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METHODS FOR COMMUNITY DIAGNOSIS OF ONCHOCERCIASIS TO GUIDE IVERMECTIN BASED CONTROL IN AFRICA
Repon of an informal consultation held in Ouagadougou from 19-21 November 1991
UNDP~ORLDBAN~O
Special Programme for Research and Training in Tropical Diseases O'DR)
The geographical designations employed and the presentation of material in this booklet do not imply the expression of any opinion whatsoever on the part of theWorld Health Organization or of the UNDP/WORLD BANK)WHO Special Programme for Research and Training in Tropical Diseases (IDR) concerning the legal status or boundaries of any country, territory, city or area. The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the UNDP/WORLD BANK/WHO Special Programme for Research and Training in Tropical Diseases (IDR) in preference to others of a similar nature that are not mentioned.
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Table of Contents
1. Introduction .......................................................................................................... 1
2. Background ............................................................................................................ 2 3. Risk of onchocercal blindness by endemicity level. ....................................... 3 4. Rapid assessment of endemicity. ....................................................................... 6 5. Public health and socio-economic importance of non-ocular pathology .... 8 6. Summary: rapid assessment methods and indicators for large scale ivermectin treatment ........................................................................ 12 6.1. Rapid assessment methods based on non-invasive examination techniques. ..................................................................................................•........ 12 6.2. Risk of blindness and endemicity levels .................................................. 15 6.3. Criteria for large-scale ivermectin treatment ......................................... 19 6.4. Non-ocular manifestations of onchocerciasis ......................................... 20 7. Conclusions ........................................................................................................... 22 8. Recommendations ............................................................................................... 22
Annex I. Provisional criteria for ivermectin treatment ...................................... 24 Annex II. Guide for the interpretation of crude blindness rates in small
communities .........................•.•..................•....•......•..............•..•••...•.......... 25 Annex
m. List of participants ................................................................................ 26
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1. INTRODUCI'ION An informal consultation on methods for community diagnosis of onchocerciasis to guide ivermectin based control in Africa was held in Ouagadougou, Burkina Faso from
19-21 November 1991. The meeting, which was chaired by Professor LD Edungbola, was sponsored by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (IDR) and hosted by the Onchocerciasis Control Programme in West Africa (OCP). Dr. E.M.Samba, Director of OCP, welcomed participants and stressed the importance of the meeting, particularly for non-OCP countries like Nigeria still in the process of defining the extent of onchocerciasis in their respective countries. He also referred to the advances being made in the area of research, where it is now possible to differentiate between animal and human onchocerciasis as well as between the forest and savanna type of onchocerciasis using the DNA probe technique. The new grounds being covered in the knowledge about the disease was stressed noting however the · paucity of information on the non-ocular pathology of the disease. He suggested that a follow-up be made by IDR to evaluate the implementation of the recommendations of the meeting. Dr. Remme introduced the objectives of the informal consultation which were: 1. To determine the validity of recently proposed indicators of the risk of onchocercal
blindness at the community level and to review recommended threshold values for inclusion of communities in large scale ivermectin treatment campaigns. 2. To determine the validity of rapid assessment methods of onchocerciasis endemicity and the risk of onchocercal blindness at the community level, with emphasis on methods based on non-invasive examination techniques. 3. To review the public health and socio-economic importance of non-ocular manifestations of onchocerciasis and the methods to assess this. 4. To identify priority areas for further research. Dr. Vlassoff stated that the meeting was relevant to the priorities of the IDR steering committee for Social and Economic Research (SER), and several areas in which the SER programme shared the concerns of the meeting were mentioned: - understanding the social and economic impact of onchocerciasis, especially the importance of skin disease.
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- rapid assessment, using social indicators and community participation, for targeting high risk communities; and - cost-effectiveness of different rapid assessment and treatment strategies. SER is currently funding a study of community diagnosis of onchocerciasis using community questionnaire approach in Nigeria which was found to be promising, with respect to targeting high risk areas for urinary schistosomiasis. This approach will be compared with biomedical rapid assessment approaches. · 2. BACKGROUND 2.1. Onchocerciasis control in Africa (Dr. F. Wurapa) Several African countries have recognized onchocerciasis as a public health and socio-economic problem and have embarked on preparations for national control. The cost of vector control, as carried out by the OCP, makes this method unaffordable for the countries outside the Programme area, and the recent introduction of ivermectin as an alternative means of control is a very welcome option for these countries. There is however still the question of who will deliver the drug, the most cost-effective mechanism to deliver the drug and the difficulty of getting services to those who need it most. There is the need to support and to strengthen the Primary Health Care system to be able to assist in the delivery. Other means of support like the activities of the Non-Governmental Organizations will be very useful additions to any mechanisms developed towards the control of onchocerciasis in Africa. In this respect it is vital that these mechanisms are such that they are sustainable and that there is community involvement. 2.2. Meeting on strategies for ivermectin distribution (Dr. S.Resnikoft) A summary of the conclusions and recommendations from a meeting on strategies for ivermecti~ distribution through Primary Health Care system, which was held in Geneva on 22-25, April1991 was provided. The main objectives of this meeting were: - to review the present status of onchocerciasis and ivermectin distribution - including non-governmental programmes - in the OCP area and outside of the OCP area; - to discuss and to compare strategies for community-based and hospital-based distribution systems; - to discuss procurement of ivermectin, logistics of distribution, training of personnel, improvement of public awareness and health education; - to review structures for ivermectin distribution including national plans, non-governmental programmes and inter-country structures. .
