Severe onchocercal dermatitis in the Ethiopian border region of Sudan

The Galabat-Metema cross-border onchocerciasis focus: The first coordinated interruption of onchocerciasis transmission in Africa

Background

Onchocerciasis transmission across international borders is not uncommon, yet a coordinated cross border stops mass drug administration (MDA) decision has not been documented.

Methods/Principle findings

The Galabat-Metema focus involves neighboring districts on the border between Sudan and Ethiopia. Mass drug administration (MDA) was provided once and subsequently twice per year in this focus, with twice-per-year beginning in Ethiopia’s Metema subfocus in 2016 and in the Sudan’s Galabat subfocus in 2008. Ov16 ELISA-based serosurveys were conducted in 6072 children under 10 years of age in the Metema subfocus in 2014, and 3931 in the Galabat in 2015. Between 2014 and 2016, a total of 27,583 vector Simulium damnosum flies from Metema and 9,148 flies from Galabat were tested by pool screen PCR for Onchocerca volvulus O-150 DNA. Only 8 children were Ov16 seropositive (all in the Metema subfocus); all were negative by skin snip PCR. The upper limit of the 95% confidence interval (UCL) for Ov16 seropositive was <0.1% for the overall focus and 0.14 positive fly heads per 2000 (UCL = 0.39/2000). However, an entomological ‘hotspot’ was detected on the Wudi Gemzu river in Metema district. The hotspot was confirmed when 4 more positive fly pools were found on repeat testing in 2017 (1.04 L3/2000 flies (UCL = 2.26/2000). Information exchange between the two countries led to stopping MDA in a coordinated fashion in 2018, with the exception of the hotspot at Wudi Gemzu, where MDA with ivermectin was increased to every three months to hasten interruption of transmission.

Conclusion

Coordinated stop MDA decisions were made by Sudan and Ethiopia based on data satisfying the World Health Organization’s criteria for interruption of onchocerciasis transmission. Definitions of entomological ‘hotspots’ and buffer zones around the focus are proposed.

Onchocerciasis is a vector-borne tropical disease caused by the parasitc worm, Onchocerca volvulus. The vector is Simulium flies that breed in fast flowing rivers and streams. The infection can cause skin disease and loss of vision, giving risk to the common name of ‘river blindness’ for the condition. Ivermectin (Mectizan) mass drug administration (MDA) given at high coverage for many years can interrupt transmission such that MDA can eventually be stopped. The present paper provides highlights of onchocerciasis transmission interruption in the first known coordinated international cross border focus with ivermectin MDA program in Africa, where 99% of the global onchocerciasis burden exists. This focus known as Galabat-Metema is shared between Ethiopia and Sudan, both of which have established a nationwide policy for elimination of onchocerciasis. The paper provides the history of MDA in the border area and the results leading a coordinated end to MDA in the focus in 2017.

Notes on distribution of Simulium damnosum s. l. along Atbara River in Galabat sub-focus, eastern Sudan

Background

Onchocerciasis is caused by a nematode worm Onchocerca volvulus, which is transmitted in Sudan by black fly vectors of the Simulium damnosum sensu lato species complex. In Sudan, the disease is found in four foci where fast flowing rivers provide suitable breeding sites for the Simulium vector flies. The construction of dams and irrigation schemes for agricultural purposes has affected black fly breeding and distribution, such as in Merowe Dam in Abu-Hamed focus, where the perennially flowing water downstream of the Dam created new vector breeding sites, thereby, changing the pattern of disease transmission and creating public health problems. Based on this situation, this study was carried out to measure the effect of the Upper Atbara and Setit Dam complex on the distribution of Simulium damnosum s.l. breeding sites and on disease elimination in the Galabat sub-focus in eastern Sudan.

Methods

Aquatic stages of Simulium were collected between October and November 2009, prior to the construction of the dam complex, and again in 2013 and 2015 while the dam complex construction was ongoing.

Results

A total of 40 breeding sites were identified at the beginning of the study. After the construction of the dam complex in 2015, seventeen previously mapped breeding sites were inaccessible as they had been flooded by the dam complex’s lake when reach its maximum size. Three species were obtained from different locations: S. damnosum s.l., S. griseicolle, and S. adersi.

Conclusions

This study has shown a link between the construction of the dam complex and a reduction in the breeding sites of black fly vectors. This reduction has limited the Galabat sub-focus to a small area at the upper Atbara River which become the end of the focus. To sustain the success achieved in onchocerciasis control in the Galabat sub-focus, disease control and its vector control should be strengthened in the area cross-boarding Sudan and Ethiopia.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4113-1) contains supplementary material, which is available to authorized users.

Pre-control relationship of onchocercal skin disease with onchocercal infection in Guinea Savanna, Northern Nigeria

Background

Onchocerca volvulus infection can result in blindness, itching and skin lesions. Previous research concentrated on blindness.

