本港傳病媒介疾病——積極防蚊守健康
刊載於《am730》，2024 年 3 月 11 日
蚊子不但擾人，還可傳播嚴重疾病。氣候變化擴大了病媒蚊種的活動範圍，增加瘧疾、寨卡病毒等疾病的輸入風險。因此，了解傳病媒介疾病的風險、病徵和預防方法對保障市民健康至關重要。
在本港，登革熱和日本腦炎的主要病媒蚊分別是白紋伊蚊 (Aedes albopictus) 和三帶喙庫蚊 (Culex tritaeniorhynchus)。叮咬過感染病毒宿主的雌蚊會帶有病毒，並透過叮咬其他人將病毒傳播。
登革熱的病徵與流感相似，包括高燒、嚴重頭痛、眼窩後疼痛、肌肉及關節痛、噁心、嘔吐及出疹，潛伏期為4至7天。有些患者沒明顯病徵，有的則病徵輕微，如只有發熱及出疹，多在一周內康復；但若染上重症登革熱 (又稱登革出血熱)，則可導致出血、休克、器官衰竭，甚至死亡。
日本腦炎由過濾性病毒引起。患者一般在被蚊子叮咬5至15天後出現病徵，包括發高燒、頭痛、頸部僵硬、神志不清、昏迷、抽筋、痙攣性癱瘓等，甚至死亡。約三成重症病例是致命的，許多康復者亦可能出現長期的神經系統問題。
以下方法可避免蚊傳疾病：一、在外露的皮膚及衣服塗上含避蚊胺 (DEET) 或派卡瑞丁 (picaridin) 等有效成分的昆蟲驅避劑 (兒童及孕婦須注意驅避劑的濃度)。二、穿著寬鬆、淺色的長袖上衣及長褲進行戶外活動；並穿上完全遮蓋足部的鞋往叢林地區。使用行人徑，避免穿過草叢或樹叢，並在空曠的地方休息。三、定期為花瓶換水、清理花盆底積水及修剪植物。同時，緊蓋貯水器皿，妥善處理垃圾及蓋好垃圾桶，以防蚊蟲滋生。最後，如須到傳病媒介疾病流行的地區，應在出發前兩個月諮詢醫生是否需要接種相關疫苗或服用預防藥物，晚上則盡量使用便攜式蚊帳。如外遊後身體不適，應盡快求醫，並告知醫生旅程中曾否被蚊叮咬等細節。
Dr Ria Sinha
醫學倫理及人文學部講師
香港大學李嘉誠醫學院臨床醫學學院
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Original article in English
The Nuisance of Mosquito Bites and the Risk of Vector-Borne Diseases in Hong Kong
From the bustling city to the rural hiking trails, Hong Kong’s residents and tourists alike face a common nuisance: mosquito bites. More than a mere annoyance, these bites can potentially transmit dangerous, debilitating diseases such as Dengue fever and Japanese Encephalitis. Climate change is also contributing to expanding the range of disease-carrying mosquito species bringing a greater threat of imported cases of malaria, Zika and West Nile virus. Understanding the risks and symptoms of vector-borne diseases, as well as how to prevent mosquito bites, is important for everyone.
The Mosquito Vectors
The primary mosquito vectors for the most common diseases, Dengue and Japanese Encephalitis, in Hong Kong are the Aedes albopictus and Culex tritaeniorhynchus mosquitoes, respectively. Aedes albopictus, also known as the Asian tiger mosquito, is commonly found in urban environments and is easily recognised by its black and white striped legs.
Female mosquitoes become carriers of these diseases when they blood feed on an infected host, usually a human or animal carrying the virus. Once a mosquito is infected, it can transmit the virus to healthy individuals through a secondary bite.
Dengue Fever: Symptoms and Risks
Dengue fever often manifests as a severe flu-like illness. Symptoms typically appear 4-7 days after being bitten by an infected mosquito and can include sudden high fever, severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, and a characteristic skin rash.
Although most people recover within a week or so, in some cases, the disease can progress to severe dengue, also known as dengue hemorrhagic fever. This severe form can cause bleeding, blood plasma leakage, and low platelet count, leading to shock, organ failure, and even death if not treated promptly.
Japanese Encephalitis: Symptoms and Risks
Japanese Encephalitis is a viral brain infection that’s mainly spread by mosquitoes in rural and suburban areas. The majority of people infected with Japanese Encephalitis virus have mild symptoms or no symptoms at all. However, for those who do develop severe symptoms, the condition can be life-threatening.
Symptoms usually appear 5-15 days after a bite from an infected mosquito and can include high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis, and ultimately death. Approximately 30% of severe cases are fatal, and many survivors have long-term neurological damage.
Preventing Mosquito Bites
Preventing mosquito bites is the first line of defence against these diseases. There are a few simple steps you can take to minimise the risk:
• Use Insect Repellent: Apply an approved insect repellent on exposed skin and clothing. Repellents containing DEET, picaridin, or oil of lemon eucalyptus are particularly effective, and there are many suitable products available in dispensaries.
• Dress Appropriately: Wear light-coloured, loose long-sleeved shirts and long pants when outdoors and cover ankles well if hiking through undergrowth. Use designated footpaths and rest in open areas if possible.
• Eliminate Mosquito Breeding Sites at home and work: Regularly empty, clean or cover containers like buckets, flower pots or vases that can hold water, as these can be ideal breeding sites for mosquitoes. Trim undergrowth and keep garbage bins covered.
• If travelling to countries where mosquito-borne diseases are endemic, seek advice on vaccines and preventive medications (chemoprophylaxis) from your doctor or a travel clinic approximately two months before departure. Use a mosquito net at night if provided. If you feel unwell on your return visit your doctor and tell them where you have travelled and if you have been bitten by mosquitoes.
While mosquito bites are a common nuisance in Hong Kong, they can also pose serious health risks. By understanding the symptoms of diseases such as Dengue fever and Japanese Encephalitis, staying vigilant, and taking steps to prevent mosquito bites at home and overseas, we can all contribute to reducing the transmission of these diseases in our city.