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:Among the conclusions and recommendations participants especially highlighted the problem of the identification of the target population for community based distribution and therefore the need for alternative methods of community diagnosis. Ideally, one would treat all persons infected with Onchocerca volvulus. However, logistic realities, dictate that priorities will have to be set so that the most severely affected communities receive treatment first and that treatment programmes then gradually expand to cover all infected communities. Selection of specific individuals for treatment is a far more difficult, unreliable and costly process than selection of communities for large-scale treatment. In some of the worst affected areas, which are usually remote, the resources are severely limited. In such places it may be necessary to concentrate- in the beginning - on communities with higher endemicity levels in which serious eye lesions and blindness are certain to occur. Besides the methods involving skin snips, participants in the meeting suggested 3 rapid assessment methods : - Prevalence of nodules, assuming that the prevalence of a nodule represents half the "true" prevalence of onchocerciasis using all available parameters. -The presence of "leopard skin" on shins is a sign that can be easily detected in adults of either sex, just by looking at the lower legs. But this is more commonly encountered in the "forest" zones of Africa than in hot savannas. - A rapid assessment of total blindness rate can be achieved by asking the head of each compound or household for the number of blind in that compound or household. Blindness rates obtained in this way are likely to include less than all those persons who cannot count finger at 3 meters and they will probably not include those with serious loss of visual fields. For each of these indicators, threshold values had been proposed above which large scale ivermectin treatment was highly desirable or a must (see Annex 1). The Geneva meeting had recommended that these proposed indicators should be validated as soon as possible, making use of available data and pre1iminary results from ongoing studies. It was this recommendation which had led to the present informal consultation in Ouagadougou. 3. RISK OF ONCHOCERCAL BLINDNESS BY ENDEMICI1Y LEVEL 3.1. Blindness patterns in the OCP (Dr. K.Y. Dadzie)
Three types of community patterns of onchocercal ocular disease have been described in the OCP area using an analytical method that relates indices of ocular onchocerciasis with the endemicity given by the community microfilarial load (CMFL)~ They are 1)
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the savanna type which is characterized by a linear relationship of all indices of ocular onchocerciasis with the CMFL, 2) the forest type which shows no relationship between indices of ocular onchocerciasis and the CMFL and which is associated with low rates of ocular lesions as well as blindness even at high CMFL levels and 3) the Sierra Leone type which shows characteristics intermediate between the savanna and the forest pattern with blindness rates which are about half that of savanna for a given CMFL. In a recent collaborative effort between the OCP and the University of Alabama in Birmingham, USA, studies with DNA probes were carried out on nodules collected from persons residing in different savanna and forest villages of the OCP area. The results of the studies showed a very good correlation of the DNA probe characterization of onchocerca volvulus with onchocercal ocular disease pattern in the OCP area. The specificity of the probe is 93.3% and the sensitivity is 94.7%. The DNA probes can therefore be used to predict the pathogenic potential of parasite populations in different areas of West Africa. It was agreed that the DNA probe will be very useful in testing the patterns of onchocerciasis in the intermediate zones. In this regard the OCP could collaborate with other countries in the analysis of specimens when the laboratory has been set up early in 1992. 3.2. Blindness and endemicity in savanna: OCP (Mr. E.S.Alley and Dr. K.Y.Dadzie)
Results based on the analysis of pre-control OCP data for 28 villages to determine the relation between ocular disease and indicators based on skin snip and nodule palpation were presented. The results showed 1) a linear relationship between prevalence of blindness and the Community Microfilarial Load (CMFL) 2) that prevalence of palpable nodules increases regularly with the CMFL up to a CMFL of 30 mf/s and then levels off thereafter and that 3) there is a reasonably good correlation between the mean number of nodules and the CMFL. Furthermore, the risk of blindness increases exponentially with the prevalence of nodules and there appears to exist an approximately linear relationship between the risk of blindness and the mean number of palpable body nodules per person. These results were regarded as promising enough to justify the ·interest in nodule palpation for the purpose of community diagnosis. However the present promising results were based on data from high endemicity zones, and it was deemed necessary to collect data in lower and medium endemicity zones to improve the usefulness of indicators based on palpable nodules. Also confirmation of whether the above relationships for the OCP savanna will hold true in other endemic areas with blinding onchocerciasis would be necessary. A further area of study would be to determine whether community data on palpable nodules are indicative of the public health importance of other onchocercal pathology. Results relating indices of ocular onchocerciasis with the CMFL in mesa-endemic OCP villages with CMFL ranging from 3 to 10 mf/s were presented. The regression lines describing the distribution of all indices of onchocercal ocular disease and the
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CMFL were similar to the regression lines that have been found previously for hyper-endemic savanna villages before vector control in OCP. The prevalence of onchocercal ocular disease was generally low as had been predicted previously, but there was a lot of scatter of the data so that no convincing inference could be drawn from the graphs. On the other hand the prevalence of skin microfilariae proved to be a better index for relating to the prevalence of all indices of ocular onchocerciasis in the range of the endemicity levels of 20% to 60% in question. Onchocercal ocular lesion hardly occurred below the prevalence of 30% skin microfilariae. It was concluded that the prevalence of skin microfilariae would be an adequate index for use in identifying communities for onchocerciasis control by ivermectin and it appeared preferable to the CMFL for this purpose. However, the data collected were too limited to allow for any definite inference to be drawn at present and it was considered desirable to pursue this study to determine threshold values which may be used in community diagnosis and identification of the population for ivermectin treatment. 