Intestinal parasitoses: diagnosis and prevention

Intestinal parasitoses in children are infections caused by protozoa (e.g., Giardia duodenalis, Cryptosporidium spp., Entamoeba histolytica) and helminths (e.g., Enterobius vermicularis - pinworm, Ascaris lumbricoides - roundworm, Trichuris trichiura - whipworm, hookworm, Hymenolepis nana - dwarf cestode). They are manifested by diarrhea, abdominal pain, flatulence, perianal itching, iron deficiency anemia and growth retardation, and sometimes are asymptomatic. The greatest vulnerability is in preschoolers and primary school children, as well as in children attending children's groups and actively contacting animals and water. [1]

The disease burden is uneven: in countries with limited sanitation and hygiene resources, soil-borne helminthiases (ascariasis, trichuriasis, and hookworm) are common, while in industrialized regions, enterobiasis and giardiasis are more common. Mass prophylactic deworming in endemic countries reaches hundreds of millions of children annually, but individual diagnosis and treatment remain the key to disease control outside of "mass treatment" programs. [2]

Transmission routes include fecal-oral (contaminated water, food, hands, surfaces, and toys), household contact (especially with enterobiasis), and cutaneous transmission through contact of feet with contaminated soil (hookworm). Waterborne transmission in swimming pools and reservoirs is also a particular concern: Giardia cysts and Cryptosporidium oocysts are resistant to chlorination and easily cause outbreaks in children's groups. [3]

Modern approaches rely on a combination of clinical examination and laboratory verification: stool microscopy with concentration methods, antigen tests, molecular polymerase chain reaction panels (for protozoal infections), and the "sticky tape test" for enterobiasis. The choice of therapy depends on the suspected pathogen: for helminths - albendazole, mebendazole, pyrantel; for giardiasis - tinidazole, nitazoxanide, metronidazole; for dwarf tapeworm - praziquantel; for strongyloidiasis - ivermectin. [4]

ICD-10 and ICD-11 codes

In ICD-10, intestinal protozoan infections are included in block A07 (for example, A07.1 - giardiasis, A07.2 - cryptosporidiosis), and helminthiases are in the range B65-B83 (including B82.0/B82.9 - "unspecified" intestinal helminthiases/parasitosis). The specificity of the code is important for epidemiological surveillance and therapy selection. [5]

In ICD-11, protozoal intestinal infections are classified in block 1A30-1A3Z (e.g., 1A31 - giardiasis, 1A32 - cryptosporidiosis), and helminthiases are classified in the sections "Helminthiases" (e.g., for taeniasis and other cestodiases). The structure allows for post-coordination of diagnosis with clinical modifiers (severity, context). [6]

Table 1. ICD codes for intestinal parasitoses in children (guidelines)

System	Chapter	Code	Name
ICD-10	Protozoal intestinal infections	A07.1	Giardiasis (Giardia)
ICD-10	Protozoal intestinal infections	A07.2	Cryptosporidiosis
ICD-10	Helminthiasis	B82.0 / B82.9	Intestinal helminthiasis, unspecified / intestinal parasitosis, unspecified
ICD-11	Protozoal intestinal infections	1A31 / 1A32	Giardiasis / Cryptosporidiosis
ICD-11	Protozoal intestinal infections	1A3Y / 1A3Z	Other/unspecified protozoal intestinal infections
[7]

Epidemiology

According to World Health Organization estimates, in 2020, more than 914 million children lived in areas endemic for soil-transmitted helminthiasis and required preventive interventions; in 2023, more than 451 million children received preventive chemotherapy (coverage of ≈51.5%). These figures illustrate the scale of the problem globally. [8]

In endemic regions, the combined prevalence of ascariasis, trichuriasis, and ancylostomiasis in children can reach 20-40% or higher; meta-analyses show significant heterogeneity across countries and even regions within countries. Moreover, in countries with high sanitary standards, giardiasis and enterobiasis are more frequently diagnosed in outbreaks associated with childcare facilities and recreational water. [9]

