Provide an overview of helminth infections.

Helminth Infections: Overview

What Are Helminth Infections?

Helminth infections are caused by parasitic worms that infect approximately 1.5 to 2 billion people worldwide, representing one of the most common infectious conditions globally, particularly affecting populations in poverty-stricken areas of Southeast Asia, the Western Pacific, and sub-Saharan Africa. 1, 2, 3

Major Categories of Helminths

Soil-Transmitted Helminths (Geohelminths)

• Ascaris lumbricoides (roundworm): Large white worms (15-35 cm) that cause intestinal obstruction, biliary complications, and Loeffler's syndrome during larval migration through lungs 4, 1
• Trichuris trichiura (whipworm): Causes dysentery, rectal prolapse in heavy infections, and symptoms mimicking inflammatory bowel disease 4, 5
• Hookworm species (Necator americanus, Ancylostoma duodenale): Penetrate skin causing "ground itch," then migrate to intestines causing chronic blood loss and iron-deficiency anemia 4, 6
• Strongyloides stercoralis (threadworm): Unique ability to autoinfect, causing larva currens rash and potentially fatal hyperinfection syndrome in immunocompromised patients 4

Trematodes (Flukes)

• Schistosoma species: Penetrate skin during freshwater exposure in Africa, causing acute Katayama syndrome in travelers or chronic hepatosplenic disease, bladder carcinoma, and portal hypertension in migrants 4
• Fasciola hepatica/gigantica: Cause biliary obstruction and hepatic abscesses 4
• Paragonimus species: Lung flukes causing pleuritic chest pain, pleural effusion, and rarely meningoencephalitis 4

Cestodes (Tapeworms)

• Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm): Cause intestinal infection with visible proglottids in stool; T. solium can cause neurocysticercosis with seizures 4, 7
• Hymenolepis species (dwarf tapeworm): Cause abdominal pain and diarrhea 4

Tissue Nematodes

• Toxocara canis/cati: Cause visceral larva migrans with hepatosplenomegaly, eosinophilia, and ocular larva migrans 4
• Onchocerca volvulus: Causes river blindness with severe pruritus, subcutaneous nodules, and ocular complications 4
• Loa loa (eye worm): Causes Calabar swelling and conjunctival worm migration 4

Clinical Presentation Patterns

Asymptomatic Carriage

• 21-33% of returning travelers and migrants with helminth infections are completely asymptomatic, making screening based on exposure history essential 4, 7
• Helminths can survive for years in the host, demonstrating remarkable immune evasion capabilities 8

Eosinophilia as Key Diagnostic Clue

• Moderate to high-grade eosinophilia (>1.5 × 10⁹/L) is the single most important laboratory finding suggesting helminth infection 4, 7
• Eosinophilia is often transient during tissue migration phases and may resolve when parasites reach the intestinal lumen, potentially causing false-negative stool tests during peak eosinophilia 4, 7
• Migrants typically show higher parasite burden with multiple species, while travelers demonstrate more pronounced eosinophilia due to acute immune response 4

Acute Syndromes

• Loeffler's syndrome: Fever, urticaria, wheeze, dry cough, and migratory pulmonary infiltrates occurring 1-2 weeks post-exposure during larval migration through lungs (Ascaris, hookworm, Strongyloides) 4, 7
• Katayama syndrome: Acute schistosomiasis presenting 2-8 weeks after freshwater exposure with fever, urticaria, hepatosplenomegaly, and marked eosinophilia (often >5 × 10⁹/L); occurs almost exclusively in newly exposed travelers 4, 7
• Larva currens: Rapidly moving serpiginous urticarial rash pathognomonic for Strongyloides migration 4, 7

Chronic Manifestations

• Iron-deficiency anemia: Chronic hookworm infection causing insidious blood loss 6, 7
• Portal hypertension and hepatosplenomegaly: Chronic schistosomiasis, more common in migrants than travelers 4
• Bladder carcinoma: Rare complication of chronic S. haematobium infection 4

Diagnostic Approach

Critical History Elements

• Freshwater swimming in Africa (especially Lake Malawi, Lake Victoria, Nile River) signals schistosomiasis risk 4, 7
• Walking barefoot on soil or sand in tropical/subtropical regions indicates hookworm or Strongyloides exposure 4, 6, 7
• Consumption of raw/undercooked meat: beef (T. saginata), pork (T. solium), fish (various flukes) 4, 7
• Unwashed vegetables or contaminated water: geohelminths (Ascaris, Trichuris, hookworm) 4, 7
• Exact timing of exposures: critical because serological tests require 4-12 weeks to become positive 4

Laboratory Testing

• Three consecutive concentrated stool specimens are required—single sample sensitivity is only 50% for many helminths 7
• Strongyloides serology should be obtained immediately in all patients from endemic areas, especially before any immunosuppression 4, 7
• Schistosomiasis serology for any freshwater exposure in Africa 4, 7
• Stool PCR offers higher sensitivity than microscopy 4
• Cellophane tape test applied to perianal area on three consecutive mornings for suspected pinworm (90% sensitivity with three tests) 7, 5

Imaging

• Chest radiograph when respiratory symptoms present to identify migratory infiltrates 7
• Abdominal ultrasound for suspected hepatosplenic schistosomiasis 7

Treatment Principles

First-Line Agents

• Albendazole 400 mg PO is the cornerstone for soil-transmitted helminths, typically repeated in 2 weeks 4, 6, 1, 9
• Ivermectin 200 μg/kg PO is essential for Strongyloides and cutaneous larva migrans 4, 6, 7
• Praziquantel is the drug of choice for schistosomiasis and most tapeworms 4

Empirical Treatment Strategy

• For asymptomatic eosinophilia in travelers from endemic areas with negative stool tests, empirical treatment with albendazole 400 mg plus ivermectin 200 μg/kg as single doses is recommended 4, 6, 7
• This approach eliminates the need for repeated stool testing with poor sensitivity and prevents serious complications 6

Critical Pitfalls to Avoid

Never Assume Single Negative Stool Test Excludes Infection

• Three consecutive specimens are mandatory for adequate sensitivity 7
• Eosinophilia may be present when stool tests are negative during tissue migration phases 4, 7

Never Use Corticosteroids Without Excluding Strongyloides

• Risk of fatal hyperinfection syndrome in immunocompromised patients 4, 7
• Always screen for Strongyloides before initiating any immunosuppression in patients from endemic areas, regardless of symptoms 4, 7

Never Treat Suspected T. solium Without Excluding Neurocysticercosis

• Praziquantel can precipitate fatal cerebral inflammation if neurocysticercosis is present 7

Recognize Serological Cross-Reactivity

• Filarial serology may be positive in strongyloidiasis; Strongyloides serology may cross-react with filariasis 4, 7
• Expert consultation is recommended when interpreting serological tests 4

Special Populations

Migrants vs. Travelers

• Migrants have higher parasite burden, multiple species infections, and chronic complications (portal hypertension, bladder carcinoma) 4
• Travelers have acute infections with pronounced eosinophilia and syndromes like Katayama and Loeffler's 4

Children

• Soil-transmitted helminths cause impairments in physical, intellectual, and cognitive development 1
• Heavy Trichuris infection can cause rectal prolapse 4
• Expert consultation recommended for children aged 12-24 months before treatment 6

Global Health Context

• Helminth infections produce a global burden of disease exceeding malaria and tuberculosis 3
• Regular deworming of at-risk populations (school-aged children) serves as the backbone of control interventions in endemic areas 9
• Concerns about benzimidazole resistance have prompted efforts to develop new control tools 1, 9