3.3. Blindness and endemicity in savanna: Kaduna, Nigeria (Mr. S.Coussens) In presenting the findings of the study on the relationship between ocular disease and community indicators based on skin snips and palpable nodules from the randomized placebo controlled trial of ivermectin in Kaduna State, Nigeria it was reported that the correlation between the CMFL and ocular indicators were generally stronger· for males than they were for females. The CMFLs were relatively low compared to the OCP findings. Also the CMFL bad a stronger correlation with sclerosing keratitis than with optic atrophy. Whereas there were no sex differences as regards the correlation between nodules and ocular indicators, for males the correlations between nodules and ocular indicators are weaker than for the CMFL and ocular indicators, except for optic nerve disease. For females, however, correlations between nodules and ocular indicators are stronger than with CMFL. It was concluded that for males the CMFL correlates better than nodules with eye disease, whereas for female it is nodules that correlate better with eye disease. Furthermore prevalence of skin microfilaria and nodules are better indicators for identifying communities where ivermectin treatment is urgent or highly desirable, than the CMFL. It was suggested that the differences in the CMFL levels between the data presented and the OCP data may have been due to the skin snip method used. It was therefore suggested that there was need for standardization of methods. 3.4. Blindness and endemicity in savanna: Cameroon (Dr. M.Boussinesq) The results of clinical examinations, mainly looking for onchocercomata and leopard . skin as well as of detailed ophthalmological examinations from 30 villages in the savanna area of the Vina du Nord Valley (North Cameroon) were presented. This area has a wide range of endemicity and the CMFL ranges from 0.3 mf to 303 mf/s. However, it was noted that because of the method used the CMFL obtained in this study was about 2.5 times that obtained using the OCP.method. The CMFL was found
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to be closely related to the sex-standardized prevalence when this is below 80%, but the CMFL can vary widely when the prevalence rate exceeds 80%. The prevalence of onchocercomata was fairly closely related to the prevalence of skin microfilaria, the prevalence of 60% and 80% corresponding to prevalence of about 30% and 40% of onchocercomata. Cases of leopard skin were seldom observed. The correlation between prevalence of infection and prevalence of blindness was weak. 4. RAPID ASSESSMENT OF ENDEMICITY. 4.1. The use of ecological and entomological information in epidemiological mapping in the OCP (Dr. A.S~k~t~li) The contribution of entomological and ecological information in the epidemiological mapping of the western extension zone of the OCP was presented. The process of zoning the entire area into entities as homogeneous as possible with regards to the vegetation, relief, river flow and tributaries, vector species and intensity of transmission was demonstrated. The end result of the mapping based on these attributes of the zones was the ability to group various zones according to the potential risk of onchocercal blindness and thus provide a crude, but rapid, first step in the identification of villages to be included in large scale ivermectin treatment. 4.2. Alternative rapid assessment methods (Prof. L.D.Edungbola) Alternative options for rapid community diagnosis of onchocerciasis to guide ivermectin-based control in Africa were introduced with reference to studies undertaken in Nigeria. Data for most indicators of onchocerciasis endemicity in Nigeria are rather incomplete and based on non-standardized methodology. Hence, while waiting for results of on-going studies to determine potential values of various indicators for rapid community diagnosis, the presentation focused primarily on "Leopard Skin" (Ls) for which reliable data are available, although restricted to the guinea savanna belt of Kwara State. The results of three studies were highlighted. The preliminary survey of the prevalence of Ls among adults in 24 villages and camps gave a range of 4.1%- 44.4%. Ught, moderate and heavy grades of depigmentation were identified. The second study was a survey of 52 villages in 5 districts for prevalences of skin rnf and Ls. The results suggested that communities with prevalences of Ls < 1%, 1-6% and > 6% represent sporadic ( < 10% prevalence of skin rnf in the population above 5 years of age), hypo-endemic (10-39% prevalence of mf) and meso-or hypo-endemic conditions ( > 40% prevalence of mf). Finally, the review of records for 1979-1983 (3,806 subjects > 5 years, in 34 villages of 4 districts) showed a good correlation between prevalence of skin rnf and prevalence of Ls. ·
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These data suggest that the prevalence of skin mf is about 5 times that of Ls. It was concluded that "Leopard skin" is a viable option for rapid community diagnosis to guide ivermectin-based control programme. However, it is recognized that: i. It should be standardized for different geographical zones; ii. The use of recognition photo-cards will enhance the reliability of its diagnosis; iii.It should be calibrated against prevalence of skin mf for different levels of endemicity; and iv. For its field application for rapid community diagnosis, adult (male) farmers should be the target population because they are the most easily accessible, least affected by socio-cultural and religious inhibitions and at highest risk of exposure to infection. 4.3. Alternative rapid assessment methods in Imo, Bendel and Plateau states in Nigeria (Dr. G.Obiri) In presenting the results of surveys in Imo, Bendel and Plateau States in Nigeria to determine if depigmentation of the shin and/or nodule palpation could serve as an index for assessing oncho endemicity in a given community, it was shown that the prevalence of oncho infection, skin depigmentation and nodule in Imo State was 39.1 %, 19.3% and 14.2% respectively. In Bendel State the results were 32.2%, 15.4% and 9.5% for infection, skin depigmentation and nodule respectively. The last survey conducted in Plateau State presented 26.1 %, 2.3% and 4.4% for oncho infection, skin depigmentation and nodule respectively. Based on the results of the surveys depigmentation and/ or skin nodule were considered promising alternative methods to skin snipping in Imo States. They are prevalent, easier to assess, and above all they are relatively cost-effective. However, this does not appear to be the case with Plateau State. Skin depigmentation and nodules are not sufficiently prevalent to be used as indicators for onchocersiasis endemicity. 4.4. Observer variation in nodule palpation (Dr. B.Boatin) In presenting the results of a study to assess the inter-observer variation between paramedicals in the palpation for onchocercal nodules, it was shown that the correlation between 4 different pairs of observers ranged between being good to excellent. In all situations there was very good agreement between observers, with the lowest and highest regression coefficient of 0.5 to 0.84 respectively. This agreement was unaffected by sex. There was however no relation between observers' findings and respondents' answer to whether or not they bad nodules. It was concluded that given the right training paramedicals could be used for the examination for nodules in the diagnosis of onchocerciasis.
