An outbreak of dengue fever in Japan -- the first since World War II -- has affected at least 22 people, the government said Monday, with all cases believed to be linked to a Tokyo park.
The health ministry said 19 new infections have been confirmed since last week.
All are believed to have visited Tokyo's Yoyogi Park or its environs, one of the major green lungs of the metropolis, popular with residents and tourists alike.
The park, one of the largest open spaces in central Tokyo, is believed to be the source of the mosquito-borne disease.
The first three sufferers, who were found to be infected last week, had also visited the park, where Tokyo officials have now sprayed about 800 litres (210 US gallons) of pesticide in a bid to kill off the insect colony.
None of those found to have contracted dengue had travelled overseas recently, the health ministry said. None is in a life-threatening condition, officials have said.
The last domestic infection of dengue fever was in 1945, although there are around 200 cases annually among Japanese who have travelled abroad, mainly in Southeast Asia.
Dengue fever is not transmitted directly from person-to-person and symptoms range from mild fever to incapacitating high temperatures, according to the World Health Organization.
There is no vaccine or any specific medicine to treat dengue and patients should rest, drink plenty of fluids and reduce the fever using paracetamol, it says.
The disease is carried by the tiger mosquito, which is endemic to Japan.
Meanwhile, shares in home pesticide maker Fumakilla were up 22.85 percent at 430 yen on the Tokyo Stock Exchange. That follows a nearly 25 percent rise one day last week.