Methods

A clinical classification system of the cutaneous changes in onchocerciasis was used for the first time in this study within the context of an early ivermectin drug trial in the savanna region of Kaduna State, northern Nigeria. Skin examinations were performed in 6,790 individuals aged 5+ years in endemic communities and 1,343 individuals in nonendemic communities.

Results / Discussion

There was increased risk for all forms of onchocercal skin disease in endemic communities with the most common finding being the presence of nodules (1,438 individuals, 21.2%), followed by atrophy (367, 6.1% of those < 50 years), acute papular onchodermatitis, APOD (233, 3.4%), depigmentation (216, 3.2%) and chronic papular onchodermatitis, CPOD (155, 2.3%). A further 645 individuals (9.5%) complained of pruritus but had completely normal skin. APOD was more common in males whereas atrophy, hanging groin and nodules were more common in females. After controlling for age and sex, microfilarial positivity was a risk factor for CPOD, depigmentation, hanging groin and nodules (OR 1.54, p = 0.046; OR 2.29, p = 0.002; OR 2.18, p = 0.002 and OR 3.80, p <0.001 respectively). Comparable results were found using presence of nodules as the marker for infection. Microfilarial load showed similar, though weaker, results. A total of 2621(38.6%) endemic residents had itching with normal skin, or had one or more types of onchocercal skin disease including nodules, which may be considered as a composite index of the overall prevalence of onchocercal skin disease.

Conclusion

Significant levels of onchocercal skin disease were documented in this savanna area, which subsequently resulted in a reassessment of the true burden of skin disease in onchocerciasis. This paper represents the first detailed report of the association of onchocercal skin disease with markers for onchocercal infection.

Onchocerciasis is a tropical parasitic infection caused by the nematode worm Onchocerca volvulus. The disease mainly occurs across tropical Africa and infection can result in blindness, debilitating itching and a variety of skin changes. Initial research concentrated mainly on the problem of blindness. A number of studies on onchocercal skin disease were performed but were difficult to interpret and compare because of the use of inconsistent terminology. Within the setting of one of the early trials of ivermectin in a savanna area of northern Nigeria, where there were known high rates of onchocercal blindness, we used a novel clinical classification of the skin changes in onchocerciasis. We identified significant levels of itching and various forms of onchocercal skin disease within these endemic communities. A positive skin-snip result proved to be a significant risk factor for the presence of chronic papular onchodermatitis (CPOD), depigmentation, hanging groin and onchocercal nodules. Comparable results were found when the presence of nodules was used as the marker for infection and similar, though weaker odds ratios were found with microfilarial load per se. The findings triggered a reassessment of the true burden of skin disease in onchocerciasis. It is the first detailed report of the association between onchocercal skin disease and markers of infection.

Seasonal Variation in Biting Rates of Simulium damnosum sensu lato, Vector of Onchocerca volvulus, in Two Sudanese Foci

Background

The abundance of onchocerciasis vectors affects the epidemiology of disease in Sudan, therefore, studies of vector dynamics are crucial for onchocerciasis control/elimination programs. This study aims to compare the relative abundance, monthly biting-rates (MBR) and hourly-based distribution of onchocerciasis vectors in Abu-Hamed and Galabat foci. These seasonally-based factors can be used to structure vector control efforts to reduce fly-biting rates as a component of onchocerciasis elimination programs.

Methods

A cross-sectional study was conducted in four endemic villages in Abu-Hamed and Galabat foci during two non-consecutive years (2007–2008 and 2009–2010). Both adults and aquatic stages of the potential onchocerciasis vector Simulium damnosum sensu lato were collected following standard procedures during wet and dry seasons. Adult flies were collected using human landing capture for 5 days/month. The data was recorded on handheld data collection sheets to calculate the relative abundance, MBR, and hourly-based distribution associated with climatic factors. The data analysis was carried out using ANOVA and Spearman rank correlation tests.

Results

Data on vector surveillance revealed higher relative abundance of S. damnosum s.l. in Abu- Hamed (39,934 flies) than Galabat (8,202 flies). In Abu-Hamed, vector populations increased in January-April then declined in June-July until they disappeared in August-October. Highest black fly density and MBR were found in March 2007 (N = 9,444, MBR = 58,552.8 bites/person/month), and March 2010 (N = 2,603, MBR = 16,138.6 bites/person/month) while none of flies were collected in August-October (MBR = 0 bites/person/month). In Galabat, vectors increased in September-December, then decreased in February-June. The highest vector density and MBR were recorded in September 2007 (N = 1,138, MBR = 6,828 bites/person/month) and September 2010 (N = 1,163, MBR = 6,978 bites/person/month), whereas, none appeared in collection from April to June. There was a significant difference in mean monthly density of S. damnosum s.l. across the two foci in 2007–2008 (df = 3, F = 3.91, P = 0.011). Minimum temperature showed significant correlation with adult flies counts in four areas sampled; the adult counts were increased in Nady village (r_s = 0.799) and were decreased in Kalasecal (r_s = - 0.676), Gumaiza (r_s = - 0.585), and Hilat Khateir (r_s = - 0.496). Maximum temperature showed positive correlation with black fly counts only in Galabat focus. Precipitation was significantly correlated with adult flies counts in Nady village, Abu-Hamed, but no significance was found in the rest of the sampled villages in both foci. Hourly-based distribution of black flies showed a unimodal pattern in Abu-Hamed with one peak (10:00–18:00), while a bimodal pattern with two peaks (07:00–10:00) and (14:00–18:00) was exhibited in Galabat.

