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 saginata
  • Echinococcosis

Trematodes (flukes)

  • Schistosoma haematobium and mansoni
  • Fasciola
  • Round worm infestations are associated with rural living and poor hygiene
    • 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
  • Lung phase
  • Migration of parasite larvae through the lungs can lead to:
  • Irritating, non-productive cough
  • Burning substernal discomfort, aggravated by coughing or deep
  • 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
  • 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
  • Heavy infections may cause:
  • Abdominal pain and anorexia
  • Bloody or mucoid diarrhoea
  • Rectal
  • 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

・ 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 Urology

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