The Tokyo Metropolitan Government closed most of Yoyogi Park on Thursday after confirming that mosquitoes caught in traps earlier this week were carrying the dengue virus, metropolitan officials said.

The discovery confirmed the park as the site of infections for dozens of people over the past several weeks. Four traps out of the 10 placed by metropolitan officials contained mosquitoes carrying the virus, the officials said.

The number of patients has risen to 49 since last week in the first domestic outbreak of dengue fever since 1945, according to the Health, Labor and Welfare Ministry.

While the patients hail from 11 prefectures, they all had recently spent time in or near Yoyogi Park, prompting mosquito traps to be installed there Tuesday.

Metropolitan officials said they closed the northern section of the 540,529 sq.-meter park. The area, known as Tokyo’s green oasis, has more than 15,300 trees.

It stretches from the children’s cycling plaza in the north to the monument commemorating the flight of the first airplane in Japan in 1910. The monument is adjacent to a road that divides the park between north and south. The southern part houses Yoyogi National Gymnasium and an outdoor stage and other facilities.The restricted area also includes the bird sanctuary and observation deck.

Dengue fever does not spread from person to person. Patients are struck with symptoms a fever around three to seven days after they are bitten by a virus-carrying mosquito, accompanied by head and muscle pains and a rash. Most cases involve mild symptoms, but some people may develop significant bleeding that can be life-threatening. Metropolitan government employees had collected 35 mosquitoes from the park last week, but none was found to carry the dengue virus.