Шистосома жапоника: Аурудың себебі, таралуы және диагностикасы

Species of fluke

Schistosoma japonicum is an important parasite and one of the major infectious agents of schistosomiasis. This parasite has a very wide host range, infecting at least 31 species of wild mammals, including nine carnivores, 16 rodents, one primate (human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Travelers should be well aware of where this parasite might be a problem and how to prevent the infection. S. japonicum occurs in the Far East, such as China, the Philippines, Indonesia and Southeast Asia.

Schistosoma japonicum was discovered in Kofu basin by Fujiro Katsurada, a pathologist in Okayama University in 1904. Later, Katsurada named the parasite Schistosoma japonicum.

Individuals at risk to infection from S. japonicum are farmers who often wade in their irrigation water, fishermen who wade in streams and lakes, children who play in water, and people who wash clothes in streams.

Once the parasite has entered the body and begun to produce eggs, it uses the hosts' immune system (granulomas) for transportation of eggs into the gut. The eggs stimulate formation of granuloma around them. The granulomas, consisting of motile cells, carry the eggs to the intestinal lumen. When in the lumen, granuloma cells disperse leaving the eggs to be excreted within feces. Unfortunately, about two thirds of eggs are not excreted, instead they build up in the gut. Chronic infection can lead to characteristic Symmer's fibrosis (also known as "clay pipe stem" fibroses, these occur due to intrahepatic portal vein calcification which assume the shape of a clay pipe in cross section). S. japonicum is the most pathogenic of the schistosoma species because it produces up to 3,000 eggs per day, ten times greater than that of S. mansoni. It is the cause of schistosomiasis japonica, a disease that still remains a significant health problem especially in lake and marshland regions. Schistosomiasis is an infection caused mainly by three schistosome species; Schistosoma mansoni, Schistosoma japonicum and Schistosoma haematobium. S. japonicum being the most infectious of the three species.

Microscopic identification of eggs in stool or urine is the most practical method for diagnosis. Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected, and urine examination should be performed if S. haematobium is suspected. Eggs can be present in the stool in infections with all Schistosoma species. The examination can be performed on a simple smear (1 to 2 mg of fecal material). Since eggs may be passed intermittently or in small amounts, their detection will be enhanced by repeated examinations and/or concentration procedures (such as the formalin – ethyl acetate technique). In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato Katz technique (20 to 50 mg of fecal material) or the Ritchie technique. Eggs can be found in the urine in infections with S. haematobium (recommended time for collection: between noon and 3 PM) and with S. japonicum. Detection will be enhanced by centrifugation and examination of the sediment. Quantification is possible by using filtration through a nucleopore membrane of a standard volume of urine followed by egg counts on the membrane. Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for S. haematobium) may demonstrate eggs when stool or urine examinations are negative. Since the eggs of S. japonicum are small, concentration techniques may be required. Biopsies are mostly performed to test for chronic schistosomiasis with no eggs. An ELISA test can be performed to test for antibodies specific to schistosomes. A positive result indicates a present or recent infection (within the past two years). Ultrasonographic examination can be performed to assess the extent of hepatic and spleen related morbidity. If necessary to enter potentially infected water, cercarial repellents and cercaricidal ointments can be applied to the skin before entering the water. Barrier cream with a dimethicone base offered high levels of protection for at least 48 hours.