This study compiled all the data on the program for more than 15 years of its implementation. However, it has some limitations inherent to the characteristics of an ecological study.
Despite these shortcomings, we have shown that after four years of launching the program, a geographical coverage of the entire territory has been achieved. This time frame is the accepted average for the mapping of endemic areas [16]. This can be explained by certain facilitating factors such as the international environment, which was favorable the day after the declaration of the WHO resolution [10] : a well-organized health system, the political will to eliminate LF, the involvement of financial partners, and above all, good community participation [17].
The rate of therapeutic coverage was within the WHO-defined efficacy limits in general [14]. Our study showed that six times out of ten, the programmatic coverage rate was above 80%. Our results are comparable to the data of Ouédraogo et al who found a therapeutic coverage rate of 80% in a study carried out in the east of the country [18]. The number of treatment rounds and the epidemiological therapeutic coverage rate were associated with LF treatment interruption. This result can be explained by social mobilization, health information and education, and training of community distributors. [17]. In addition, it is important to emphasize that the population's experience with mass treatment during the fight against onchocerciasis could explain the acceptability of the treatment, since Burkina Faso was an endemic country [17, 19, 20].
The slight regression in drug coverage reported over the years 2016 and 2017 would likely be related to the population fatigue, or adverse drug reactions [21].
The major effect of this therapeutic coverage is the reduction of 96.81% of the median prevalence of microfilaremia at the sentinel sites from 8.16–0.26%. Also, the median parasite density decreased from 1531mf/µl to 67mf/µl, a reduction of 95.62%. Ouédraogo et al in a study conducted in the eastern region of Burkina Faso found 95.14% of reduction [18], while Simonsen et al in Tanzania in the Tanga district after eight rounds of treatment recorded a reduction from 75.5–89.6% of the baseline parasite density [22]. These results reflect the microfilaricidal efficacy of the ALB + IVM [14, 23, 24]. However, despite this good and effective therapeutic coverage, nine sites still remain endemic. They are located in three regions: the southwest, the center-east and the east. The hypotheses that may explain the persistence are: intense transmission, a higher initial parasite load. Also, they border Côte d'Ivoire, Ghana and Togo, which favors population migration. [25]. In addition, persistence can be explained by climatic, environmental, and demographic factors that are favorable to transmission as demonstrated by the study of Stanton et al. which found that the duration of the rainy season, variability of the normalized vegetation index, and population density were significantly associated with the prevalence of LF in a positive way. [26]. Some other reasons may be mentioned such as non-adherence of the population to drugs, population flows through migration [27]drug resistance [28].. Most studies identify non-compliance as the main cause. This poor compliance can be explained by the fear of adverse effects, alcohol consumption, absence of community dispensers, the socio-anthropological interpretation of the disease and the inadequacy of information, education and communication in health [21, 29–33]. Moreover, the persistence of transmission could be explained by the low macrofilaricidal activity of the drug combination used, so we wait for the death of adult worms to break the transmission [34]. Also, these regions have the lowest rates of coverage in LLINs 65.6% for Centre-East, 68.5% for East and 58% for South-West for a national average of 75.3% according to the results of the survey on malaria indicators 2017–2018 [35].
Therefore, for these regions the adoption of other control strategies such as directly observed drug distribution and intake, biannual treatment, vector control through the use of long lasting insecticide nets ( LLINs), synchronized cross-borders campaigns, and the WHO-recommended ivermectin, diethylcarbamazine, albendazole triple therapy will contribute to the elimination of LF as a public health problem [36–38].
Preliminary results from a randomized clinical trial being conducted in Côte d'Ivoire report improved efficacy of triple therapy compared to dual therapy with a 10-fold reduction in microfilaremia [39].
So, our study showed that 87.14% of the 70 health districts interrupted transmission and stopped MDA, thus under epidemiological surveillance in order to detect a recrudescence of LF transmission. Transmission assessment surveys conducted at 2, 4 and 6 years after treatment cessation did not show an increase in cases. The WHO threshold was never reached. Nana-Djeunga H.C et al in northern Cameroon [40] found similar results to ours. A study conducted in southeastern Tanzania in the Rufiji region noted an absence of filarial-ag positive cases after 12 years of treatment discontinuation and in Togo after 3 years. [41]. In contrast to our results, Coulibaly et al found in Mali an increase in the prevalence of filarial antigen in children aged 6–7 years after 5 years of cessation of treatment [42]. This result can be explained by the fact that the study was carried out in an area of co-infection with Loa loa and Mansonia perstans, which have antigens responsible for cross-reactions in immuno-chromatographic tests [43]. At the end of this study, we consider relevant the implementation of some recommendations in order to accelerate the elimination of LF as a public health problem.