Ivermectin treatment of onchocercal skin lesions: observations from a placebo-controlled, double-blind trial in Malawi

Onchocerciasis drug development: from preclinical models to humans

Twenty diseases are recognized as neglected tropical diseases (NTDs) by World Health Assembly resolutions, including human filarial diseases. The end of NTDs is embedded within the Sustainable Development Goals for 2030, under target 3.3. Onchocerciasis afflicts approximately 20.9 million people worldwide with > 90% of those infected residing in Africa. Control programs have made tremendous efforts in the management of onchocerciasis by mass drug administration and aerial larviciding; however, disease elimination is not yet achieved. In the new WHO roadmap, it is recognized that new drugs or drug regimens that kill or permanently sterilize adult filarial worms would significantly improve elimination timelines and accelerate the achievement of the program goal of disease elimination. Drug development is, however, handicapped by high attrition rates, and many promising molecules fail in preclinical development or in subsequent toxicological, safety and efficacy testing; thus, research and development (R&D) costs are, in aggregate, very high. Drug discovery and development for NTDs is largely driven by unmet medical needs put forward by the global health community; the area is underfunded and since no high return on investment is possible, there is no dedicated drug development pipeline for human filariasis. Repurposing existing drugs is one approach to filling the drug development pipeline for human filariasis. The high cost and slow pace of discovery and development of new drugs has led to the repurposing of “old” drugs, as this is more cost-effective and allows development timelines to be shortened. However, even if a drug is marketed for a human or veterinary indication, the safety margin and dosing regimen will need to be re-evaluated to determine the risk in humans. Drug repurposing is a promising approach to enlarging the pool of active molecules in the drug development pipeline. Another consideration when providing new treatment options is the use of combinations, which is not addressed in this review. We here summarize recent advances in the late preclinical or early clinical stage in the search for a potent macrofilaricide, including drugs against the nematode and against its endosymbiont, Wolbachia pipientis.

The African Programme for Onchocerciasis Control: impact on onchocercal skin disease

OBJECTIVES

To assess the long-term impact of the African Programme for Onchocerciasis Control on itching and onchocercal skin disease (OSD).

METHODS

Seven study sites in Cameroon, Sudan, Nigeria and Uganda participated. Two cross-sectional surveys were conducted of communities meso- and hyper-endemic for onchocerciasis before and after 5 or 6 years of community-directed treatment with ivermectin (CDTI). Individuals were asked about any general health symptoms including itching and underwent full cutaneous examinations. Onchocercal skin lesions were documented according to a standard classification.

RESULTS

Five thousand one hundred and ninety three people were examined in phase I and 5,180 people in phase II. The presence of onchocercal nodules was a strongly significant (P < 0·001) risk factor for all forms of onchocercal skin disease: APOD (OR 1·66); CPOD (OR 2·84); LOD (OR 2·68); reactive skin lesions (OR 2·38) and depigmentation (OR 3·36). The effect of community-directed treatment with ivermectin was profound. At phase II, there were significant (P < 0·001) reductions in the odds of itching (OR 0·32), APOD (OR 0·28); CPOD (OR 0·34); reactive skin lesions (OR 0·33); depigmentation (OR 0·31) and nodules (OR 0·37). Reduction in the odds of LOD was also significant (OR 0.54, P < 0.03).

CONCLUSIONS

This first multi-country report of the long-term impact of CDTI reveals a substantial reduction in itching and OSD. APOC operations are having a major effect in improving skin health in poor rural populations in Africa.

Research for control: the onchocerciasis experience

Onchocerciasis control has been very successful in Africa and research has played a critical role. An overview of the main epidemiological and implementation research activities undertaken over the last 20 years in collaboration with the African onchocerciasis control programmes and of the impact this research had on control is given. The research included the development of epidemiological modelling and its application in programme evaluation and operational planning, research on disease patterns and disease burden in different bioclimatic zones to justify and guide control operations, community trials of ivermectin to determine its safety for large-scale use and its impact on transmission, rapid assessment methods to identify target communities for treatment and community-directed treatment for sustained drug delivery. Lessons learned during this unique collaboration between research and control are discussed.