Giardiasis is one of the most common protozoan causes of diarrhea in children; the risk of outbreaks increases in the summer and during visits to swimming pools, water parks, lakes, and rivers. Cryptosporidiosis is also often associated with water and child care facilities; it is more severe in young children and immunocompromised patients. [10]

Mass deworming (albendazole, mebendazole) is administered to school- and preschool-aged children once or twice a year, depending on prevalence. With coverage of ≥75% of children in a zone, the risk of serious consequences is reduced; by 2023, 20 countries had achieved this target for schoolchildren. [11]

Table 2. Epidemiological landmarks

Indicator	Rating / fact
Children in need of STH prevention (2020)	>914,000,000
STH prevention coverage (2023)	≈451,000,000 children (≈51.5%)
Common protozoal agents in children	Giardia, Cryptosporidium, Entamoeba histolytica
Frequent helminthiasis in children	Enterobius, Ascaris, Trichuris, hookworms, Hymenolepis nana
[12]

Reasons

Common protozoan pathogens include Giardia duodenalis (lamblia), Cryptosporidium spp., Entamoeba histolytica, and, less commonly, Cystoisospora belli and Cyclospora cayetanensis (especially in immunodeficiencies and foodborne outbreaks). Lamblia are characterized by cysts that are resistant in the external environment; infection occurs through ingestion of a minimal number of cysts. [13]

Helminthiasis in children is caused by roundworms ( Ascaris, whipworm, hookworm ), pinworms (Enterobius), and cestodes (Hymenolepis nana; less commonly, taeniasis). Enterobiasis is transmitted by contact, while STH (soil-borne helminths) are transmitted through soil/vegetables/unwashed hands; Hymenolepis nana can support autosuperinvasion. [14]

Strongyloides stercoralis is less common but important due to the risk of hyperinfection in immunosuppressed individuals; its diagnosis and treatment have their own peculiarities (ivermectin is the first-line treatment in children ≥15 kg). Schistosomiasis is not a "classical" intestinal parasitosis in the narrow sense, but mixed diarrhea patterns are possible in traveling adolescents. [15]

Important environmental factors include water and children's groups: outbreaks of giardiasis and cryptosporidiosis have been repeatedly described in swimming pools, water parks, and preschools. The resistance of Cryptosporidium oocysts to chlorine and the "low infectivity" of Giardia explain the high risk in these settings. [16]

Table 3. Common pathogens and transmission routes

Group	Pathogen	The main route
Protozoa	Giardia duodenalis	Water, hands, surfaces, food
Protozoa	Cryptosporidium spp.	Water (including swimming pools), contact
Helminths	Enterobius vermicularis	Contact-household, eggs around the anus
Helminths	Ascaris, Trichuris, hookworms	Soil, unwashed vegetables/hands, walking barefoot
Cestodes	Hymenolepis nana	Fecal-oral, autosuperinvasion
[17]

Risk factors

Children aged 1-9 years attending kindergartens and schools, families with inadequate sanitation and hygiene, and limited access to clean water and safe sanitation are at high risk. Additional risk factors include contact with animals and playing in sand/soil. [18]

Water-related risk factors include swimming and playing in pools and open water, especially when water hygiene practices are not followed (eg, going into the water while having diarrhea, swallowing water, infrequent toilet breaks, and diaper changes). These conditions contribute to outbreaks of giardiasis and cryptosporidiosis. [19]

Immunocompromise, including acquired immunocompromise, increases the severity of protozoan diarrhea (e.g., cryptosporidiosis). Strongyloides are susceptible to immunosuppression and corticosteroid therapy, as hyperinfection is possible. [20]

Travel and migration from endemic regions increases the risk of a variety of parasitoses; some programs (e.g., for refugees) include screening/presumptive therapy based on body weight and regional risks (e.g., Loa loa when planning ivermectin). [21]

Pathogenesis

Protozoa damage the small intestinal mucosa, disrupting parietal digestion and absorption: Giardia attach to the brush border of enterocytes, causing malabsorption, flatulence, and steatorrhea. Cryptosporidia infect the epithelium and microvilli, causing watery diarrhea and dehydration. [22]

