The Japanese health ministry said yesterday it had found a patient who contracted dengue fever while in the country, the first time that has happened in nearly 70 years.
Around 200 Japanese are infected with the disease while travelling overseas annually, but no domestic infection had been confirmed since 1945, according to the Health, Labor and Welfare Ministry.
The patient, a Japanese teenager with no record of overseas travel, ran a high fever late this month and has stayed in a hospital in the city of Saitama. Her condition was stable.
The infection is likely to have occurred in Japan through a mosquito which bit a person who caught the virus overseas, the ministry said.
The National Institute of Infectious Diseases is probing whether there are other infected people living close to the teenager and has called on prefectural governments to be wary of the disease. The disease does not spread directly from person to person.
Dengue fever, which often occurs in tropical and subtropical areas in Asia, Latin America and Africa, is transmitted by tiger and dengue mosquitoes.
In Japan, tiger mosquitoes live in a region up to the southern part of Aomori prefecture in the north of the country. Even if an outbreak occurs, it is expected to be limited both in affected areas and contagion period as mosquitoes do not necessarily carry the virus and cannot survive in winter.
Sufferers are struck with a sudden fever around three to seven days after transmission, accompanied by head and muscle pains and a rash. Most sufferers have mild symptoms, but some may develop bleeding, which can be life-threatening.
Most patients are only given antipyretic medicine for treatment, as there are no effective drugs or vaccines.
Up to August 17 there had been 98 confirmed cases of dengue infection from overseas this year.
In August last year, a German tourist who visited Kyoto and Nagano prefectures was diagnosed with the disease after returning home.