Treatment of onchocerciasis. The ocular effects of ivermectin and diethylcarbamazine

Onchocerca volvulus microfilariae in the anterior chambers of the eye and ocular adverse events after a single dose of 8 mg moxidectin or 150 µg/kg ivermectin: results of a randomized double-blind Phase 3 trial in the Democratic Republic of the Congo, Ghana and Liberia

BACKGROUND

After ivermectin became available, diethylcarbamazine (DEC) use was discontinued because of severe adverse reactions, including ocular reactions, in individuals with high Onchocerca volvulus microfilaridermia (microfilariae/mg skin, SmfD). Assuming long-term ivermectin use led to < 5 SmfD with little or no eye involvement, DEC + ivermectin + albendazole treatment a few months after ivermectin was proposed. In 2018, the US FDA approved moxidectin for treatment of O. volvulus infection. The Phase 3 study evaluated SmfD, microfilariae in the anterior chamber (mfAC) and adverse events (AEs) in ivermectin-naïve individuals with ≥ 10 SmfD after 8 mg moxidectin (n = 978) or 150 µg/kg ivermectin (n = 494) treatment.

METHODS

We analyzed the data from 1463 participants with both eyes evaluated using six (0, 1-5, 6-10, 11-20, 21-40, > 40) mfAC and three pre-treatment (< 20, 20 to < 50, ≥ 50) and post-treatment (0, > 0-5, > 5) SmfD categories. A linear mixed model evaluated factors and covariates impacting mfAC levels. Ocular AEs were summarized by type and start post-treatment. Logistic models evaluated factors and covariates impacting the risk for ocular AEs.

RESULTS

Moxidectin and ivermectin had the same effect on mfAC levels. These increased from pre-treatment to Day 4 and Month 1 in 20% and 16% of participants, respectively. Six and 12 months post-treatment, mfAC were detected in ≈5% and ≈3% of participants, respectively. Ocular Mazzotti reactions occurred in 12.4% of moxidectin- and 10.2% of ivermectin-treated participants without difference in type or severity. The risk for ≥ 1 ocular Mazzotti reaction increased for women (OR 1.537, 95% CI 1.096-2.157) and with mfAC levels pre- and 4 days post-treatment (OR 0: > 10 mfAC 2.704, 95% CI 1.27-5.749 and 1.619, 95% CI 0.80-3.280, respectively).

CONCLUSIONS

The impact of SmfD and mfAC levels before and early after treatment on ocular AEs needs to be better understood before making decisions on the risk-benefit of strategies including DEC. Such decisions should take into account interindividual variability in SmfD, mfAC levels and treatment response and risks to even a small percentage of individuals.

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.

How does onchocerciasis-related skin and eye disease in Africa depend on cumulative exposure to infection and mass treatment?

Background

Onchocerciasis (river-blindness) in Africa is targeted for elimination through mass drug administration (MDA) with ivermectin. Onchocerciasis may cause various types of skin and eye disease. Predicting the impact of MDA on onchocercal morbidity is useful for future policy development. Here, we introduce a new disease module within the established ONCHOSIM model to predict trends over time in prevalence of onchocercal morbidity.

Methods

We developed novel generic model concepts for development of symptoms due to cumulative exposure to dead microfilariae, accommodating both reversible (acute) and irreversible (chronic) symptoms. The model was calibrated to reproduce pre-control age patterns and associations between prevalences of infection, eye disease, and various types of skin disease as observed in a large set of population-based studies. We then used the new disease module to predict the impact of MDA on morbidity prevalence over a 30-year time frame for various scenarios.

Results

ONCHOSIM reproduced observed age-patterns in disease and community-level associations between infection and disease reasonably well. For highly endemic settings with 30 years of annual MDA at 60% coverage, the model predicted a 70% to 89% reduction in prevalence of chronic morbidity. This relative decline was similar with higher MDA coverage and only somewhat higher for settings with lower pre-control endemicity. The decline in prevalence was lowest for mild depigmentation and visual impairment. The prevalence of acute clinical manifestations (severe itch, reactive skin disease) declined by 95% to 100% after 30 years of annual MDA, regardless of pre-control endemicity.

Conclusion

We present generic model concepts for predicting trends in acute and chronic symptoms due to history of exposure to parasitic worm infections, and apply this to onchocerciasis. Our predictions suggest that onchocercal morbidity, in particular chronic manifestations, will remain a public health concern in many epidemiological settings in Africa, even after 30 years of MDA.

Onchocerciasis, also known as river blindness, is the second most common infectious cause of blindness worldwide, but also leads to serious skin conditions. Large-scale interventions are ongoing to control and eliminate the disease in Africa, yet the impact of these interventions on onchocercal morbidity is largely unknown. Here, we predict the trends in a wide spectrum of skin and eye disease due to onchocerciasis after up to 30 years of annual mass drug administration (MDA) with ivermectin. To this end, we have developed a novel disease framework within the established ONCHOSIM model. We show that annual MDA will rapidly reduce the prevalence of acute clinical conditions, whereas the prevalence of chronic clinical manifestations will decline much more slowly. The new disease framework was validated with several data sources and reproduced morbidity trends adequately, making the framework applicable for more refined disease prevalence predictions by taking account of treatment history in Africa. Such predictions are essential for accurate estimates of disability-adjusted life years lost due to onchocerciasis by 2025.