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4.5. Rapid assessment using community questionnaires (Mr. S.Cousens)
The preliminary results of rapid assessment methods using questionnaires to elicit responses from villagers about whether they considered themselves blind or not showed that the correlation between the prevalence of blindness reported by individuals and the prevalence of blindness as measured by ophthalmological examination was 0.52 for males and 0.36 for females. Questionnaires administered by villagers following a brief training session yielded the following correlation with the prevalence of measured blindness: leopard skin, 0.41; recognition of blackflies, 0.47; problem with blackfly biting 0.37. All the above correlations are higher than those observed for the CMFL and for the prevalence of palpable nodules. 4.6. Multi-centre study of rapid assessment methods in Nigeria (Dr. Ojodu)
Plans for a multi-centre study of rapid assessment methods for community diagnosis of onchocerciasis in Nigeria and the results of a nationwide epidemiological survey of onchocerciasis from 22 states were presented. The available results indicated that the prevalence on onchocerciasis infection varies widely across the states. The multi-centre study, which is funded under the joint IDR/NOCP onchocerciasis operational research initiative, is designed to determine the relationships between the prevalence of skin rnf and combinations of the following; depigmentation of the shin, presence of nodules, blindness, muscular/skeletal pain and itching/rash. 5. PUBLIC HEALTH AND SOCIO-ECONOMIC IMPORTANCE OF NON-OCULAR PATHOLOGY 5.1. Review of non-ocular onchocercal pathology (Dr. K.Awadzi)
In the review of the non-ocular onchocercal pathology and their public health importance, a broad classification of dermal, lymphatic and systemic lesions were provided and the dermal and lymphatic lesion were further categorized into generalized or local. The various lesions that have been determined to be associated in West Africa with 0. volvulus infection were set out as follows: skin atrophy, skin depigmentation, lymphoedematous skin thickening, lymphoedema of the external genitalia, lymphadenopathy femoral/ inguinal and hanging groin. It was shown that skin atrophy and skin microfilaria occur more commonly in the savanna than in the forest, whereas it is the other way round for the rest of the lesions. In considering the social and community aspects of onchocerciasis the following factors were addressed: simulium bites, pruritis, dermal and lymphatic lesions, onchocercomata, systemic effects, community diagnosis and effects of therapy i.e drugs -ivermectin- and/or nodulectomy.
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5.2. Onchocercal skin disease in Equatorial Guinea (Dr. J.Mas) In a study carried out in 1987 to determine the onchocerciasis situation on the island of Bioko (Equatorial Guinea), the total population of 1799 people living in 13 villages in the cocoa plantations and tropical forest were surveyed. Parasitological and physical examinations were carried out. The overall prevalence and mean microfilarial density were 75.2% and 36.12 mf per skin respectively. The prevalence of clinical manifestations were as follows; 560 (31.2%) with onchocercomata, 518 (28.8) with dermatitis, depigmentation and atrophy and 753 (41.9%) with lymphadenopathy and lymphoedema. Blindness due to all causes was 13 (0.8% ). It was concluded that almost the whole population (62,000) is at risk of onchocerciasis infection. 5.3. Onchocercal skin disease and endemicity in the OCP (Dr. B.Boatin) The results from the analysis of the pre-control data of 33 savanna and 5 forest villages on skin disease and relations with endemicity levels in the OCP were presented. The results showed that there was virtually no relationship between acute (lesions due to scratch and onchodermatitis) or chronic ( hyperkeratosis lichenoid change and atrophy) lesions and prevalence of skin mf or with the CMFL Depigmentation of shin however showed some correlation with prevalence of skin mf and the CMFL In most of the villages where the prevalence of depigmentation of the shin exceeded 6%, the CMFL was greater than 10 mf/s. The prevalence of depigmentation of shin showed rather a weak relationship with blindness. It was concluded that depigmentation of shin was the most promising of the onchocercal skin lesion for community diagnosis but it lacks sensitivity with regards to estimating onchocercal blindness. 5.4. Onchodennata and ivennectin in Malawi (Dr. G.Burnham) The relationship between 0. volvulus and skin disease resulting from death of microfilariae is subtle and complex. Periodic episodes of microfilarial destruction are mounted by the body's immune system which result in acute inflammatory (or reactive) changes to the skin. The various enzymes and proteins released in the destructive process (especially by eosinophils) are thought to be responsible for chronic skin changes such as atrophy and depigmentation. In the course of the WHO-sponsored ivermectin trial in Malawi, 106 adults with severe or moderately severe onchocercal skin lesions were treated with ivermectin or placebo annually and their skin lesions assessed every 6 months. These 106 persons represented about 6% of the adult population of the two areas where the trial was conducted. Papular, oedematous and excoriated lesions tended to wax and wane during the 18 months of observation. Many, but not all persons receiving ivermectin showed improvement in skin disease. Changes in the extent of papular disease as well as the severity of papular lesions was the most obvious change and these changes were most
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pronounced during the first 6 months after ivermectin. lvermectin also produced significant changes in lichenification of the skin but these lesions regressed more gradually. Some ivermectin recipients showed little or no change in their skin lesions whereas some persons who received the placebo had improvement in skin disease. Over all, ivermectin produced significant improvement in papular and lichenified lesions of 0. volvulus as compared with placebo. Assessing papular dermatitis and lichenification due to onchocerciasis can give a rough estimate of the extent to which the disease affects a community. Because of fluctuations in the extent and severity of these more acute skin changes, assessing the prevalence of depigmented lesions would provide a more stable index of the prevalence of Onchocerciasis. 5.5. Onchocercal skin disease and ivennectin in Liberia (Dr. M.Pacqu~) The findings of the study on the improvement in onchocercal skin disease after ivermectin treatment in Liberia were presented as follows; following a single dose of ivermectin, there was a significant improvement of onchocercal skin disease in the first 3 months after treatment. Lesions were worse at 6 months compared to 3 months after treatment, but still better than at pre-treatment. As to the effect on 'Leopard skin', the study was in- conclusive. The benefit of ivermectin treatment on skin disease was most prominent in those with the most severe onchodermatitis. There is the possibility to use onchodermatitis as an evaluation tool (indicator) in ivermectin treatment. 5.6. Social impact of onchocercal skin disease in rural Nigeria (Dr. D.S.Obikeze) By a unique combination of the natural and social science methodologies of physical examination, skin snips biopsies, questionnaire administration, in-depth interviews and focils group discussions, this study investigates the socio-cultural dimensions of onchocerciasis disease in a rural Nigerian community based on a sample of238 infected adolescent girls (10- 19 years) and their families drawn from three villages in the community. Etteh people are essentially non-literate (86%) farmers who spend most of the day in the farmland along the flood plains of Ubelle river which is the main breeding sites of the blackfly. Exposure to the bites of the vector is therefore high and continuous all the year round. The overall infection rate among adolescent girls in the community was 36.6%. Various manifestations of the disease- nodules, onchodermatitis, lizard skin, leopard skin, hanging groin - were present.
