Soil-Transmitted Helminthiases

Dr Arun Mitra

Dept of Community and Family Medicine, AIIMS, Bibinagar

2026-04-06

Learning Objectives

  • Name the four causative organisms of STH and their transmission routes
  • Describe the global burden and at-risk populations
  • Recognise clinical features of light and heavy infections
  • Outline WHO-recommended treatment and prevention strategies

How many people are infected with intestinal worms?

  • 500 million?
  • 1 billion?
  • 1.5 billion?

Answer

1.5 billion people — 24% of the world’s population

What are Soil-Transmitted Helminthiases?

  • Parasitic worm infections caused by nematodes (roundworms)
  • Transmitted through contaminated soil
  • Classified as Neglected Tropical Diseases (NTDs)
  • Disproportionately affect the poorest communities
  • Worms do not multiply inside the human host

Etiology & Transmission

The Four Causative Organisms

Organism Common Name Transmission
Ascaris lumbricoides Roundworm Faecal-oral (ingestion of eggs)
Trichuris trichiura Whipworm Faecal-oral (ingestion of eggs)
Necator americanus / Ancylostoma duodenale Hookworm Percutaneous (skin penetration)
Strongyloides stercoralis Threadworm Percutaneous + autoinfection

Two Transmission Routes

Faecal-Oral

Ascaris & Trichuris

  • Unwashed vegetables
  • Contaminated water
  • Children: hand-to-mouth from soil

Percutaneous

Hookworm & Strongyloides

  • Bare skin contact with soil
  • Barefoot walking/working
  • Agricultural workers, miners

Life Cycle: Ascaris & Trichuris

  1. Eggs passed in faeces into soil
  2. Mature in warm, moist soil (2–3 weeks)
  3. Ingested via contaminated food, water, or soil
  4. Hatch in intestine → mature into adult worms
  5. Ascaris larvae: hepato-pulmonary migration (Löffler syndrome)

Ascaris lumbricoides: Adult Worms

A. lumbricoides — female (thicker, left) and male (thinner, right). Females can reach 20–35 cm.

Ascaris lumbricoides: Egg in Soil

Fertilised egg — oval, bile-stained, characteristic mammillated outer shell.

Life Cycle: Hookworm

  1. Eggs passed in faeces → hatch in soil
  2. Filariform (L3) larvae — the infective stage
  3. Larvae penetrate bare skin → “ground itch”
  4. Migrate to lungs → coughed up → swallowed
  5. Mature in small intestine → attach to mucosa
  6. Feed on blood: 0.03–0.2 mL/worm/day

Hookworm: Egg Stages

Hookworm egg — thin-shelled, oval, with developing embryo.

Later stage — multiple blastomeres visible inside thin shell.

Hookworm: Adult Worm

Adult hookworm — C-shaped body, dark from blood meal.

Intestinal mucosa with hookworms attached and feeding.

Hookworm: Mouth Parts

Light microscopy — cutting plates to anchor to mucosa.

Scanning electron microscopy — teeth clearly visible.

Life Cycle: Strongyloides stercoralis

  • Similar percutaneous entry as hookworm
  • Unique: autoinfection cycle — can persist for decades
  • Hyperinfection in immunocompromised patients (steroids, HTLV-1)
  • ~600 million people infected globally
  • Often missed — standard stool microscopy has poor sensitivity

Global Burden

Key Numbers (WHO, 2024)

  • 1.5 billion people infected (24% of world population)
  • 883 million children need treatment annually
  • 505 million children treated in 2024 (57.2% coverage)
  • DALYs reduced by >50% between 2010–2019

At-Risk Populations

  • Preschool children — 260 million in endemic areas
  • School-age children — 654 million requiring treatment
  • Adolescent girls — 108 million in transmission zones
  • Pregnant & lactating women — 138.8 million at risk
  • Occupational groups — tea-pickers, miners, agricultural workers

Geographic Distribution

Highest burden in:

  • Sub-Saharan Africa
  • South and Southeast Asia
  • Latin America

India has the highest absolute burden globally.

Clinical Features & Diagnosis

Clinical Spectrum

Important

Light infections are often asymptomatic. Morbidity is proportional to worm burden.

