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Serious Limitations of the Current Strategy to Control Soil Transmitted Helminths and Added Value of Ivermectin Mass Administration: A Population-Based Observational Study in Cameroon

Background: Soil-transmitted helminth (STH) infections remain an important public health concern in sub-Saharan Africa. School-based mass drug administration (MDA) using the anthelminthic drug Mebendazole/Albendazole have succeeded in controlling morbidity and mortality associated to these diseases but failed to interrupt their transmission. In areas were filarial diseases are co-endemic, another anthelminthic drug (ivermectin) is distributed at the community level. It was previously demonstrated that ivermectin is a very broad spectrum highly effective drug, including against STH. One can therefore hypothesizes that ivermectin-based MDA administer to a broader population can help interrupting STH transmission. We therefore compared the prevalence and intensity of STH infections between two health districts with very contrasting histories to ivermectin mass distributions, so-called community directed treatment with ivermectin (CDTI). 
 
Methods: 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. Prevalence and intensity of infection by different STH species were compared between Akonolinga and Yabassi health districts to decipher the impact of ivermectin-based MDA on STH transmission. 
 
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 to infest the study population, with prevalence significantly higher in Akonolinga health district (43·3%; 95% CI: 38·1-46·6) compared to Yabassi health district and (2·5%; 95% CI: 1·1-5·1) (chi-square: 90·8; df: 1; p < 0·001). 
 
Interpretation: These findings (i) confirm 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 MDA on prevalence and intensity of A. lumbricoides and T. trichiura infections, and (iii) suggest that ivermectin-based PCT might be helpful in interrupting STH transmission. 
 
Funding Statement: European Union (Grant Agreement: EDCTP-RegNet2015-1045) through the 57 Central Africa Network on Tuberculosis Aids/HIV, Malaria and NTDs (CANTAM2) 
 
Declaration of Interests: The authors declare that they have no competing interests. 
 
Ethics Approval Statement: An ethical clearance was obtained from the Faculty of Medicine and Biomedical Sciences Institutional review board (N°294/UY1/FMSB/VDRC/CSD) and administrative authorizations were granted by the Akonolinga and Yabassi District Medical Officers.