Gnathostomiasis: causes, symptoms, diagnosis, and treatment

Gnathostomiasis is a zoonotic, parasitic disease caused by Gnathostoma.


Causes

Human are mainly infected by Gnathostoma spinigerum. Gnathostoma spinigerum adults are stout, (13.5 - 16.2)mm × (1.1 - 1.4)mm in size, cylindrical, bright red, slightly transparent, with a head bulb armed by 8 - 11 rows of hooks, with anterior and rear spines. The adults are parasitic in the masses on the stomach wall of the definitive host such as dogs and cats, and the eggs fall into the gastrointestinal cavity through the holes and are excreted through feces. The eggs are elliptical, 69.3μm × 38.5μm in size. Each egg contains 1 - 2 egg cells. The eggs are hatched into eggs containing first-stage larvae in 7 days. After first molt in 2 days, the larvae get out from the eggs and develop into ensheathed second-stage larvae. After the second-stage larvae are swallowed by first intermediate host Cyclopidae, the larvae desheath, penetrate the stomach wall, migrate to the body cavity, and develop into early third-stage larvae in 7 - 10 days. After Cyclopidae infected by the larvae are swallowed by fishes, mainly snakehead, loach, and rice field eel, most larvae migrate into the liver and muscles, where they encyst and develop into late three-stage larvae in 1 month. The larvae are infective to the definitive host such as cats and dogs. After the definitive host ingests the fish containing the late third-stage larvae, the larvae decyst in the stomach and migrate through the intestinal wall to the liver, muscles or connective tissue, where the larvae develop into forth-stage larvae. Eventually, the larvae return to the stomach wall, resulting in some masses under the mucous membranes, where the larvae gradually develop into adults. There are one or several adults in a mass.

After some animals, such as frogs, snakes, fowls, pigs, and many kinds of primates, ingest infected fish, the larvae cannot develop but can survive for a long time. These animals are called transport hosts.

All animals, such as dogs, cats, and pigs, that can discharge the eggs of Gnathostoma are the source of infection. Humans are not the suitable parasitic hosts for Gnathostoma. The parasitic Gnathostoma are usually third-stage larvae or sexually immature adults in the human body. The larvae have horizontal stripes and small spines on the surface, and the head bulb is armed by 4 rows of hooks. The larvae are 2.5 - 4.0mm long. The larvae can survive in the human body for several years, up to 10 years.


Signs and Symptoms

Humans are not suitable hosts for Gnathostoma. After invasion of the human body, the larvae cannot develop, but they can migrate, and multiple organs and tissues can be involved. Once important organs, such as the brain, eyes, lungs, and liver, are invaded, there are serious consequences.

Cutaneous gnathostomiasis

As a result of the migration of the larvae, tunnels between the epidermis and dermis or subcutaneous tissues may be formed, causing cutaneous larva migrans, manifested by creeping eruption or intermittent subcutaneous migratory masses, red local skin, sometimes burning sensation, edema, and pruritus. There is not obvious pain. Sometimes, there are abscesses and nodules. There may be increased erythrocyte sedimentation rate, and sometimes the larvae can escape from the abscess. Masses can occur on the forehead, face, occipital region, chest, abdomen, and arms. Eosinophilia may occur in 10% - 75% of patients.

Visceral gnathostomiasis

The larvae can also migrate in or colonize the digestive tract, respiratory tract, urinary system, and nervous system, causing visceral larva migrans, manifested by intermittent migratory masses, local edema, pain, acute or chronic inflammation, and massive eosinophils, plasma cells, neutrophils, and lymphocytes infiltration. Hemorrhage, necrosis, and fibrosis may occur, and masses may occur on the stomach wall.


Diagnosis

If there are clinical manifestations and a history of ingestion of undercooked fish, chicken, or duck, the disease can be suspected. If the larvae are found in the lesions, the disease can be diagnosed.


Treatment

The treatment regimen is albendazole 400mg orally twice daily for 3 weeks.

Surgical extraction is required in the treatment of ocular gnathostomiasis.