Gnathostomiasis

Synonyms: Yangtze oedema, Choko-Fuschu Tua Chid, wandering swelling

Lifecycle

Gnathostomiasis is caused by infection with the roundworm nematode Gnathostoma spinigerum, and rarely G. hispidum, which infect vertebrate animals.

• The life cycle starts when eggs are released from the stomach wall in a definitive host. Definitive hosts include pigs, dogs, cats and wild animals, eg otters, tigers and leopards. They pass into water within faeces.

• Approximately seven days later they have become larvae which hatch and are ingested by crustaceans of the genus Cyclops. This is the first intermediate host.

• Whilst still in the crustacean they migrate through its tissues and mature into second and third stage larvae.

• At this point they can be eaten by either a second intermediate host or a definitive host. They enter the gastric wall, mature to third stage larvae and then encyst.

• If meat is eaten from an infected definitive host, the larvae excyst, and migrate through liver and connective tissue before returning to the stomach four weeks later.

• Here they form a tumour and mature into adults after 6-8 months. 8-12 months after initial ingestion the worms will mate and a new batch of eggs will pass into the host's faeces.

• Humans are infected by ingestion of third stage larvae in infected meat, fish or infected water containing second stage larvae in Cyclops. Humans are, however, a paratenic host (an animal acting as a substitute intermediate host of a parasite, usually having acquired the parasite by ingestion of the original host), and the larva does not develop beyond the third stage, although it may migrate through the tissues for up to 12 years.

Epidemiología

Incidencia

Gnathostomiasis is uncommon, even in endemic areas such as Southeast Asia, South America, the Middle East and Australia. Its incidence is increasing, mainly due to changing dietary habits, and increasing tourism. Case reports are emerging from around the world:¹²

• It is most common in Thailand and Japan.

• In Thailand it is the most common parasitic infection of the central nervous system (CNS) and 6% of subarachnoid haemorrhages in adults and 18% of those in children are due to gnathostomiasis.³

• There is no predilection for race, age or sex.

Factores de riesgo

• Travel within, and eating uncooked food from, an endemic area.

• Factors related to occupational or dietary exposure to the larvae.

• Raw or undercooked freshwater fish: cebiche (also called ceviche or seviche) - the national dish of Peru, but common to all Latin America; sushi and sashimi in Japan, sum-fak in Thailand.

Presentación

Within 24-48 hours after ingestion, larvae invade the gastric wall and cause eosinophilia and various symptoms. Clinical features include:

• General: mild malaise, fever, urticaria, anorexia, nausea, vomiting, diarrhoea and epigastric pain.

• Skin: most commonly migratory, nodular panniculitis,⁴ soft tissue eruptions, boils and nodules in one or several areas.

• Pulmonary: cough, chest pain, dyspnoea or haemoptysis. Patient may cough up worm.

• Genitourinary: haematuria, urinary retention.

• Ophthalmological: decreased visual acuity, blindness, photophobia, pain, uveitis, iritis, intraocular haemorrhage. Raised intraocular pressure. Retinal scarring/detachment.

• Ear: decreased hearing and/or tinnitus.

• CNS: radiculomyelitis, encephalitis, meningitis. Neuritic pain followed by paralysis or decreased sensation for several days. Cranial nerve palsies. Stiff neck. Evidence of raised intracranial pressure.

Diagnóstico diferencial

• Other Infections: schistosomiasis, taeniasis, hookworm infection, ascariasis, Bancroft's filariasis, angiostrongyliasis, anisakiasis, and intestinal protozoal diseases.

• Other causes of cutaneous and viscreal larva migrans: paragonimiasis, sparganosis and toxocariasis. None is as active and mobile as gnathostomiasis.

• Other causes of swellings: maggots of tumbu or other flies, or sandflea.

• Inflammatory conditions: appendicitis,⁵ cholecystitis, cystitis, salpingitis, peptic ulcer, fibromyalgia, amoebic meningoencephalitis, aseptic meningitis.

Investigaciones

• Full blood count; eosinophilia may be present in up to 70% of cases,⁶ particularly during larval active migration phases. May exceed 50% of circulating white cells.⁷ Leukocytosis is also seen.

• Urinalysis; may show haematuria. The worm may also be seen.

• Sputum examination may reveal a worm.

• Plain X-ray; may show pulmonary lobar consolidation, collapse, effusions, pneumothorax or hydropneumothorax.

Gestión

Education and prevention are important - see below.

Farmacológico

• Anti-helmintics, eg albendazole, have an increasing role in complementing surgical intervention, with cure rates of up to 94%.⁸

  • Adult dose is 400 mg orally qd/bd for 21 days.

  • Paediatric dose is 15 mg/kg/day divided bd/qd for 21 days. Not to exceed 800 mg/day.

  
  Is poorly soluble in water, but well absorbed if taken with a fatty meal.

• An alternative is ivermectin 0.2 mg/kg for 2 days.⁹ This has been shown to have cure rates of 100% at this high dose, but is less effective than albendazole at low dose.¹⁰¹¹

• Pregnancy contra-indicates the use of anti-helmintics. There have been three documented cases of intrauterine transmission of gnathostomiasis.¹²

• Corticosteroids may have an additional role in reducing CNS inflammation caused by gnathostomiasis.

Quirúrgico

The only definitive treatment is surgical removal of the worm. This is possible only when it is superficial and accessible.

Complicaciones

• Hemorragia subaracnoidea

• Neumonía

• Sepsis

• Paralysis

• Intrauterine transmission

• Long-term neurological sequelae

Pronóstico

Gnathostomiasis is seldom fatal, except in CNS disease. Mortality rate is 8-25%, with 33% of survivors having neurological sequelae.¹³ Long-term morbidity is due to tissue injury during migration.

Prevención

Emphasise the need to avoid exposure.

• Ingestion of raw and undercooked meat should be avoided in endemic areas. However, if unavoidable, eat in reputable establishments using commercially frozen ingredients. Freezing meat at -20°C for 3-5 days kills the larvae.

• Marinating the meat in vinegar for 6 hours, or in soy sauce for 12 hours, kills the larvae.

• Contaminated water should be boiled for 5 minutes before use.

• Gloves should be worn, or the hands washed frequently if exposure to contaminated water or flesh is likely.

Historical

Sir Richard Owen first identified the nematode genus Gnathostoma. He identified the roundworm Gnathostoma spinigerum in the stomach of a young tiger that had died at London Zoo in 1836.
The first human case was described by Levinson in 1889.
It was not until 1934 that further series of human cases were described, followed by identification of an increasingly larger number of freshwater animals known to be naturally infected.