Association between microfilarial load and excess mortality in onchocerciasis: an epidemiological study

Background Infection with the parasitic filarial nematode Onchocerca volvulus can lead to severe visual impairment and ultimately blindness. Excess mortality has been noted among people with onchocerciasis, but it is not clear whether this effect is entirely due to blindness, or mediated by some more direct effects of the infection. Methods We assessed the relations between infection with O volvulus, visual acuity, and host mortality with data obtained by the Onchocerciasis Control Programme in West Africa from 2315 villages in 11 countries. Findings 297 756 people were eligible for follow-up, and accumulated 2 579449 person-years of follow-up from 1971 through 2001. 24517 people died during this period; 1283 (5.2%) of these deaths were due to onchocerciasis. Mortality of the human host was significantly and positively associated with increasing microfilarial burden (p<0•00001), but not with blindness after adjustment for microfilarial load and other variables. Overall, after adjustment for microfilarial load and other variables, female individuals had a risk of death about 7.5% lower than males (p<0•00001). Rates of mortality peaked in the mid 1980s but generally decreased thereafter. Interpretation We have shown a direct relation between O volvulus microfilarial load and host mortality in a comprehensive dataset and in both sexes.