'Leopard skin' as a rapid diagnostic index for estimating the endemicity of African onchocerciasis

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Assessment and monitoring of onchocerciasis in Latin America

Onchocerciasis has historically been one of the leading causes of infectious blindness worldwide. It is endemic to tropical regions both in Africa and Latin America and in the Yemen. In Latin America, it is found in 13 foci located in 6 different countries. The epidemiologically most important focus of onchocerciasis in the Americas is located in a region spanning the border between Guatemala and Mexico. However, the Amazonian focus straddling the border of Venezuela and Brazil is larger in overall area because the Yanomami populations are scattered over a very large geographical region. Onchocerciasis is caused by infection with the filarial parasite Onchocerca volvulus. The infection is spread through the bites of an insect vector, black flies of the genus Simulium. In Africa, the major vectors are members of the S. damnosum complex, while numerous species serve as vectors of the parasite in Latin America. Latin America has had a long history of attempts to control onchocerciasis, stretching back almost 100 years. The earliest programmes used a strategy of surgical removal of the adult parasites from affected individuals. However, because many of the adult parasites lodge in undetectable and inaccessible areas of the body, the overall effect of this strategy on the prevalence of infection was relatively minor. In 1988, a new drug, ivermectin, was introduced that effectively killed the larval stage (microfilaria) of the parasite in infected humans. As the microfilaria is both the stage that is transmitted by the vector fly and the cause of most of the pathologies associated with the infection, ivermectin opened up a new strategy for the control of onchocerciasis. Concurrent with the use of ivermectin for the treatment of onchocerciasis, a number of sensitive new diagnostic tools were developed (both serological and nucleic acid based) that provided the efficiency, sensitivity and specificity necessary to monitor the decline and eventual elimination of onchocerciasis as a result of successful control. As a result of these advances, a strategy for the elimination of onchocerciasis was developed, based upon mass distribution of ivermectin to afflicted communities for periods lasting long enough to ensure that the parasite population was placed on the road to local elimination. This strategy has been applied for the past decade to the foci in Latin America by a programme overseen by the Onchocerciasis Elimination Program for the Americas (OEPA). The efforts spearheaded by OEPA have been very successful, eliminating ocular disease caused by O. volvulus, and eliminating and interrupting transmission of the parasite in 8 of the 13 foci in the region. As onchocerciasis approaches elimination in Latin America, several questions still need to be addressed. These include defining an acceptable upper limit for transmission in areas in which transmission is thought to have been suppressed (e.g. what is the maximum value for the upper bound of the 95% confidence interval for transmission rates in areas where transmission is no longer detectable), how to develop strategies for conducting surveillance for recrudescence of infection in areas in which transmission is thought to be interrupted and how to address the problem in areas where the mass distribution of ivermectin seems to be unable to completely eliminate the infection.

CD4(+), CD8(+), immunoglobulin status and ocular lesions among some onchocerciasis-infected rural Nigerians

CD4(+), CD8(+), immunoglobulin status and ocular lesions of some onchocerciasis-infected rural Nigerians as manifested by the presence of microfilariae in their skin snips and some chronic symptoms of the parasitic infestation were evaluated. The highest mean CD4(+) and mean microfilarial (mff) load of 560 +/- 20.46 unit cells/microl and 20 mff/mg were recorded among the individuals within the second decade of life, while the least mean CD4+ and mff load of 307.20 +/- 11.23 unit cell/microl and 6.5 mff/mg occurred among volunteers after 60 years of age. The highest mean CD8(+) of 388.00 +/- 23.71 unit cells/microl occurred at the third decade of life. The individuals above 60 years had the least mean CD8(+) of 350.25 +/- 11.90 unit cells/microl. The volunteers had mean CD4(+) of 372.45 +/- 109.02 unit cells/microl and mean CD8(+) of 359.42 +/- with an overall CD4(+):CD8(+) ratio of 1.04. The mean CD4(+) and mean CD8(+) had positive correlation with the mean microfilarial load (r = 0.52 and r = 0.40), respectively. The mean IgE, IgG, lgA, IgM, and IgD were 2,074.82 +/- 823.09, 19.36 +/- 2.49, 3.88 +/- 0.26, 3.59 +/- 0.38, and 0.29 +/- 0.19 mg/dl, and these immunoglobulins negatively correlated with the mean microfilarial load at r = -0.02, r = -0.15, r = -0.82, r = -0.37, and r = 0.26, respectively. Among these immunoglobulins evaluated, only mean IgE (2,074.82 +/- 823 ng/ml) was statistically different from the control subjects (0 mg/dl) at t = 3.39, P < 0.05. In all, the prevalence of the visual impairment and lesions were low. Among the six visual lesions, namely, cataract, choroidoretinitis, iridocyclitis, glaucoma, sclerosing keratitis, and optic atrophy encountered in Egoro-Eguare, only optic atrophy and sclerosing keratitis was reported among the children. The female adults had the highest prevalence of reduced vision 20(43.5%). Also, the prevalence of choroidoretinitis (2.2%) and iridocyclitis (2.2%) were the least prevalent ocular lesions reported among these female adults. The depletion of the CD4(+) contributed to the low prevalence of visual impairment and lesions in this locality. The depleted CD4(+), CD8(+), and the lower values of IgA, IgM, and IgG contributed in the maintenance of chronicity of onchocerciasis in Egoro-Eguare, Nigeria.