Conclusion

Transmission of onchocerciasis in both foci showed marked differences in seasonality, which may be attributed to ecology, microclimate and proximity of breeding sites to collection sites. The seasonal shifts between the two foci might be related to variations in climate zones. This information on black fly vector seasonality, ecology, distribution and biting activity has obvious implications in monitoring transmission levels to guide the national and regional onchocerciasis elimination programs in Sudan.

Chemotherapy in the treatment, control, and elimination of human onchocerciasis

Onchocerciasis treatment is one of the most positive stories in tropical medicine although major challenges remain to reaching the ultimate goal of disease elimination. Such challenges are to be expected when the therapeutic goal is to kill and safely remove a large multistage, efficient, metazoan infectious agent such as Onchocerca volvulus that has an exceptionally complicated relationship with its host. Successful control of onchocerciasis has often been hampered by host reactions following chemotherapy, that can sometimes cause significant tissue pathology. Presence of other filariae, particularly Loa loa, in endemic onchocerciasis-treatment areas also poses severe problems due to adverse reactions caused by drug-induced death of the coincident microfilariae of this usually clinically benign species. Although ivermectin has been very successful, there is a need to enhance the progress toward elimination of onchocerciasis; new drugs and their efficient use are keys to this. The permanent absence of Onchocerca microfilaridermia, defined as the lack of resurgence of skin microfilarial loads after treatment, is the ultimate characteristic of a useful new chemotherapeutic agent. Several drugs are under investigation to achieve this, including the reassessment of currently available and previously tested agents, such as the antibiotic, doxycycline, which targets the adult parasites through its anti-Wolbachia endosymbiont activity. Flubendazole, a benzimidazole derivative approved for treatment of human gastrointestinal nematodes, is also being considered for repurposing as a macrofilaricide to aid in the achievement of eradication. The managerial challenges existing at the population level also need to be addressed; these include drug-distribution fatigue, the need to include noncompliant people, civil unrest in endemic areas, political cross-border issues, restrictions of age and pregnancy, and complications due to integration with other treatment programs. It is likely that a panel of chemotherapeutic options, new and old, supported by strong and effective distribution systems will be the best way to address challenges of treatment and elimination of this infection. Future research should also address management of treatment and control, and consider how new treatment paradigms can be incorporated to meet time lines set for global elimination by 2025.

Detection of circulating parasite-derived microRNAs in filarial infections

Filarial nematodes cause chronic and profoundly debilitating diseases in both humans and animals. Applications of novel technology are providing unprecedented opportunities to improve diagnosis and our understanding of the molecular basis for host-parasite interactions. As a first step, we investigated the presence of circulating miRNAs released by filarial nematodes into the host bloodstream. miRNA deep-sequencing combined with bioinformatics revealed over 200 mature miRNA sequences of potential nematode origin in Dirofilaria immitis-infected dog plasma in two independent analyses, and 21 in Onchocerca volvulus-infected human serum. Total RNA obtained from D. immitis-infected dog plasma was subjected to stem-loop RT-qPCR assays targeting two detected miRNA candidates, miR-71 and miR-34. Additionally, Brugia pahangi-infected dog samples were included in the analysis, as these miRNAs were previously detected in extracts prepared from this species. The presence of miR-71 and miR-34 discriminated infected samples (both species) from uninfected samples, in which no specific miRNA amplification occurred. However, absolute miRNA copy numbers were not significantly correlated with microfilaraemia for either parasite. This may be due to the imprecision of mf counts to estimate infection intensity or to miRNA contributions from the unknown number of adult worms present. Nonetheless, parasite-derived circulating miRNAs are found in plasma or serum even for those species that do not live in the bloodstream.

Filarial parasites commonly infect humans and animals, especially in tropical settings. The strongly debilitating panel of diseases they cause in humans contributes to an entrenched cycle of poverty. For efficient treatment strategies, reliable diagnostic tests are necessary. We investigated the potential of parasite-derived microRNAs (miRNAs; short non-coding RNA molecules present in eukaryotes) as biomarkers of infection. Using deep-sequencing technologies and bioinformatics, we identified over two-hundred mature miRNA candidates of nematode origin in plasma from Dirofilaria immitis-infected dogs. Similarly, we discovered twenty-one miRNA candidates predicted to be released by Onchocerca volvulus in infected human sera. We developed two RT-qPCR assays for the detection of D. immitis miR-71 and miR-34 in dog plasma that discriminated infected from uninfected samples. We demonstrated the presence of filarial miRNAs in host blood, regardless of localization in their respective hosts, and suggest that they are suitable targets for detection by RT-qPCR.