Drug-induced uveitis: A review

Uveitis maybe induced by the use of various medications known as drug-induced uveitis (DIU), though rare it is an important cause of uveitis which one needs to be aware of. The drugs may be administered through any route including systemic, topical, and intravitreal. Ocular inflammation can be in the form of anterior, intermediate, posterior or pan uveitis, and rarely may present as episcleritis and scleritis. Identification of drug as the offending agent of uveitis is important as many a times stopping the drug may help recover the uveitis or the concomitant use of corticosteroids. An extensive literature review was done using the Pubmed. An overview of DIU is provided as it is important for us to be aware of this clinical entity.

Ocular Demodex: a systematic review of the clinical literature

PURPOSE

There is increasing clinical and research interest in the potential contribution of Demodex to ocular surface disease. The aim of this systematic review was to summarise and synthesise current clinical evidence relating to the aetiology, diagnosis and treatment of ocular Demodex.

RECENT FINDINGS

A comprehensive literature search was performed in OVID Medline, OVID Embase, and clinical trial registries, for studies published between 1990 and August 2019, examining Demodex on the ocular surface. The review included primary clinical research studies and systematic reviews of primary clinical research studies, where Demodex was considered in the context of the ocular surface and/or adnexa. Studies were categorised using the National Health and Medical Research Council evidence hierarchy. Risk of bias assessment was performed using validated tools for studies categorised as providing Level I or II evidence. A total of 87 studies were eligible for inclusion, including two systematic reviews. Most studies (60%) were observational, describing the prevalence of ocular Demodex in different clinical populations. There was a high degree of variability in the epidemiological data derived from cross-sectional aetiology studies. There was mostly consistent evidence to support an association between ocular Demodex and chronic blepharitis. Seven diagnostic test-accuracy studies were identified, which considered a range of techniques, including slit lamp examination for cylindrical eyelash collarettes and/or eyelash manipulation techniques, light microscopic evaluation of epilated eyelashes and in vivo confocal microscopy. There is currently no accepted gold-standard diagnostic method for ocular Demodex. For intervention studies, there was one systematic review, 11 published randomised trials, six trial registry entries, and nine case series. Despite a number of recent trials, the appropriate treatment regimen for ocular Demodex (including the optimal criteria and timing of an intervention) is not clearly established.

CONCLUSIONS

This comprehensive narrative synthesis has captured the landscape of clinical evidence relating to the prevalence, aetiology, diagnosis and treatment of ocular Demodex. There remain opportunities to enhance understanding of its role in ocular surface disease, best diagnostic approaches and optimal treatment protocols.

Neurological syndromes driven by postinfectious processes or unrecognized persistent infections

PURPOSE OF REVIEW

The immune system serves a critical role in protecting the host against various pathogens. However, under circumstances, once triggered by the infectious process, it may be detrimental to the host. This may be as a result of nonspecific immune activation or due to a targeted immune response to a specific host antigen. In this opinion piece, we discuss the underlying mechanisms that lead to such an inflammatory or autoimmune syndrome affecting the nervous system. We examine these hypotheses in the context of recent emerging infections to provide mechanistic insight into the clinical manifestations and rationale for immunomodulatory therapy.

RECENT FINDINGS

Some pathogens endure longer than previously thought. Persistent infections may continue to drive immune responses resulting in chronic inflammation or development of autoimmune processes, resulting in damage to the nervous system. Patients with genetic susceptibilities in immune regulation may be particularly vulnerable to pathogen driven autoimmune responses.

SUMMARY

The presence of prolonged pathogens may result in chronic immune stimulations that drives immune-mediated neurologic complications. Understanding the burden and mechanisms of these processes is challenging but important.

Preclinical evaluation of avermectins as novel therapeutic agents for alcohol use disorders

