Intestinal parasitic infection among rural schoolchildren in Taiz, Yemen: School-based assessment of the prevalence and associated risk factors

A cross-sectional survey was performed among schoolchildren in rural areas of the western Taiz governorate from 1 February to 31 March 2019. For this study, two rural districts (Almawasit & Sabir Almawadim) were recruited (Fig. 1). Convenience sampling was used to identify rural communities for this study. This was due to a security concern, as most of the districts in this governorate have been under siege since 2015. An official list provided by the Taiz Governorate’s General Directorate of Education was then used to select two schools from each district randomly. There are two schools selected, Khalid bin Alwaleed School in the Dhabab area and Saba School in the Aleayn area, both in Sabir Almawadim District. Furthermore, Dhabab Bani Hammad School and 26th September School have been selected from the Almawasit district. The schools were picked based on these criteria: there are over 100 students enrolled; the principal has agreed to be part of the study, and there haven’t been any threats of war or kidnapping.

Fig. 1

Taiz governorate (44.01°E and 13.34°N) is located in Yemen’s southern region, 280 kilometers from the capital Sana’a. It is surrounded on the west by the Red Sea, on the north by the governorates of Hodeida and Ibb, on the south by the governorate of Lahj, and on the east by the governorate of Al-Dhale. It is one of the country’s most densely inhabited governorates, with approximately 2.9 million aggregate population and 12,605 km² land area. Taiz governorate’s people are primarily farmers and merchants. Rural regions of Taiz governorates are dominantly inhabited by nearly 80 % of the population as compared to urban areas (20 %).

Taiz governorate consists of two biological zones: a mountainous highland zone on the east coast and a lowland coastal area on the west coast. The temperature fluctuates between relatively hot and cool during the year, with an average annual temperature of around 26 °C. The humidity level varies between 70 % and 90 %, and the average annual rainfall is about 200 mm. These areas are considered rural, with farmlands that depend on streams, underground wells, and ponds as the primary water source. The schools included in this study are close to valleys with streams, wells, and ponds. Most of the population in these areas worked in agriculture, and almost all mothers did not have a job, while fathers worked as farmers or laborers. Most houses do not have piped water, while only 20 % have electricity (connected to generators only at night).

Students in four (4) selected schools in rural areas of the Taiz governorate were included in the study. The participants were recruited through convenience sampling. Students attending grades 1 – 9 of formal education who participated in the study were invited to participate when we visited each school.

Of the 520 children eligible for the study, 15 refused to participate, did not provide their parents or guardians with an informed consent form, and 27 did not provide fecal and urine samples. As a result, a total of 478 schoolchildren aged 6 – 15 years old who provided suitable fecal or urine samples for analysis, filled out the questionnaires, and consented to participate in the study, were included in the analysis. Of the 478 students recruited, 118 were from the Khalid bin Alwaleed School, 123 from the Saba School in the Sabir Almawadim district, 112 from the Dhabab Bani Hammad School, and 125 from the 26^th September School in the Almawasit district. Most of the children had dirty unclipped fingernails and played outside with bare feet during the visit to the study areas. Some children spend part of their leisure time playing and swimming in streams or pools. In these study areas, poverty is prevalent, and poor housing and living conditions are typical.

Participants were lucidly informed of the purpose of the study prior to data collection. Parasites were detected by collecting 10 grams of fresh stool samples in screw-capped plastic containers of 100 mg capacity equipped with an applicator stick. The participants were instructed to collect sufficient samples aseptically. Following appropriate safety precautions and standard operating procedures, samples were immediately labeled and transported to the laboratory at ambient temperature. Using a wet mount preparation technique with saline, all stool samples were processed and examined for intestinal parasite cysts, trophozoites, eggs, and larvae using Olympus microscope model CX21 at 100x and 400x magnifications.

A face-to-face interview using a pretested and validated questionnaire was used to solicit information about the sociodemographic (age, gender, family size, and education level of parents) and environmental and behavioral factors (handwashing habits before meals, defecation habits, eating unwashed fruits and vegetables, source of drinking water, the pattern of swimming in a river/pond, washing clothes/utensils in open water, and the presence of animals in the house) (Al-Harazi, 2016).

