Yangtse Oedema (Gnathostomiasis)

Synonyms: Yangtze Oedema, Creeping Eruption, Larva Migrans, Chok-Fuschu Tua Chid, Wandering Swelling, Visceral Larva Migrans

Gnathostomiasis is caused by infection with the roundworm nematode Gnathostoma spingerum, and rarely 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, wild animals e.g otters, tigers, leopards. They pass into water within faeces.
• Approximately 7 days later they have become larvae which hatch and are ingested by the crustacean 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, migrate through liver and connective tissue before returning to the stomach 4 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 hosts faeces.
• Humans are infected by ingestion of 3rd stage larva in infected meat, fish or infected water containing 2nd stage larva 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 do not develop beyond the 3rd stage, though it may migrate through the tissues for up to 12 years.

Incidence

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.^1,2It 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.

Risk Factors

• 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.

• 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, intra-ocular 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.

• Other Infections: Schistosomiasis, Taenia, hookworm infection, ascariasis, Bancroftian filiariasis, angiostrongyliasis, anisakiasis, and intestinal protozoal diseases.
• Other causes of larva migrans: paragonimiasis, sparganosis, and toxicariasis. None are as active and mobile as gnathostoma.
• 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.

• Full blood count; eosiniphilia 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.

Drugs

• Anti-helminths e.g. Albendazole has an increasing role in complementing surgical intervention, with cure rates of upto 94%.⁸
  • Adult dose is 400mg orally qd/bd for 21 days.
  • Paediatric dose 15mg/kg/day divided bd/qd for 21 days. Not to exceed 800mg/day.
  Is poorly soluble in water, but well absorbed if taken with a fatty meal.
• Alternative is Invermectin 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.^10,11
  Pregnancy contra-indicates the use of anti-helminths. There have been 3 documented cases of intrauterine transmission of gnathostomiasis.¹²
• Corticosteroids may have an additional role in reducing CNS inflammation caused by gnathostomiasis.

Surgical

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

• Subarachnoid haemorrhage
• Pneumonia
• Sepsis
• Paralysis
• Long term neurological sequelae

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.

• 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 degrees centigrade 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.

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 of ruptured aorta, 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.