Japanese encephalitis in mainland china.

Japanese encephalitis (JE) is a seasonal epidemic disease with a 50-year recorded history in China. Its characteristics can be summarized as follows: (i) it is a seasonal epidemic disease; approximately 90% of cases are recorded in July, August, and September each year. The peak of JE onset is 1 month earlier in South China than in the north of the country; (ii) the disease is highly sporadic. It is rare for more than two cases to appear simultaneously in one family; (iii) most affected children are under 15 years old; (iv) the disease is widely distributed in all areas of the nation except Qinghai Province, Xinjiang Uygur Autonomous, and Tibet. Due to widespread application of the JE vaccine, the number of JE cases has decreased significantly nationwide, from 174,932 cases of morbidity in 1971 to 5,097 cases in 2005.