Gnathostomiasis

Gnathostomiasis, also known as larva migrans profundus, is the human infection caused by any of six species of nematodes in the genus Gnathostoma, which infect vertebrates as second intermediate and primary hosts.

Signs and symptoms

A few days after ingestion epigastric pain, fever, vomiting, and loss of appetite resulting from the migration of larvae through the intestinal wall to the abdominal cavity will appear in the patient. meningitis, encephalitis and eosinophilia. Eosinophilic myeloencephalitis may also result from invasion of the central nervous system by the larvae. The most common cause in the Americas is G. binucleatum. G. hispidium and G. doloresi occur in East and Southeast Asia; the former has also been found in Eastern Europe. G. nipponicum occurs only in Japan and China.

Transmission

alt=|thumb|Life-cycle of Gnathostoma

Gnathostomiasis is transmitted by the ingestion of third-stage larvae from raw or insufficiently cooked second intermediate or paratenic hosts such as freshwater fish, snakes, poultry, or frogs. Monopterus albus is an invasive species in North America, but no Gnathostoma infections in humans have yet been conclusively identified in the US.

It is unclear if humans can be infected from drinking water contaminated with infected copepods.

Life cycle

Life cycle in definitive hosts

Adult worms are found in a tumor located in the gastric wall of the definitive hosts and release eggs into the host's digestive tract. The eggs are then released with feces and in about a week hatch in water to develop into first stage larvae. Larvae are then ingested by minute copepods of the genus Cyclops. Once entering the copepod, the larvae penetrate the gastric wall of their intermediate host and begin to develop into second-stage and even early third-stage larvae. Within this second intermediate or definitive host the larva repeat a similar pattern of penetrating the gastric wall but then continue to migrate to muscular tissue and develop into advanced third-stage larvae. If the cyst containing flesh of these hosts is ingested by a definitive host, such as dogs, and cats, the cysts are ingested and the larvae escape the cysts and penetrate the gastric wall.

Epidemiology

Endemic areas include Asia, Mexico, India and parts of South Africa. Even though it is endemic in areas of Southeast Asia and Latin America, it is an uncommon disease. However, researchers have noticed recently an increase in incidence. This disease is most common in both Thailand and Japan. In Thailand, it is the most common cause of central nervous system parasitic infections. As of 2020, about 5,000 cases of Gnathostomiasis have been reported globally. However it was not until 1889 that the first human case was described by Levinson when he found the Gnathostoma larva in an infested Thai woman. The lifecycle of G. spinigerum was described by Svasti Daengsvang and Chalerm Prommas from Thailand in 1933 and 1936. This delay in identification of the parasite in humans is because humans are not a definitive host for this parasite making infection from this parasite rare. Gnathostomiasis infection is rare because the parasite must be digested when it has reached its third larvae stage, providing only a short time in which the parasite can infect humans. It is uncommon for the larvae to penetrate the skin of individuals exposed to contaminated food or water without ingestion.

References

External links

Gnathostomiasis at CDC
Gnathostomiasis at eMedicine