Status of human onchocerciasis transmission in the Adamaoua region of Cameroon after 20 years of ivermectin mass distribution.

Introduction: Significant progress has been made in onchocerciasis control through mass distribution of ivermectin among affected human populations, fostering optimism for disease elimination. However, despite these considerable advances, the elimination of the disease remains a major challenge in many African foci. This paper describes the current situation of onchocerciasis in Adamaoua Region of Cameroon after 20 consecutive years of ivermectin mass treatment.

Materials and methods: The study was conducted between August and September 2020 in Adamaoua Region of Cameroon. Onchocerciasis endemicity was assessed through parasitological and clinical diagnosis. Microfilarodermia and nodule prevalences assessed in 2020 were compared to those of 1998-2002 and 2010-2013 surveys using the Chi-square (X 2) statistic test.

Results: A total of 4,814 participants aged between 5 and 108 years, including 50.4% men and 49.6% women were enrolled in the study. The nodule and microfilaria prevalences reported from this sub-sample were 0.87 [0.64 - 1.19] % and 0.77 [0.54 - 1.07] %, respectively. At the community level, the mf prevalences ranged from 0.5% to 4.5%. Globally, the community microfilarial loads (CMFL) were < 0.5 mf/ss. The survey therapeutic coverage rates were between 40% and 78%, lower than those reported (79% - 83%) by the NOCP. The coverage rates in ivermectin treatment in all age groups of the population were below 65%, except for the 40-50 age group where it was ≈70%.

Conclusion: The results of this study show a drastic decline in onchocerciasis prevalences after 20 consecutive years of CDTI, indicating a significant progress towards stopping O. volvulus transmission in Adamaoua Region. However, additional efforts are needed to increase the population coverage in ivermectin treatment in order to stop the parasite transmission in this region.