Onchocerciasis Control In Africa Research Articles

From 'control to elimination': a strategic change to win the end game.

Strategies for elimination evolve from early use of available tools, to elaboration of control strategies, through to 'elimination.' Onchocerciasis control in Africa demonstrates this evolution. Early strategies used vector control but later used mass distribution of ivermectin. Elimination in Africa though was not thought to be possible; however, with excellent coverage of ivermectin distribution it was demonstrated that treatment could be stopped on the Senegal Mali border stimulating a new policy of elimination of transmission where possible. This new policy must not be business as usual but will require redefining treatment areas, improving quality of data, and flexibility of strategies to fit the new paradigm.

15 years of APOC—a lifetime of public health evidence

The sculpture Sightless Among Miracles outside WHO headquarters in Geneva, Switzerland, celebrates the ongoing successes of onchocerciasis control in Africa. At the unveiling of the sculpture in 1999, the Onchocerciasis Control Programme (OCP), a joint effort of four UN agencies, had been running for 25 years. In that time, it covered 30 million people in 11 countries in sub-Saharan Africa, primarily through a programme of regular larvicide spraying in an effort to control the Simulium vector of Onchocerca volvulus.

Traditional kinship system enhanced classic community-directed treatment with ivermectin (CDTI) for onchocerciasis control in Uganda

The challenges of community-directed treatment with ivermectin (CDTI) for onchocerciasis control in Africa have been: maintaining a desired treatment coverage, demand for monetary incentives, high attrition of community distributors and low involvement of women. This study assessed how challenges could be minimised and performance improved using existing traditional kinship structures. In classic CDTI areas, community members decide upon selection criteria for community distributors, centers for health education and training, and methods of distributing ivermectin. In kinship enhanced CDTI, similar procedures were followed at the kinship level. We compared 14 randomly selected kinship enhanced CDTI communities with 25 classic CDTI communities through interviews of 447 and 750 household members and 127 and 64 community distributors respectively. Household respondents from kinship enhanced CDTI reported better performance (P<0.001) than classic CDTI on the following measures of program effectiveness: (a) treatment coverage (b) decision on treatment location and (c) mobilization for CDTI activities. There were more female distributors in kinship enhanced CDTI than in classic CDTI. Attrition was not a problem. Kinship enhanced CDTI had a higher number of community distributors per population working among relatives, and were more likely to be involved in additional health care activities. The results suggest that kinship enhanced CDTI was more effective than classic CDTI.

Community-directed interventions for priority health problems in Africa: results of a multicountry study

To determine the extent to which the community-directed approach used in onchocerciasis control in Africa could effectively and efficiently provide integrated delivery of other health interventions. A three-year experimental study was undertaken in 35 health districts from 2005 to 2007 in seven research sites in Cameroon, Nigeria and Uganda. Four trial districts and one comparison district were randomly selected in each site. All districts had established ivermectin treatment programmes, and in the trial districts four other established interventions - vitamin A supplementation, use of insecticide-treated nets, home management of malaria and short-course, directly-observed treatment for tuberculosis patients - were progressively incorporated into a community-directed intervention (CDI) process. At the end of each of the three study years, we performed quantitative evaluations of intervention coverage and provider costs, as well as qualitative assessments of the CDI process. With the CDI strategy, significantly higher coverage was achieved than with other delivery approaches for all interventions except for short-course, directly-observed treatment. The coverage of malaria interventions more than doubled. The district-level costs of delivering all five interventions were lower in the CDI districts, but no cost difference was found at the first-line health facility level. Process evaluation showed that: (i) participatory processes were important; (ii) recurrent problems with the supply of intervention materials were a major constraint to implementation; (iii) the communities and community implementers were deeply committed to the CDI process; (iv) community implementers were more motivated by intangible incentives than by external financial incentives. The CDI strategy, which builds upon the core principles of primary health care, is an effective and efficient model for integrated delivery of appropriate health interventions at the community level in Africa.

The World Bank

The control of human onchocerciasis (river blindness) is one of the most successful global partnerships ever supported by the World Bank. Mectizan mass treatments have greatly contributed to this success and have shaped the strategies of the programmes in which the World Bank has been involved - the Onchocerciasis Control Programme (OCP), which covered onchocerciasis control in West Africa until 2002, and the African Programme for Onchocerciasis Control (APOC), which is currently working in 30 countries, to protect millions of people from onchocerciasis. Through the strategy of community-directed treatment with ivermectin (CDTI), onchocerciasis control in Africa was transformed from a technologically-driven and vertical health initiative to a community-directed process of treatment and empowerment. Together, CDTI and the donation of Mectizan also reduced costs, producing one of the most effective and affordable disease-control schemes ever seen, and the CDTI strategy is now being applied to other disease-control initiatives. The onchocerciasis programmes have also been exemplary in shaping partnerships with communities, countries, the World Health Organization, governments, non-governmental development organizations, and the private sector. The Bank's involvement in onchocerciasis control has helped mobilize funds, giving confidence to other donors. More than U. S.$800 million was raised for both the OCP and APOC (excluding the initial costs of Mectizan). With these funds and the commitment of the partners involved, high coverages have been achieved in the Mectizan distributions. The Bank is confident that, during the years to come, the partners will continue their success, and that the APOC will achieve its goals by the target date for its closure, in 2015.