The deleterious effects of alcohol use disorders (AUDs) on human health have been documented worldwide. The enormous socioeconomic burden coupled with lack of efficacious pharmacotherapies underlies the need for improved treatment strategies. At present, there is a growing body of preclinical evidence that demonstrates the potential of avermectins [ivermectin (IVM), selamectin (SEL), abamectin (ABM), and moxidectin (MOX)] in treatment of AUDs. Avermectins are derived by fermentation of soil micro-organism, Streptomyces avermitilis, and have been extensively used for treatment of parasitic infections. From the mechanistic standpoint, avermectins are positive modulators of purinergic P2X4 receptors (P2X4Rs). P2X4Rs belong to P2X superfamily of cation-permeable ion channels gated by adenosine 5'-triphosphate (ATP). Building evidence has implicated a role for P2X4Rs in regulation of ethanol intake and that ethanol can inhibit ATP-gated currents in P2X4Rs. Investigations using recombinant cell models and animal models of alcohol drinking have reported that IVM, ABM, and MOX, but not SEL, were able to antagonize the inhibitory effects of ethanol on P2X4Rs in vitro and reduce ethanol intake in vivo. Furthermore, IVM was shown to reduce ethanol consumption via P2X4R potentiation in vivo, supporting the involvement of P2X4Rs in IVM's anti-alcohol effects and that P2X4Rs can be used as a platform for developing novel anti-alcohol compounds. Taken together, these findings support the utility of avermectins as a novel class of drug candidates for treatment of AUDs.

Drug-induced uveitis

INTRODUCTION

Drug-induced uveitis is a well described but often overlooked and/or misdiagnosed adverse reaction to medication. There are an increasing number of medications that have been related to the onset of intraocular inflammation. Identification of these inciting agents may decisively help the diagnostic algorithm involving new cases of uveitis.

AREAS COVERED

This review intends to be an updated comprehensive, practical guide for practitioners regarding the main drugs that have been associated with uveitis. A classification proposed by Naranjo et al. in 1981 for establishing potential causality is applied examining possible mechanisms of action. A guide for clinicians about the rationale of these observations when dealing with patients with uveitis is provided.

EXPERT OPINION

Several agents with different routes of administration (systemic, topical and/or intraocular) may cause intraocular inflammation. The mechanism behind ocular inflammation is frequently unknown. Clinicians should be aware of the potential drug effect to optimize diagnosis and management of such patients.

Sustainable control of onchocerciasis: ocular pathology in onchocerciasis patients treated annually with ivermectin for 23 years: a cohort study

The evolution and persistence of ocular pathology was assessed in a cohort of Onchocerca volvulus infected patients treated annually with ivermectin for 23 years. Patients were resident in rural Central and Kara Region of Togo and ocular examinations included testing of visual acuity, slit lamp examination of the anterior eye segment and the eye fundus by ophthalmoscopy. Before ivermectin treatment, vivid O.volvulus microfilariae (MF) were observed in the right and left anterior eye chamber in 52% and 42% of patients (n = 82), and dead MF were seen in the right and left cornea in 24% and 15% of cases, respectively. At 23 years post initial treatment (PIT), none of the patients (n = 82) presented with MF in the anterior chamber and cornea. A complete resolution of punctate keratitis (PK) lesions without observable corneal scars was present at 23 years PIT (p<0.0001), and sclerosing keratitits (SK) lessened by half, but mainly in patients with lesions at early stage of evolution. Early-stage iridocyclitis diminished from 42%(rE) and 40%(lE) to 13% (rE+lE)(p<0.0001), but advanced iridocyclitis augmented (p<0.001) at 23 years PIT compared to before ivermectin. Advanced-stage papillitis and chorioretinitis did not regress, while early-stage papillitis present in 28%(rE) and 27%(lE) of patients at before ivermectin regressed to 17%(rE) and 18%(lE), and early-stage chorioretinitis present in 51%(rE+lE) of cases at before ivermectin was observed in 12%(rE) and 13%(lE) at 23 years PIT (p<0.0001). Thus, regular annual ivermectin treatment eliminated and prevented the migration of O. volvulus microfilariae into the anterior eye chamber and cornea; keratitis punctata lesions resolved completely and early-stage sclerosing keratitits and iridocyclitis regressed, whilst advanced lesions of the anterior and posterior eye segment remained progressive. In conclusion, annual ivermectin treatments may prevent the emergence of ocular pathology in those populations still exposed to O.volvulus infection.

Trial Registration: www.pactr.orgPACTR201303000464219)

Drug-induced uveitis

A number of medications have been associated with uveitis. This review highlights both well-established and recently reported systemic, topical, intraocular, and vaccine-associated causes of drug-induced uveitis, and assigns a quantitative score to each medication based upon criteria originally described by Naranjo and associates.

Elimination of human onchocerciasis: history of progress and current feasibility using ivermectin (Mectizan(®)) monotherapy

We review and analyze approaches over a 65 year period that have proven successful for onchocerciasis control in several different epidemiological settings. These include vector control with the goal of transmission interruption versus the use of mass drug administration using ivermectin (Mectizan(®)) monotherapy. Ivermectin has proven exceedingly effective because it is highly efficacious against Onchocerca volvulus microfilariae, the etiological agent of onchocercal skin and ocular disease and the infective stage for the vector. For these reasons, the drug was donated by the Merck Company for regional control programs in Africa and the Americas. Recurrent treatment with ivermectin at semi-annual intervals also impacts adult worms and result in loss of fecundity and increased mortality. Using a strategy of 6-monthly treatments with high coverage rates, the Onchocerciasis Elimination Program for the Americas has interrupted transmission in seven of the thirteen foci in the Americas and is on track to eliminate onchocerciasis in the region by 2015. Treatments given annually or semi-annually for 15-17 years in three hyperendemic onchocerciasis foci in Mali and Senegal also have resulted in a few infections in the human population with transmission levels below thresholds postulated for elimination. Follow-up evaluations did not detect any recrudescence of infection or transmission, suggesting that onchocerciasis elimination could be feasible with Mectizan(®) treatment in some endemic foci in Africa.