Modelling the impact of ivermectin on River Blindness and its burden of morbidity and mortality in African Savannah: EpiOncho projections

Background

The African Programme for Onchocerciasis Control (APOC) has refocused its goals on the elimination of infection where possible, seemingly achievable by 15–17 years of annual mass distribution of ivermectin in some African foci. Previously, APOC had focused on the elimination of onchocerciasis as a public health problem. Timeframes have been set by the World Health Organization, the London Declaration on Neglected Tropical Diseases and the World Bank to achieve these goals by 2020–2025.

Methods

A novel mathematical model of the dynamics of onchocercal disease is presented which links documented associations between Onchocerca volvulus infection and the prevalence and incidence of morbidity and mortality to model outputs from our host age- and sex-structured onchocerciasis transmission framework (EpiOncho). The model is calibrated for African savannah settings, and used to assess the impact of long-term annual mass administration of ivermectin on infection and ocular and skin disease and to explore how this depends on epidemiological and programmatic variables.

Results

Current onchocerciasis disease projections, which do not account for excess mortality of sighted individuals with heavy microfilarial loads, underestimate disease burden. Long-term annual ivermectin treatment is highly effective at reducing both the morbidity and mortality associated with onchocerciasis, and this result is not greatly influenced by treatment coverage and compliance. By contrast, impact on microfilarial prevalence and intensity is highly dependent on baseline endemicity, treatment coverage and systematic non-compliance.

Conclusions

The goals of eliminating morbidity and infection with ivermectin alone are distinctly influenced by epidemiological and programmatic factors. Whilst the former goal is most certainly achievable, reaching the latter will strongly depend on initial endemicity (the higher the endemicity, the greater the magnitude of inter-treatment transmission), advising caution when generalising the applicability of successful elimination outcomes to other areas. The proportion of systematic non-compliers will become far more influential in terms of overall success in achieving elimination goals.

Interruption of Onchocerca volvulus transmission in the Abu Hamed focus, Sudan

Abu Hamed, Sudan, the northernmost location of onchocerciasis in the world, began community-directed treatment with ivermectin (CDTI) in 1998, with annual treatments enhanced to semiannual in 2007. We assessed the status of the parasite transmission in 2011 entomologically, parasitologically, and serologically. O-150 pool screening showed no parasite DNA in 17,537 black flies collected in 2011 (95% confidence interval upper limit [95% CI UL] = 0.023). Skin microfilariae, nodules, and signs of skin disease were absent in 536 individuals in seven local communities. Similarly, no evidence of Onchocerca volvulus Ov16 antibodies was found in 6,756 school children ≤ 10 years (95% CI UL = 0.03%). Because this assessment of the focus meets the 2001 World Health Organization (WHO) criteria for interrupted transmission, treatment was halted in 2012, and a post-treatment surveillance period was initiated in anticipation of declaration of disease elimination in this area. We provide the first evidence in East Africa that long-term CDTI alone can interrupt transmission of onchocerciasis.

Elimination of onchocerciasis from Africa: possible?

Human onchocerciasis, a parasitic disease found in 28 African countries, six Latin American countries and Yemen, causes blindness and severe dermatological problems. In 1987, efforts to control this infection shifted from vector approaches to include the mass distribution of ivermectin - a drug donated by Merck & Co. for disease control in Africa and for disease elimination in the Americas. Currently, almost 25 years later, with the Americas being highly successful and now approaching elimination, new evidence points towards the possibility of successful elimination in Africa. We suggest several major changes in the programmatic approach that through focused goal-directed effort could achieve global elimination of onchocerciasis by 2025.

Polymerase chain reaction pool screening used to compare prevalence of infective black flies in two onchocerciasis foci in northern Sudan

Onchocerciasis remains an important debilitating disease in many areas of Africa, including Sudan. The status of infection transmission in 2007 was assessed in the vectors of two disease foci in Sudan: Abu Hamed in northern Sudan, which has received at least 10 years of annual treatment and Galabat focus in eastern Sudan, where only minor, largely undocumented treatment activity has occurred. Assessment of more than 30,000 black flies for Onchocerca volvulus infectious stage L3 larvae by using an O-150 polymerase chain reaction protocol showed that black fly infectivity rates were 0.84 (95% confidence interval = 0.0497-1.88) per 10,000 flies for Abu Hamed and 6.9 (95% confidence interval = 1.1-16.4) infective flies per 10,000 for Galabat. These results provide entomologic evidence for suppressed Onchocerca volvulus transmission in the Abu Hamed focus and a moderate transmission rate of the parasite in the Galabat focus.

