The number of syphilis cases in Japan this year has exceeded 10,000 for the first time since comparable data became available in 1999.

Japan's National Institute of Infectious Diseases says 10,141 cases were reported as of October 23. That is about 1.7 times the figure for the same period last year, which was a record high.

Syphilis is a bacterial infection transmitted mainly through sexual contact. Symptoms may quickly disappear, or not appear at all. So, infected people could spread the disease without knowing.

Syphilis can cause serious symptoms in the brain or heart. If pregnant women are infected, it could lead to miscarriage or babies born with abnormalities.

Kobe University Associate Professor Shigemura Katsumi says infection cases are increasing at a faster-than-expected pace, and that he is worried about further spreading.

Shigemura warns that syphilis is not a special disease and anyone can get infected. He adds that he wants people to take protective measures such as using condoms.