A randomized, double-blind, controlled trial of the effects of ivermectin at normal and high doses, given annually or three-monthly, against Onchocerca volvulus: ophthalmological results

A three-year randomized, controlled, double-blind trial was conducted in Cameroon to determine whether ivermectin, given at three-monthly intervals and/or at high doses (800 microg/kg), had a greater effect on adult Onchocerca volvulus than standard doses (150 microg/kg annually). As several patients complained of transitory subjective visual problems after treatment, some of them being of an unexpected type, we organized two series of detailed ophthalmological examinations to evaluate whether they were associated with ocular lesions. Analysis showed that these complaints were significantly more frequent in the two groups treated with high doses of ivermectin than in the reference group. In the ophthalmological examinations, the only differences recorded between the groups were a lower prevalence and mean number of microfilariae in the anterior chamber in the groups treated three-monthly, and, at the first examination round, a higher prevalence of early lesions of the iris in the group treated at high doses annually. These findings do not allow us to explain the cause of the transitory ocular complaints, nor why they were more frequent in the groups treated at high doses. However, one may conclude that using doses of ivermectin higher than the standard one should be considered with caution.

Pharmacology of ivermectin

Ivermectin is a semi-synthetic macrocyclic lactone (Fig. I) active in single low doses against many parasites - particularly nematodes and arthropods. It has been registered for animal health use since early 1985, and was earlier this year approved for human use by the French Directorate o f Pharmacy and Drugs. Of particular interest is ivermectin's potential as a micro filaricide for treatment o f onchocerciasis. Clinical trials leave little doubt about the potential o f ivermectin as a therapeutic tool for symptomatic relief from the effects o f infection with Onchocerca volvulus, and the drug is also recognized to have potential in reducing transmission o f the parasite. The manufacturers (Merck, Sharp and Dohme) recently arranged to provide the drug free o f charge to the WHO for mass trials against onchocerciasis in 12 African and Central American countries. In this article we focus on the pharmacological properties o f ivermectin, with a brief consideration of its absorption, fate, excretion and side-effects, and a discussion o f its micro filaricidal action.

The life and times of ivermectin — a success story

Since its introduction more than 20 years ago, ivermectin has proved to be one of the most successful therapeutic drugs in veterinary medicine, as well as the basis of one of the most successful public-health programmes of the past century. The drug arose from a unique international collaboration between the public and private sectors. The development process also incorporated the world's first and largest drug-donation programme and involved a unique association between governments, non-governmental organizations and industry. The drug is now being used, free of charge, in two global disease-elimination programmes that are benefiting millions of the world's poorest people.

Assessment of ivermectin therapeutic efficacy on third-stage larvae of Lagochilascaris minor in mice experimentally infected

In this study we evaluated the potential action of ivermectin on third-stage larvae, both at migratory and encysted phases, in mouse tissues after experimental infection with Lagochilascaris minor. Study groups I and II consisted of 120 mice that were orally administered 1,000 parasite eggs. In order to assess ivermectin action upon migratory larvae, group I (60 mice) was equally split in three subgroups, namely I-A, I-B, and I-C. On the 7th day after inoculation (DAI), each animal from the subgroup I-A was treated with 200 micrograms/Kg ivermectin while subgroup I-B was given 1,000 micrograms/Kg, both groups received a single subcutaneous dose. To assess the drug action on encysted larvae, group II was equally split in three subgroups, namely II-A, II-B, II-C. On the 45th DAI each animal was treated with ivermectin at 200 micrograms/Kg (subgroup II-A) and 1,000 micrograms/Kg (group II-B) with a single subcutaneous dose. Untreated animals of subgroups I-C and II-C were used as controls. On the 60th DAI all animals were submitted to larva search. At a dose of 1,000 micrograms/Kg the drug had 99.5% effectiveness on third-stage migratory larvae (subgroup I-B). Ivermectin efficacy was lower than 5% on third-stage encysted larvae for both doses as well as for migratory larvae treated with 200 micrograms/Kg.

Onchocerciasis in Ecuador: evolution of chorioretinopathy after amocarzine treatment

AIMS

To investigate the impact of the macrofilaricidal drug, amocarzine, on the evolution of chorioretinopathy in onchocerciasis.

METHODS

A prospective uncontrolled cohort study was performed using subjects infected with Onchocerca volvulus in a hyperendemic onchocerciasis focus in Esmeraldas Province in Ecuador. Study subjects were recruited into four cohorts in which ophthalmic and parasitological data were collected for 2, 3, 4, and 5 years respectively.

