Current decline in schistosome and soil-transmitted helminth infections among school children at Loum, Littoral region, Cameroon

Introduction Soil-transmitted helminth infections (STHs) and schistosomiasis have serious consequences for the health, education and nutrition of children in developing countries. As Loum is known as a highly endemic commune for these infections, several deworming campaigns have been carried out in the past. The purpose of this study was to determine any changes that have occurred since then in the characteristics of these infections among schoolchildren in this site. Methods A cross-sectional study was conducted in October 2016 on 289 schoolchildren. Stool and urine samples were collected and examined to determine the prevalence and intensity of helminth infections. Results The highest prevalence was noted for Schistosoma haematobium (34.2%), followed by Ascaris lumbricoides (8.6%), S. mansoni (4.9%) and Trichuris trichiura (4.9%) in decreasing order. A prevalence of less than 2% was noted for each of the other two helminths. The highest mean intensity was found for S. haematobium (39.6 eggs/10 ml of urine), followed by A. lumbricoides (24.2 eggs per gram of faeces: epg), Strongyloides stercoralis (16.6 epg) and Schistosoma mansoni (12.3 epg). The prevalence of T. trichiura was significantly higher in boys and that of S. haematobium in children aged 10 years or older, while the differences between other values of prevalence or between egg burdens were not significant. Conclusion Compared with values reported in 2003, the prevalence and intensity of schistosomiases and STH infections in Loum has sharply decreased in 2016. Confirmation of this decrease in the years to come allowed to space deworming campaigns among schoolchildren.


Introduction
Schistosomiasis and soil-transmitted helminthiases (STHs) are among the most common infections in humans living in tropical and subtropical countries and where sanitation is rare. They remain public health problems in the poorest developing world and are mostly found in rural areas of low-and middle-income areas [1]. Lack  According to Pullan et al. [4], 819.0, 464.6 and 438.9 million people are infected with A. lumbricoides, T. trichiura and hookworms, respectively. Human mortality caused by these STH infections is rare.
In contrast, the morbidity and the harmful effects of these infections on socio-economic development are enormous [5,6]. Control of schistosomiasis and STH infections is focused on disease reduction through large-scale mass drug administration (MDA) programs implemented periodically and on prevention of people through education for the population health, drinking water, adequate sanitation and personal hygiene [7,8].
In Cameroon, schistosomiasis and STH infections are important parasitic diseases. More than 5 million people are at risk of schistosomiasis and 2 million people are currently infected with Schistosoma haematobium or S. mansoni. Two species of STH, A. lumbricoides and T. trichiura, are widely distributed throughout the country and it is estimated that more than 10 million people are infected with gastrointestinal worms [9][10][11]. The highest levels of schistosomiasis transmission were observed in northern Cameroon, whereas STH infections were more prevalent in the southern part [12,13]. School-aged children were the most infected and polyparasitism very common, with a high proportion of children carrying at least two parasite species [9]. Since 2003, some campaigns for helminth detection and deworming have taken place throughout the country. School-aged children were treated with mebendazole throughout the country, while Praziquantel was only distributed in areas of high endemicity for schistosomiasis. According to Tchuem-Tchuenté et al. [11], transmission of schistosomiasis increased in several health districts, while there was a significant decline in STH infections. These authors recommended continuation of annual or biannual mass drug administration (MDA) campaigns for STH infections and extension of Praziquantel in communities identified as moderate to high risk for schistosomiasis. In view of these findings, it was interesting to determine the current state of these parasitoses in a highly endemic area via the following two questions: were the prevalence values of schistosomiasis and STH infections decreasing? What was the parasitic load of these helminths in schoolchildren? To answer these two questions, stool and urine samples were collected in October 2016 from 289 schoolchildren in the commune of Loum (West Cameroon). These samples were examined to detect helminth species and count their eggs. In a second step, the results obtained will be compared with those reported by Tchuem-Tchuenté et al. [14] for the children of five schools of Loum.  [14][15][16]. According to Tchuem-Tchuenté et al. [14], the main sites of schistosomiasis transmission have been identified in areas adjacent to the Mbette river and its tributaries.

Study design
In Loum, two public primary schools (CEBEC A, SANDA 2) were chosen for three reasons: a) schoolchildren belong to the age group of the most affected population; b) individuals in this age group are less hesitant to undergo mass examinations; c) these results could be compared with those of previous studies because they were performed on the same school population. Two other criteria led us to select these institutions: 1) the distance between each school and the Mbette River to check whether the proximity of the school or its distance from the river affected the prevalence of parasitic infections in children, and 2) the strong awareness of teachers and parents/guardians to the problems caused by polyparasitism in children. The sample size was calculated using the following formula [17]:

Sample collection and examination
Stool and urine samples were collected each morning from each participant and were placed in 60 mL screw-cap vials with indication of gender, age of the child and school. These samples were stored in a portable cooler and transported to the laboratory at the Université des Montagnes for examination on the same day. The two techniques used were those that Tchuem-Tchuenté et al. [14] used in their study.
Each urine sample was shaken vigorously to ensure adequate dispersion of eggs and 10 mL were filtered through a Whatmann® Nuclepore membrane. The filter was then examined to detect the presence of S. haematobium eggs. Stool samples were examined by the thick smear technique using a 41.7 mg Kato-Katz template and each slide was read immediately after its preparation. Parasite eggs were identified according to the keys by Thienpont et al. [18] and Kaufmann [19]. The results were expressed as the numbers of helminth eggs per 10 mL of urine (S. haematobium) or per gram of faecal matter (epg) for each species of helminth found in the stools.