Helminths act differently: Ascaris and Trichuris injure the mucous membrane and cause inflammation; hookworms lead to chronic blood loss and iron deficiency anemia; Enterobius causes nocturnal anal itching and sleep disturbances, enhancing autoinoculation. Hymenolepis nana maintains persistent carriage through autosuperinvasion. [23]

Strongyloides forms an autoinfection with larval migration; in immunosuppressed patients, a rapid generalized course with high mortality is possible - hence the caution when prescribing ivermectin and the mandatory exclusion of Loa loa in endemic regions. [24]

The child's immune response, nutritional status, and gut microbiota influence symptom severity and outcomes; in young children, prolonged episodes of diarrhea and malabsorption are associated with delayed physical growth.[25]

Symptoms

Typical complaints include diarrhea, cramping abdominal pain, flatulence, rumbling, nausea, loss of appetite, and fatigue. Giardiasis often causes foul-smelling, greasy stools and bloating; cryptosporidiosis causes watery diarrhea with the risk of dehydration. Some children are asymptomatic, but they remain a source of infection. [26]

Enterobiasis presents with nocturnal perianal itching, sleep disturbances, and sometimes abdominal pain and vaginal itching in girls; parents often see white "worms" in the perianal area. Symptoms are cyclical and often recur without simultaneous treatment of all contact factors. [27]

Soil-borne helminthiases can present with chronic diarrhea, abdominal discomfort, growth retardation, and iron deficiency anemia (especially with hookworm infections). Strongyloidiasis is often asymptomatic, but in immunosuppressed individuals, fever, cough, diarrhea, and septic complications are possible. [28]

Warning signs requiring immediate evaluation include: repeated vomiting, severe dehydration, blood in the stool, high fever, severe abdominal pain, and decreased consciousness. In infants, fluid and electrolyte balance rapidly deteriorates, so early rehydration and monitoring are essential. [29]

Classification, forms and stages

Based on etiology, parasitoses are divided into protozoan (giardiasis, cryptosporidiosis, amebiasis, etc.) and helminthic (enterobiasis, STH, cestodiasis, strongyloidiasis). Co-infections are common in mixed foci, which complicates diagnosis and requires combination therapy. [30]

By course - acute diarrheal forms, chronic and recurrent; asymptomatic carriage is important for outbreak control (e.g., enterobiasis in the family/kindergarten, giardiasis in a kindergarten). By severity - mild, moderate, severe diarrhea with the risk of dehydration and nutritional deficiencies. [31]

By route of infection - water/food (Giardia, Cryptosporidium), contact-household (Enterobius), soil-transmissible (Ascaris, Trichuris, hookworms), autosuperinfection (H. nana, Strongyloides). This classification helps to develop prevention. [32]

For public health programs, a distinction is made between endemic STH, where mass deworming is indicated, and “focal” protozoal infections, where sanitary measures, water control, and spot therapy are more important. [33]

Table 4. Clinical and etiological classification (simplified)

Class	Examples	A typical clinic	The key to diagnosis
Protozoa	Giardia, Cryptosporidium	Watery/oily diarrhea	Antigen tests/PCR
Helminths	Enterobius, Ascaris, Trichuris	Itching, anemia, pain	Tape test, stool microscopy
Cestodes	Hymenolepis nana	Subclinical → discomfort	Eggs/antigens, response to therapy
Nematode	Strongyloides	Often asymptomatic	Serology/PCR (as indicated)
[34]

Complications and consequences

Prolonged or repeated episodes of diarrhea in children under 5 years of age lead to dehydration, nutritional deficiencies, and the risk of delayed physical development. Iron deficiency anemia associated with hookworm infection reduces cognitive and physical performance. [35]

In immunosuppressed individuals, strongyloidiasis can rapidly spread (hyperinfection) with bacteremia and high mortality - timely detection and treatment are critically important. [36]

In cryptosporidiosis in immunocompromised children, diarrhea may be prolonged, with deterioration of nutritional status; therapy with nitazoxanide is indicated for immunocompetent children, and in immunocompromised children, it is decided individually. [37]

Mixed parasitoses are common in adolescent travellers, requiring attention to schistosomiasis and taeniasis; unrecognised cases maintain foci and increase the risk of familial transmission. [38]