RESULTS

Complete ophthalmic follow up was obtained for 294 individuals in the four cohorts. The incidence of retinal pigment epithelial atrophy tended to remain constant between cohorts while that of chorioretinal scarring with a greater observation period. The incidence rate of cases with new or extending chorioretinal lesions was greater with an increasing period of follow up. An association was seen between the cumulative microfilarial loads in the skin and the development of new chorioretinal lesions (p < 0.05). No relation was noted between cumulative microfilarial loads and the progression of existing disease.

CONCLUSION

Amocarzine therapy did not prevent the natural evolution of chorioretinal disease. It was suggested that ocular microfilariae were necessary for the induction of chorioretinopathy in previously unaffected eyes and that extension of existing disease might also be related to the presence of ocular microfilariae or to other immunological mechanisms.

Onchocerciasis in Ecuador: changes in prevalence of ocular lesions in Onchocerca volvulus infected individuals over the period 1980-1990

Trends in prevalence rates of onchocercal ocular lesions were examined over the period 1980 to 1990 using data from two cross-sectional surveys. There was evidence for increasing prevalence of anterior chamber microfilariae, iridocyclitis, optic atrophy, and chorioretinopathy. Large increases in prevalence, in particular, were seen for posterior segment lesions: optic atrophy increased from 2.7% to 6.4% and chorioretinopathy from 8.8% to 35.6%. Greatest increases in these lesions were seen in the Chachi which was attributed to the large increases in prevalence of microfilariae in the anterior chamber particularly in those aged 30 years or greater. The study findings suggest that ocular onchocerciasis is evolving in parallel with the well documented parasitological changes.

Interleukin 4 and T helper type 2 cells are required for development of experimental onchocercal keratitis (river blindness)

Inflammation of the corneal stroma (stromal keratitis) is a serious complication of infection with the nematode parasite Onchocerca volvulus. Because stromal keratitis is believed to be immunologically mediated in humans, we used a murine model to examine the role of T cells and T helper cell cytokines in the immunopathogenesis of these eye lesions. BALB/c mice immunized subcutaneously and injected intrastromally with soluble O. volvulus antigens (OvAg) developed pronounced corneal opacification and neovascularization. The corneal stroma was edematous and contained numerous eosinophils and mononuclear cells. Stromal keratitis in immunized mice was determined to be T cell dependent based on the following observations: (a) T cell-deficient nude mice immunized and injected intrastromally with OvAg fail to develop corneal pathology; and (b) adoptive transfer of spleen cells from OvAg-immunized BALB/c mice to naive nude mice before intrastromal injection of OvAg results in development of keratitis. OvAg-stimulated lymph node and spleen cell cytokine production was dependent on CD4 cells and included interleukin (IL)-4 and IL-5, but not interferon gamma, indicating a predominant T helper type 2 cell-like response. Inflamed corneas from immunized BALB/c mice and from reconstituted nude mice had greatly elevated CD4 and IL-4 gene expression compared with interferon gamma. Mice in which the IL-4 gene was disrupted failed to develop corneal disease, demonstrating that IL-4 is essential in the immunopathogenesis of O. volvulus-mediated stromal keratitis.

Studies on filariasis in Bauchi State, Nigeria. 1. Endemicity of human onchocerciasis in Ningi Local Government Area

The endemicity of human onchocerciasis was assessed in eight rural, at-risk communities in Ningi Local Government Area, Bauchi State, Nigeria, between July 1990 and March 1991. Of the 1536 subjects skin-snipped, 334 (21.7%) were positive for Onchocerca volvulus microfilariae. Surprisingly, there was a significant inverse relationship between prevalence and mean microfilarial load (r = -0.608; P < 0.05). Males were more likely to be infected than females (P < 0.01) and cattle rearers (71.0% infected), farmers (49.8%) and fishermen (40.0%) had significantly higher prevalences than students/schoolchildren, housewives or traders (P < 0.001). Pruritus and itchy eyes were recorded in all age groups and appeared in much younger subjects than any other manifestations of the infection. Prevalence and onchocercal blindness were linearly related to intensity of infection. The epidemiological significance of these findings, in terms of a future community-wide programme of long-term chemoprophylaxis with Mectizan, is highlighted.

Ivermectin dosing based on physical appearance

Ivermectin is a safe and effective microfilaricide which has been shown to have a beneficial impact on some onchocercal eye lesions. Current requirements for the distribution of ivermectin are that patients be weighed, and that their dose be determined according to their weight. This requirement increases the cost of distributing the drug to communities in need of treatment and, when scales breakdown, may lead to the suspension of distribution. Data are presented on a simple, alternative method of dose assessment based on the physical appearance of the patient. Fifteen assessors achieved an overall level of agreement with the weight-based schedule of 86% on a sample of 6420 patients. The level of agreement varied between assessors, from 73% to 95%. About 6% of the population would have received doses outside the range of the current weight-based schedule. We believe that the current insistence that each individual's dose of ivermectin be determined by weighing will hamper efforts to distribute the drug to those most in need of it and that our data indicate that workers can be trained to distribute ivermectin safely without weighing every individual. We would welcome confirmation of our findings from other populations.

