Citation Chai JY, Sohn WM, Kim DC, Kim SR, Kim E, Lee HR, Lee S, Shin S, Suh DY, Rojas CRT, Munayco CV. High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru. Parasites Hosts Dis 2026;64(2):161-167.

• Received: October 1, 2025 • Accepted: November 28, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
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Abstract

The Belén District in Loreto Region, Peru, is known for its extensive riverfront areas, where many houses are built on stilts and float during the rainy season. We conducted fecal examinations on 997 schoolchildren (ages 4–14 years; 488 boys, 497 girls) across 4 schools in Belén using the Kato-Katz thick smear and formalin-ethyl acetate sedimentation techniques. The results revealed high rates of soilborne helminths and waterborne protozoan infections, with an overall parasite-positive rate of 79.7%. The primary helminth species were Ascaris lumbricoides (39.2%), Trichuris trichiura (33.2%), Hymenolepis nana (3.4%), hookworms (2.1%), and Enterobius vermicularis (1.5%). The main pathogenic protozoans were Giardia lamblia (20.9%) and Entamoeba histolytica/E. dispar (14.2%), along with Cryptosporidium-like coccidian (4.6%). Non-pathogenic protozoans included Entamoeba coli (31.5%), Endolimax nana (15.1%), and Blastocystis hominis (3.7%). The intensity of soilborne helminth infections was very high for A. lumbricoides (average eggs per gram of feces per child: 18,589), followed by T. trichiura (1,501) and hookworms (160). The prevalence of anemia, often associated with malnutrition, was moderate at 33.1% (298 anemic children among 901 examined). Mass deworming was initiated with albendazole 400 mg, 3 times a year, in conjunction with health education and environmental sanitation. Metronidazole was administered once at a dose of 200 mg 3 times daily for 10 days. A notable finding in this study was that soilborne and waterborne parasites are both highly prevalent among schoolchildren in the floating villages of the Belén District, Loreto Region. Sustained mass deworming is urgently needed and the WASH program is crucial.
Key words: Ascaris lumbricoides, Trichuris trichiura, Giardia lamblia, Entamoeba histolytica, Belén District, Peru

Various types of infectious diseases, including viral, bacterial, and parasitic infections, pose major health issues in Peru [1]. The nationwide prevalence of human immunodeficiency virus is estimated at 0.45%, while tuberculosis affects 117 per 100,000 people, and malaria incidence is 258 per 100,000 [1]. The population also experiences high rates of diarrheal diseases caused by enteric pathogens, including Ascaris, Giardia, enterotoxigenic Escherichia coli, Shigella, and Helicobacter [1]. Strongyloides stercoralis [2] and Cyclospora cayetanensis [3] are also common diarrheal pathogens in Peru. Consequently, malnutrition, stunting, and anemia are frequent among children in various parts of Peru [4], especially in the Loreto Region [5-10].

Loreto is the largest department in Peru, covering nearly one-third of the country and the upper parts of the Amazon River (Fig. 1A, B). The Belén District in Maynas Province is known for its extensive riverfront areas, where many houses, built on stilts, float during the rainy season (Fig. 1C), which lasts about 4 to 5 months each year. Residents may be exposed to various soilborne intestinal helminth infections during the dry season (Fig. 2A, B) and could be vulnerable to waterborne intestinal protozoans during the rainy season.

The prevalence of soilborne helminthiases has been documented in Belén [5,6] and nearby areas, including Mariscal Ramón Castilla, Putumayo, and Requena [7], as well as Padre Cocha [8] and Santo Tomás [9]. However, waterborne protozoan infections are rarely reported in this district, likely due to limited diagnostic capacity and the lack of attention within the local health surveillance system. In June 2024, we examined fecal samples from schoolchildren living in floating villages in Belén and found very high rates of soilborne and waterborne parasitic infections. We also observed that many of these children had anemia, which suggests a long history of malnutrition. In this report, we provide details on intestinal helminthic and protozoan infections, as well as the prevalence of anemia.

Fecal samples were collected from 997 schoolchildren (488 boys, 497 girls, and 12 of unknown sex) from 4 elementary schools in Belén, Loreto Region. The children’s ages ranged as follows: 4–5 years (n=92), 6–7 years (n=192), 8–9 years (n=290), 10–11 years (n=293), 12–14 years (n=99), and unknown age (n=31). Informed consent was obtained from all children, their parents, and/or school guardians.

