Yoyogi park Tokyo dengue fever
Health workers spray insecticide at Tokyo's Yoyogi parkJIJI PRESS/AFP/Getty Images

At least 34 people have contracted dengue fever in Japan, in the first outbreak of the tropical disease to hit the country in almost 70 years.

The health ministry has confirmed 12 new cases, adding to the 22 that had been previously reported. It said the patients are in stable condition.

Health officials said all those who fell ill appeared to have been infected while visiting a popular park in Tokyo.

Dengue is a mosquito-borne viral infection that causes flu-like illness and occasionally develops into a potentially lethal complication called severe dengue, according to the World Health Organization.

The virus, typical of tropical and sub-tropical climates, is transmitted to humans through tiger mosquito bites and has an incubation period of four to 10 days.

Among the latest reported cases were two local celebrities, models Saaya, 20, and Eri Aoki, 25, who were dispatched to the capital's Yoyogi Park in August on an assignment for a TV variety show, local media reported.

Health workers have since been spraying the park, one Tokyo's largest open spaces, with approximately 800 litres of pesticide to kill the insects and control the spread of the disease.

Beside high temperatures, symptoms include severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, rashes and swollen glands.

Cases of people who have contracted the virus abroad are reported in Japan each year. However, the last outbreak of the disease for which there is no vaccine or specific drug was reported in the country in 1945.

The health ministry said it's possible local mosquitos contracted the virus from tourists.