Effects of repeated doses of ivermectin on ocular onchocerciasis: community-based trial in Sierra Leone

Ivermectin seems to be a safe and effective treatment for onchocerciasis when given in a single dose, but less is known about the effects of repeated doses. Also, there seem to be differences in its effectiveness in anterior and posterior segment ocular disease. The ocular effects of ivermectin were studied in 586 villagers who were taking part in a double-blind, placebo-controlled, randomised trial in Sierra Leone. Only those who had received four doses, with 6-month intervals, of ivermectin or placebo were eligible. The 296 ivermectin-treated subjects and the 272 who received placebo were comparable with respect to age, sex, Onchocerca infection, blindness, and visual impairment before treatment. After treatment, the ivermectin group had less anterior segment disease than the placebo group, with significantly lower prevalences of microfilariae in the anterior chamber and cornea, and punctate keratitis (all p less than 0.001), and iritis (p less than 0.05). There was no significant difference in the prevalence of sclerosing keratitis, optic atrophy, or chorioretinitis between the groups. Visual acuities tended to be better in the ivermectin group, but the difference was not significant. There was a small but significant (p less than 0.01) excess of vascular sheathing in the ivermectin group. These differences persisted when subjects who were blind or visually impaired at baseline were excluded from analysis. The long-term effects of ivermectin, particularly on posterior segment disease, need further evaluation. In the mean time, the mass distribution of ivermectin should be promoted for all communities with hyperendemic onchocerciasis at risk of anterior segment disease.

Changes in ocular onchocerciasis after two rounds of community-based ivermectin treatment in a holo-endemic onchocerciasis focus

In a longitudinal study to determine the effect of annual community-based treatment of ocular onchocerciasis with ivermectin, the population living in the 3 most affected villages in the holo-endemic onchocerciasis focus of Asubende in Ghana were re-examined 16 and 24 months after initiating treatment. Ocular microfilarial loads had decreased to very low levels in nearly all of the 334 examined persons who were treated twice. Only very few subjects had ocular loads of 32 microfilariae or more in the anterior chamber of the eye, but this was not associated with deterioration of ocular lesions. Important regression of both early and advanced lesions of the anterior segment of the eye was observed, which was highly statistically significant with respect to iridocyclitis. Lesions of the posterior segment of the eye remained stable. Though no systematic change in the visual acuity of the population was observed, 3 new cases of blindness occurred in persons who already had eye lesions at such an advanced stage that ivermectin treatment could no longer affect the outcome. The results suggest that annual ivermectin treatment is adequate to control onchocercal ocular disease even in populations with very high endemicity levels.

Ocular manifestations of onchocerciasis in a rain forest area of west Africa

The epidemiology and natural history of onchocerciasis and its ocular complications in rain forest areas are poorly understood. The present study was conducted on a rubber plantation in a hyperendemic area in the rain forest of Liberia, West Africa, where 800 persons were examined. The prevalence of infection was 84% overall 29% had intraocular microfilariae, and 2.4% were blind in one or both eyes. Onchocerciasis was the cause of all binocular blindness and one-third of all visual impairment. Over half of the visual impairment caused by onchocerciasis was due to posterior segment diseases. Chorioretinal changes were present in 75% of people, and included intraretinal pigment clumping in 52% and retinal pigment epithelium atrophy in 32%. Atrophy of the retinal pigment epithelium was associated with increasing age and severity of infection. Intraretinal pigment was strongly associated with anterior uveitis. There was a strong correlation between uveitis and the inflammatory chorioretinal sequelae: retinitis, intraretinal pigment, subretinal fibrosis, and optic neuropathy. These findings indicate that considerable visual impairment associated with rain forest onchocerciasis is common and is due largely to chorioretinal disease.

Points of action in the campaign against blindness in developing countries

This article provides a survey of the problems of prevention of blindness in developing countries. The World Health Organization estimates that 31 million people are blind and 15 million people partially-sighted. The main cause of blindness is cataract. Other causes are trachoma, glaucoma, xerophthalmia, river blindness, corneal scars and leprosy. Prevention or treatment of these causes is possible in more than 80% of cases. The number of blind persons, however, is still increasing due to the increase in population and the immense shortage of all kinds of ophthalmological equipment and personnel. An effective strategy for the prevention of blindness in developing countries should focus on: more cheap cataract operations, increasing teaching facilities for ophthalmic personnel, integration of ophthalmic care into the general health system and the promotion of blindness prevention in political organizations.

