Prevalence and distribution of ocular onchocerciasis in three ecological zones in Nigeria

The African Programme for Onchocerciasis Control (APOC) sponsored a baseline study in Nigeria between 1998 and 1999 on the prevalence and distribution of Onchocerciasis. The randomly selected 1,064 subjects in the baseline study underwent detailed eye examination in Cross River (rain forest), Taraba (savanna) and Kogi (forest-savanna) States. This paper compares and contrasts the public health significance of ocular onchocerciasis in these ecological zones. A blindness prevalence of 2.4% was recorded in the study, onchocerciasis being responsible for 30.2% of the bilaterally blind subjects. Onchocerciasis-induced blindness prevalence was relatively high in the rain forest and forest savanna zones of Cross River and Kogi States, Cross River having the highest site-specific prevalence (50.0%), followed by Kogi (41.7%). Taraba recorded only 27.3%. Other conditions identified included glaucoma, optic nerve disease and cataract rates of which were also found to be high among the population (6.9%, 6.5 % and 8.9% respectively). Anterior segment onchocercal lesions, punctate and sclerosing keratitis were the predominant features of the infection in the savanna zone (14.1% and 6.3% respectively), while posterior segment lesions were much more common in the forest zone. The need to sustain the present efforts to control onchocerciasis through mass ivermectin treatment is recommended.

Utility and effectiveness of computerised motion sensitivity screening tests in rural onchocercal community survey

BACKGROUND

Non-invasive tool of community diagnosis for onchocercal endemicity needs to be identified and ascertained for their utility and effectivity in order to facilitate the control of onchocerciacis in sub-Saharan Africa

OBJECTIVE

To determine the utility and effectiveness of the Wu-Jones Motion Sensitivity Screening Test (MSST) in detecting optic nerve diseases in onchocercal-endemic rural Africa.

METHODS

MSST was applied to sampled subjects in the selected communities of Raja in Sudan; Bushenyi in Uganda; Morogoro in Tanzania; and of Ikom, Olamaboro and Gashaka in Nigeria. Basically, six points within the central field of vision were repeatedly tested at 1/3 meter from the screen of a laptop computer in a room darkened. Motion sensitivity was expressed as a percentage of motion detected in the individual eye and this was averaged for the community.

RESULTS

A total of 3,858 eyes of 2,072 patients were examined. Seventy-six percent of the subjects completed the test, at an average test time of 120.4 (66.7) seconds. The overall mean motion sensitivity of all eyes tested was 88.49 (17.49%). At a cut-off point of 50%, 6.4% of all subjects tested were subnormal, while at 70% cutoff, 13.3% were subnormal. The highest proportion of 50% cutoff sub-normality was recorded at Morogoro at 12.7%.

CONCLUSION

Motion Sensitivity Screening Test was widely accepted and easily administered to the rural and largely illiterate subjects studied. Our data suggest that the proportion of severe field defects by MSST in a community, with cutoff at 33%, best correlates with optic nerve disease prevalence, while proportion of defect from a higher cut-off level at about 50%, best correlates with overall ocular morbidity.

A multi-centre study of community-directed ivermectin distributors' (CDDs') involvement in other healthcare and development programme activities in Cameroon, Togo, Sudan, Nigeria and Uganda

A multi-centre study to determine whether community-directed distributors (CDDs) are capable of carrying out additional healthcare and developmental activities in their communities was carried out in Cameroon, Nigeria, Sudan, Uganda and Togo to ascertain the potential effects of their involvement on the implementation of community-directed treatment with ivermectin (CDTI). Both quantitative and qualitative methods were used to collect data from households, community-directed distributors, community leaders, and health workers. The results showed no major decrease in the CDDs' performance in CDTI: on the contrary, the involvement of CDDs in other health and development activities motivated them to perform their CDTI functions better. However, the results did not show any significant increase in therapeutic coverage of ivermectin distribution. The expansion of the CDDs' experience to include additional healthcare and development related activities would be of interest to onchocerciasis control programmes--it will strengthen CDTI sustainability through greater integration.

Patterns of epidemiology and control of onchocerciasis in west Africa

This paper summarizes the work of the Onchocerciasis Control Programme (OCP) in West Africa, a programme which over a 22 year history has reduced the public health problems of blinding onchocerciasis in eleven countries of West Africa through vector control and, more recently, ivermectin distribution. The paper emphasizes the different approaches to control the programme has developed in the different parts of the programme area which have been determined by the epidemiology of the disease (savanna/forest form), the migratory characteristics of the vectors, intensity of the disease before commencement of treatment, the combined impact of vector control and ivermectin and the likelihood of infiltration of infective blackflies from outside the programme area. The programme has constantly monitored the impact of operations on the trends in prevalence, incidence, annual transmission potential, ocular morbidity and species of fly populations, and as a result, has identified areas where special interventions are required until the programme comes to an end in 2002. The paper illustrates the changes in intensity of infection as measured by community microfilarial load and annual transmission potential over the duration of the programme control activities. The paper also defines and justifies the control strategies in different areas and identifies areas for special interventions.

[Control of onchocerciasis vectors in West Africa: description of the logistics adapted for a large-scale public health program]

The Onchocerciasis Control Programme (OCP) in West Africa, launched in 1974, includes 11 participating countries and covers more than one million square kilometres. The aim of the OCP is to control blinding onchocerciasis (river blindness) which is caused by the savannah strain of Onchocerca volvulus transmitted by the Simulium damnosum complex. There is no effective macrofilaricide, so vector control to prevent the transmission of the parasite remains the method of choice, despite the availability of ivermectin, a drug which controls ocular morbidity. The potential value of vector control has been demonstrated by the original programme: 14 years activity has eliminated the disease as a public health problem in the areas included. This strategy requires adapted logistical support involving (i) widespread insecticide coverage (27,000 km of river are treated by the OCP during the rainy season), (ii) frequent (weekly) application of larvicide and (iii) prolonged intervention due to the life-span of the worm in the human reservoir, estimated to be approximately 14 years. We describe the vector control operations and their organisation 20 years after the initiation of the OCP. The OCP can be divided into 5 areas of logistic activity. The first covers activities involving insecticide and fuel management for the OCP as a whole: assessment of the requirements for the following year, ordering from insecticide and petrol suppliers, stocking fuel and insecticide at the depots covering the area. The second activity is the treatment of rivers with insecticide. This includes treating the ground with larvicide, the aerial operations run by an independent company supplying 12 helicopters on contract to the OCP, and use of satellite beacons for retransmitting of hydrological data. The third activity is monitoring the impact of larvicides on both the target (adult and larval S. damnosum) and on other fauna (fish, crustaceans and other insects). The fourth activity is field data collection and its processing. This involves a data transmission network to facilitate stock management insecticide application and entomological and hydrological surveillance using computer systems. The fifth activity is the coordination of vector control operations, technical and administrative staff and estimations of the funds available to the Vector Control Unit. The logistic aspects of other large-scale-insect-control programmes world-wide are considered, and the possibility of using the OCP as a model for such programmes (both public health and agricultural) is assessed.