Hong Kong medical specialists on Thursday advised residents and hospitals to ramp up mosquito control measures as the city reported three new imported cases of chikungunya fever, including avoiding areas with stagnant water and dense foliage at the most dangerous times of the day – dawn and dusk, and ensuring that mosquito-repellent sachets contain mugwort and lemongrass.

One new case that was reported on Wednesday involves a 79-year-old woman from Southern District who stayed in Foshan, Guangdong province for the entire July. She developed fever and joint pain on Tuesday and was admitted to Queen Mary Hospital on Wednesday. Laboratory tests confirmed a chikungunya infection.

The other cases involve a 55-year-old man with underlying conditions and his 10-year-old son from Kwai Tsing district. They visited Bangladesh on July 12 and returned on Sunday. The man became ill on July 27, while the boy developed symptoms on Friday. Both tested positive for chikungunya after seeking treatment in Hong Kong. Their two household contacts remain asymptomatic and under medical surveillance.

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The Centre for Health Protection in Hong Kong has alerted health authorities in Guangdong and Bangladesh and continues epidemiological investigations. Residents are reminded to avoid sites where conditions make it easy for mosquitos to breed, and to take protective measures, especially when traveling. Avoiding mosquito bites remains the key to preventing chikungunya, officials said.

So far, the city has logged four cases of the mosquito-borne disease, all of them imported. The disease often causes fever and joint pains, with other common symptoms such as muscle pain, headaches, nausea, fatigue and rashes. Symptoms are generally self-limiting and last a few days.

Respiratory specialist Leung Chi-chiu said the risk of infected travelers seeding local transmission is “higher than normal,” as the summer holiday season is driving travel to regions that are susceptible to major outbreaks like the continent of Africa, Southeast Asia, and nearby Foshan, in Guangdong province.

Residents should defer nonessential travel to high-risk regions, Leung added, and if travel is essential, non-negotiable safeguards – including rigorous repellent use – must be employed, said the expert in communicable diseases.

Intense heat and record rainfall might have turbocharged breeding grounds for local aedes albopictus mosquitoes, also known as Asian tiger mosquitos — key carriers of chikungunya, Leung added. “Rain also washes away insecticides, which demands constant vigilance.”

Leung said that in addition to personal protection – such as wearing long sleeves and long pants – and mosquito control, early detection of imported cases is paramount.

Hospitals must enact strict containment protocols around confirmed cases, including targeted elimination of mosquitos on the perimeters and areas they are frequently found in. For high-risk individuals – like close contacts of confirmed cases – he added, hospitals may even provide self-isolation support.

“Controlling imported cases is comparatively manageable; once the virus establishes in the local mosquito population, disease containment might become more challenging and resource-intensive,” Leung said.

Burning mugwort indoors to combat humidity while repelling mosquitoes is a strategy suggested by traditional Chinese medicine (TCM) practitioner Chan Wing-kwong, alongside the use of sachets containing mugwort and lemongrass.

“Mugwort is easily accessible,” Chan said, explaining that it is available in moxa sticks on many store shelves. Lemongrass is commonly used for culinary purposes and found in supermarkets.

The Food and Environmental Hygiene Department has been working closely with authorities and stakeholders to enhance mosquito control measures. This initiative involves clearing stagnant water in high-risk areas like construction sites, as well as eliminating adult mosquitoes.

Residents are advised to take special mosquito prevention and control measures at home and in other environments during heavy rain. These precautions include inspecting outdoor areas and household items to prevent water accumulation, and a breeding ground for mosquitoes. Additionally, residents should cover water containers such as buckets and basins regularly to deter mosquito breeding.

Albert Au Ka-wing, head of the Centre for Health Protection’s Communicable Disease Branch, said that those returning to Hong Kong from areas affected by such diseases are advised to apply insect repellent for 14 days. They should monitor their personal health closely, in particular symptoms such as fever, joint pains and rashes. Au added that residents should seek medical advice promptly if they feel unwell, and share their travel details with their doctor for clinical diagnosis and testing if that is considered necessary.

READ MORE: Health authorities strengthen anti-mosquito measures in HK

Leung highlighted the need for such measures as a “critical firewall” to prevent local mosquitoes biting potentially infected individuals and acquiring the virus.

Au also urged residents not to self-medicate, particularly with aspirin or non-steroidal anti-inflammatory drugs, such as ibuprofen. These drugs may have serious side effects and even potentially fatal complications, particularly for children, Au said.

The chikungunya fever hit Foshan city in early July, causing over 6,000 infections locally. On Saturday, Hong Kong reported its first case, a 12-year-old boy who developed a fever, rash, and joint pain after traveling to Foshan in July.

Contact the writers at wanqing@chinadailyhk.com