Clinical responses in human onchocerciasis: parasitological and immunological implications

Onchocerciasis can cause severe dermal and ocular disease due, it is thought, to the events surrounding the destruction of the microfilarial stage. The evolution of papular pruritic dermatitis and punctate keratitis is clearly related to the killing of microfilariae. Other more chronic changes such as dermal and epidermal atrophy are probably due to repeated episodes of microfilarial killing. It is common to find that not all patients are, at any one time, mounting clinically obvious destructive host responses against the microfilariae, and such individuals can carry very high loads of parasites without any apparent adverse effects. The immunological basis of the differences between these types of patients forms one of the most important questions in the pathogenesis of onchocerciasis today. Various explanations are now emerging. These include immunosuppressive factors and variation in the form of Onchocerca volvulus antigens presented to the host. Clinical presentations of this disease appear to reflect variations in host responses and can be used to provide information concerning the protective immune responses an individual can mount against this parasite.

Cell adherence to microfilariae of Onchocerca volvulus: a comparative study

The conditions were examined for in vitro antibody-mediated adherence of granulocytes to microfilariae of Onchocera volvulus and Dirofilaria immitis. Reactivity in human sera from patients in endemic foci in Sudan was specific for O. volvulus and no reactions were observed with heterologous Onchocerca species or with Mansonella perstans. Microfilariae from skin, nodules or adult female worms were satisfactory targets for cell adherence, and the cells involved were almost exclusively eosinophils. The reaction was inhibited by indomethacin but not by nordihydroguaiaretic acid, an inhibitor of leukotriene production. Agents that slowed or stopped microfilarial motility (e.g. nifedipine, lidocaine, chloroquine) inhibited the reaction, probably by reducing target/cell contact. Ivermectin did not enhance the reaction, and in the absence of cells exerted only slight effects on the movement of microfilariae at higher concentrations (greater than 10 micrograms/ml). Antibody activity was labile, and did not persist well through freeze-thaw cycles. Some differences between homologous and heterologous mixtures (microfilariae/cells/serum) were seen but they could not be resolved satisfactorily. There were no apparent geographical differences between microfilariae from different foci in Sudan. In the D. immitis system neutrophils were the dominant cell type adhering to microfilariae, and the activity was stable to storage and freeze-thaw. No enhancement was detectable with diethylcarbamazine. Antibody activity was absorbable with microfilarial antigens and was reduced by agents that inhibited microfilarial motility. In dogs, adherence-mediating antibody was seen only in amicrofilaraemic animals with occult infection, and in only a minority of these sera. In humans the relationship to clinical findings was less clear, but patients with punctate keratitis were the most likely to have positive serum and were the most reactive in the assay. This system may therefore offer some insights into disease mechanisms in vivo, and its molecular mechanisms deserve further characterization.

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.

Cutaneous pathology in onchocerciasis associated with pronounced systemic T-helper 2-type responses to Onchocerca volvulus

BACKGROUND

Of 18 million people world-wide who are infested with the tissue nematode Onchocerca volvulus, more than 30% are considered to have skin lesions, the pathomechanisms of which are poorly understood.

OBJECTIVES

To relate skin changes associated with onchocerciasis to parasitological findings and systemic cellular immune responses.

METHODS

In the course of a genetic study, 691 members of 241 families exposed to hyperendemic O. volvulus transmission and free of other filarial or schistosomal infestations were studied clinically, by counting palpable Onchocerca nodules and skin microfilariae, by measuring peripheral blood cell (PBC) counts and total serum IgE, and by determining PBC in vitro proliferation and cytokine secretion in response to O. volvulus antigen.

RESULTS

Of 691 individuals studied, 219 presented with onchocerciasis-associated skin changes. The groups of individuals with and without skin lesions neither differed in prevalences nor in average numbers of microfilariae. Compared with individuals without skin lesions, pronounced systemic T-helper (Th) 2-type responses were found with a trend of increasing intensity in the order of depigmentation, papular dermatitis, atrophy and lichenified dermatitis. Differences between the groups were most pronounced for serum IgE, less so for eosinophilia, and relatively weak for PBC proliferation and interleukin-5 secretion.

CONCLUSIONS

Skin lesions in onchocerciasis are associated with a spectrum of increasing generalized Th2-type responses ranging from low reactivities in cases of depigmentation alone to strong reactivities in cases of lichenification.

Onchocerciasis: the clinical and epidemiological burden of skin disease in Africa