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The people of Etteh did not associate the Ubelle river with the breeding sites of the blackfly; rather they believed that it breeds in Iroko tree. It is a belief among some that killing a blackfly will attract many more, therefore it is better not to kill one. They generally do not associate the bite of the fly with onchodermatitis, hanging groin or leopard skin. Nodules are considered minor ailments although onchodermatitis is considered serious disease. Pregnancy conditions are believed to worsen the disease. Onchodermatitis (Ekwa) is believed to be caused by charm and witchcraft or by inheritance; to be transmitted by personal contact, sharing of personal effects, and stepping on infected bath water. It is believed to be curable using modem medicine or by traditional methods using "Iriyi" plant and pertinent rituals. "Ekwa" condition has very grave social, economic and psychological implications for victims in this community. Young women and men with this disease are discriminated against, humiliated by peers, avoided by friends and stigmatized by the society. Married women with "ekwa" lose the affection of their husbands while the marriage chances of infected persons are very adversely affected, if not totally ruined. "Ekwa" patients produce less, spend more time and money seeking cure, and when they tap wine, people are reluctant to buy it from them. Teachers report that children with the disease lack concentration in class and consequently are bad performers. Psychologically, onchodermatitis engenders withdrawal behaviour, isolationism and societal maladjustment on the part of the infected individual.
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6. SUMMARY: RAPID ASSESSMENT METHODS AND INDICATORS FOR LARGE SCALE IVERMECTIN TREATMENT
The meeting reviewed the information provided during the above presentations, as well as a large body of community-based data on the epidemiology of onchocerciasis in various areas of Africa, i.e. data for Nigeria (Kaduna, Kwara and Plateau States), Cameroon, Equatorial Guinea, liberia, Malawi and nine OCP countries. Three working groups were formed: one on non-invasive rapid assessment methods of endemicity, one on the risk of blindness in relation to endemicity and related guidelines for large scale ivermectin treatment in the savanna, and one on the public health and socio-economic importance of other manifestations of onchocerciasis. Furthermore, a multi-country analysis was undertaken of available data on rapid assessment methods and blindness patterns. The findings of the three groups, including the preliminary results of the multi-country analysis, were discussed in plenary. A subgroup, appointed during the meeting, met in March 1992 in Ouagadougou to complete and verify the multi-country analysis and to expand it by including additional data for adult males. The results of these activities are summarized below. 6.1. Rapid assessment methods based on non-invasive examination techniques. The meeting considered the following non-invasive examination techniques as possible replacements of the skin snip technique in the rapid assessment of onchocerciasis endemicity: - Examination for depigmentation of shin - Nodule palpation - Reported blindness rate - Pruritis and rash - Musculo-skeletal pain - Community questionnaire Pruritis and rash were discarded on the basis that they are rather non-specific according to evidence presented. Because of insufficient information on musculo-skeletal pain and on the use of community questionnaires in onchocerciasis no further consideration could be given to these. However, the meeting was of the opinion that community questionnaires are a priority research area. The use of the rate of blindness, calculated on the basis of the number of blind reported by key informants, is an alternative means of commmunity diagnosis which has definite merit because of its simplicity and rapidity. However, as is the case for all estimates of the rate of total blindness, irrespective of cause, it lacks both sensitivity and specificity in all but the most severely affected villages in the savanna.
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·The examination for depigmentation of shin (Leopard skin) and nodule palpation were discussed in detail. Table 1 gives a grading of the two methods according to different criteria, and Figures 1 and 2 show the information available to the meeting on the relationship between the prevalence of these alternative methods and prevalence of skin mf. Having considered all these, the meeting concluded that depigmentation of shin and nodules palpation are the most promising alternative methods for community diagnosis of onchocerciasis. However, due cognisance of local peculiarities must be taken into consideration in adopting either of them for field application.
