Schistosomiasis japonica: causes, symptoms, diagnosis, treatment

Japanese schistosomiasis is a chronic tropical trematodosis of Southeast Asia, characterized by predominant damage to the gastrointestinal tract and liver.

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Epidemiology of Japanese schistosomiasis

Mature helminths parasitize in the vessels of the portal and mesenteric veins of humans and some domestic and wild animals: cattle and small cattle, dogs, cats, mice, rats, rabbits, pigs, monkeys, etc. The female begins laying eggs 4 weeks after infection. Each female can lay 1,500-3,000 eggs per day. The eggs pass through the intestinal wall and are excreted with feces. Eggs appear in feces 6-10 weeks after infection. Intermediate hosts are small freshwater mollusks of the genus Oncomelania. The duration of development of the larval stages of schistosomes in mollusks is 4-12 weeks. Cercariae live in water for up to 3 days, but retain their invasive ability only for the first 30 hours.

Japanese schistosomiasis is registered in Asian countries: Indonesia, China, Malaysia, the Philippines, Japan, Korea. It is widespread both in the zone of humid tropical forests and in subtropical regions. Schistosomiasis, found in Cambodia, Laos and Thailand, is called Mekong. It is more common in children under 10 years old.

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What causes Japanese schistosomiasis?

Japanese schistosomiasis is caused by Schistosoma japonicum. The male is 12-20 mm, the female is 12-28 mm. The cuticle of the male is smooth, without tubercles. The intestinal branches are connected at the back of the body. There are 6-8 testes, medium in size. The uterus of the female takes up about half of the body, contains from 50 to 100 eggs. The eggs are broadly oval, with a short lateral spine, their size is 70-100 x 50-65 µm, they contain a mature miracidium.

Pathogenesis of Japanese schistosomiasis

The pathogenesis of Japanese schistosomiasis is similar in many ways to that of S. mansoni. However, S. japonicum lays approximately 10 times more eggs and releases them simultaneously in large batches, which leads to a massive introduction of eggs into various organs: the liver, lungs, and others, in which severe damage to blood vessels and tissues develops. Clusters of eggs in the intestinal walls begin to calcify after several months, which leads to the formation of granulomas, the formation of which is accompanied by exudation and necrosis. Intensive egg production leads to the development of violent allergic reactions. Liver fibrosis with portal hypertension usually develops 1-7 years after infection. CNS damage is characteristic, which is observed in 2-4% of cases. In this case, the development of granulomas is detected in both the gray and white matter of the brain.

Symptoms of Japanese Schistosomiasis

In the acute phase of the disease with intensive invasion 2-3 weeks after infection, patients develop a fever, skin rashes with angioedema appear. The following symptoms of Japanese schistosomiasis appear: headaches in the abdominal area, diarrhea up to 10 times a day with mucus and blood. During this period, bronchitis and bronchopneumonia may develop. The liver and spleen are enlarged. High eosinophilia, leukocytosis are determined in the peripheral blood, and ESR increases.

In the chronic period of the disease, the leading symptoms of Japanese schistosomiasis associated with damage to the large intestine are observed. Diarrhea with mucus and blood is noted. Sometimes intestinal obstruction develops due to the accumulation of eggs. There are severe lesions of the upper digestive tract with the formation of ulcers of the stomach and duodenum, as well as malignant tumors in these organs. Liver damage leads to the development of portal hypertension. With damage to the central nervous system, neurological symptoms can appear as early as 6-8 weeks after infection. Jacksonian epilepsy is often recorded, meningoencephalitis and paralysis may develop. Without treatment and a long course of the disease, cachexia develops.

Diagnosis of Japanese schistosomiasis

Diagnosis of Japanese schistosomiasis is by detecting eggs in the faeces using the same methods as for Manson intestinal schistosomiasis. In the late stage, rectal biopsy is often crucial.

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Treatment of Japanese schistosomiasis

Japanese schistosomiasis has a less favorable prognosis than other intestinal schistosomiasis. In this regard, praziquantel is prescribed in an increased daily dose of 60-75 mg/kg and divided into three doses during the day. The effectiveness of treatment is 60%. Symptomatic and pathogenetic treatment of Japanese schistosomiasis is also used.

How to prevent Japanese schistosomiasis?

Prevention of Japanese schistosomiasis is the same as for urogenital schistosomiasis. In addition, infected domestic animals are identified and treated. Cattle feces on farms and in places where infected animals graze must be disinfected. Cattle must be provided with drinking water free of cercariae.