An attempt was made to assess the true public-health importance of onchocercal skin disease throughout the African region and hence provide an objective basis for the rational planning of onchocerciasis control in the area. The seven collaborative centres that participated in the study (three in Nigeria and one each in Ghana, Cameroon, Tanzania and Uganda) were all in areas of rainforest or savannah-forest mosaic where onchocercal blindness is not common. A cross-sectional dermatological survey was undertaken at each site following a standard protocol. At each site, the aim was to examine at least 750 individuals aged 5 years and living in highly endemic communities and 220-250 individuals aged 5 years and living in a hypo-endemic (control) community. Overall, there were 5459 and 1451 subjects from hyper-and hypo-endemic communities, respectively. In the highly endemic communities, the prevalence of itching increased with age until 20 years and then plateaued, affecting 42% of the population aged 20 years. There was a strong correlation between the prevalence of itching and the level of endemicity (as measured by the prevalence of nodules; r=0.75; P<0.001). The results of a multivariate logistic regression analysis showed that, at the individual level, the presence of onchocercal reactive skin lesions (acute papular onchodermatitis, chronic papular onchodermatitis and/or lichenified onchodermatitis) was the most important risk factor for pruritus, with an odds ratio (OR) of 18.3 and 95% confidence interval (CI) of 15.19-22.04, followed by the presence of palpable onchocercal nodules (OR=4.63; CI=4.05-5.29). In contrast, non-onchocercal skin disease contributed very little to pruritus in the study communities (OR=1.29; CI=1.1-1.51). Onchocercal skin lesions affected 28% of the population in the endemic villages. The commonest type was chronic papular onchodermatitis (13%), followed by depigmentation (10%) and acute papular onchodermatitis (7%). The highest correlation with endemicity was seen for the prevalence of any onchocercal skin lesion and/or pruritus combined (r=0.8; P<0.001). Cutaneous onchocerciasis was found to be a common problem in many endemic areas in Africa which do not have high levels of onchocercal blindness. These findings, together with recent observations that onchocercal skin disease can have major, adverse, psycho-social and socio-economic effects, justify the inclusion of regions with onchocercal skin disease in control programmes based on ivermectin distribution. On the basis of these findings, the World Health Organization launched a control programme for onchocerciasis, the African Programme for Onchocerciasis Control (APOC), that covers 17 endemic countries in Africa.

Onchocerca volvulus: genetic diversity of parasite isolates from Sudan

Onchocerciasis in Sudan exists in three distinct foci which exhibit differing clinical presentations. Previous studies have demonstrated that a tandemly repeated Onchocerca sequence family with a unit repeat length of 150 bp (the O-150 family) is a useful marker for deducing relationships among different O. volvulus populations. In the current study, the O-150 repeat families of O. volvulus from Sudan were analyzed and compared to each other and to those of parasites from West Africa. Similar to West African and American O. volvulus, the O-150 families of the Sudanese parasites could be divided into clusters within which little or no intracluster variation was evident, suggesting that the O-150 family in these parasites was subject to the forces of concerted evolution. Statistical analysis of the O-150 families from the different Sudanese parasite isolates, employing a nested algorithm based on an analysis of variance, revealed that O. volvulus endemic to the northern focus at Abu Hamed were significantly different from all other O. volvulus populations examined to date. In contrast, parasites from the southern and eastern foci of Sudan were indistinguishable from those endemic to the West African savanna. The significance of these data are discussed in light of knowledge of the biogeography and biology of transmission of O. volvulus in Africa.

Community based distribution of ivermectin in eastern Sudan: acceptability and early post-treatment reactions

A study to monitor ivermectin acceptability and post-treatment reactions during mass community distribution was carried out in eastern Sudan, where severe reactive onchodermatitis is prevalent. Of 1081 individuals eligible for treatment, 1076 (99.5%) accepted the ivermectin. Post-treatment reactions were monitored by self reporting, 5 d after a single dose of about 150 micrograms/kg (range 103-200 micrograms/kg); 230 persons reported adverse events (21.4%). No reaction was rated as severe. The most common problem was itching with cutaneous papular eruptions (16.2%). Local oedematous swelling was the second most common and the most slowly resolving complaint (5.4%), followed by musculoskeletal pain. There was a high acceptance rate of the treatment and remarkable tolerance of the post-treatment effects, probably due to efforts made to prepare the community to expect reactions to ivermectin, widespread awareness of the beneficial effects of treatment by villagers who had participated in clinical trials previously, and the encouragement we gave to the population to become involved in improvement of their health care services. Single doses of ivermectin resulted in good clinical responses and created much goodwill among villagers. Improvements in physical fitness, ability to work, and freedom from musculoskeletal pain were reported at the 3 months' follow-up. We recommend that, during mass distribution of ivermectin, community involvement in planning overall health improvement should be included, since the treatment initiates the process well. In areas where sowda syndrome is prevalent, medical surveillance for 3 d or more should be considered.

Ivermectin treatment in severe asymmetric reactive onchodermatitis (sowda) in Sudan

Ivermectin efficacy and post-treatment reactions in asymmetric severe reactive ochodermatitis (sowda) were studied in 8 patients with sowda syndrome and 6 with mild generalized onchodermatitis in Sudan. Initial skin snips from 12 patients contained microfilariae (1-9 per mg skin). Patients were treated in hospital with a single oral dose of c. 150 micrograms/kg ivermectin (103-200 micrograms/kg) and monitored for frequency and severity of post-treatment reactions for 4 weeks. Serial samples of heparinized blood were collected over the first 24 h after treatment for determination of ivermectin pharmacokinetics. Skin snips from all patients on days 3 and 28 revealed no microfilariae. Post-treatment reactions were more common and severe in individuals with sowda; they consisted mainly of musculoskeletal pain, local swellings with pitting oedema, and lymph gland tenderness and enlargement. No relation was established between these reactions, the microfilarial infection intensity, or the plasma pharmacokinetic profiles. A single oral dose of ivermectin cleared the skin of microfilariae and led to improvement of symptoms and dermatological signs of sowda, but resulted in more marked reactions than in cases of generalized onchodermatitis.