Table 1: Grading of two rapid assessment methods of onchocerciasis endemicity
{; Criteria Sensitivity, Specificity Cost Rapidity Level of skill to be acquired .,~
Nodule palpation good
Depigmentation of shin fair
low fair takes few hours training only yes very safe good
very low good takes few hours training only yes very safe very good
Non-invasive Safety Acceptability
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Fig.1: Prevalence of nodules by prevalence of mf Results for population above 5 years of age
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Upon recommendation of the meeting, the subgroup which met in March 1992 reviewed additional information on assessment methods which are based on data for adult males only. A very close relationship was observed between the prevalence of mf in adult males and in the total population in 308 OCP villages (see Figure 3) and this provides strong support for the conclusion that rapid assessment of endemicity may be limited to examination of adult males only. Fig.3: Prevalence of mf in adult males and in the total populotio1 Results for 308 villages from the Western Extension area of the OCP
100
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en en
go 80
E ::l
70
"'0 0
60 50 40 30
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,
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60
80
100
Prevalence of mf in the total village population (as %)
6.2. Risk of blindness and endemicity levels A large amount of data were reviewed on the prevalence of blindness in relation to
the prevalence of skin microfilariae, nodules and leopard skin from the OCP, Kaduna and Plateau states in Nigeria and the Cameroon. It was noted that the resource areas of the data were all savanna areas stretching from West to Central Africa. It was recognized that there might have been differences in the methods of data collection on nodules and leopard skin and that there were differences the classification of blindness. The blindness rat~s for the OCP and Kaduna State in Nigeria referred to blindness due to onchocerciasis only but the blindness rates for Plateau State and the Cameroon referred to total blindness. Different methods of conducting skin snips were also used but these could be corrected for by applying available correction factors. Fig. 4-9 show the results of the final analysis of the data for OCP, Kaduna and Cameroon after verification and standardization by the subgroup which met in March 1992 in Ouagadougou. The prevalence of blindness in these figures represents onchocercal blindness for OCP and Kaduna, and total blindness for Cameroon.
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~ fl)
Fig.4: Prevalence of blindness by prevalence of mf 10 9 8 7 6 • • • Villages with more than 150 inhabitants only OCP, pre-control Kaduna, Nigeria Ndrth Cameroon
0
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• • • • • • •• •• • •• • •
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20
80
Prevalence of mf above the age of 5 years (as %)
Fig.5: Prevalence of blindness by prevalence of mf in adult males ......... ~
Cl)
10
Villages with more than 150 inhabitants only • • • OCP, pre-control Kaduna, Nigeria North Cameroon
0
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9
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60 40 80 100 20 Prevalence of mf among males above the age of 20 years (as %)
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Fig.6: Prevalence of blindness by prevalence of nodules
Ill
~ 0 0 I ll
Villages with more than 150 inhabitants only 10
....
9
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>.
• • •
OCP, pre-control Kaduna, Nigeria North Comeroon
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Prevalence of nodules above the age of 5 years (as %)
Fig. 7: Prevalence of blindness by prevalence of nodules in adult males ,....,
Ill 0 Ill
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Villages with more than 150 inhabitants only 10
.... 0
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OCP, pre-control Koduno, Nigeria North Cameroon
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Prevalence of nodules in moles above the o.ge of 20 years (as ?.)
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. -18-
Fig.B: Prevalence of blindness by prevalence of leopard skin .......
11)
~
Villages with more than 150 inhabitants only 10
0
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.... 0
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OCP, pre-control Kaduna, Nigeria North Cameroon
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Prevalence of leopard skin above the age of 5 years (as %)
Fig.9: Prevalence of blindness by prev.of leopard skin in adult males Villages with more than 150 inhabitants only 10 11)
.... 0
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Prevalence of leopard skin in males above the age of 20 years (as %)
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The relationship between the prevalence of blindness and the prevalence of skin microfilariae, nodules and leopard skin, as shown in Fig.4-9, was fairly uniform. The major difference concerned the relatively low rates of blindness in the villages in Cameroon compared to the OCP villages with similar endemicity levels. 6.3. Criteria for large-scale ivermectin treatment The results of the analysis supported most of the recommendations with respect to the "provisional criteria for ivermectin treatment" as put together in the April meeting in Geneva on "the strategies for ivermectin distribution through primary health care systems" (Doe. WHO/PBL/91.24; see annex I of the present document for a copy of the table with "provisional criteria for ivermectin treatment"). The main exceptions were the provisional threshold levels for the prevalence of positive skin snips in adult males, which were shown to be too low compared to the provisional levels for the other indicators. The CMFL remains the best index of the risk of blindness in hyper endemic communities, but because of the need for accurate counting of microfilariae, it is not very suitable for rapid assessment purposes. Nevertheless, the meeting recommended that wherever possible the CMFL should be measured to provide baseline data which will allow the future evaluation of the impact of ivermectin delivery in preventing onchocercal blindness. On the basis of the final results of the multi-country analysis, and to ensure internal consistency between the different criteria, the meeting proposed some adjustments of the provisional criteria developed during the April meeting in Geneva. The proposed adjustments are given in table 2. Concerning the usefulness of reported blindness rates, the meeting considered that questioning of the key informants in the population for information on blindness is simple, easy and straightforward but the interpretation of the information might be subject to a lot of errors, some of which are related to the size of the population. To aid in the better interpretation of the information on reported blindness rates, a table was prepared which gives for different village sizes the number of blind to be observed before it can be concluded that the risk of blindness is significantly higher than 1% and 2% respectively (see Annex ll). The meeting in considering standardisation and simplicity in the collection of data on rapid assessment recommended that rapid assessment should be limited to examinations in adult males aged 20 years and over. A preference was expressed for the use of the prevalence of palpable nodules in adult males as the indicator of choice for rapid assessment of the risk of onchocercal blindness in the community. For villages not exceeding 300-500 people, it was recommended that all adult males are examined
•
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Table 2. Proposed adjustment of provisional criteria for ivermectin treatment (numbering refers to original table as given in Annex I; underlined figures are those which remain unchanged) Assessment method 1.2 fr~alcn~c of mf in skin snill males and females of all ages males over 20 years 2. Ra12id assessment methods 2.1 fr~alence of nodules Males and females of all ages Males over 20 years 2.2 Leo12ard skin Males and Females of all ages Males over 20 years (not yet available during Geneva meeting)
Urgent
Highly desirable ~Q%-52%
CiQ% imd QV~[ 90%and over
70%-89%
20%and over 40% and ewer
10%-19% 20%-39%
lQ% and over 20%and over
not useful not useful
for palpable nodules. In larger villages, samples of adult males might be taken. However, the sampling frame should be designed carefully to ensure an adequate sample size and to account for heterogeneity of exposure between different sections of the population which may be significant in larger communities. 6.4. Non-ocular manifestations of onchocerciasis The meeting reviewed the presented information on non-ocular disease in onchocerciasis, including its public health and socio-economic importance, and the effect of ivermectin on skin disease. N owthat there is effective treatment against onchocerciasis and blindness need not occur, there is need for greater attention to be paid to the non-ocular manifestations of the disease. These non-ocular manifestations are both physical and socio-economic in nature. 6.4.1. friority areas for further study From data presented during this meeting, the non-ocular manifestations of onchocerciasis which seem most amenable to reversal by ivermectin are the skin lesions
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produced by infection, and the social stigma which arises principally from disfiguring onchocercal skin disease. It is felt that these data warranted the following recommendations: a. Skin disease
- A standard system for classification of skin lesions due to onchocerciasis be established - There is a need to establish the optimum treatment protocol for persons with skin lesions of onchocerciasis - Although the benefits of ivermectin in acute onchocercal skin lesions seems clear, there is a need to establish the effects of sustained ivermectin treatment in preventing chronic skin lesions due to 0. volvulus infection.