This project was approved through a memorandum of understanding between Peru and Korea (2024-06-03), signed by Gerencia Regional de Salud (GERESA) and Unidad de Gestión Educativa (UGEL), Loreto, Peru, along with Medipeace Global NGO, Seoul, Korea, and Medipeace Regional Office, Lima, Peru. The title of the project is “Enhancing child health through strengthening intestinal parasite infection management capacity in Loreto, Peru (2024–2026).”

Fecal examinations were carried out using 2 methods [10]: the Kato-Katz thick smear (n=982 children) and the formalin-ethyl acetate sedimentation technique (n=964 children). For each child, one slide sample was prepared with each method and examined microscopically by 5 parasitology experts. To estimate the infection intensity of soilborne helminths, including A. lumbricoides, Trichuris trichiura, and hookworms, eggs per gram of feces (EPG) were calculated by multiplying 24 by the number of eggs detected on each Kato-Katz smear for each child, assuming that the fecal volume on each smear is 41.7 g [10]. The classification of infection intensity followed recommendations from the World Health Organization (WHO) [11]. In the detection of protozoan cysts/oocysts, special staining techniques, such as Ziehl-Neelsen modified acid-fast staining, were not performed. Molecular genetic techniques were not employed in this study for detecting intestinal helminths or protozoans.

To assess anemia (iron-deficiency anemia), blood samples were collected from 901 schoolchildren, and hemoglobin concentration (Hb, g/dl) was measured using the HemoCue Hb 301 Analyzer (HemoCue). Anemia was defined as a hemoglobin level below 11.5 g/dl for children aged 5–11 years, based on WHO guidelines, and categorized into mild, moderate, and severe anemia for individuals and populations [12].

Seven species of helminths and 9 species of protozoa were identified. The overall parasite prevalence was unexpectedly high at 79.7% (Table 1) [12]. The most common helminth (eggs) was A. lumbricoides (39.6%), followed by T. trichiura (33.1%), Hymenolepis nana (3.4%), hookworms (2.2%), Enterobius vermicularis (1.5%), small trematode eggs (0.2%), and large trematode eggs (0.1%). The most prevalent protozoan was Entamoeba coli (31.5%), followed by Giardia lamblia (20.9%), Endolimax nana (15.1%), Entamoeba histolytica (including E. dispar) (14.2%), Cryptosporidium-like coccidian (4.6%), Blastocystis hominis (3.7%), Iodamoeba bütschlii (2.0%), Entamoeba hartmanni (1.6%), and Chilomastix mesnili (1.0%). The number of anemic children was 298 (33.1%) out of 901 examined, which is considered moderate in group anemia level according to WHO guidelines (Table 1) [12]. Cases of mild and moderate anemia were observed in 118 (13.1%) and 175 (19.4%) children, respectively, while severe anemia was observed in 5 (0.6%). Age did not show a significant trend in the prevalence of anemia. However, the correlation between current parasitic (helminth or protozoan) infections and anemia was statistically insignificant (P>0.05, by chi-square tests).

The severity of infection, as indicated by EPGs, varied by soilborne helminth species (Table 2) [11]. The proportions of moderate and severe infections with A. lumbricoides were notably high, at 46.7% and 12.3%, respectively, while the rates for T. trichiura were lower, at 14.7% and 2.6%. All hookworm cases were mild infections (100%). The average EPG counted 18,589 for A. lumbricoides, 1,584 for T. trichiura, and 160 for hookworms.

We consider the overall parasite infection rate of 79.7% in this area to be exceptionally high. It is also noteworthy that both soilborne and waterborne parasitic infections are very common in this region. This appears to be linked to seasonal environmental changes: during the dry season (7 to 8 months each year), the village is exposed to contaminated ground soil with various soilborne helminths, while in the rainy season (4 to 5 months each year), houses float, surrounded by unsanitary water, and are exposed to diverse waterborne pathogens, including intestinal protozoans. Most of the toilet systems in this area are inadequate, which significantly increases the risk of soilborne and waterborne parasitic infections.