A clinical classification and grading system of the cutaneous changes in onchocerciasis

Although onchocerciasis is one of the most important diseases of the skin and eye in the tropical world, to date there has been no formal consensus regarding the description and terminology of skin lesions. Furthermore, the contribution of cutaneous pathology to the morbidity and socio-economic effects of the disease has been largely neglected. We present a clinical classification and grading system for recording the cutaneous changes of onchocerciasis, and propose that this system be used as a standard method of description to convey clinical information between workers in all endemic areas to assist local and comparative research.

Adverse reactions to ivermectin treatment for onchocerciasis. Results of a placebo-controlled, double-blind trial in Malawi

A three-year placebo-controlled, double-blind trial involving 7148 persons was conducted to determine adverse reactions to ivermectin given annually for treatment of onchocerciasis by mass distribution. Musculoskeletal pains, oedema of the face or extremities, itching and papular rash were statistically associated with ivermectin treatment in the first year. In the second year of treatment these reactions were less frequently reported, although still more prevalent in ivermectin recipients. During the third year of treatment all persons received ivermectin. Persons who had missed ivermectin treatment in the second year did not have significantly more adverse reactions after treatment in the third year. Those who had received placebo during the first 2 years reported some adverse reactions more frequently following ivermectin than did those who had received ivermectin from the beginning of the study. Oedema was the adverse reaction of greatest concern to patients and this involved the face most commonly. A single episode of bullous skin lesions developed in 5 persons who had received ivermectin. These lesions did not reoccur with subsequent treatment. No episode of hypotension after treatment was observed.

The profile of IgG and IgG subclasses of onchocerciasis patients

In this study Onchocerca gutturosa was compared with O. volvulus in an ELISA test to detect Onchocerca-specific IgG and IgG subclasses. The test was developed and standardized to detect Onchocerca-specific IgG and IgG subclasses in sera of onchocerciasis patients and endemic controls. Onchocerca volvulus and O. gutturosa crude water-soluble antigens showed no significant difference in detecting onchocerca-specific IgG antibody (T = 1.88, P greater than 0.05). The levels of IgG subclasses varied greatly. IgG4 showed the highest detected mean level (0.84 +/- 0.59) and the other three subclasses showed considerably lower mean levels (IgG1 = 0.27 +/- 0.16, IgG2 = 0.24 +/- 0.17, IgG3 = 0.28 +/- 0.12). The status and score of skin lesions were found to have significant effect on the IgG and IgG subclasses levels (all P less than 0.001). IgG4 showed a positive correlation with the microfilarial (Mf) load (r = 0.21, P less than 0.03). IgG3 levels have a significant negative correlation with the Mf load (r = -0.23, P less than 0.02). The biological significance of these IgG and IgG subclasses in onchocerciasis is discussed.

Suppression of human lymphocyte responses to specific and non-specific stimuli in human onchocerciasis

Characterization of in vitro lymphocyte responsiveness was performed on selected groups of onchocerciasis patients from Sudan and Sierra Leone. These patients manifested a very broad range of clinical signs and showed widely divergent parasite infection intensities. Lymphocyte proliferative responses to soluble Onchocerca volvulus antigen (sAg) were poor in infected persons; mitogen and PPD responses were maintained in the normal range in one group of patients from southwestern Sudan, but were profoundly depressed in a group from N.E. Sudan. Proliferative responses and interferon-gamma (INF-gamma) secretion were very significantly depressed in the presence of live microfilariae of O. volvulus or secretions/excretions (S/E) from microfilariae (mf) or from female, but not male, adult parasites. Lymphocyte responses were maintained near normal when exogenous IL-2 was added to these cultures. The results indicate that O. volvulus infection and its clinical consequences are not consistently associated with systemic deficits in immune responsiveness. However, suppression of lymphocyte reactivity by mf and S/E in vitro suggests that direct parasite intervention in host cell responses could be taking place in vivo, perhaps at the local microenvironment level; mediated by effects on cytokine production.