Engaging the Community: An Interview with Uche Amazigo

Engaging the Community: An Interview with Uche Amazigo

Microfilarial distribution of Loa loa in the human host: population dynamics and epidemiological implications

Severe adverse events (SAEs) following ivermectin treatment may occur in people harbouring high Loa loa microfilarial (mf) densities. In the context of mass ivermectin distribution for onchocerciasis control in Africa, it is crucial to define precisely the geographical distribution of L. loa in relation to that of Onchocerca volvulus and predict the prevalence of heavy infections. To this end, we analysed the distribution of mf loads in 4183 individuals living in 36 villages of central Cameroon. Mf loads were assessed quantitatively by calibrated blood smears, collected prior to ivermectin distribution. We explored the pattern of L. loa mf aggregation by fitting the (zero-truncated) negative binomial distribution and estimating its overdispersion parameter k by maximum likelihood. The value of k varied around 0.3 independently of mf intensity, host age, village and endemicity level. Based on these results, we developed a semi-empirical model to predict the prevalence of heavy L. loa mf loads in a community given its overall mf prevalence. If validated at the continental scale and linked to predictive spatial models of loiasis distribution, this approach would be particularly useful for optimizing the identification of areas at risk of SAEs and providing estimates of populations at risk in localities where L. loa and O. volvulus are co-endemic.

Experimental studies on the transmission of Onchocerca volvulus by its vector in the Sanaga valley (Cameroon): Simulium squamosum B. Intake of microfilariae and their migration to the haemocoel of the vector.

As large-scale ivermectin distribution is becoming the mainstay of onchocerciasis control in Africa, the issue of its impact on local transmission is increasing in importance. The vector competence of Simulium squamosum B in the severe focus of the Sanaga valley, Cameroon, was therefore investigated, by feeding 1320 flies on 14 carriers of Onchocerca volvulus microfilariae (mff). The results enabled the relationships between skin microfilarial load, microfilarial intake by the flies, the proportion and mean number of ingested mff that succeed in reaching the fly's haemocoel, and the frequency distribution of the ingested mff to be described, as functions of time post-engorgement (p.e.) and parasite density (while taking account of possible measurement error in the predictor variable). The proportion of flies with haemocoelic mff and the mean number of mff/fly increased up to 3 h p.e. The proportion of flies with ingested mff was non-linearly related to mean intake, via the negative-binomial distribution, with the overdispersion parameter k best described as an increasing (power) function of the mean. Approximately one in every three ingested mff escaped imprisonment by the peritrophic matrix, irrespective of the skin microfilarial load or the intake of mff. The relationship between successful and input mff is nearly linear (indicating proportionality) in S. squamosum B. These results are compared with those from O. volvulus-S. damnosum s.l. combinations in other West African foci.

The challenge of establishing community-directed treatment with Mectizan in Uganda.

Onchocerciasis is a major public health problem in Uganda, affecting 17 of the country's 39 districts. 1995 data indicate that of the 19 million Ugandans, 1.8 million were at risk of infection and 1.36 million were already infected. 1.3 million Ugandans in 2255 villages are currently being targeted for annual treatment with Mectizan (ivermectin, MSD). 74% of the targeted villages are hyperendemic and 18% are meso-endemic for the disease. The control of onchocerciasis in Uganda through the mass distribution of Mectizan began in the early 1990s, as a result of collaboration between the Ministry of Health and 4 nongovernmental development organizations. With the aim of eliminating onchocerciasis as a public health problem in Uganda, the national program now reaches all communities known to be affected by the disease in all but 1 district, and achieved a mean treatment coverage of 75% in 1995 and 1996. However, with results of a 1996 World Health Organization study suggesting that community-directed treatment should be the main method of onchocerciasis control in Africa, Uganda's national onchocerciasis task force must now reorient its current program from community-based to community-directed treatment. This latter approach gives communities a greater role in distributing Mectizan.

Onchocerciasis and Chagas' disease control: the evolution of control via applied research through changing development scenarios.

This paper addresses the development of control strategies of two different parasitic diseases and identifies commonalities which have contributed to the success of regional intercountry programmes of onchocerciasis control in Africa, the Onchocerciasis Control Programme (OCP), and the new African Programme for Onchocerciasis Control (APOC) and the Chagas' Disease Control Programme in the southern cone of South America.

The WHO Onchocerciasis Control Programme: Retrospect and prospects

The history of onchocerciasis control in Africa and the genesis of the WHO Onchocerciasis Control Programme in West Africa (OCP) are briefly reviewed. The importance of experience gained in anti-locust campaigns in helping to plan the OCP is stressed. Members of the Simulium damnosum species complex are the vectors of onchocerciasis, which OCP is controlling with insecticide treatments on the stretches of rivers where the Simulium breed. Migrations of flies have been responsible for reinfestations of controlled areas and the spread of insecticide resistance. The management of these problems and related research are described, but it is emphasized that despite setbacks OCP is achieving its aims. A strategy for the future is outlined: vector control supplemented by chemotherapy is expected to continue until the year 2004.