Regarding soilborne parasitic infections, several reports have been documented in Belén and its surrounding areas [5-9]. In Belén, the prevalence of any helminth infection, including A. lumbricoides, T. trichiura, and hookworms, was reported at 37.0% among preschool-age children, which is lower than the 57.6% found in the current study; however, helminth infections in preschool children from this resource-poor community were linked to stunting and anemia [5]. In another study in Belén, the prevalence of any helminth, including A. lumbricoides, T. trichiura, and hookworms, ranged from 72.2% to 78.1% among schoolchildren, which is significantly higher than the 57.6% seen in this study [6]. In a study conducted across 3 neighboring areas, Mariscal Ramón Castilla, Putumayo, and Requena, the prevalence of any helminth was 49.5%, slightly lower than the prevalence reported here [7]. However, the prevalence of individual helminth species, A. lumbricoides, T. trichiura, and hookworms in these neighboring areas, was 37.2%, 22.8%, and 2.8%, respectively [7], which is quite similar to the figures in this study: 39.2%, 33.2%, and 2.1%. In Padre Concha, an area adjacent to Belén, the prevalence of A. lumbricoides was 16.1%, and T. trichiura was 1.6% among children [8], substantially lower than in this study. In Santo Thomás, another neighboring area, the prevalence of A. lumbricoides was 25.2%, and T. trichiura was 18.5% among preschool children [9], also lower than the figures reported here.

The infection intensity of A. lumbricoides was notably high among the schoolchildren surveyed in this study. The average EPG of 18,589 per infected child indicates that the average number of A. lumbricoides worms infected per child could be as many as 30, based on a previous report in Korea [13]. Similarly, the average EPG of T. trichiura was 1,584, suggesting that the worm burden per infected child might reach up to 45 worms, assuming a daily fecal output of 200 g and a daily egg output of 7,000 [14]. In contrast, the severity of hookworm infection in this region appears to be low, with an average EPG of 160, implying an average worm load of about 3 to 4 worms, assuming a daily egg output of 9,000 [14].

The widespread presence of intestinal protozoans in this area was previously underreported. It should be noted that G. lamblia, E. histolytica, and Cryptosporidium-like coccidians are well-known pathogenic organisms that can cause diarrhea, malnutrition, and anemia, especially in children [15]. The cyst stage of E. dispar, a non-pathogenic amoeba, appears morphologically identical to that of E. histolytica, but the trophozoite stage of E. dispar can be distinguished by the absence of red blood cells within its cytoplasm [15]. In our study, G. lamblia had a prevalence of 20.9%, which is higher than the 13.7% reported in a previous study conducted among patients with diarrhea in a rural town of the Peruvian Amazon [16]. However, the 20.9% rate was lower than the 27.9% found in another study focusing on the lowland forest ecoregions of Peru [17]. The prevalence of E. histolytica/E. dispar was 14.2% in this study, while E. coli, a marker of fecal water contamination, was present at 31.5%. The prevalence of E. histolytica/E. dispar in this area was notably lower compared to the 23.8% recently reported from the Amhara region in Ethiopia [18]. Conversely, the prevalence of G. lamblia in this study was significantly higher than the 7.3% reported in the same area of Ethiopia [18]. Therefore, water pollution with intestinal protozoans appears to be a significant concern in this district.

We found that anemia was quite common among the surveyed schoolchildren. The proportion of anemic children in this survey was 33.1%, which is considered a moderate level according to WHO guidelines [12]. Anemia can result from various conditions, including malnutrition, bleeding, sex (female), infectious diseases, and hematologic or genetic disorders. Therefore, the nutritional status of the surveyed children seems to be poor. However, no statistical significance was noted between the current parasitic infections and anemia. The prevalence of hookworms in our study was 2.2%, which is unlikely to have a significant impact on anemia. However, ongoing and repeated soilborne and waterborne parasitic infections in this area are undoubtedly contributing factors to malnutrition and anemia. Additionally, malaria may also be a contributing factor for anemia, as the Loreto Region has a high endemicity of malaria due to Plasmodium falciparum and P. vivax [19].

Limitations of this study include the lack of special staining, such as the Ziehl-Neelsen technique, for detecting Cryptosporidium-like oocysts. Additionally, molecular methods were not employed to distinguish between E. histolytica and E. dispar infections.

Following this study, mass deworming with albendazole 400 mg in a single dose per child (3 times a year) has been implemented together with health education and environmental sanitation. Mass deworming should continue for at least 10 years or longer to effectively control soilborne helminthiases in this area. Anti-protozoal treatment with metronidazole was also given to those infected with G. lamblia and/or E. histolytica/E. dispar at a dose of 200 mg 3 times daily for 10 days per child. For the management and control of waterborne protozoan infections, the water, sanitation, and hygiene (WASH) program [20] should be implemented urgently in this area.