b. Social stigma associated with onchocerciasis - Evidence presented concerning the social stigma produced by the skin lesions of onchocerciasis needs to be validated in other locations - Any effect which ivermectin might have in reversing this stigma needs to be investigated c. Other socio-economic effects Although no data was presented concerning other socio-economic effects of onchocerciasis which might be potentially reversible, such possible benefits of ivermectin were felt to warrant consideration. Such areas which could be considered included reduction in productivity, effects on school performance, and the social and economic costs of seeking and receiving treatment. A need was also perceived to assess the costs to the health care system of onchocerciasis and how ivermectin might reduce or redistribute these costs. 6.4.2. Other potential areas of research which are of lesser priority Possible non-ocular effects of onchocerciasis which might be reversible by ivermectin but do not, at this time, require urgent study, are: - Systemic manifestations of onchocerciasis involving organ systems other than the eye and skin - Any shortening of life associated with 0. volvulus infection - Interaction between 0. volvulus infection and other infections such as lllV - Effects of onchocerciasis in pregnancy and fertility - Lymphatic manifestations of onchocerciasis - Musculo-skeletal pain
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7. CONCLUSIONS
The meeting reviewed a large body of epidemiological information on onchocerciasis in various areas of West, Central and East Africa in order to assess among others the validity of recently proposed guide-lines for large scale ivermectin treatment, and arrived at the following main conclusions: 1. The relationship between blindness rates and endemicity levels appears to be fairly uniform in most of the savanna areas that were considered.
2. The CMFL is a good measure of endemicity but it's relationship with the risk of blindness is difficult to interpret in the lower endemicity range. Therefore, the prevalence of infection is a better indicator for decision making on large scale ivermectin treatment. The use of the crude blindness rate as an alternative method of community diagnosis has some merits, but lacks sensitivity and specificity in small communities. 3. The results of a multi-country analysis of data on endemicity and morbidity at the community level supported most of the provisional criteria for large scale ivermectin treatment, as defmed during a meeting in April 1991 in Geneva. However, the provisional thresholds for the prevalence of positive skin snips in adult males and for the prevalence of palpable nodules in all ages groups were not consistent with the other provisional threshold values. 4. The importance of non-ocular onchocercal morbidity, particularly skin lesions, and their socio-economic impact was recognized. However, information in this area is grossly inadequate, especially in "forest" areas which are endemic for 0. volvulus strains that rarely cause blindness. 5. The meeting considered several alternative diagnostic methods for rapid assessment of en~emicity by reviewing data from several savanna areas - OCP area, Kwara, Kaduna and Plateau states in Nigeria, and north Cameroon - and concluded that nodules palpation and depigmentation of the shin (leopard skin) are suitable alternatives. 8. RECOMMENDATIONS
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1. Examination for depigmentation of the shin and palpation for nodules may be used as alternative methods for community diagnosis of onchocerciasis. 2. Rapid assessment methods using skin snips, palpation of nodules, and recognition of depigmentation of the shin may be limited to the examination of adult males (20 years and above) only.
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3. In the light of the presently available data, the provisional criteria for inclusion of communities in large scale ivermectin treatment programmes should be adjusted as follows: large scale ivermectin treatment should be considered urgent (a must) in all communities in the savanna for which the prevalence of microfilariae in skin snips among adult males is greater than 90%, or the prevalence of palpable nodules in the total population is greater than 20% (see table 2). 4. The meeting stressed that the proposed threshold values are only intended as broad guide-lines for the planning of ivermectin based control. Control programmes are encouraged to use the epidemiological information provided in the present report in order to determine, in the light of available resources, which threshold values are most appropriate for their particular situation. 5. It is recommended that the table in annex II, which takes the size of the community into account, is used in the interpretation of crude blindness rates for the purpose of community diagnosis. 6. A system for standardized classification of onchocercal skin lesions in epidemiological surveys should be developed. 7. Further research on the social and economic importance of onchocercal skin disease is urgently required for forest areas endemic for 0. volvulus strains that rarely cause blindness.
