p>6<p>Minimum of 1 mg from each iliac crest and calf with a 2 mm corneoscleral punch.</p>7<p>Aseptical excision of all palpable nodules under 2% xylocaine anaesthesia.</p>8<p>Blood sampling time points for pharmacokinetics (PK) on day 1–4: within 2 hours of drug administration, 1, 2, 4, 8, 24, and 72 hours after treatment.</p