When to see a doctor

Seek immediate medical attention if your child exhibits signs of dehydration (dry mouth, infrequent urination, lethargy), blood in the stool, high fever, severe abdominal pain, or repeated vomiting. These symptoms in a child require immediate evaluation and rehydration. [39]

Consult a pediatrician if diarrhea persists for more than 7-10 days, nocturnal anal itching occurs, there are multiple episodes of diarrhea in a family/group, after traveling, or after exposure to potentially contaminated water/food. A parasite test and, if necessary, treatment will be prescribed. [40]

If “white worms” are visible in the perianal area of a child with nocturnal itching, it is permissible to begin treatment for enterobiasis simultaneously in all household members and carry out sanitary measures without delaying the “tape test”. [41]

Children with immunosuppression, growth retardation, iron deficiency anemia and chronic diarrhea require extensive diagnostics with a focus on parasitosis (including PCR panels). [42]

Diagnostics

The first step is a clinical and epidemiological assessment: duration and nature of bowel movements, dehydration, contact with sick people, travel, swimming in pools/lakes/rivers, contact with animals, and drinking water from questionable sources. This allows us to narrow the range of pathogens and select tests. [43]

Next, a stool sample is analyzed for eggs and parasites (microscopy) using mandatory concentration methods. To increase sensitivity, it is recommended to examine at least three samples, collected 2-3 days apart, with proper preservation (10% formalin, PVA, according to laboratory requirements). [44]

When giardiasis, cryptosporidiosis, and amebiasis are suspected, antigen tests and molecular polymerase chain reaction panels improve the accuracy. Multiplex panels accelerate the detection of pathogens in children with acute diarrhea and outbreaks, although their clinical "added value" to outcomes depends on the context. [45]

For enterobiasis, the "gold standard" is the "sticky tape test": in the morning, before using the toilet and performing hygiene, sticky tape is applied to the skin around the anus for three consecutive mornings and taken for microscopy. Routine stool analysis for enterobiasis is uninformative. [46]

Table 5. Diagnostic "keys"

Situation	Test	Comment
Persistent diarrhea	Stool ×3, concentration + antigen/PCR	Increases sensitivity
Suspected enterobiasis	"Tape Test" in the morning x3	CDC standard
Severe dehydration	Electrolytes, creatinine	Severity assessment
Immunodeficiency	Expanded PCR panel	According to the readings
[47]

Differential diagnosis

It's important to distinguish between viral and bacterial gastroenteritis (rotavirus, norovirus, salmonella, shigella) and parasitic infections: viruses typically have a more acute onset and vomiting, while bacteria cause fever and bloody stools, while parasitic infections are more often chronic or intermittent. Clinical examination, rapid PCR panels, and culture/antigen tests are helpful. [48]

Irritable bowel syndrome in schoolchildren can mimic giardiasis (pain, flatulence), but parasitic infections are more often associated with epidemiological exposure, fluid intake, nutritional deficiencies, and positive test results. In adolescents, inflammatory bowel disease should be considered with bloody stools and weight loss. [49]

Lactose intolerance can worsen diarrhea after giardiasis; temporary lactose restriction and treatment of the underlying condition can help. Girls with enterobiasis may develop vulvovaginitis, which is often mistaken for a primary gynecological problem. [50]

In travellers, schistosomiasis, amoebiasis and combined infestations should be excluded; collection of an epidemiological history is critical for the selection of tests and therapy. [51]

Table 6. “What we confuse with” and how to distinguish

Suspicion	Tips for parasitosis	What helps?
Viral diarrhea	Duration >7-10 days, outbreak in garden/water	Antigen/PCR for parasites
Bacterial diarrhea	Negative bacterial PCR/cultures	Parasitological tests
IBS in a schoolchild	Epidemiological contacts, water factor	Repeated stool tests x3
Gynecological complaints	Night itching, enterobiasis	Tape Test
[52]

Treatment

Therapy begins with rehydration and correction of electrolyte imbalances, especially in children under 5 years of age. For moderate dehydration, oral rehydration solutions are sufficient; for severe dehydration, intravenous infusions with monitoring are recommended. A soft diet is recommended, with temporary restriction of excess sugars and lactose in cases of secondary malabsorption. [53]