Research for control: the onchocerciasis experience

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

Knowledge and beliefs about causes, transmission, treatment and control of human onchocerciasis in rural communities in south western Nigeria

Descriptive and quantitative information on onchocerciasis transmission and control were collected using focus group discussions and structured questionnaire to determine what changes if introduced, could upset the established human-vector-parasite relationship in limiting transmission. People's knowledge of cause of infection and transmission was very poor. Of the 1012 people interviewed, only 3% related the clinical manifestations of onchocerciasis to Simulium bites. Thirty six percent had no idea of the cause of infection while the rest attributed the clinical symptoms of the disease to many other causes. People's knowledge of the current treatment and control measures was also poor. However an impressive knowledge of the daily and seasonal distribution of Simulium flies was observed. The study identifies the need for health education campaigns aimed at relating the clinical manifestations of onchocerciasis to Simulium bites. This could help people in taking personal protective measures and seeking appropriate treatment.

Onchocerciasis in Taraba State, Nigeria: clinical-epidemiological study of at-risk males in Bakundi District

An epidemiological study of 1366 adult males from fourteen communities of Bakundi district of Taraba State, Nigeria was carried out to establish the prevalence and intensity of onchocerciasis. The findings of the study showed that 45.2% of subjects were infected. Ten communities had infection rates in excess of 30%. Lizard skin and leopard skin were seen in 3.5% and 2.0%, respectively, and increased with increasing age. Hanging groin (2.6%) and scrotal enlargement (8.6%) were also observed. There was a good correlation between the infection rate on one hand and the presence of nodules (r = 0.85, P < 0.05), hanging groin (r = 0.56, P < 0.05) and scrotal enlargement (r = 0.62, P < 0.05) on the other. There was also a significant correlation between the intensity of infection on the one hand and lizard skin (r = 0.67, P < 0.05), leopard skin (r = 0.88, P < 0.05) and hanging groin (r = 0.82, P < 0.05) on the other. Those who worked in the fields (such as hunters, farmers and fishermen) had higher infection than others because of frequent contact with the vector. Extensive surveys of all suspected river valleys must be carried out to identify all those communities which will benefit from ivermectin treatment.

Independent evaluation of onchocerciasis rapid assessment methods in Benue State, Nigeria

OBJECTIVE

To evaluate the prevalence of palpable nodules or skin depigmentation as rapid indicators of onchocerciasis epidemicity in at-risk communities.

METHOD

We examined data collected in Benue State on 11035 individuals in 32 villages to evaluate these rapid assessment methods.

RESULTS

The prevalence of palpable nodules correlates more closely with microfilarial prevalence (r=0.68, P<0.001) and community microfilarial load (r=0.64, P<0.001) than the prevalences of skin depigmentation or other potential rapid indicators. The recommended cut-off value for palpable nodules of 20% or more in males aged >20 years had a sensitivity of 94% and specificity of 50% compared to a cut-off of 40% or more for microfilarial prevalence in all ages. This would mean that in these 32 villages 17 of 18 would have been correctly identified for treatment, and a further 7 at lesser risk would have been targeted for treatment.

CONCLUSIONS

Skin snipping and parasitological examination can be replaced by the simpler method of palpating onchocercal nodules to identify communities at serious risk of onchocerciasis. This has important operational benefits for onchocerciasis control programmes.

Estimation of age specific incidence rates of childhood burns from a prevalence survey of burn scars

OBJECTIVES

This paper describes two methods of estimating the age specific incidence rates of childhood burns from a prevalence survey of burn scars.