Notes

Author contributions

Conceptualization: Chai JY, Shin S, Kim SR. Data curation: Chai JY, Kim SR, Lee HR, Kim E. Formal analysis: Chai JY, Kim SR, Kim E. Funding acquisition: Chai JY, Kim SR, Lee S, Shin S, Suh DY. Investigation: Chai JY, Sohn WM, Kim DC, Kim SR, Kim E, Lee HR, Rojas CRT. Methodology: Chang T, Sohn WM, Kim DC, Kim SR. Project administration: Chai JY, Kim SR, Lee S, Shin S, Suh DY, Munayco CV. Supervision: Chai JY, Shin S, Munayco CV. Validation: Chai JY, Kim SR. Visualization: Chai JY. Writing-original draft: Chai JY. Writing- review and editing: Chai JY, Kim SR, Munayco CV.

Conflict of interest

Woon-Mok Sohn serves as an editor of Parasites, Hosts and Diseases but had no involvement in the decision to publish this article. No other potential conflicts of interest relevant to this study were reported.

Funding

This project is supported by the Korea International Cooperation Agency (KOICA) (2024-2026).

Acknowledgments

We thank the staff at the regional reference laboratory of Loreto, Peru, for their assistance with collecting fecal samples from schoolchildren, preparing the Kato-Katz thick smears, and performing the formalin-ethyl acetate sedimentation technique. Medipeace’s health promotion activities in Peru are officially endorsed by the National Superintendency of Public Registries, Peru (operational document No. 2023-4228651).

Fig. 1.

The surveyed area in Belén, Maynas Province, Loreto Region, Peru. (A) Map showing the Loreto Region (red color) and Peru. (B) Map showing the Belén District, Maynas Province (red circle, arrowed). Small numbers represent districts. (C) A photo showing a floating village during the rainy season in the Belén District.

Fig. 2.

Photos showing the village of the Belén District, Loreto region, during the dry season. (A) A photo showing a plenty of trashes in a village side. (B) Another village side showing trashes.

Table 1.

Prevalence of helminth and protozoan parasites among schoolchildren in the Belén District, Loreto Region, Peru (June 2024)

Table 1.
Variable	No. positive (%)
All parasites
No. examined	997^a
No. positive for any kind of protozoa or helminths	795 (79.7)
Helminth parasites
No. examined	982
No. positive for any kind of helminths	566 (57.6)
Ascaris lumbricoides	385 (39.2)
Trichuris trichiura	326 (33.2)
Hymenolepis nana	33 (3.4)
Hookworms	21 (2.1)
Enterobius vermicularis	15 (1.5)
Small trematode eggs^b	2 (0.2)
Echinostomatid egg^c	1 (0.1)
Protozoan parasites
No. examined	964
No. positive for any kind of protozoa	542 (56.2)
Entamoeba coli	304 (31.5)
Giardia lamblia	201 (20.9)
Endolimax nana	146 (15.1)
Entamoeba histolytica^d	137 (14.2)
Cryptosporidium-like^e	44 (4.6)
Blastocystis hominis	36 (3.7)
Iodamoeba bütschlii	19 (2.0)
Entamoeba hartmanni	15 (1.6)
Chilomastix mesnili	10 (1.0)
Hemoglobin level (Hb, g/dl)
No. examined	901
≥11.5 (no anemia)	603 (66.9)
11.0–11.4 (mild anemia)	118 (13.1)
8.0–10.9 (moderate anemia)	175 (19.4)
≤7.9 (severe anemia)	5 (0.6)
Total anemic^f schoolchildren	298 (33.1)

^aIncluding boys and girls of 4–14 years of age in 4 primary schools. No significant differences in the prevalence were noted between boys and girls and among different age groups (data not shown);

^bSmall trematode eggs of 27–30 µm in length having an operculum, likely heterophyid eggs;

^cA large trematode egg of around 100 µm in length having an operculum and abopercular wrinkling, likely echinostomatid eggs;

^dInclusive of Entamoeba dispar;

^eSmall, round objects, 4-5 µm in diameter; special stain, such as Ziehl-Neelsen acid-fast staining, was not performed;

^fAnemia was defined as Hb levels lower than 11.5 g/dl for 5–11 years of age [12].

Table 2.

Intensity of infection in EPG of soilborne helminths among schoolchildren in the Belén District, Loreto Region, Peru (June 2024)

Table 2.
Species of helminth	No. of children examined	Mild infection		Moderate infection		Severe infection		Average EPG/infected child
Species of helminth	No. of children examined	EPG range^a	No. (%)	EPG range^a	No. (%)	EPG range^a	No. (%)	Average EPG/infected child
Ascaris lumbricoides	349	1–4,999	143 (41.0)	5,000–49,999	163 (46.7)	≥50,000	43 (12.3)	18,589
Trichuris trichiura	306	1–999	253 (82.7)	1,000–9,999	45 (14.7)	≥10,000	8 (2.6)	1,584
Hookworms	17	1–1,999	17 (100)	2,000–3,999	0 (0)	≥4,000	0 (0)	160

EPG, eggs per gram of feces.

