Soil Transmitted Helminthiasis Overview

Soil Transmitted Helminthiasis (STH)

• STH are a group of parasitic nematode worms that cause human infection
• They are transmitted through contact with parasite eggs or larvae that thrive in warm, moist soil of tropical and subtropical countries
• STH is one of the most common infections worldwide, affecting primarily deprived communities
• Children are most commonly affected
• Climate, poverty, and inadequate water supplies and sanitation significantly impact transmission

Types of Soil-Transmitted Helminths

• Roundworms (Ascaris lumbricoides): infects over 1 billion people
• Whipworms (Trichuris trichiura): infects 795 million people
• Hookworms (Necator americanus & Ancylostoma duodenale): infects 740 million people
• Other types include Strongyloides stercoralis

Transmission

• Infection occurs through ingestion of eggs from contaminated soil or active penetration of the skin by larvae in the soil.
• Soil must be warm and moist for the eggs to mature (2–4 weeks depending on the worm type)
• Common sources of transmission include:
  • Contaminated water
  • Vegetables not properly cooked, washed, or peeled
  • Children playing in contaminated soil and putting their hands in their mouths
• Feces containing eggs contaminates the soil
• No direct person-to-person transmission

Epidemiology

• Climate plays a significant role in transmission requiring adequate moisture and warmth
• Poverty and inadequate sanitation are also critical determinants
• STH species commonly co-endemic in areas with these conditions
• High infection rates occur in sub-Saharan Africa, the Americas, China, and East Asia

Prevalence in Different Communities

• Prevalence rates vary depending on community type
• Urban slums have the highest prevalence (68.7%)
• Rural/estate communities have a moderate prevalence (67.2%)
• Orang Asli communities have a high prevalence (77.8%)

Clinical Manifestations

• Most STH infections are asymptomatic (5-10 worms)
• Heavy infections might cause nutritional deficiency, abdominal pain, diarrhea, weight loss, and intestinal obstruction in children
• Lung migration of larvae may result in allergic manifestations like asthma, or pulmonary signs (Loeffler's syndrome)
• Migrations of adult worms may cause blockage of bile ducts, gallbladder, liver, appendicitis, and ectopic lesions

Diagnosis

• Identification of fertilised or unfertilised eggs in human feces using direct fecal smears, concentration techniques (e.g., Kato Katz technique), and other methods

Pathology

• The intensity of host reactions depends on the worm burden
• Lung migration of larvae can cause pulmonary signs, and allergies like asthma or urticaria.
• Intestinal ascariasis causes competition for food leading to malnutrition, anemia, fluid retention, and intestinal obstruction

Prevention and Treatment

• Control strategy involves treating once or twice annually, targeting preschool and school-aged children, women of childbearing age, lactating women, and high-risk adults in certain occupations (e.g., tea-pickers, miners)
• Treatment relies on antihelminthic drugs (Mebendazole, Albendazole)
• Personal hygiene, proper sanitation, and avoidance of using feces as fertilizer are also critical preventative measures.

Ascaris lumbricoides

• Largest intestinal roundworm causing ascariasis
• Adult female (20-35cm), male (10-25cm)
• Fertilised egg is broadly oval (45-75 x 35-50 µm)
• Thick shell with brown bile-stained, mammilated outer covering (albumin layer)
• Inside vitelline layer
• Infertile: more elongated (80-90 µm), prominent mammilations, disorganised globular internal contents

Trichuris trichiura

• Also known as whipworms
• Long slender, threadlike anterior portion, thicker posterior portion resembling a whip handle
• Adult worm 30-50 mm, with a coiled tail in the male having the spicule
• Eggs are oval (barrel-shaped), bile-stained, with a thick smooth shell and a prominent polar plug at each end
• Egg measures 45-55µm x 20-23µm

Life Cycle of Ascaris lumbricoides

• Eggs are ingested and develop in the small intestine
• Larvae penetrate intestinal walls and migrate to lungs
• Larvae are coughed up, swallowed, and mature in the small intestine
• Fertilized eggs are passed in the feces.

This quiz explores Soil Transmitted Helminthiasis (STH), a significant group of parasitic infections affecting predominantly children in tropical and subtropical regions. Understand the types of helminths, their transmission routes, and the socio-economic factors influencing these infections. Test your knowledge on this global health issue affecting vulnerable communities.