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.
- Migration of parasite larvae through the lungs can lead to:
- 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
- Usually no symptoms, but high worm burden may cause:
- 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
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