A 79-year-old woman who often visited the Zoological and Botanical Gardens has become the first person this year to contract dengue fever in the city, prompting health officials on Tuesday to urge the public to take extra steps to avoid mosquitoes. Some 81 people have been treated for the mosquito-borne disease this year in Hong Kong. But 79 of those were classified as imported cases, with one case still under investigation . Dengue fever is transmitted to humans through bites from infective female Aedes mosquitoes – a common species that can also spread Zika. The Centre for Health Protection said the dengue patient, who has underlying illnesses, had no recent travel history. She lives on Shelley Street in Central, and often visited the Zoological and Botanical Gardens. Mosquito infestation in Hong Kong reaches ‘alert’ level, index shows, prompting fears of dengue and Zika virus transmission She developed a skin rash about two weeks ago and was treated at Queen Mary Hospital. After being admitted for two days, she was discharged on August 27, in a stable condition. Blood tests on Monday night confirmed she had dengue fever. Earlier this month, another woman who lived in Central was found to have the tropical disease, and also reported that she had visited the gardens in Mid-levels. She was bitten by mosquitoes in Hong Kong and on the mainland. “We are conducting extensive investigations with the Food and Environmental Hygiene Department to ascertain if both cases are linked with a view to controlling the possible spread,” said a spokesman for the centre. He said the centre would conduct site visits and speak to the patient. Severe dengue fever is potentially fatal. Without proper treatment, the fatality rate of severe dengue can exceed 20 per cent, the spokesman said. He urged the public to maintain strict environmental hygiene and take measures to avoid mosquitoes both locally and during travel. “Early referral and prompt control are critical to prevent further local spread,” the spokesman said. “We will issue letters to doctors and hospitals to alert them to the case. “At present, there is no locally-registered dengue vaccine available in Hong Kong.” Travellers are urged to be alert to the dengue risk and take preventive measures like wearing loose, light-coloured, long-sleeved tops and trousers, and use Deet-containing insect repellent on exposed parts of the body and clothing. After returning from dengue endemic areas, people should continue to apply insect repellent for 14 days, according to the Centre for Health Protection . Anyone feeling unwell after returning from a trip should seek medical advice as soon as possible and provide travel details to their doctor. The public can also report mosquito problems to government departments via the hotline 1823.