Impact of ivermectin on illness and disability associated with onchocerciasis

The Onchocerciasis Control Program (OCP), one of the most successful vertical disease control programs in the history of public health, came to an end in 2003 with devolvement of responsibilities for control program activities passed to the countries affected. Fortunately, 15 years ago the Mectizan Distribution Program (MDP) was founded to provide a complementary approach to controlling the disabling consequences of this parasitic infection. With over 250 million doses of ivermectin distributed over the past 15 years, the MDP is well on its way to both solidifying the progress made by the OCP and extending program reach well beyond the boundaries of the OCP. Through the extensive clinical testing protocols implemented in a variety of countries in Aftica, ivermectin has been proven to be a safe and highly effective treatment for onchocerciasis. Regular distribution to populations living in endemic areas has demonstrated significant reductions in blinding ocular complications, transmission, and disability caused by onchocercal skin disease. As yet undocumented, are the likely significant impact regular population dosing with ivermectin has on intestinal helminth infections, lymphatic filariasis, and human scabies infection. While there are significant barriers to continued program success, focussed attention on expanding and improving community-directed ivermectin distribution is likely to lead to further progress against this resilient infection.

The effect of 5 years of annual treatment with ivermectin (Mectizan) on the prevalence and morbidity of onchocerciasis in the village of Gami in the Central African Republic

To assess the impact of 5 years of annual community treatment with ivermectin (Mectizan) on the prevalence of onchocerciasis and onchocerciasis-associated morbidity, data collected, before and after such treatment, in the village of Gami, in a hyper-endemic area of the Central African Republic, were analysed. Skin snips from all the villagers treated in 1990 and/or 1995 were used to assess the prevalence and intensity of infection with Onchocerca volvulus. Ocular and dermatological morbidity was assessed by ophthalmological and clinical examinations of the same subjects. Following the five annual treatments, there was a reduction in the prevalence of infection and a dramatic decrease in the microfilarial load of the community. The prevalences of pruritus, onchocercal nodules and impaired vision were all significantly reduced. The results emphasise the long-term benefits of the mass-treatment programmes, particularly for children aged <10 years.

Development of reactive onchocercal skin lesions during a placebo-controlled trial with ivermectin among persons without lesions at baseline

Clinical trials of the effects of ivermectin on onchocercal skin disease have documented reduction in itching, but a less than clear benefit on reactive skin lesions. It has been suggested that one of the positive effects might be the prevention of new lesions. A study among a rural adult farming population in southwestern Nigeria provided ivermectin in three treatment groups and a placebo to community members who were examined and treated at 3-monthly intervals over a 15-month period. Among the 1206 people recruited for the study, 627 (52%) had no lesions at baseline examination. Atotal of 291 participants without baseline lesions attended all five follow-up examinations, and only their results were analysed. Members of all four groups developed new lesions, but those receiving ivermectin had a consistently lower proportion of lesions than the placebo group. This difference reached statistical significance at the 5% level in three of the five periods and was below the 10% level at the other two periods. These findings are suggestive of an inhibiting effect of ivermectin among those without lesions at the beginning of a community treatment programme, and justify community treatment as a way of limiting morbidity and social stigma associated with these lesions.

Drug treatment of tropical parasitic infections: recent achievements and developments

