Nematode infections

Infection/Epidemiology

Clinical features/Diagnosis

Treatment

Ascariasis (roundworms)1
Ascaris lumbricoides

Distribution: worldwide, mainly in tropical and subtropical

Transmission: ingestion of ascaris eggs

  • During larval migration
    Loeffler ’s syndrome: transient pulmonary symptoms (dry cough, dyspnoea, wheezing) and mild fever.
  • Once adult worms are present in the intestine
    Abdominal pain and distension. In general, the diagnosis is made when adult worms are expelled from the anus (or occasionally from the mouth). Ascaris are large (15-30 cm), cylindrical worms, pinkish-white, with slightly tapered ends.
  • Complications
    Ascariasis is usually benign, but massive infestation may cause intestinal obstruction (abdominal pain, vomiting, constipation), especially in children < 5 years. Worms may accidentally migrate to gall bladder, liver or peritoneum, causing jaundice, liver abscess, or peritonitis.
  • Ascaris eggs may be detected through parasitological examination of stools.

albendazole PO single dose
Children > 6 months and adults:
400 mg
(200 mg in children > 6 months but < 10 kg)
or
mebendazole PO for 3 days
Children > 6 months and adults:
100 mg 2 times daily
(50 mg 2 times daily in children > 6 months but < 10 kg)

Trichuriasis (whipworms)1
Trichuris trichiura

Distribution and transmission:
as for A. lumbricoides

  • In heavy infection: abdominal pain and diarrhoea.
  • In massive infection: chronic bloody diarrhea, tenesmus, rectal prolapse due to frequent attempts to defecate, especially in children.
    Worms may sometimes be seen on the rectal mucosa when prolapsed: these are grayish-white, 3-5 cm in length, in the shape of a whip, with a thickened body and a long, threadlike extremity.
  • Trichuris eggs may be detected through parasitological examination of stools.

albendazole PO for 3 days
Children > 6 months and adults:
400 mg once daily
(200 mg once daily in children > 6 months but < 10 kg)
or
mebendazole PO for 3 days, as for ascariasis.
A single dose of albendazole or mebendazole is often insufficient.

Ankylostomiase1
Ancylostoma duodenale
Necator americanus

Distribution: tropical and subtropical regions

Transmission: larval skin penetration following contact (feet, hands) with contaminated soil

  • During larval penetration/migration
    Cutaneous signs (pruritic papulo-vesicular rash at the site of penetration, usually the feet) and pulmonary symptoms (similar to ascariasis).
  • Once adult worms are present in the intestine
    Mild abdominal pain. Attachment of the parasite to the mucosa leads to chronic blood loss and anaemia (in endemic areas, antihelminthic treatment is recommended for patients with iron-deficiency anaemia).
  • Hookworm eggs may be detected through parasitological examination of stools.

albendazole single dose (as for ascariasis) is much more effective than mebendazole single dose.
When using mebendazole, a 3-day treatment (as for ascariasis) is recommended.
Treatment of anaemia (Chapter 1).

Strongyloidiasis
Strongyloides stercoralis

Distribution: humid tropical regions

Transmission: larval skin penetration and auto-infection

  • Acute strongyloidiasis
    • During larval penetration/migration: cutaneous signs (erythema and pruritus at the site of penetration, which may persist several weeks) and pulmonary symptoms (similar to ascariasis).
    • Once larvae are present in the intestine: gastrointestinal symptoms (bloating, abdominal and epigastric pain, vomiting, diarrhoea).
  • Chronic strongyloidiasis
    Intestinal larvae may re-infect their host (auto-infection) by penetrating through the intestinal wall or by migrating transcutaneously from perianal skin. Chronic infections result in prolonged or recurrent pulmonary and gastrointestinal symptoms. Transcutaneous migration of intestinal larvae gives rise to a typical rash (larva currens), mainly in the anal region and on the trunk: sinuous, raised, linear, migrating lesion, intensely pruritic, moving rapidly (5 to 10 cm/hour) and lasting several hours or days.
  • Complications
    Hyperinfection (massive infestation) results in exacerbation of pulmonary and gastrointestinal symptoms, and possible dissemination of larvae to atypical locations, (CNS, heart, etc.). This form occurs mainly in patients receiving immunosuppressive therapy (e.g. corticosteroids).
  • Strongyloides larvae may be detected through parasitological examination of stools.

First line treatment is:
ivermectin PO2 single dose
Children > 15 kg and adults:
200 micrograms/kg, on an empty stomach

While less effective, a 3-day treatment with albendazole PO (as for trichuriasis) may be an alternative.

Hyperinfections are refractory to conventional therapy. Prolonged or intermittent multiple-dose regimens are required.

Enterobiasis (pinworms)
Enterobius vermicularis

Distribution: worldwide

Transmission: faecal-oral route or auto-infection

  • Anal pruritus, more intense at night, vulvovaginitis in girls (rare). In practice, the diagnosis is most often made when worms are seen on the perianal skin (or in the stool in heavy infestation). Pinworms are small (1 cm), mobile, white, cylindrical worms with slightly tapered ends.
  • Pinworm eggs may be collected from the anal area (scotch tape method) and detected under the microscope.

albendazole PO single dose, as for ascariasis
or
mebendazole PO single dose
Children > 6 months and adults:
100 mg
(50 mg in children > 6 months but < 10 kg)
A second dose may be given after 2 to 4 weeks.

Trichinellosis
Trichinella sp

Distribution: worldwide, particularly frequent in Asia (Thailand, Laos, China, etc.)

Transmission: consumption of raw or undercooked meat containing trichinella larvae (pork, wart-hog, bear, dog, etc.)

  • Enteric phase (1 to 2 days after ingestion of infected meat)
    Self-limited episode of diarrhoea and abdominal pain lasting several days.
  • Muscular phase (about 1 week after ingestion)
    High fever; muscular pain (ocular [pain on eye movement], masseters [limitation of mouth opening], throat and neck [pain with swallowing and speech], trunk and limbs); facial or bilateral peri-orbital oedema; conjunctival haemorrhage, subungual haemorrhage; headache. Typical features are not always present and the patient may present with a non-specific flu-like syndrome.
    Other features, such as dietary habits (consuming pork/raw meat), suggestive symptoms (fever > 39 °C and myalgia and facial oedema) in several individuals who have shared the same meal (e.g. ceremony) or hypereosinophilia > 1000/mm3, reinforce the clinical suspicion.
  • Definitive diagnosis: muscle biopsy; serology (ELISA, Western Blot).

albendazole PO for 10 to 15 days
Children > 2 years:
5 mg/kg 2 times daily
Adults:
400 mg 2 times daily
or
mebendazole PO for 10 to 15 days
Children > 2 years:
2.5 mg/kg 2 times daily
Adults:
200 mg 2 times daily

plus, regardless of which anti- helminthic is chosen:
prednisolone PO
0.5 to 1 mg/kg once daily for the duration of treatment



Footnotes
Ref Notes
1 Roundworms, whipworms and hookworms frequently co-infect the same host. This should be taken into account when prescribing antihelminthic treatment. [ a b c ]
2 The migrating larvae of Ancylostoma braziliense and caninum (hookworms of cats and dogs) also present as a pruritic, inflammatory, creeping eruption in humans (cutaneous larva migrans) but with a slower rate of progression and a longer duration (several weeks or months). Treatment is with albendazole (400 mg single dose or once daily for 3 days in children > 6 months and adults; 200 mg in children > 6 months but < 10 kg) or ivermectin (200 micrograms/kg single dose).