  • Most infected individuals have no symptoms
  • Clinical disease appears with heavy worm loads
  • Chronic, subclinical effects accumulate silently over years
  • Greatest impact: children’s growth and cognition

Clinical Features by Organism

Feature Ascaris Trichuris Hookworm
GI Abdominal pain, obstruction Bloody diarrhoea, tenesmus Epigastric pain
Nutritional Malabsorption Iron-deficiency anaemia Severe anaemia
Unique Löffler syndrome; biliary obstruction Rectal prolapse Ground itch
Cognitive Impaired growth Impaired cognition Impaired development

Trichuris trichiura: Adult Worm & Egg

Whip-shaped worm — thin anterior, thick posterior.

Barrel-shaped egg with diagnostic polar plugs.

Trichuris trichiura: Embryonated Egg

Infective stage — larva visible coiled inside the barrel-shaped shell.

Diagnosis

Standard Methods

  • Direct stool smear
  • Kato-Katz technique (WHO standard)
  • Formol-ether concentration

Strongyloides

  • Baermann funnel technique
  • Agar plate culture
  • Serology (ELISA)

Note

In MDA programmes, treatment is given without prior individual diagnosis.

Mini Case Discussion

Case

A 7-year-old boy from a tribal hamlet in Jharkhand: chronic abdominal pain, distended abdomen, failure to thrive. Mother reports he passes “long white worms” in stool. Pale, underweight.

  1. Most likely diagnosis?
  2. What investigation?
  3. Could he have co-infection? Why?

Treatment & Prevention

Three Pillars of STH Control

MDA

  • Periodic deworming
  • Target: ≥75% coverage
  • School health days

WASH

  • Safe drinking water
  • End open defecation
  • Handwashing with soap

Health Education

  • Shoe-wearing promotion
  • Hygiene in schools
  • Behaviour change

Why MDA Alone Is Not Enough

  • Deworming reduces worm burden but does not prevent re-exposure
  • Without sanitation, reinfection occurs within months
  • MDA = treatment, not elimination
  • MDA + WASH + Health Education → sustainable control

WHO 2030 Roadmap Targets

  • Eliminate STH morbidity in pre-school and school-age children
  • Establish STH control in adolescent girls and pregnant women
  • Establish strongyloidiasis control in school-age children
  • Ensure universal access to basic sanitation in endemic areas

Case Study & Quiz

Programme Design Exercise

Scenario

You are Medical Officer in a PHC in rural MP. Baseline STH prevalence: 45% in school-age children. Design a deworming programme.

  1. Which drug, dose, and frequency?
  2. What age groups to target?
  3. Through which delivery platform?
  4. What complementary interventions beyond MDA?

Expected Answers

  1. Albendazole 400 mg, once yearly (20–50%) or twice yearly (≥50%)
  2. Pre-school (1–4 yr) + school-age (5–15 yr) + women of reproductive age
  3. School-based deworming; Anganwadi for preschoolers
  4. WASH improvements, health education, footwear promotion

Q1: Transmission Route

Which STH is transmitted by larval skin penetration?

    1. Ascaris lumbricoides
    1. Trichuris trichiura
    1. Necator americanus
    1. All of the above

Answer: c) Hookworm — filariform larvae penetrate bare skin

Q2: Nutritional Impact

Most significant nutritional consequence of hookworm?

    1. Vitamin A deficiency
    1. Iron-deficiency anaemia
    1. Protein-energy malnutrition
    1. Zinc deficiency

Answer: b) Hookworms feed on blood (0.03–0.2 mL/worm/day)

Q3: MDA Threshold

WHO recommends MDA when baseline STH prevalence exceeds:

    1. 10%
    1. 20%
    1. 50%
    1. 75%

Answer: b) Once yearly if 20–50%; twice yearly if ≥50%

Q4: Clinical Presentation

Heavy Trichuris trichiura infection may present with:

    1. Löffler syndrome
    1. Intestinal obstruction
    1. Rectal prolapse
    1. Ground itch

Answer: c) Rectal prolapse — characteristic of heavy Trichuris in children

Q5: Treatment Facts

Which is TRUE about STH?

    1. Worms multiply inside the human host
    1. Light infections are usually symptomatic
    1. Albendazole 400 mg covers Ascaris, Trichuris, and hookworm
    1. Ivermectin is the drug of choice for Ascaris

Answer: c) Albendazole 400 mg single dose covers all three

Recap

Five Things to Remember

  1. 1.5 billion infected — most common infections on Earth
  2. Four organisms, two routes — faecal-oral and percutaneous
  3. Morbidity is dose-dependent — light infections are silent
  4. Treatment is simple — Albendazole 400 mg, single dose
  5. MDA + WASH + Education — drugs alone are not enough

References

Questions?

Thank You!