Soil-transmitted helmenthiasis (STH) and Schistosomiasis (SCH) are the two most common Neglected Tropical Diseases (NTDs) affecting economically deprived people living in warm and moist tropical areas. STH is caused by helminths of the roundworms (Ascaris lumbricoides), the whipworms (Trichuris trichiura) and the hookworms (Ancyclostoma dodenale or Necator americanus). Humans are infected by these helminthes through ingestion of eggs contaminated with soil or penetration of the skin by larvae grown on soil from egg excreted from infected individuals in areas of poor sanitation and hygiene [1]. An estimated 2 billion world population was infected by STHs in 2010: 438.9 million, 819.0 million and 464.6 million were infected by Hookworm, A.lumbricoides and T.trichiura respectively [2, 3].
Schistosomiasis (SCH) is caused by blood flukes of the genus Schistosoma. Humans become infected when the larval form of the parasite is released into the water when the snail host penetrates the skin. Transmission of SCH was reported from 78 countries, but 90% of moderate-to-heavy infections requiring preventive chemotherapy (PC) live in Africa. There are two major forms of SCH (intestinal and urogenital) with the intestinal form caused by S.mansoni being the most common in Ethiopia [4].
In Ethiopia, about 79 million people, including 25.3 million SAC were living in STH endemic areas while the corresponding numbers for intestinal SCH were 37.3 million and 12.3 million in 2013[5]. The 2013 and 2015 national SCH and STH mapping carried out in Ethiopia revealed that the overall prevalence of STH infection was 21.7% with the most prevalent parasite being A. lumbricoides (12.8%) followed by Hookworm (7.6%) and T. trichiura (5.9%). The burden of SCH was 3.5% at national level and regional prevalence was 2.6% in South Nations Nationalities and Peoples Regional (SNNPR) state where the present study area is located. This region was the 2nd most STH high burden region (42.4%) next to Gambella (58.1%) among the nine regional states and two city administrations found in Ethiopia [6].
The morbidity from STH depends on the intensity of infection. It is attributable to their chronic nature and insidious impact on the health and quality of life than mortality. In moderate to heavily infected individuals, STH impairs the physical growth, cognitive development and micronutrient deficiencies leading to poor school-performance and absenteeism in SAC; reduced work productivity in adults and adverse pregnancy outcomes [3].
Symptoms associated with SCH were due to the reaction of the body to the eggs lodged in the blood vessels. Intestinal SCH can result in abdominal pain, diarrhea and blood in the stool. In advanced stage of the disease, there is enlargement of the spleen and liver, which is associated with accumulation of the fluid in the peritoneal cavity and the hypertension of abdominal blood vessels. In children, SCH causes anemia, stunting and reduced ability to learn. In some chronic cases, SCH can lead to death. WHO estimated that the annual death rate due to SCH was 200 000 globally[4]
To overcome the morbidities from STH and SCH, WHO recommended chemoprevention as a public health intervention to reduce the worm burden among young children, preschool children, SAC, adolescent girls and women of the reproductive age group. Systematic review of published trials indicated that the egg reduction rate of a single dose of drugs (400 mg albendazole or 500 mg Mebendazole) used for STH was above the WHO threshold and can be continued to reduce the worm burden and associated morbidities [1]. In contrast to this, there was evidence from Uganda indicating that as the number of rounds of MDA with Praziquantel (PZQ) for the treatment of SCH increases, the egg reduction rate falls below the recommended threshold of 95% egg reduction rate[7]. A recently conducted study in Ethiopia concluded that therapeutic efficacy of PZQ 40 mg/kg was promising on both egg reduction rate and cure rate [8].
Ethiopia has launched the national NTD control program in November 2015 and targeted to eliminate morbidity due to STH and SCH among SAC by 2020 and break transmission by 2025. There were 100% geographic coverage and the individual treatment coverage was 77% and 76.5% for SCH and STH respectively in the 1st nationwide deworming campaign [5, 9]. However, the coverage validation survey undertaken by one of the authors of this manuscript, as principal investigator in March 2019, indicated that the treatment coverage varied widely per districts ranging from 54.4–91.6% for STH and 59.7–89.6% for SCH[10].
Though PC and other supplementary interventions reduced the prevalence and intensity of STH infections, the reduction was spatiotemporally heterogeneous suggesting stringent monitoring and evaluation of the deworming process to be undertaken in different contexts[11]. A cross-sectional study conducted in agricultural area in Indonesia showed that STH infection remained high after 15 years of deworming campaign between 2003 and 2018. In Indonesia, the prevalence of STH infection was 91.3% in 2003 and reduced to 57.2% in 2018 [12].
Depending on the performance of MDA, the reduction in the prevalence of any STH infection varied widely in Kenya. The reduction in the prevalence of STH infection ranged from 90.0–27.5% after deworming from 2012 to 2017[13]. In similar, the prevalence of SCH infection also remained high as revealed by a study conducted in Tanzania. The prevalence of SCH infection among the whole population age above 1 year in Ljinga Island in Tanzania was 68.9%. Despite PZQ treatment was given only for SAC, the highest prevalence of SCH among SAC (86.1%) indicate that the reinfection was high, warranting for the need of supplementary intervention to achieve elimination and transmission break targets [14]. The reinfection of STH among SAC in Chencha district reached 93.4% of the baseline prevalence within three months post mass drug distribution campaign [15].
Studies assessing the prevalence of STH and SCH infection revealed that it varied both spatially and temporally. Recent studies conducted in Ethiopia indicated that the prevalence of STH infection with different diagnostic technique ranged from 9.5% in Gurage Zone in South-central Ethiopia [16] to 52.4% in southwestern Ethiopia [17]. In Hawassa town, capital of SNNPR, the prevalence of any kind of intestinal parasitic infection was 42.4% [18]. Articles reviewed originating from other African countries indicated that the prevalence of STH infections ranged from 1% in a study conducted after two months of MDA in Cameroon [19] to 40.0% in Kenya [20]. The highest prevalence (57.2%) was seen in the Agricultural area in Indonesia [12] while it was 27.9% Myanmar in Asia [16, 21].
STH and SCH infections were common in areas where sanitation and hygiene is poor, in the dry season [17] and with certain socio-demographic characteristics [22]. In contrast to this and biological plausibility, STH infection did not varied with provision of water supply, hand washing facility, sanitation facility, drinking water and provision of behavioral change education and promotion from 2014 to 2017 in Laos [23]. SCH infection was commonly associated with being male gender [24], practices linked to river such as irrigation [25], swimming or crossing river and other sanitation and hygiene related factors [26–28]. The highest prevalence of SCH infection of the reviewed articles [14, 24, 28–31] was seen in Tanzania [14].
SCH and STH morbidity elimination and transmission breaking targets need consistent monitoring and evaluation of the interventions to get lessons and customize the existing interventions. However, the SCH transmission foci are not exhaustively identified, the impact of the existing interventions on the distribution of STH and SCH were poorly addressed in hard to-reach areas like Dara Mallo and Uba Debretsehay districts. Therefore, the present study was primarily aimed to estimate the prevalence of STH and SCH infections, the intensity of the infections after five years PC against STH among SAC. In addition, factors affecting STH and S.mansoni infections were assessed in Dara Mallo and Uba Debretsehay districts. The findings of this study will be used by decision makers to customize the existing interventions or look for supplementary interventions to accelerate reaching the set targets of morbidity elimination and transmission break of STH and SCH.