Immediately after collection, saline or iodine wet preparations of stool samples were prepared and microscopically inspected using 10X and 40X objectives. Furthermore, stool sediments were examined using a formol-ether sedimentation method, following standard guidelines (Williams, 2000).

The data was analyzed using the IBM SPSS Statistics version 20.0 (IBM Corp., Armonk, NY, USA). The odds ratio, the 95 % confidence interval, and the P value were calculated accordingly. A descriptive analysis of the distribution of the study subjects about the variables was performed. A fitted binary logistic regression analy sis model was completed after cross-tabulating each explanatory variable with the outcome variable while checking the fulfillment of chi-square assumptions. Univariate analysis was conducted to select variables for multivariate analysis. Finally, bivariate analysis was performed to choose variables for the multivariate analysis. All variables with a P value < 0.25 were used for the multivariate analysis utilizing forward stepwise logistic regression and were considered to have a significant association at P ≤ 0.05.

A total of 478 students from four (4) primary schools in Almawasit and Sabir Almawadim districts participated in the study. The participants’ ages ranged from 6 to 15 years and were divided into two age groups according to a previous study (Mahdy et al., 2008) (i.e., 6 – 10 and 11 – 15). The 6 to 10-year-old age group accounted for 72.0 % (344/478) of participation, followed by the 11 to 15-year-old age group, which accounted for 28.0 % (134/478) (Table 1). Males made up more than half of the participants, 56.7 % (271/271). About 47.1 % (225) of the student’s parents are literate. Additionally, half of the participants (242/478) were from families with five or more members (Table 1).

As presented in Table 2, the total prevalence of parasitic intestinal infections among 478 examined rural schoolchildren in Taiz was 51.26 % (245/478). Notably, infections of protozoal parasites were predominantly observed over helminthic infections, accounting for 30.3 % (145/478) and 20.9 % (100/478) of all infections, respectively. G. lamblia and E. histolytica/dispar moshkovskii were the most common IPIs among schoolchildren (15.5 % (74/478) and 14.9 % (71/478), respectively). However, S. mansoni was the most common, 13.0 % (62/478) helminth, followed by Ascaris lumbricoides 3.8 % (18/478) and Trichurius trichuria 2.9 % (14/478). On the other hand, E. vermicularis was the least common helminth among schoolchildren, 1.3 % (6/478). Most of the students, 37.4 % (179/478), were infected with a single parasite species. In contrast, 4.4 % (21/478) and 1.7 % (8/478) of cases had double and triple infections.

Table 3 reveals no statistically significant variation in overall protozoa infection rates based on gender. Both males and females were infected with G. lamblia at comparable rates (16.2 % vs. 14.5 %, respectively), with no statistically significant differences (P =0.602). In contrast, the overall helminthic infections prevalence rate was slightly higher among females (22.7 %) than males (19.6 %) without statistically significant differences (P =0.462).

Table 4 shows statistically significant differences (P < 0.018) between the overall infection rates with protozoa by age group. Schoolchildren aged ≤10 years old, on the other hand, had a significantly higher (P< 0.014) infection rate with G. lamblia than those aged >10 years old (18.0 vs. 9.0 %, respectively). Though a higher infection rate of S. mansoni was observed among those aged > 10 years old than those aged ≤10 years old (15.7 % vs. 11.9 %, respectively), a significant difference (P > 0.05) was not found. In addition, Ascaris lumbricoides show a trend of infection rate among those aged ≤10 years old than those aged >10 years old (4.9 % vs. 0.8 %, respectively) with a statistically significant difference (P< =0.032).

Univariate analysis revealed seven factors associated with intestinal parasite infections (Table 5), including students aged ≤10 (OR= 1.391, 95% CI 1.054–1.837), students who do not practice unwashed hands before eating (OR= 1.753, 95% CI 1.157–2.657), defecate in open field (OR= 2.558, 95% CI 1.157–2.657), eating unwashed fruits and vegetables (OR= 3.299, 95% CI 2.252–4.831), drinking unprotected stream/well water (OR=2.457, 95% CI 1.689–3.575), dirty unclipping fingernail (OR= 2.725, 95% CI 1.868–3.976), and existing of animals inside the house (OR= 2.395, 95% CI 1.636–3.507). All other factors, including gender, family size, parents’ education level, swimming in streams, rivers, and ponds, and the use of open water sources in washing clothes and utensils, were not significantly linked to the prevalence of IPIs among schoolchildren. Multivariate analysis using forward stepwise logistic regression confirmed that schoolchildren with unwashed hands were 2.07 times more probably to present IPIs than those with clean hands before (Adjusted OR= 2.077, 95% CI 1.281–3.368), and those who defecated in the open field were twice as likely to get infected with IPs (Adjusted OR=1.869, 95% CI 1.216–2.874). In contrast, schoolchildren who ate washed fruits and vegetables were 0.289 less likely to exhibit IPIs than those who ate unwashed fruits and vegetables, and those who clipped their fingernails (Adjusted OR=0.545, 95% CI 0.352–0.845) were half as likely to exhibit IPIs compared with those with dirty unclipping (Table 5).

