Prevalences of Loa loa microfilaraemia throughout the area endemic for the infection.

Several cases of encephalopathy recorded in Cameroon since 1991 were in patients with very high, coincident, Loa loa microfilaraemias who had been treated with ivermectin for onchocerciasis. There was thus an urgent need to identify those areas where loiasis is hyperendemic, and where specific monitoring procedures should be developed if large-scale ivermectin treatment of onchocerciasis is to be implemented. In the present review, the available data on Loa endemicity are detailed and maps showing the prevalence of Loa microfilaraemia throughout the area endemic for the infection are presented. By superimposing these maps on those which show where onchocerciasis is meso- or hyper-endemic, it is now possible to identify several areas, in south-eastern Nigeria, southern and central Cameroon, the south of the Central African Republic, Equatorial Guinea, Gabon, and the north and west of the Democratic Republic of the Congo (ex-Zaire), where ivermectin treatment, although indicated, is most likely to lead to adverse reactions because of L. loa infections. Additional surveys, to delineate the areas highly infected with L. loa more accurately, are required.