Ethical considerations
The present study was approved by the National Ethics Committee of

Parameters studied
The prevalence of each helminth infection was calculated using the ratio between the number of infected schoolchildren and the total number of children involved in this study. Fisher's exact test was used to study the relationships between the prevalence of infections and the gender of children, their sex or their school. Four age groups were considered: <7 years, from 7 to 9 years, from 10 to 12 years and >12 years. All prevalence values are given with their 95% confidence intervals. The second parameter was the intensity of each helminth infection, measured by the number of eggs. Individual values noted for this last parameter were averaged and the standard deviations calculated taking into account the parasite species. The normality of these intensities was analyzed using Shapiro-Wilk test [20]. As the distribution of these values was not normal, the Scheirer-Ray-Hare test was used to establish levels of significance. All these analyses were performed using software R 3.3.0 [21].

Prevalence of helminth infections
Five species of helminths: A. lumbricoides, S. mansoni, Strongyloides stercoralis, Taenia saginata and T. trichiura, were noted in stool samples of these children. In urine samples, Schistosoma haematobium was the single parasite found in the urine samples. Of the 289 schoolchildren, 125 were infected with one or more parasite species, so the overall prevalence of these infections was 43.2%. The highest prevalence (34.2%) was noted for S. haematobium. In the case of STH infections, the prevalence was 8.6% for A. lumbricoides, 4.9% for S. mansoni, 4.9% for T. trichiura, 1.6% for Taenia saginata) and 1.2% for Strongyloides stercoralis (Table 1). No hookworm eggs were found in these stool samples.
The prevalence of T. trichiura was significantly higher (p = 0.041) in boys than in girls, while there was no significant difference between the prevalence of other parasites and the sex of children ( Table 1).
The distribution of infected children in relation to the four age groups is shown in Table 2. The prevalence of S. haematobium infection was significantly higher (p = 0.028) in children aged 10 years or older, whereas there was no significant difference in prevalence values for the five other species of parasites in relation to the age of children.
No significant difference between the prevalence values of each helminth infection was noted when the school factor is taken into account (data not shown).

Polyparasitism
Two helminth species were noted in 14 schoolchildren. Four of them were infected with A. lumbricoides and S. haematobium, two with A. lumbricoides and S. mansoni, two with A. lumbricoides and T. saginata, and the two others with A. lumbricoides and T. trichiura. Schistosoma haematobium was noted in the other six children in association with S. mansoni (2 children), T. trichiura (2) and T. saginata (1). A triple infection with A. lumbricoides, S. haematobium and T. trichiura was noted in a single child.

Intensity of snail infections
The highest number of eggs (Table 3) was found for S. haematobium (a mean of 39.6 eggs/10 ml of urine), followed by A. lumbricoides (24.2 epg), S. stercoralis (16.6 epg) and S. mansoni (12.3 epg) in decreasing order. The mean intensity in stool samples was 7.7 epg and 10.0 epg for T. saginata and T. trichiura, respectively. Table 3 and Table 4 show the numbers of helminth eggs in the urines and stools of children in relation to their gender and age, respectively. All the differences between these intensities of infections were not significant, whatever parasite species and the factor studied.

Discussion
The results noted in this study were compared with those reported by Tchuem-Tchuenté et al. [14] among other schoolchildren of Loum in 2003. According to these authors, the prevalence was 62.8% for S. haematobium, 65.5% for A. lumbricoides and 47.7% for T. trichiura, while it was 34.2%, 8.6% and 4.9%, respectively, in this study (Table   1). Similarly, egg abundance in 2003 was 54 eggs/10 mL of urine for S. haematobium, 3636 epg for A. lumbricoides and 619 epg for T. trichiura [14], whereas it was 39.6 eggs/10 mL of urine, 24.2 epg, and 10.0 epg, respectively (Table 3). These data demonstrate that the prevalence and intensity of these three helminth infections have significantly decreased over the past fourteen years and this is probably a consequence of annual deworming campaigns performed at Loum during this period to control schistosomiasis and STH infections. Preventive chemotherapy, recommended by Gabrielli et al. [22], is therefore effective in controlling STH infections and schistosomiasis in areas of high transmission such as Loum. Our results agree with the observations of Tchuem-Tchuenté et al. [11] who noted a current decline in schistosomiasis and STH infections in the Littoral region, whatever schistosome and STH species. However, another explanation based on the greater awareness of teachers and parents/guardians from these two schools to problems caused by to S. haematobium and STH infections in children cannot be completely excluded. Because of the high impact of deworming campaigns on the prevalence and intensity of these infections, our results might justify reducing the frequency of deworming campaigns, as currently recommended by World Health Organization [23].
Two other helminths were also found in the stools of several children indicating the species [26]. The prevalence of T. saginata (1.6%) noted in this study was close to that reported by Asaava et al. [27] in  Tables   Table 1: prevalence of STH infections and schistosomiasis in the schoolchildren of Loum in relation to their gender    Trichuris trichiura 10.0 ± 3.5 10.5 ± 3.5 10.0 ± 3.1