The onchocerciasis focus at Kinsuka/Kinshasa (Republic of Zaire) in 1985. II. Parasitological and clinical aspects

Since the antivectorial control in 1948, the parasitological and clinical aspects of the onchocerciasis focus at Kinsuka/Kinshasa have not been studied further until now. The population examined was selected for its daily contact with the vector. It constituted 143 adults, including fishermen, stonebreakers and women cultivators, and 26 children aged from 10 to 16 years. People were subjected to an ophthalmological examination as well as to an investigation for Onchocerca volvulus microfilariae. Adults were examined for the presence of nodules as well as for dermal and lymphatic manifestations of onchocerciasis. The microfilaria carrier rate (MfCR) was 59.2%. The mean microfilaria density (MfD) was 9.7 mf mg-1. Only 20% of the adults presented with small onchocercal nodules. Cutaneous lesions were mild. Lymphatic complications such as adenolymphocele, hydrocele and elephantiasis of the lower limbs were observed in 18% of the adults. No one was blind from onchocerciasis, although nine patients of 60 years or over had lost the use of one eye. Punctate keratitis occurred commonly in young people. Ocular lesions, except for punctate keratitis, developed progressively after 55 years and they became worse with the degree of infection, age and length of stay. Hyperendemic and insufferable in 1940, onchocerciasis has become, in 1985, hypoendemic and no longer a public health problem. One could deduce that a situation similar to that in Kinsuka may occur within 30 years in other foci which are today hyperendemic and where prophylaxis has been started.

Health aspects of resettlement in Ethiopia

The literature on health implications and effects of government-sponsored resettlement in Ethiopia is reviewed with the objective of providing an initial evaluation of the health status of settlers and the health hazards of resettlement in western Ethiopia. Emphasis is on the 1984/85 resettlement program, which resulted in the movement of about 600,000 drought victims from northern and central Ethiopia to the western part of the country. Malaria, trypanosomiasis, onchocerciasis, yellow fever, nonfilarial elephantiasis, sand-flea infestation, and psychological stress are identified as immediate and greater health hazards than in the areas of settler origin, based on the geographic distribution and ecology of the major communicable, nutritional, and geochemical diseases in Ethiopia, and on the impact of program deficiencies on settler health. More studies are needed on the epidemiology and ecology of bancroftian filariasis, visceral leishmaniasis, dracunculiasis, eye and skin diseases, tuberculosis, meningitis, intestinal parasitism, diarrhea, and calorie/protein malnutrition before their public health and economic significance in settlements can be evaluated. Schistosomiasis appears to be less common, for the time being, in resettlement areas than in the areas of outmigration. Research needs and constraints in resettlement planning, implementation, and operation are identified, and some recommendations made for disease control programs.

Onchodermatitis--correlation between skin disease and parasitic load in an endemic focus in Ecuador

Onchocerciasis is a chronic parasitic infection in which infiltration of the skin by microfilariae has been associated with a number of different pathological changes. This survey compared the prevalence of different forms of skin disease in two villages, one of which was located within the endemic zone for onchocerciasis (Zapallo Grande), in a lowland rain forest area of western Ecuador. The commonest skin diseases in both villages were scabies, pyoderma and pityriasis versicolor. In addition changes closely correlated with the presence of microfilariae in skin snips were found in Zapallo Grande--such as atrophic gluteal changes, and acute and chronic papular dermatitis. The only other skin disease associated with onchocerciasis was widespread tinea corporis due to T. rubrum. The Amerindians in the endemic onchocerciasis area were more likely than Negroes to have generalized atrophic changes of the skin, whereas in the latter group significant numbers of individuals had no obvious skin lesions but large numbers of microfilariae were detected in skin snips. Acute papular dermatitis was common in both groups and in biopsied lesions microfilariae could usually be identified within the epidermis or close to the dermo-epidermal junction. One patient had developed severe reactive onchodermatitis (Sowda). Swabs taken from onchocercal skin lesions showed no evidence of skin surface carriage of Staphylococcus aureus. Changes classically associated with onchocerciasis such as pretibial hypopigmentation (leopard skin) and hanging groin were notably absent in this population.

A histocytochemical study of the macrophages present in tissue responses to adult Onchocerca volvulus

Immunocytochemical and histochemical properties of macrophages present in the subcutaneous chronic inflammatory responses surrounding adult Onchocerca volvulus (nodules) in human tissues were examined. Macrophages with strong non-specific esterase (NSE) and acid phosphatase (AcPase) activities but weak adenosine triphosphatase (ATPase) activity and HLA-DR expression (NSE+++, AcPase+++, ATPase-/+, HLA-DR-/+) were present in the centre of nodules. Many of the cells adhering to the surface of worms were NSE+++, AcPase+++, ATPase-, HLA-DR+++. The inner zone of the fibrous capsule of nodules contained macrophages with the profile NSE+++, AcPase-, ATPase-/+, HLA-DR-/+. A fourth type, NSE+++, AcPase-/+, ATPase-/+, HLA-DR+++, was located in the outer zone of the capsule, frequently within perivascular accumulations of macrophages, lymphocytes and plasma cells. Active fibroblasts were identified at the inner edge of the fibrous capsule by alkaline phosphatase staining. A feature of all nodules examined was the presence of lipid-filled macrophages, demonstrated by Oil Red O stain; these cells were usually situated in zones adjacent to the centre of nodules, and were of the NSE++, AcPase++, ATPase-/+, HLA-DR-/+ type. Lipid accumulation was not found to be related to the clinical status of the patients studied. The origin and functional significance of this lipid is unknown.