Impact of preventive chemotherapy on transmission of soil-transmitted helminth infections in Pemba Island, United Republic of Tanzania, 1994–2021

Abstract

Soil-transmitted helminth (STH) infections cause significant morbidity in children and women of reproductive age. The World Health Organization (WHO) recommends preventive chemotherapy (PC) of at-risk populations with anthelminthics to control these infections. Historically, STH are very intensively transmitted in Pemba Island (Zanzibar). A survey conducted in 1994 in 12 schools estimated a STH prevalence near to 100%. This extremely high prevalence induced the introduction of PC in the island; initially, however, PC was not regularly administered because of difficulties linked to drug procurement. A second STH survey, conducted in 2011, in 24 schools estimated a prevalence of STH of 89%; after this survey, PC was regularly administered until 2018. We conducted a survey in 2021 using the same method as that used in 2011. The prevalence of STH was evaluated at 80% (95% CI 78.1–81.5) and most of the STH cases were due to Trichuris trichiura. More than 32% (95% CI 30.3–34.0) of the children investigated had infections of moderate or heavy intensity. PC has been conducted for over 25 years in Pemba Island. However, despite its beneficial impact, both the prevalence and the intensity of STH infections remain high, and the intervention has been insufficient in controlling STH morbidity. This is probably due to a combination of irregular PC, climatic conditions favourable to STH transmission, the low sensitivity of T. trichiura to benzimidazoles, high population density and poor sanitation. Improvement of sanitation coverage remains a key measure to permanently reduce the prevalence and intensity of STH. Possible changes to the present PC approaches to better control STH in Pemba would be (i) to assure high coverage in all schools, (ii) to use mebendazole instead of albendazole given its better activity on T. trichiura and (iii) to use a combination of ivermectin and mebendazole to further increase anthelminthic efficacy on T. trichiura.

Effectiveness of ivermectin mass drug administration in the control of soil-transmitted helminth infections in endemic populations: a systematic review and meta-analysis

“…A total of 21 papers (reporting 25 studies) met the inclusion criteria for the systematic review [ 17 – 25 , 34 – 45 ] and 15 of these papers (reporting 19 studies) were included in the meta-analysis [ 17 – 22 , 24 , 25 , 35 , 36 , 39 , 41 – 43 , 45 ] (Fig. 1 ).…”

“…Table 1 lists individual studies included in the systematic review with their characteristics while Table 2 provides an aggregated summary of the study characteristics. Of the 25 studies included in the systematic review, 17 (68%) used ivermectin and albendazole as their PC regimen [ 20 – 25 , 34 , 36 , 38 – 41 , 43 , 45 ] and 8 (32%) used ivermectin with no other anthelminthic drugs [ 17 – 19 , 35 , 37 , 42 , 44 ]. Nine studies used additional drugs in addition to ivermectin and/or albendazole [ 19 , 34 , 36 , 38 – 41 , 44 ].…”

“…Of the 25 studies included in the systematic review, 17 (68%) used ivermectin and albendazole as their PC regimen [ 20 – 25 , 34 , 36 , 38 – 41 , 43 , 45 ] and 8 (32%) used ivermectin with no other anthelminthic drugs [ 17 – 19 , 35 , 37 , 42 , 44 ]. Nine studies used additional drugs in addition to ivermectin and/or albendazole [ 19 , 34 , 36 , 38 – 41 , 44 ]. There was no head-to-head comparison of ivermectin versus ivermectin and albendazole.…”

“…There was no head-to-head comparison of ivermectin versus ivermectin and albendazole. Ivermectin was distributed to entire through community-wide MDA for all studies [ 17 – 25 , 34 – 45 ]. Onchocerciasis ( n = 3) (17, 34, 37) and scabies ( n = 3) (18, 39, 43) were the primary diseases targeted for studies using ivermectin only.…”

“…Onchocerciasis ( n = 3) (17, 34, 37) and scabies ( n = 3) (18, 39, 43) were the primary diseases targeted for studies using ivermectin only. In studies using ivermectin and albendazole combined, albendazole was mostly distributed to entire communities through MDA together with ivermectin ( n = 13) [ 21 – 25 , 36 , 39 , 41 , 43 , 45 ], although four studies complemented MDA efforts with school-based targeted PC [ 20 , 34 , 38 , 40 ] with albendazole only on alternating timelines. Lymphatic filariasis was the most commonly targeted primary disease, representing 64% of these studies ( n = 16) (19, 21, 22, 33, 35, 36, 38, 40–42, 44, 46).…”