METHODS

A prevalence survey of burn scars was carried out in 1992 on 15,742 Ghanaian children aged 5 years or less. Nine hundred and fifty five (6.1%) of these children had scars from burn, and for 630 (66%) of these children, additional information about the burn incident, including the child's age at the time of the burn, was obtained from the mother two to three months later. Thirty four per cent of mothers of children with burn scars were not interviewed due to absence, relocation, or inaccessibility. Age specific incidence rates of burns were estimated for eight age groups using two methods. In method I, the number of incident cases of burns for each age group were estimated from the burn scars by subtracting the estimated contribution of scars from burns that had occurred at earlier ages. In method II, the estimate was based on the mother's recall of the age of the child at the time of the burn.

RESULTS

Slightly different results were obtained with the two methods, and problems were noted with both methods.

CONCLUSION

We recommend the use of these methods for estimating age specific incidence rates from retrospective population surveys for health conditions which result in long term residual markers.

Rapid assessment of onchocerciasis prevalence and a model for selecting communities for ivermectin distribution in West Africa

Analysis of the prevalence of onchocerciasis in an area of north-east Nigeria indicates that clinical symptoms are generally good predictors of the rate of onchocerciasis infection and of the mean microfilarial density in infected individuals. However, differences between regions and anomalous communities within regions make reliance on a single indicator dubious. Use of multivariate equations was tested, but offered little improvement over bivariate ones and an algorithmic approach, making use of local knowledge of factors which might complicate interpretation, is proposed instead. The framework is suggested as a basis for screening, although a larger database is required to produce definitive equations.

Lay reporting of elephantiasis of the leg in northern Ghana

Within a large scale community trial in northern Ghana lay interviewers were trained to inquire about and identify elephantiasis of the leg by the use of local terms and simple examination of respondents. This was repeated a year later after moving the interviewers to different geographical areas. The proportions of extended family compounds reported to have at least one member with elephantiasis of the leg were 12.2% and 12.1 % respectively in the first and second surveys (kappa = 0.60). 'Blind' re-examination of a sub-sample by a physician showed a high level of agreement with the lay interviewer's findings in the first and second surveys (kappa = 0.67 and 0.82 respectively). This study has shown that lay people, even with minimal training, can obtain repeatable and valid estimates of the prevalence of elephantiasis of the leg, at least within an area where local terms for the condition are available. This method could potentially be used for other diseases with visible manifestations.

Risk factors for childhood burns: a case-control study of Ghanaian children

STUDY OBJECTIVE

To study risk factors for childhood burns in order to identify possible preventive strategies.

DESIGN

Case-control design with pair matching of controls to cases in relation to age, sex, and area of residence. The cases and controls were identified by a community based, multisite survey. The effects of host and socioenvironmental variables reported by mothers were investigated in a multivariate analysis using conditional logistic regression.

SETTING

A developing country setting the Ashanti Region in Ghana.

PARTICIPANTS

These comprised 610 cases aged 0-5 years who had been burned (as evidenced by a visible scar) and 610 controls with no burn history.

MAIN RESULTS

The presence of a pre-existing impairment in a child was the strongest risk factor in this population (OR = 6.71; 95% CI 2.78, 16.16). Other significant risk factor included: sibling death from a burn (OR = 4.41; 95% CI 1.16, 16.68); history of burn in a sibling (OR = 1.79; 95% CI 1.24, 2.58); and storage of a flammable substance in the home (OR = 1.51; 95% CI 1.03; 2.21). Maternal education had a protective effect against childhood burns, although this effect was not strong (OR = 0.76; 95% CI 0.55, 1.05).

CONCLUSIONS

Community programmes to ensure adequate child supervision and general child wellbeing, particularly for those with impairments, as well as parental education about burns are recommended, to reduce childhood burns in this region of Ghana. The public should bed advised against storing flammable substances in the home.

Human onchocerciasis in the lower Jos Plateau, central Nigeria: the prevalence, geographical distribution and epidemiology in Akwanga and Lafia local government areas

An investigation of human infection with Onchocerca volvulus and the resulting clinical disease was carried out for the Nigerian National Onchocerciasis Control Programme between July and August 1989 [corrected]. The survey covered 10.6% of the rural population in 41 savanna villages of central Nigeria. Of the 8451 self-selected individuals examined, 900 (10.6%) had skin microfilariae (Mf). There were differences between villages in both endemicity and intensity of infection, but in general the number of both Mf carriers and cases of clinical onchocerciasis increased with age. The disease in the Mf carriers showed as blindness (0.8%), onchocercal nodules (0.6%), leopard skin (1.6%) and pruritus (2.8%). Of 35 persons with lymphatic complications, 19 had hanging groin, 10 had elephantiasis and six had hydrocoele. Onchocerciasis was mesoendemic in the rocky northern escarpments, and became hypoendemic and sporadic in the southern uplands of sedimentary geological origin.