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ANNEX I. Provisional criteria for ivennectin treatment Reproduced from "Strategies for lvermectin Distribution through Primary Health Care Systems". World Health Organization. Document WHO/PBL/91.24, page 17.
PROVISIONAL CRIT!ltiA* FOR. IVERHECTIN nEATKENT
Urgent (lflltt)
Highly desirable
1.
METHODS INVOLVING SKIN SNIPS
1.1
Intensity of mf/s CKFL (Adults over 20, both sezes) CKFL (Adult males over 20 [sample of 30]) 10 and over 15 and over 5-9 5-14
•
1.2
Prevalence of positive skin snip Males and females of all ages Males over 20 years (sample of 30) 60X and over BOX 40-59X 40-79X
2.
RAPID ASSESSMENT METHODS
2.1
Prevalence of nodules Males and females of all ages Males over 20 years 30X and over 40X and over 15-29X 20-39X
2.2
"Leopard skin"
on
shins lOX and over 5-9X
Males and females of all ages 2.3 Total blindness rate (in whole population in an onchocerciasis area, based on 300-1000 people from several communities)
2X
lX
* Based on Onchocerciasis Control Programme savanna data.
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ANNEX 11. Guide for the interpretation of crude blindness rates for small communities, with reference to the criteria for lvermectin treatment In annex I.
Number of inhabitanItS 1
Number of blind
2 0 0 0 0 0 0 0 0 0 0
3
4
5
6
7
8
9
10
11
12
50 75 100
0 0 0 0 0 0 0 0 0 0
* * 0 0 0 0 0 0 0 0
0
125 150 200 250 300 400 500
** * * * 0 0 0 0 0 0
** ** * * * 0 0 0 0 0
** ** ** * * * 0 0 0 0
** ** ** ** ** * * * 0 0
** ** ** ** ** * * * * 0
** ** ** ** ** ** * * * 0
** ** ** ** ** ** ** * * *
** ** ** ** ** ** ** * * *
** ** ** ** ** ** ** ** * *
O: Blindness rate not significantly greater than 1% (P>O.OS) *: Blindness rate significantly greater than 1% (P<O.OS) **:Blindness rate significantly greater than 2% (P<O.OS)
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ANNEX Ill. List of participants Participants: AWADZI, Dr.K., Onchocerciasis Chemotherapy Research Centre, P.O.Box 144, Hohoe, Ghana BOATIN, Dr. B., Onchocerciasis Control Programme in West Africa, B.P.549, Ouagadougou, Burkina Faso (Rapporteur). BOUSSINESQ, Dr.M., Antenne ORSTOM aupres du Centre Pasteur du Cameroun. B.P.1274, Yaounde, Cameroun. BURNHAM, Dr.G., Department of International Health, School of Hygiene and Public Health, the John Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205, USA COUSENS, Mr.S., Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine. Keppel St. London, WCIE 7HT, United Kingdom. DADZIE, Dr. K.Y., Onchocerciasis Control Programme in West Africa, B.P.549, Ouagadougou, Burkina Faso. EDUNGBOLA, Prof.L.D., Department of Medical Microbiology and Parasitology, Faculty of Health Sciences, University of llorin, PMB 1515, llorin, Nigeria (Chairman). MAS, DrJ ., Onchocerciasis Control Programme, Spanish Cooperation, Ministry of Health of Equatorial Guinea, c/o / Ambajada de Espana, Malabo, Equatorial ~uinea (unable to participate due to problems with flight connections). OBIKEZE, Dr.D.S., Department of Sociology and Anthropology, University of Nigeria, Nsukka, Nigeria. OBIRI, Dr.G.U., University of Alabama at Birmingham, School of Medicine, Division of Geographic Medicine, Birmingham, Alabama 35294, USA RESNIKOFF, Dr.S., Organisation pour la Prevention de la Cecite, 58 av Bosquet, 75007 Paris, France (Rapporteur). SEKETEU, Dr.A, Onchocerciasis Control Programme in West Africa, B.P.549, Ouagadougou, Burkina Faso.
.,
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SOUMBEY-ALLEY, Mr.E., Onchocerciasis Control Programme in West Africa, B.P549, Ouagadougou, Burkina Faso. Secretariat: REMME, DrJ.H.F., UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, World Health Organization, 20 av Appia, · CH-1211 Geneva 27, Switzerland SAMBA, Dr.E.M., Director, Onchocerciasis Control Programme in West Africa, B.P.549, Ouagadougou, Burkina Fa5o.
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VLASSOFF, Dr.C., UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, World Health Organization, 20 av Appia, CH-1211 Geneva 27, Switzerland WURAPA, Dr.F.K., Regional Office for Africa, World Health Organization, B.P.6, Brazzaville, Congo. Observers: GEMADE, Dr.E.I.I., Nigerian Onchocerciasis Control Programme, Field Base, 1 Golf Course RD, P.O.Box 503, Kaduna, Nigeria. GONZALEZ, Dr.C., River Blindness Foundation, P.O.Box 7772, Jos, Plateau State, Nigeria. OGBU-PEARCE, MRS., Nigerian Onchocerciasis Control Programme, Ministry of Health, P.M.B.102009, Makurdi, Benue State, Nigeria. OGUNBA, Dr.E.O., National Onchocerciasis Control Programme, Federal Secretariat Phase 11, Federal Ministry of Health, PMB 12597, Ikoyi- Lagos, Nigeria. OJODU, Dr.K.A., Disease Control and International Health Department, National Onchocerciasis Control Programme, Federal Secretariat Phase ll, Federal Ministry of Health, PMB 12597, Ikoyi - Lagos, Nigeria. PACQUE, Dr.M., Sight Savers, s/c IOTA, B.P.248, Bamako, Mali.
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