Additionally, univariate analysis was performed based on a single Giardia infection (Table 6). It was found that age, practice of defecation in open fields (OR= 2.094, 95% CI 1.184–3.704), eating unwashed fruits and vegetables (OR= 2.987, 95% CI 1.766–5.052), drinking from unprotected stream water (OR= 4.998, 95% CI 2.833–8.817), washing clothes/utensil in open water sources (OR= 2.082, 95% CI 1.292–3.538), dirty unclipping fingernails houses (OR= 2.137, 95% CI 1.292–3.535), and existing of animals inside houses (OR= 1.967, 95% CI 1.113–3.478) were a significant predictor of giardiasis. Logistic regression analysis confirmed that the practice of defecation in an open field (Adjusted OR= 1.473, 95% CI 0.830–2.522), drinking from unprotected stream water (Adjusted OR= 2.261, 95% CI 0.879–3.473), and eating unwashed fruits or vegetables (Adjusted OR = 1.238, 95% CI 0.133–2.425) were a significant risk factor for Giardia infection.

Regarding the behaviors possibly associated with Schistosoma mansoni among schoolchildren, practices such as defecation in open fields (OR = 1.017; 95% CI 0.173–2.947, P =0.041), swimming in rivers/ponds (OR = 2.471; 95% CI 1.667–3.046, P=0.001), and washing clothes/utensils in open water sources (OR = 2.473; 95% CI 1.260–3.865, P =0.013) were significantly associated with Schistosoma mansoni infection among schoolchildren. However, eating without washing hands (OR = 0.590; 95% CI 0.309–1.126, P = 0.106), eating unwashed fruits and vegetables (OR = 0.681; 95% CI 0.393–1.181, P = 0.170), drinking unprotected water (OR = 0.715; 95% CI 0.413–1.240, P = 0.213), and dirty unclipping fingernails (OR = 0.685; 95% CI 0.400–1.174, P = 0.167) were not significantly associated with Schistosoma infection. Multivariate analysis identified that practicing swimming in the river/ponds (adjusted OR = 1.826; CI 1.048–3.183; P = 0.034), and practicing open defecation, especially near water sources (adjusted OR = 2.383; CI 1.302–4.363; P = 0.005) as independent risk factors for Schistosoma mansoni infection among schoolchildren (Table 7).

Unwashed hands habits before eating, open field defecation behavior, eating unwashed fruit and vegetables, lacking safe drinking water, dirty unclipped fingernails, and the presence of animals inside their houses were found to be major risk factors for the prevalence of IPI among school children in this rural area (p < 0.05). These findings are consistent with previous studies performed elsewhere in Yemen, e.g. (Al-Harazi, 2016; Alyousefi et al., 2011). The degree of association between IPIs and other risk factors was determined by multivariate logistic regression (Table 5). Unwashed before eating, open field defecation, unwashed fruits and vegetables, and dirty unclipped fingernails were all identified as predictors of IPIs among the study’s participants. Participants who defecated in open fields were twice as at risk as those who defecated in latrines. On the other hand, students’ practices of washing fruits were found to be significantly related to IPIs. Compared to students who always washed fruits and vegetables, those who did not were three times more likely to become infected. Additionally, students who did not frequently clean and clip their fingernails were about three times as likely to develop IPIs as those who did. These results are consistent with those reported in other studies (Abossie et al., 2014; Gebretsadik, 2016; Hailegebriel, 2017).