Longitudinal study of lesions of the posterior segment in onchocerciasis

Onchocerciasis is a major cause of blindness, and much of the blindness due to onchocerciasis is caused by chorioretinitis. Little is known about the progression of lesions in the posterior segment in either untreated or treated disease. The authors studied the progression of onchocercal chorioretinitis in 57 patients from 1 to 3 years. Changes were documented from detailed ocular examinations, fundus photographs, and fluorescein angiograms, and included live intraretinal microfilariae, intraretinal hemorrhages, cotton-wool opacities, intraretinal pigment, white and shiny intraretinal deposits, retinal pigment epithelial window defects, and atrophy. Depigmentation at the edge of chorioretinal scarring progressed at a rate of up to 200 microns per year. Ivermectin or mebendazole treatment did not appear to alter the progress of depigmentation at the edge of chorioretinal scars. These observations suggest that onchocercal chorioretinitis is associated with early changes in the retina and retinal pigment epithelium, and that disease in the posterior segment may progress rapidly.

Decrease in adverse reactions after repeated ivermectin treatment in onchocerciasis

We assessed the side-effects after multiple single-dose treatment with ivermectin (150 micrograms/kg) in onchocerciasis patients form a hyperendemic area in Sierra Leone, in order to investigate whether medical surveillance was always necessary. After initial treatment 87 onchocerciasis patients were examined for adverse reactions. Fourty-four of these 87 patients (51%) received a second dose of ivermectin 5 months later and thirty-five (40%) received a third dose one year later. The side-effects after the second and third doses were significantly diminished, when compared with the initial dose of ivermectin in the treatment of onchocerciasis (chi2 test p less than 0.005, resp. p less than 0.008). Side-effects requiring therapy were observed in 32% of patients after the first dose, in 18% after the second dose and in 11% after the third dose of ivermectin. Severe side-effects (9%) were only seen after the initial ivermectin dose. All the severe adverse reactions appeared within 48 hours. In view of our findings, it seems necessary that the first treatment with ivermectin should take place under strict medical supervision during at least two days. Five months after treatment with a single dose of ivermectin 29 out of 44 patients (66%) still had a positive skin-snip test. Seven months after the second dose 15 of 35 patients (43%) had a positive skin-snip count. Since almost half of the patients had a positive skin-snip test despite two treatments with ivermectin, it could be argued that in hyperendemic areas treatment should consist of at least two doses in the first year.

Ocular involvement in patients with onchocerciasis after repeated treatment with ivermectin

We assessed ocular changes after therapy at six and 12 months with ivermectin (150 micrograms/kg of body weight) in a 12-month prospective study of 29 patients with ocular onchocerciasis and 15 patients with onchocerciasis without ocular involvement. The patients lived in a hyperendemic area in Sierra Leone, West Africa, where no vector control was instituted. Five months after initial treatment, the microfilarial load in skin and eyes had decreased significantly (P less than .0000), but 28 of 44 (63%) patients had positive skin-snip test results and nine of 29 (31%) patients with ocular involvement had active ocular disease. Twelve months after initial treatment, 15 of 41 (37%) patients had positive skin-snip test results and eight of 26 (31%) showed active ocular involvement. All patients with persistent ocular disease after therapy showed evidence of active onchocerciasis at that time, which suggests that a dose of ivermectin at six-month intervals is not sufficient for intensely infested patients with severe ocular disease. We developed an ocular involvement score to evaluate the patient's total ocular status and observed a significant relation between the pretreatment severity of ocular involvement and the persistence of active ocular disease after treatment with ivermectin.

Onchocerciasis

Onchocerciasis is a devastating blinding disease caused by the parasite Onchocerca volvulus that infects about 80 million people, causing blindness and visual impairment in 1-2 million people. In hyperendemic areas, more than half of the population will become blind from onchocerciasis before they die. Blindness is the most important effect of the disease and results, in part, from direct invasion of the eye by microfilariae. The recent development of ivermectin has revolutionized our ability to treat this disease. An annual oral dose of only 150 mg/kg completely suppresses the disease manifestations. Programs for the community-based mass distribution of ivermectin are now being conducted and promise to control this major blinding scourge.

Ivermectin: a long-acting microfilaricidal agent

Ivermectin is a macrocyclic lactone (fermentation) product and actinomycete (Streptomyces avermitilis) that possesses an unusually broad spectrum of potent activity against several species of nematodes, arachnids, and insects that parasitize domestic animals. From clinical trials in humans it has been found to be microfilaricidal, killing microfilariae of Onchocerca volvulus (the parasite causing onchocerciasis), and interrupting its transmission by the black fly vector. Dermal microfilariae density in patients are reduced to near zero levels for 6-12 months after a single oral dose of ivermectin 0.15-0.2 mg/kg. Its precise mechanism of action is unknown. It has a time to maximum concentration of 2.7-4.3 h, and an elimination half-life of 28 +/- 10 h. When compared with an oral solution the tablet dosage form has a relative bioavailability of approximately 60 percent. Not much is known about its metabolism in humans, and the unchanged drug is not detected in the urine. Controlled clinical trials have shown ivermectin to be associated with milder side effects than diethylcarbamazine, the current drug of choice for onchocerciasis therapy. It does not cause the severe Mazzoti-type (anaphylactoid) reactions that are associated with diethylcarbamazine use. Ivermectin is effective, safer, and more tolerable than diethylcarbamazine. It should, therefore, replace diethylcarbamazine as the drug of choice for onchocerciasis therapy.