Giardiasis is treated with tinidazole (a convenient single dose), nitazoxanide, or metronidazole; the choice depends on age, tolerance, and availability. The CDC lists these three options as primary options for children; if ineffective, a change in class or a repeat course may be necessary. It is important to treat all symptomatic patients and monitor household members for relapses. [54]

Cryptosporidiosis in immunocompetent children is treated with nitazoxanide (suspension approved from age 1; tablets from age 12); in cases of immunodeficiency, treatment is individualized, with an emphasis on correcting immune status and supportive therapy. Swimming pools should be avoided for 14 days after diarrhea has stopped due to the chlorine-resistant nature of oocysts. [55]

Enterobiasis is treated with mebendazole, albendazole, or pyrantel; the standard dose is two doses, 14 days apart (these medications kill the worms, but not the eggs, so repeat treatment is necessary). All family members and close contacts are treated simultaneously; hand hygiene, daily changing and washing of linens, and wet cleaning are increased. [56]

Soil-transmissible helminthiases in individual patients are treated with albendazole or mebendazole according to local protocols; in mass deworming programs, the dose and frequency depend on the background prevalence (1-2 times per year). For children under 24 months, the WHO recommends half the dose of albendazole for MDA. [57]

Hymenolepis nana (dwarf tapeworm) is treated with praziquantel at a single dose of 25 mg/kg; alternatives include niclosamide (not available in some countries) and nitazoxanide. In case of relapse, repeat the dose after 10-14 days and strengthen sanitary measures due to autosuperinfestation are considered. [58]

Strongyloides stercoralis requires special attention: in children ≥15 kg, the drug of choice is ivermectin 200 mcg/kg for 1-2 days; an alternative is albendazole 400 mg twice daily for 7 days. Before using ivermectin in risk areas, Loa loa (daytime blood smears) should be excluded, otherwise severe encephalopathy is possible. [59]

Post-etiotropic support includes correction of iron deficiency in ancylostomiasis, nutritional support for malabsorption, and monitoring of the child's growth and weight. In cases of recurrent giardiasis, household factors and water sources are assessed, and health education is provided to the family and children. [60]

Multiplex PCR panels can speed up the selection of targeted therapy in outbreaks and in severe patients, but do not always shorten the duration of symptoms; use should be justified by the clinical and epidemiological context, and positive results are interpreted taking into account carriage. [61]

Supportive measures: in case of severe itching due to enterobiasis - local hygiene and short nails; in case of cryptosporidiosis - strict water hygiene, avoiding visiting swimming pools for 2 weeks after the cessation of diarrhea; in case of giardiasis - a ban on swallowing water in swimming pools, frequent breaks for infants and thorough hand washing. [62]

Table 7. Medicinal guidelines (children)

Infection	First-line drug(s)	Note
Giardiasis	Tinidazole, nitazoxanide, metronidazole	Age/Tolerance Selection (CDC)
Cryptosporidiosis	Nitazoxanide (≥1 year)	Immunodeficiency - individual
Enterobiasis	Mebendazole/albendazole/pyrantel	2nd dose after 14 days; treat all contacts
Hymenolepis nana	Praziquantel 25 mg/kg ×1	Consider recurrence in case of relapse
Strongyloides	Ivermectin (≥15 kg)	Rule out Loa loa before treatment
[63]

Prevention

Household hygiene: wash hands with soap for at least 20 seconds after using the toilet, changing diapers, handling animals, and before eating; use separate cutting boards and thoroughly wash fruits and vegetables. In children's groups - daily wet cleaning, disinfection of toys, and training of staff and children. [64]

Water safety: Do not swallow water in pools or other bodies of water; do not visit a pool if you have diarrhea or for 14 days after it has stopped (especially if you have confirmed giardiasis/cryptosporidiosis). For hiking/cottage use boiling water or certified filters. [65]

For enterobiasis - simultaneous treatment of all household members, daily change and washing of bed linen and pajamas in the first days, morning shower, short nails, wet dusting; these measures are continued for at least 2 weeks after the last dose. [66]

