Gnathostomiasis - An Overview

Introduction:

Gnathostomiasis is known by different names in different countries, such as Tau-cheed in Thailand, Wood bury bug in Australia, Choko-Fushu, Tua chid, or Chokofishi in Japan, Shanghai’s rheumatism in China, and Yangtze river edema. Gnathostomiasis is a food-borne parasitic zoonotic infection (contracted from animals). A third-stage larva of several species of nematode genus Gnathostoma causes it. The most common species that cause this disease in humans is Gnathostoma spinigerum. People are usually infected by eating undercooked or raw freshwater fish, eels, frogs, birds, and reptiles. Most common in South America, Africa, and Asia, particularly in Japan and Thailand, the disease is more prevalent in the endemic areas. Consumption of raw or undercooked meat is more common in these regions. Increased tourist visits to these endemic areas have increased the incidence of this specific but rare disease affecting several organs.

How Are People Infected With Gnathostoma?

The definitive hosts are cats, dogs, leopards, and other fish-eating mammals, where the adult worms live in the stomach wall and produce a tumor-like mass. The adult worm releases the eggs in the stomach, which are then passed out through feces. The parasite fails to reach sexual maturity in human hosts.

How Does the Disease Spread?

The parasite fails to reach sexual maturity in the human host. Cats, dogs, leopards, and other fish-eating mammals are the definitive hosts where the adult worms live in the stomach wall and produce a tumor-like mass. The adult worm releases the eggs in the stomach, which are then passed out through the feces.

• Eggs become embryonated in freshwater, and eggs release first-stage larvae after about seven days. They are ingested by the first intermediate host, a water flea or copepod, where they develop into second-stage larvae.

• When infected copepods are ingested by a second intermediate host (fish, eels, frogs, birds, and reptiles), the second-stage larvae are freed in the intestine and develop into third-stage larvae.

• When the definitive host ingests the second intermediate host, the third-stage larvae develop into adult parasites in the stomach wall.

• After about six months, they grow into adults and complete the life cycle.

• After eight to twelve months, eggs are released into the environment in the host’s stool.

• Humans are usually infected with third-stage larvae of Gnathostoma species by eating raw or cooked freshwater fish.

What Are the Clinical Features of Gnathostomiasis?

Generalized symptoms develop within 24 to 48 hours after ingesting larvae. However, many individuals do not develop any symptoms during the early phase.

• Symptoms include loss of appetite, nausea, vomiting, diarrhea, and abdominal pain. This phase may last for two or three weeks.

• When the parasite moves under the skin, the people may experience itchy, painful red swelling. The swelling develops within three to four weeks after the ingestion of the parasite.

• The parasite can enter organs, including the eyes, ears, lungs, bladder, and brain, causing several symptoms.

Cutaneous Gnathostomiasis:

The symptoms appear as non-pitting edema.

• Swelling may be pruritic, painful, and erythematous.

• Usually, the swelling is solitary, but it may be multiple.

• The most common sites are the trunk and upper limbs.

Visceral Gnathostomiasis:

Visceral gnathostomiasis is due to the spread of larvae within the body and causes several manifestations all over the body, including the brain, eyes, and lungs.

Pulmonary symptoms:

• Cough.

• Chest pain.

• Pleural effusion.

• Haemoptysis (small amount of blood mixed with sputum by a forceful cough).

• Pneumothorax (leakage of air between the lungs spaces and chest wall).

Gastrointestinal Symptoms:

• Severe pain and fever.

• It can be mistaken for appendicitis and intestinal obstruction.

Genitourinary Symptoms:

• Uncommon.

• Vaginal bleeding.

• Passage of larvae in urine.

• hematospermia (blood in semen).

• Hematuria (blood in the urine).

Ocular (Eye) Symptoms:

• Glaucoma.

• Retinal scarring.

• Intraocular hemorrhage.

• Retinal detachment.

• Iritis (inflammation of the middle layer of the eye).

• Uveitis (inflammation of uvea).

Auricular (Ear) Symptoms:

• Sensorineural hearing loss.

• Mastoiditis (an infection that infects the mastoid bone behind the ear).

Central Nervous System (CNS) Symptoms:

• Coma.

• Subarachnoid hemorrhage.

• Cranial nerve palsies.

• Eosinophilic meningitis.

• Paralysis of limbs.

• Radicular pain in the limbs.

• Loss of sensation.

• Headache.

How Is Gnathostomiasis Diagnosed?

The diagnosis is considered in patients with swelling that move around the skin and elevated level of eosinophils. Gnathostomiasis is diagnosed by:

• Serological Tests include Enzyme-linked immunosorbent assay (ELISA) for L3 immunoglobulin G antibody.

• Magnetic Resonance Imaging (MRI) shows a diffuse enlargement of the spinal cord. This test shows regions with white-gray matter enlargement. MRI brain imaging shows a hemorrhagic tract and scattered deep intracerebral hemorrhage with diffuse, fuzzy white matter lesions with nodular enhancement.

• Complete Blood Count (CBC) Test - The test shows an elevated level of eosinophils. Eosinophils percentage may exceed more than the white blood cells (WBCs).

What Is the Treatment of Gnathostomiasis?

• Generally prescribed treatment for gnathostomiasis is the surgical removal of solitary nodules, effective only if the worms are in favorable positions. In addition to surgical excision, as well as antiparasitic drugs are prescribed.

• Albendazole and Ivermectin drugs are prescribed to eliminate the parasites.

• Albendazole is recommended at 400 mg daily for 21 days after the surgical excision.

• Ivermectin is recommended at 200 ug/mg as a single dose.

• Relapse can occur for up to seven months after treatment, so regular follow-up with a health professional is strictly advised.

How Can Gnathostomiasis Be Prevented?

The following measures can prevent the incidence of Gnathostomiasis:

• Raising public health awareness through educational campaigns will help eliminate and control the spread of parasites. The best strategy to prevent the infection is to educate the population living in the endemic areas.

• Avoiding consumption of eating raw and undercooked meat by individuals living in the endemic area.

• Effective methods to kill the larvae are adequate cooking and freezing the infected meat to -20 degrees C for three to five days.

• Traveling to areas with high prevalence should be avoided.

• Avoid using contaminated fresh water in areas where the parasite is more common.

• Wearing gloves when handling raw meat.

• Wash hands with soap and water before and after preparing the food.

Conclusion:

Gnathostomiasis is most commonly pervasive in endemic areas due to poor awareness and diagnosis. Raising awareness and education on handling animal products and their consumption in the population inhabiting the endemic areas will help reduce the occurrence. Traveling to endemic areas should be avoided, and tourists should be advised to avoid consuming raw or undercooked meat.