Human loa loa (Cobbold, 1864) (Filaroidea: Onchocercidae) morbidity distribution in northern Enugu State, Nigeria: implications for onchocerciasis control

Abstract

A cross-sectional epidemiological investigation was conducted in Nsukka senatorial zone of Nigeria to evaluate the use of specific clinical signs/symptoms in the assessment of the endemicity, prevalence and morbidity of Loa loa infection in areas meso-endemic for onchocerciasis, and to evaluate the results in respect of the probability of occurrence of adverse reactions, post-treatment with ivermectin in areas presumed to be hypo-, meso-, and hyper endemic for Loa loa infection and morbidity. Standard questionnaire based on the key clinical manifestations of loiasis were administered and the microfilaraemic levels of respondents determined at both community and individual levels. The results showed that the clinical symptoms/signs were known in all the study communities. Altogether 22.0% of respondents (n=1600) positively indicated having experienced either Loa loa infection and/ or Calabar swelling. Based on the questionnaire indices, an intercommunity prevalence of 21.9% (range 17.50 - 27.50%) was established. An overall community median microfilaraemia (mf) prevalence of 19.4% (range 15.0 - 26.3%) was also recorded. A microfilaraemia prevalence >20% was however established in >35% of the study communities indicating the possibility of adverse reaction after ivermectin administration. More males (n=203, 12.7%) than females (n=109, 6.8%) were microfilaraemic. Linear logistic regression indicated that Loa loa infection was significantly associated with age (adjusted odds ratio: 1.12, 95% confidence interval: 1.00-1.14, p<0.001). The intercommunity mean intensity of microfilarial load varied (range 112 ± 25 – 205 ± 30).The best diagnostic performance was obtained for reported history of L. loa with a sensitivity of 100% and a specificity of 94.6%.