A number of recent reports about children suffering fever and paralyses from unknown causes has prompted National Institute of Infectious Diseases to start investigating nationwide for similar cases.
Some of the children were infected with enterovirus D68, and the national institute has been studying if the virus is responsible for the symptoms.
Enterovirus is a general term for viruses including those causing hand, foot and mouth disease and polio.
According to the health ministry, reports started coming in in August show 47 children aged up to 11 in about 20 prefectures developed symptoms of paralyses. Out of eight patients who were infected with viruses, enterovirus D68 was detected in two toddlers.
In the United States, more than 1,000 children were infected with the virus last year. Experts are cautious because some of them later developed paralyses. Since the virus is usually prevalent from summer to autumn, a health ministry official said it is hard to expect the number of patients to surge further this year.
Patients often suffer paralyses only in the hands or legs, making it hard for doctors to think they are infected with the virus, said Ryutaro Kira, head of the department of neurology at Fukuoka Children's Hospital.
Since 2005, there have been more than 200 patients infected with the virus in Japan. Washing hands can be an effective way to protect oneself from the virus, which can be transmitted by sneezing.