Changes in ocular onchocerciasis four and twelve months after community-based treatment with ivermectin in a holoendemic onchocerciasis focus

The impact of ivermectin mass treatment on ocular onchocerciasis was studied in a holoendemic focus of blinding onchocerciasis in Ghana. A cohort of 417 persons, 369 of whom were treated, was followed up at 4 and 12 months after treatment. The mean ocular microfilarial load in the anterior chamber of the eye and in the cornea of treated persons was reduced to less than 20% and 10% of the pretreatment levels respectively at the 4 months follow-up but had increased significantly by 12 months. Lesions of the eye at the advanced stage of development remained stable. There was significant regression of early lesions of the anterior segment of the eye, particularly iridocyclitis, after ivermectin treatment. In view of the substantial increase of ocular microfilarial loads after 12 months, 6-monthly treatment may be indicated in such highly endemic foci. However, long-term observation is needed to give a correct estimate of the full benefit to be derived from mass treatment with ivermectin.

Ivermectin treatment of onchocerciasis

Ivermectin is a recently developed macrocyclic lactone that has widespread antiparasitic activity. A series of clinical trials has shown that ivermectin is safe and effective in the treatment of human infection with Onchocerca volvulus. Although it is rapidly microfilaricidal, it does not cause a severe reaction as is seen with diethylcarbamazine treatment. The drug also temporarily interrupts production of microfilaria but has no known long-lasting effects on the adult worms. In patients with onchocerciasis, a single oral dose of ivermectin (150 micrograms/kg) repeated once a year leads to a marked reduction in skin microfilaria counts and ocular involvement. At this dose, ivermectin causes minimal side effects and appears to be sufficiently free of severe adverse reactions to be used on a mass scale. Its use promises to revolutionise the treatment of onchocerciasis.

Side-effects of ivermectin in treatment of onchocerciasis

In a prospective study to determine the tolerance for and safety of ivermectin therapy for onchocerciasis in a hyperendemic area in Sierra Leone, 28 (32%) of 87 patients had adverse reactions that required treatment with acetylsalicylic acid and antihistamines, but none of the observed adverse reactions were considered life-threatening. A significant relation was found between the frequency and severity of side-effects and the degree of parasite infestation, as quantified by the skin-snip counts. Free administration of ivermectin to severely infected onchocerciasis patients is not recommended without some form of medical supervision.

Effect of single-dose ivermectin therapy on human Onchocerca volvulus infection with onchocercal ocular involvement

Ivermectin has shown promise as a potentially safe and effective microfilaricidal drug for the treatment of onchocerciasis. Several limited studies have shown it to have fewer side effects, especially ocular complications, than the currently available drug, diethylcarbamazine. The detailed ocular findings in 200 moderately to heavily infected Liberians who were enrolled in a safety and dose-finding study are presented. They received either 0, 100, 150, or 200 micrograms/kg of ivermectin and were followed up for 12 months. In clinical studies so far carried out ivermectin in a dose of 100, 150, or 200 micrograms/kg has not been associated with any major adverse reactions nor were there any sight-threatening effects even in the presence of severe ocular disease. Each of these doses significantly reduced the ocular microfilaria load for at least 12 months when compared with either the placebo (p less than 0.05) or pretreatment values (p less than 0.001). However, the 100 and 150 micrograms/kg doses caused fewer minor side effects than the higher dose. These results confirm that ivermectin in a single oral dose may be a safe and effective microfilaricidal drug for the treatment of onchocerciasis and that it appears to be free of major ocular side effects.

Onchocerciasis--a potential revolution in its treatment

Onchocerciasis is a major blinding disease affecting at least 28 million people in Africa and Latin America. Although a large-scale vector control program has been highly successful in limiting transmission of infection in West Africa, there has not been a satisfactory form of treatment available for those already infected or those living in other areas. Despite the fact that two drugs, diethylcarbamazine and suramin, are active against the filarial parasite that causes onchocerciasis, their use is severely limited by their toxicity and the reaction they induce. A newly developed drug, ivermectin, appears to offer a major revolution in the treatment of onchocerciasis. In a series of clinical trials, ivermectin has been shown to be an extremely effective microfilaricide which induces only minimal side effects. Ivermectin is given as a single oral dose which can be repeated on an annual basis. In view of its safety and efficacy and its ease of administration, it seems likely that ivermectin will be suitable for use in mass chemotherapy programs against onchocerciasis.