According to Table 2, about 15 % of students were infected with Giardia lamblia, followed by Entamoeba histolytica/dispar and Schistosoma mansoni. Logistic regression confirmed that open field defecation behavior, eating unwashed fruit and vegetables, and drinking unprotected water were all risk factors for Giardia lamblia infection. As a result, the risk of infection with Giardia lamblia was doubled in study subjects who defecated in open fields (OR = 2.094, 95% CI 1.184–3.704 P = 0.001), roughly threefold in those who ate unwashed fruits and vegetables (OR = 2.987, 95% CI 1.766–5.052 P = 0.001), and fivefold in those who drank from unsafe rivers and streams (OR = 4.998,95% CI 2.833–8.817 P = 0.001) compared with those who used latrine, not eating unwashed fruits and vegetables, and drank from unsafe rivers and streams (Table 6). Another study found that this parasite had a high prevalence among school children in Yemen (20 – 45 % and 30 – 35 %) and other countries (Alamir et al., 2013; Choy et al., 2014).

Schoolchildren of 10 years old or younger are significantly more likely to be infected with Giardia lamblia than those older than 10 years. This might be because they have relatively poorer personal hygiene habits. Meanwhile, schoolchildren from Hadhramout (16.8 %) and Ibb (14.0 %) had similar infection rates with Entamoeba histolytica/disorder dispar (55, 56). However, children from Al-Mahweet and Ibb recorded higher infection rates of 64.0 % and 33.7 %, respectively (Alsubaie et al., 2016; Alwabr et al., 2016).

Among the study participants, the third most prevalent parasite was Schistosoma mansoni, with 13.0 %. Students’ swimming habits in rivers and ponds may account for this high prevalence rate. Additionally, open defecation or urination in or near water may have contributed to Schistosoma mansoni infection in study subjects (Table 7). An interesting finding was the absence of Schistosoma haematobium in the studied children. These results are consistent with earlier studies conducted in Taiz and other governorates (T. H. Alharazi et al., 2021; Alharbi et al., 2019; Al-Shamiri et al., 2011). In contrast, S. haematobium was found to be the predominant species in other governorates, such as Sana’a and Almahweet, rather than S. mansoni (Alwabr et al., 2016; Hany et al., 2015). This variance in species distribution may be explained by the occurrence of suitable freshwater snails that act as the necessary molluscan hosts (Rabone et al., 2019; Sady et al., 2013). In terms of gender, the current study demonstrated no statistically significant difference in schistosomiasis prevalence between male and female subjects. Furthermore, Sady et al., 2013 found that male children with schistosomiasis did not have a significantly higher infection rate than female children.

Of soil-transmitted helminths, only A. lumbricoides and T. trichiura were present with a low prevalence rate compared to studies carried out in Al-Mahweet (Alwabr et al., 2016), Ibb (Alsubaie et al., 2016), and Aden (Al-Abd et al., 2021). This may be attributed to the difference in educational levels and climates. Oppositely, hookworms and S. stercoralis were not found among schoolchildren in the current study. This is similar to reports from previous studies (Al-Qobati et al., 2012; bin Mohanna et al., 2014; MB, 2017; Singh Khadka et al., 2019; Sitotaw et al., 2020). However, hookworms and S. stercoralis have low prevalence rates in Ibb among schoolchildren, reporting 1.2 % and 0.8 % prevalence rates, respectively (Alsubaie et al., 2016).

Although Enterobius vermicularis infections are easily persistent because of autoinfection, the current study found that the prevalence rate was low among rural students in Taiz (1.3 %). Generally, E. vermicularis infection was found in children from various Yemeni governorates at rates ranging from 0.8 % to 13.0 % (Al-Haddad et al., 2010; Al-Shibani et al., 2009; Alsubaie et al., 2016; Alwabr et al., 2016). In such a susceptible group, it is surprising that E. vermicularis were extremely low in prevalence. The low prevalence of E. vermicularis was probably due to the inadequacy of the coproparasitological techniques used to detect it.

One limitation of the study was the prevalence of infection with S. manasoni and soil-transmitted helminths instead of the intensity of infection. Reasons for this include the lack of resources and the unavailability of Kato-Katz kits on the local market. Additionally, stool specimens were obtained once from each participant, while conventional identification of intestinal parasites requires at least three specimens taken on three different days. Furthermore, due to security concerns, we selected only two rural districts in this governorate (Almawasit & Sabir Almawadim).