^aDefined by the World Health Organization in 2011 [11].

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High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru

Parasites Hosts Dis. 2026;64(2):161-167. Published online March 24, 2026

DOI: https://doi.org/10.3347/PHD.25088

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High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru

Parasites Hosts Dis. 2026;64(2):161-167. Published online March 24, 2026

DOI: https://doi.org/10.3347/PHD.25088

Figure

High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru

Fig. 1. The surveyed area in Belén, Maynas Province, Loreto Region, Peru. (A) Map showing the Loreto Region (red color) and Peru. (B) Map showing the Belén District, Maynas Province (red circle, arrowed). Small numbers represent districts. (C) A photo showing a floating village during the rainy season in the Belén District.

Fig. 2. Photos showing the village of the Belén District, Loreto region, during the dry season. (A) A photo showing a plenty of trashes in a village side. (B) Another village side showing trashes.

Fig. 1.

Fig. 2.

High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru

Variable	No. positive (%)
All parasites
No. examined	997^a
No. positive for any kind of protozoa or helminths	795 (79.7)
Helminth parasites
No. examined	982
No. positive for any kind of helminths	566 (57.6)
Ascaris lumbricoides	385 (39.2)
Trichuris trichiura	326 (33.2)
Hymenolepis nana	33 (3.4)
Hookworms	21 (2.1)
Enterobius vermicularis	15 (1.5)
Small trematode eggs^b	2 (0.2)
Echinostomatid egg^c	1 (0.1)
Protozoan parasites
No. examined	964
No. positive for any kind of protozoa	542 (56.2)
Entamoeba coli	304 (31.5)
Giardia lamblia	201 (20.9)
Endolimax nana	146 (15.1)
Entamoeba histolytica^d	137 (14.2)
Cryptosporidium-like^e	44 (4.6)
Blastocystis hominis	36 (3.7)
Iodamoeba bütschlii	19 (2.0)
Entamoeba hartmanni	15 (1.6)
Chilomastix mesnili	10 (1.0)
Hemoglobin level (Hb, g/dl)
No. examined	901
≥11.5 (no anemia)	603 (66.9)
11.0–11.4 (mild anemia)	118 (13.1)
8.0–10.9 (moderate anemia)	175 (19.4)
≤7.9 (severe anemia)	5 (0.6)
Total anemic^f schoolchildren	298 (33.1)

Species of helminth	No. of children examined	Mild infection		Moderate infection		Severe infection		Average EPG/infected child
Species of helminth	No. of children examined	EPG range^a	No. (%)	EPG range^a	No. (%)	EPG range^a	No. (%)	Average EPG/infected child
Ascaris lumbricoides	349	1–4,999	143 (41.0)	5,000–49,999	163 (46.7)	≥50,000	43 (12.3)	18,589
Trichuris trichiura	306	1–999	253 (82.7)	1,000–9,999	45 (14.7)	≥10,000	8 (2.6)	1,584
Hookworms	17	1–1,999	17 (100)	2,000–3,999	0 (0)	≥4,000	0 (0)	160

Table 1. Prevalence of helminth and protozoan parasites among schoolchildren in the Belén District, Loreto Region, Peru (June 2024)
a

Including boys and girls of 4–14 years of age in 4 primary schools. No significant differences in the prevalence were noted between boys and girls and among different age groups (data not shown);

Small trematode eggs of 27–30 µm in length having an operculum, likely heterophyid eggs;

A large trematode egg of around 100 µm in length having an operculum and abopercular wrinkling, likely echinostomatid eggs;

Inclusive of Entamoeba dispar;

Small, round objects, 4-5 µm in diameter; special stain, such as Ziehl-Neelsen acid-fast staining, was not performed;

Anemia was defined as Hb levels lower than 11.5 g/dl for 5–11 years of age [12].

Table 2. Intensity of infection in EPG of soilborne helminths among schoolchildren in the Belén District, Loreto Region, Peru (June 2024)

EPG, eggs per gram of feces.

Defined by the World Health Organization in 2011 [11].

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High prevalence of soilborne and waterborne parasitic infections among schoolchildren, Belén District, Loreto Region, Peru

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