Insecticide resistance in the Simulium damnosum S. L. vectors of human onchocerciasis: distributional, cytotaxonomic and genetical studies

Human onchocerciasis is a debilitating disease caused by the filarial parasite Onchocerca volvulus (Leukart). The parasite is transmitted by dipterous insects of the family Simuliidae. ln West Africa, transmission is by members of lhe Simulium damnosum (Theobald) species complex. The manifestations of the disease are mainly dermal, lymphatic and ocular, the most severe of which is blindness hence the common name 'river blindness'. The disease is found in parts of Latin America, the Yemen and Sub-Sahara Africa. lt affects some 17.7 million people world-wide with 500,000 severely visually disabled and some 27O,00O blind. ln West Af rica, which is the most affected area, there are over 5 million infected with onchocerciasis and about 148,000 blind. ln view of this, the Onchocerciasis Control Programme in West Africa (OCP), one of the biggest vector control operations covering parts of 11 countries was started in 1975 by the World Health Organization to control onchocerciasis as a disease of public health and socio-economic importance. The initial strategy of the OCP was the application of insecticides to the breeding sites of the insect vectors. ln the OCP, temephos an organophosphate insecticide (OP) was the only chemical used for the initial five years due to its selective mode of action. Resistance to temephos first appeared in 1980 in a population of S. soubrense/S.sanctipauli on the Bandama river in Southern Côte d'lvoire. Later, similar resistant populations of the same species were identified in other river basins in the C6te d'lvoire. ln 1981 Chlorphoxim, also an OP, was used as a replacement for temephos in areas where resistance to temephos had been detected but a similar pattern of resistance was soon detected against chlorphoxim Careful monitoring of resistance to temephos has shown that it has spread to all river basins and different species of the S. damnosum complex at one time or another within the OCP area. Resistance to insecticides demands that large quantities and more novel and toxic chemicals have to be used in the fight against insects and other arthropod pests. This has important economic, operational and environmental demands. ln the West African vector control programme mentioned above, a rotation of 6 insecticides is used to manage insecticide resistance. This strategy places a major constraint on the operations of the Programme (OCP) due to the logistic need of stocking insecticides in the field

Apoc impact assessment study Onchocerciasis: baseline ophthalmological Survey in southwestern Sudan

A cross-sectional survey of eye disease supported by the African Programme for Onchocerciasis Conffol (APOC) was carried out in October 1998, in Raja, Sudan, a Savanna ecological zone to determine the prevalence and distribution of onchocercal eye disease. Detailed eye examination including measurement of visual field using the Wu-Jones computerized Motion Sensitivity Screening Test (MSST) were carried out. A total of 481 individuals were examined, of which 379 underwent detailed eye examination. A high prevalence of blindness (8.1%) from all causes was recorded. Onchocerciasis-induced eye disease was responsible for blindness in 56.40/o of all blind persons. Of the 38 persons who had visual impairment, 13 (2.7%) were severely affected. As many as 91 (24.0%) persons had microfilariae (mfs) in the anterior chamber (AC) and /or cornea with the highest prevalence of 29.3Yo and 28.8% respectively, recorded among the young and active individuals. This age group (15-24yeus) also had the highest prevalence (15.3%) of flufff corneal opacities. Sclerosing keratitis was present in 46 (12.1%) subjects while iridocyclitis was diagnosed in 9.0% with the highest prevalenc e of 25 .0o/o noted in the 45 - 54 age group. Prevalence of blinding cataract was 54.1% while that of glaucoma was12.2%. Presumed optic nerye disease, a known pathway to onchocercal blindness was observed in 19.6% with one third of this percentage already at the advanced stage. Another common pathway to blindness, chorioretinitis, affected 15.2% of the subjects of which 7.2% had reached advanced stages.Prevalence of abnormal visual fields was 6.6Yo. Posterior segment oncho disease was found to be the main ocular pathology in 15.6% subjects followed closely by 13.5% whose main cause was anterior segment oncho lesion. Both sexes were almost equally affected. Ocular findings in this area particularly among the young conform to high intensity levels of onchocerciasis infection and therefore require urgent effective intervention to forestall further devastating oncho-induced blindness and alleviate the socio-economic burden imposed on this population.

Endémie onchocerquienne au Niger prospection dans la vallée du Bas-Goroubi

Sont rapportés les conditions générales et les résultats d'une enquête, d'évaluation épidémiologique de 6 villages prospectés dans une région, bénéficiant depuis 1977 d'une campagne visant au contrôle du vecteur, par l'action d'insecticides. S'il y a une baisse considérable du potentiel de transmission de la maladie, il persiste encore des sujets très jeunes ayant des biopsies cutanées positives.Des études de_ ce type sont indispensables pour juger de l'efficacité de la campagne de lutte contre l'onchocercose sur l'évolution de la maladie dans la population humaine