Helminthiasis

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Introduction

Helminths are parasitic worm infestations that cause variable symptoms in humans.

Helminths are broadly classified as Nematodes (round worms), Cestodes (Tapeworms) and Trematodes (Flukes)

Nematodes (round worms)

  • Ascaris
  • Ancylostoma (hookworm)
  • Enterobius (pinworm)
  • Trichiuris (whipworm)
  • Strongyloides stercoralis

Cestodes (flat worms/tapeworms)

  • Taenia solium and Taenia saginata
  • Echinococcosis

Trematodes (flukes)

  • Schistosoma haematobium and mansoni
  • Fasciola

Round worm infestations are associated with rural living and poor hygiene.

  • Most are soil-transmitted
  • Prevalent among school children and young adults
  • Acquired through soil and faeco-oral contamination

Flat worms and tape worms are acquired by eating under-cooked contaminated meat or fish

Bladder worms (S. haematobium) are acquired by wading through streams and ponds contaminated with the vector snails

Clinical features

Depends on the infecting helminth:

Ascariasis

  • May be asymptomatic
  • Lung phase
    • Migration of parasite larvae through the lungs can lead to:
      • Irritating, non-productive cough
      • Burning substernal discomfort, aggravated by coughing or deep inspiration. 
  • Dyspnoea
    • Blood-tinged sputum
  • Intestinal phase:
    • Usually no symptoms, but high worm burden may cause:
      • Abdominal Pain
      • Features of small bowel
      • Features of perforation, Intussusception, Volvulus
      • Biliary tree occlusion: biliary colic, cholecystitis, cholangitis, pancreatitis, intrahepatic abscess
  • Effects of migration of an adult worm up the oesophagus:
    • Coughing
    • Oral expulsion of the worm

Hookworm

  • Most are asymptomatic.
  • Maculo-papular dermatitis
  • Mild transient pneumonitis
  • Epigastric pain, often with post-prandial accentuation
  • Diarrhoea
  • Weakness
  • Shortness of breath
  • Skin depigmentation
  • Anaemia and protein deficiency

Enterobiasis

  • Perianal pruritus, worse at night owing to the nocturnal migration of the female worms.
  • Skin excoriation and bacterial superinfection
  • Abdominal pain
  • Weight loss
  • Vulvo-vaginitis
  • Pelvic/perineal granulomas

Trichuriasis

  • Light infections are asymptomatic.
  • Heavy infections may cause:
    • Abdominal pain and anorexia
    • Bloody or mucoid diarrhoea
    • Rectal prolapse
    • Growth retardation

Strongyloidiasis

  • Distinguished from other round worms by its ability to replicate in the human host.
  • Can thus persist for decades without further exposure of the host to exogenous infective larvae
  • Acute strongyloides
    • Initial sign is localized pruritus and erythematous rash at site of skin
    • Tracheal irritation
    • Dry cough
    • Mid-epigastric abdominal pain
    • Nausea
    • Diarrhoea
    • Gastrointestinal bleeding
    • Repeated autoinfection leads to recurrent serpiginous maculopapular or urticarial rash along the buttocks, perineum, and thighs- “larva currens”.
  • Chronic strongyloides
    • Generally asymptomatic
    • Recurrent urticaria: buttocks and wrists
    • Mild chronic colitis
    • Weight loss
    • Small bowel obstruction
    • Nephrotic syndrome
    • Cardiac arrythmia
    • Recurrent asthma
    • Arthritis
    • Malabsorption
  • Hyperinfection syndrome and disseminated strongyloidiasis.
    • Associated with subclinical infection and use of corticosterioids
    • Depressed immunity leads to widespread larvae
    • Hyperinfection syndrome associated with GIT and lung
    • In disseminated strongyloidiasis larva invades multiple organs
    • Mortality is high for both conditions

Trichinellosis

In the first week after infection (gut invasion):

  • Diarrhoea
  • Abdominal Pain
  • Constipation
  • Nausea
  • Vomiting

In the second week after infection (muscle invasion):

  • Fever
  • Periorbital and facial oedema
  • Haemorrhages (subconjunctival, retinal and nail bed)
  • Maculopapular rash
  • Headache
  • Cough
  • Dyspnoea
  • Dysphagia
  • Tachyarrhythmias
  • Heart failure
  • Encephalitis
  • Pneumonitis

Schistosomiasis

See Urinary Schistosomiasis

Investigations

  • Stool examination for ova and parasites
  • Urine examination: microscopy
  • Haematology: eosinophilia and anaemia may be present
  • Serology and CT scan may be required in some instances

Drug Treatment

Hookworm

  • Mebendazole: Adult and child: 100 mg orally every 12 hours for 3 days; iron supplementation may be given if anaemia is present.
  • Albendazole: Adult and child: 400 mg orally once

Ascaris

  • Mebendazole: Adult and child: 100 mg orally every 12 hours for 3 days
  • Albendaozole: Adult and child: 400 mg orally once
  • Ivermectin: 150-200 μg/kg orally once

Trichuris

  • Mebendazole: Adult and child: 100 mg orally every 12 hours for 3 days
  • Albendaozole: Adult and child: 400 mg orally for 3 days
  • Ivermectin: 200 μg/kg/day orally for 3 days

Enterobius

  • Pyrantel pamoate: Adult and child: 10 mg/kg orally once; repeat dose 2 weeks later; several treatments may be necessary

Trematodes

  • Praziquantel :
    • Adult 40 mg/kg given orally at once provides up to 80% cure rates
    • Child over 4 years: 20 mg/kg followed after 4 - 6 hours by a further dose of 20 mg/kg.
  • Praziquantel is effective in all human cases caused by schistosomes

Cestodes

  • Praziquantel
    • Adult: 40 mg/kg given orally at once

Or:

  • 20 mg/kg followed by another 20 mg/kg after 4 - 6 hours
  • Child over 4 years: 20 mg/kg followed 4 - 6 hours by a further dose of 20 mg/kg (20 mg/kg 3 times daily for one day for S. japonicum infections)

Notable adverse drug reactions, contraindications and caution

  • Avoid mebendazole in pregnant women
  • Side effects of praziquantel include abdominal pain, headache, dizziness and skin rashes

Prevention

  • Good personal and food hygiene
  • Access to safe and potable water
  • Regular deworming
  • Adequate cooking of food and meats