Life cycle in humans
Infection of humans by gnathostomiasis is accidental because humans are not one of the definitive hosts of the parasite and do not allow the parasite to complete its life cycle. Infection in humans follows ingestion of raw or insufficiently cooked infected intermediate hosts. The ingested third stage larva migrates from the gastric wall and its migration results in the symptoms associated with infection by gnathostomiasis. The third stage larvae dont return to the gastric wall preventing it from maturing into adult worms, leaving the life cycle incomplete. Instead the larvae continue to migrate unpredictably unable to develop into adults, so eggs are seldom found in diagnostic tests. This also means the number of worms present in humans is a reflection of the number of third stage larvae ingested. Diagnosis
Diagnosis of gnathostomiasis is possible (with microscopy) after removal of the worm. The primary form of diagnosis of gnathostomiasis is the identification of larva in the tissue. Serological testing such as enzyme-linked immunosorbent assay (ELISA) or the Western blot are also reliable but may not be easily accessible in endemic areas.CT scanning or MRI can be used to help identify a soft tissue worm and when looking at CNS disease it can be used to reveal the presence of the worm. The presence of haemorrhagic tracks on gradient-echo T2-weighted MRI is characteristic and possibly diagnostic. Prevention
The best strategies for preventing accidental infection of humans is to educate those living in endemic areas to only consume fully cooked meat.
The most prescribed treatment for gnathostomiasis is surgical removal of the larvae but this is only effective when the worms are located in an accessible location. In addition to surgical excision, albendazole and ivermectin have been noted in their ability to eliminate the parasite. Albendazole is recommended to be administered at 400 mg daily for 21 days as an adjunct to surgical excision, while ivermectin is better tolerated as a single dose. Ivermectin can also serve as a replacement for those that cant handle albendazole 200 ug/kg p.o. as a single dose. However, ivermectin has been shown to be less effective than albendazole. Epidemiology
Endemic areas include Asia, Mexico, India and parts of South Africa. Originally believed to be confined to Asia, in the 1970s gnathostomiasis was discovered in Mexico, and found in Australia in 2011. 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, but in Thailand it is responsible for most of the observed parasitic CNS infection. It has long been recognised in China, but reports have only recently appeared in the English literature. History
The first case of Gnathostoma infection was identified by Sir Richard Owen when inspecting the stomach of a young tiger that had died at London Zoo from a ruptured aorta.