Drug development offers potential solutions to a number of tropical health diseases, although the expense of pharmaceutical research and lack of return on investment has limited the production of new agents. The greatest successes have been through the development of single dose therapy and mass treatment control programmes for a number of diseases. We review some of the current treatment regimens for malaria, intestinal helminth infection, onchocerciasis, filariasis and schistosomiasis, and their use in clinical practice. Geographical spread and emergence of drug resistant parasites have hindered the control of malaria, the most important global parasitic infection. Artemisinin compounds have proved effective antimalarial agents producing rapid reduction of parasite load and can be used in combination treatment regimens to combat multidrug resistance. Intestinal helminth infections are widespread, giving rise to nutritional deficiencies and impaired childhood cognitive development. Pregnant women in developing countries are at increased risk of morbidity. Treatment with a single dose benzimidazole such as albendazole or mebendazole has beneficial effects on morbidity and rates of transmission. Diethylcarbamazine has been used in the treatment of onchocerciasis and human filariasis. A complicated escalating dose regimen over several weeks is associated with systemic and allergic reactions and may require corticosteroid cover. Simplified regimens for mass population treatment with ivermectin have proved useful and been used in combination with single dose albendazole and diethylcarbamazine. The African Programme for Onchocerciasis Control in West and Central Africa has been one of the most successful mass control programmes virtually eliminating new infections by a combination of chemotherapy, education and vector control. Schistosomiasis is of increasing importance as a result of the creation of new snail habitats by agricultural and economic development. Praziquantel has become the most widely available and effective chemotherapy for schistosomiasis. There have been a number of reports of persistent schistosome egg shedding after treatment posing concerns about the emergence of drug resistance. Eflornithine has been successfully used in patients with human trypanosomiasis failing melarsoprol therapy however expense and availability have limited its potential. Mass control treatment programmes have targeted schoolchildren, adolescents and pregnant women. The integration of schistosomiasis, onchocerciasis, filariasis and helminth control programmes has been considered as a cost-effective method of delivering treatment. It is likely that future control will be based on this optimisation and integration of existing regimens, rather than the development of new agents.

The effects of ivermectin on onchocercal skin disease and severe itching: results of a multicentre trial

OBJECTIVE

To determine the effects of ivermectin in annual, 3-monthly and 6-monthly doses on onchocercal skin p6isease (OSD) and severe itching.

METHOD

A multicentre, double-blind placebo controlled trial was conducted among 4072 residents of rural communities in Ghana, Nigeria and Uganda. Baseline clinical examination categorized reactive skin lesions as acute papular onchodermatitis, chronic papular onchodermatitis and lichenified onchodermatitis. Presence and severity of itching was determined by open-ended and probing questions. Clinical examination and interview took place at baseline and each of 5 subsequent 3-monthly follow-up visits.

RESULTS

While prevalence and severity of reactive lesions decreased for all 4 arms, those receiving ivermectin maintained a greater decrease in prevalence and severity over time. The difference between ivermectin and placebo groups was significant for prevalence at 9 months and for severity at 3 months. Differences between placebo and ivermectin groups were much more pronounced for itching. From 6 months onward, the prevalence of severe itching was reduced by 40-50% among those receiving ivermectin compared to the trend in the placebo group.

CONCLUSION

This is an important effect on disease burden as severe itching is for the affected people the most troubling complication of onchocerciasis. The difference among regimens was not significant, and the recommended regimen of annual treatment for the control of ocular onchocerciasis appears also the most appropriate for onchocerciasis control in areas where the skin manifestations predominate. The final determination of the effect on skin lesions requires a longer period of study.

Skin problems in the traveler

Skin lesions are common in travelers and include a mix of mundane dermatologic problems and rare diseases acquired only in remote or tropical regions. The morphology, distribution, and progression of the lesions are useful in assessing possible causes. Early in the evaluation it is important to determine whether the patient might have a process that is rapidly progressive, treatable, or transmissible. In addition to routine laboratory studies, biopsy and serologic tests are often necessary to confirm a specific diagnosis.

Anthelmintics. A comparative review of their clinical pharmacology

Virtually all the important helminth infections in humans can be treated with one of 5 anthelmintics currently in use: albendazole, mebendazole, diethylcarbamazine, ivermectin and praziquantel. These drugs are vital not only for the treatment of individual infections, but also useful in controlling transmission of the more common infections. This article reviews briefly the pharmacology of these 5 drugs, and then discusses current issues in the use of anthelmintics in the treatment and/or control of soil-transmitted nematode infections, filariasis, onchocerciasis, schistosomiasis (and other trematode infections), neurocysticercosis and hydatidosis. Mebendazole and albendazole are most effective against intestinal nematodes, but are contraindicated during the first trimester of pregnancy. The efficacy of prolonged therapy with these 2 drugs for treatment of larval cestode infections has not yet been established. Diethylcarbamazine is widely used to treat and control lymphatic filariasis, but adverse effects related to death of microfilariae or damage to adult worms may be marked. While ivermectin has been used in the treatment of patients with onchocerciasis, it is also undergoing investigation against lymphatic filariae. Praziquantel, used to treat schistosome infections, is also effective in other trematode infections and adult cestode infections.