Serious limitations of the current strategy to control Soil-Transmitted Helminths and added value of Ivermectin/Albendazole mass administration: A population-based observational study in Cameroon

Background Soil-transmitted helminth (STH) infections remain a public health concern in sub-Saharan Africa. School-based mass drug administration (MDA) using the anthelminthic drug Mebendazole/Albendazole have succeeded in controlling morbidity associated to these diseases but failed to interrupt their transmission. In areas were filarial diseases are co-endemic, another anthelminthic drug (Ivermectin) is distributed to almost the entire population, following the community-directed treatment with ivermectin (CDTI) strategy. Since Ivermectin is a broad spectrum anthelmintic known to be effective against STH, we conducted cross-sectional surveys in two health districts with very contrasting histories of Ivermectin/Albendazole-based PC in order to investigate whether CDTI might have contributed in STH transmission interruption. Methodology Cross-sectional surveys were conducted in two health districts with similar socio-environmental patterns but with very contrasting CDTI histories (Akonolinga health district where CDTI was yet to be implemented vs. Yabassi health district where CDTI has been ongoing for two decades). Stool samples were collected from all volunteers aged >2 years old and analyzed using the Kato-Katz technique. Infections by different STH species were compared between Akonolinga and Yabassi health districts to decipher the impact of Ivermectin/Albendazole-based MDA on STH transmission. Principal findings A total of 610 and 584 participants aged 2–90 years old were enrolled in Akonolinga and Yabassi health districts, respectively. Two STH species (Ascaris lumbricoides and Trichuris trichiura) were found, with prevalence significantly higher in Akonolinga health district (43.3%; 95% CI: 38.1–46.6) compared to Yabassi health district (2.5%; 95% CI: 1.1–5.1) (chi-square: 90.8; df: 1; p < 0.001). Conclusion/significance These findings (i) suggest that Mebendazole- or Albendazole-based MDA alone distributed only to at-risk populations might not be enough to eliminate STH, (ii) support the collateral impact of Ivermectin/Albendazole MDA on A. lumbricoides and T. trichiura infections, and (iii) suggest that Ivermectin/Albendazole-based PC could accelerate STH transmission interruption.
Author summary Decades of preventive chemotherapy (PC) using Mebendazole/Albendazole among school-aged children had not significantly decreased STH prevalence and intensity of infection, and Mathematical modelling demonstrated that interruption in STH transmission cannot be achieved unless MDA are broadened to an important proportion of the entire population. Concurrently, Ivermectin has been considered as a wonder drug because of (i) its applications in veterinary medicine, (ii) its tremendous impact on its initial indication in human medicine (river blindness), and (iii) its large spectrum of activity up to quite unsuspected effects on Human Immunodeficiency Virus (HIV). The efficacy of Ivermectin on STH has therefore been largely documented since the 2000s. Since Ivermectin/Albendazole-based MDA is administered to almost the entire population, we conducted cross-sectional surveys in two health districts with very contrasting histories of Ivermectin/Albendazole mass distributions to investigate whether Ivermectin/Albendazole-based PC might have interrupted STH transmission. Our findings confirm that Mebendazole- or Albendazole-based MDA alone and administered only to at-risk groups is not enough to eliminate STH and suggest that PC with Ivermectin (in combination to Albendazole) administered almost to the entire population would have contributed to STH transmission interruption. These observations are supportive of revision of WHO guidelines and recommendations to fight against STH.