In endemic regions, participation in mass deworming programs (albendazole/mebendazole on a schedule of 1-2 times a year) is recommended, with children under 24 months of age being prescribed a half dose of albendazole in the MDA. [67]

Table 8. Prevention by risk environment

Wednesday	Measures
House/kindergarten	Hand washing, cleaning, and toy hygiene
Pool/reservoir	Do not swallow water; "14 days no swimming" after diarrhea
Kitchen	Washing vegetables/fruits, separate boards
Endemic area	Participation in deworming according to WHO
[68]

Forecast

Most children, with timely treatment, fully recover within 3-14 days. Relapses are associated with reinfection within the family/group, poor hygiene, and insufficiently simultaneous treatment of contacts (the classic case is enterobiasis). [69]

Chronic giardiasis and STH infections with poor hygiene can lead to nutritional deficiencies and growth retardation; mass deworming and targeted sanitation programs improve population outcomes. [70]

Cryptosporidiosis in immunocompromised children can be protracted; prognosis is determined by immune status and access to clean water and specialized care. [71]

Strongyloidiasis, with its rare but severe hyperinfectious course, requires vigilance and strict adherence to treatment and screening algorithms. [72]

FAQ

Is it always necessary to have a stool sample tested for eggs and parasites?
If diarrhea lasts more than 7-10 days, there is a water factor, contact with sick people, or symptoms of enterobiasis, then yes. To increase sensitivity, three stool samples are required, 2-3 days apart, and concentration methods are used. [73]

How to treat "worms" in the entire household if a child has enterobiasis?
The standard treatment is two doses of the medication (mebendazole/albendazole/pyrantel) given 14 days apart to all family members simultaneously, plus enhanced hygiene for two weeks after the last dose. [74]

What treatment should I choose for giardiasis in a child?
The CDC lists tinidazole, nitazoxanide, and metronidazole as effective options; the choice depends on age, tolerability, and local recommendations. In case of relapse, a change of drug/repeat of the course and sanitary measures may be necessary. [75]

Is ivermectin dangerous for children?
For the treatment of strongyloidiasis, the drug is recommended for children weighing 15 kg or more; for milder cases, the decision is made on an individual basis. In areas endemic for Loa loa, daily blood smears are performed before administering ivermectin to avoid neurotoxicity. [76]

Is it possible to "just take a suppository/syrup for worms just in case"?
No. In non-endemic settings, treatment is best performed after laboratory confirmation and identification of the pathogen in order to select the correct medication and regimen. The exception is mass programs in endemic regions, as recommended by the WHO. [77]

Additional tables for practice

Table 9. Stool collection and transportation (minimum requirements)

Paragraph	Requirement
Number of samples	≥3, in 2-3 days
Conservation	10% formalin/PVA - according to laboratory instructions
Methods	Concentration (sedimentation/flotation), then microscopy
Safety	PPE, surface treatment, avoid cross-contamination
[78]

Table 10. "Water" rules for families

Situation	Recommendation
Before/after swimming	Shower with soap, especially the genital/perianal areas
During	Avoid swallowing water; toilet breaks; change diapers away from water
After diarrhea	Avoid swimming for 14 days (Giardia/Crypto)
Travel/hiking	Boil, filter, avoid raw water
[79]

Table 11. Rapid therapy regimens (summary for the physician)

Infection	Scheme (children)	Source
Enterobiasis	Pyrantel/mebendazole/albendazole, repeat after 14 days	CDC
Giardiasis	Tinidazole/nitazoxanide/metronidazole	CDC
Hymenolepis nana	Praziquantel 25 mg/kg ×1	CDC/AAP
Strongyloides	Ivermectin 200 mcg/kg 1-2 days (≥15 kg)	CDC
[80]

Table 12. When a clinic is sufficient

Scenario	Is the start of empiricism permissible?	Explanation
Nighttime itching + visible pinworms	Yes, in parallel, sanitary measures	A common situation in the family
Acute watery diarrhea in kindergarten	Depends on severity; examine the lesion	Preferably confirm
Immunosuppression + persistent diarrhea	No, advanced diagnostics are needed.	Risk of severe course
[81]