Update on mosquito-borne diseases
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There have been no new cases of CF in the past week in Hong Kong. So far this year, Hong Kong has recorded a total of nine confirmed CF cases. All are imported cases. All cases have recovered and been discharged without complications. From 2016 to 2019, Hong Kong recorded between one and 11 imported cases annually.
For dengue fever (DF), there have been no new cases in the past week in Hong Kong either. There have been 41 imported DF cases recorded so far this year. A total of 161 cases of DF were recorded in 2024, including 156 imported and five local cases.
For Japanese encephalitis (JE), Hong Kong has recorded one imported JE case from the Philippines this year. In the past five years (from 2020 to 2024), no JE cases were recorded in Hong Kong, and a total of 10 cases were recorded between 2016 and 2019 (including six locally infected cases).
"The current high temperatures and rainfall levels continue to pose risks of transmission of various mosquito-borne diseases in Hong Kong. Aedes albopictus, which is the vector for chikungunya virus, dengue virus and Zika virus, is common in Hong Kong. Although these mosquito-borne diseases are not transmitted from person to person, during the early stage after the onset of symptoms (especially when a fever is present), the blood of infected patients contains a large amount of virus, which is infectious to mosquitoes. If people are bitten by mosquitoes during the communicable period, further local transmission via mosquitoes is possible," the Controller of the CHP, Dr Edwin Tsui said.
"JE is prevalent in rural areas of Asia and the Western Pacific Region, especially in the hot season. As Culex mosquitoes (including Culex tritaeniorhynchus), the primary vector for JE, can be found in Hong Kong, especially in the rural areas, there is also a risk of transmission of JE locally. Culex mosquitoes breed in areas where there is a lot of stagnant water, and pigs or wild birds are natural hosts of the JE virus. Culex mosquitoes become infected when they bite pigs or wild birds infected with the JE virus. The infected mosquitoes then transmit the virus to humans and animals during biting. Therefore, members of the public should take proper mosquito control measures both locally and during travel. We must make a concerted effort in eliminating mosquito breeding, so as to cut the transmission links of mosquito-borne diseases in the community," Dr Tsui added.
Continuously strengthening prevention and control of mosquito-borne diseases
The Food and Environmental Hygiene Department (FEHD) is conducting vector investigations and targeted mosquito control operations and will intensify mosquito prevention and control measures at the residence of the CF patients, as well as locations visited after the onset of symptoms. These measures include:
- carrying out intensive fogging in the scrubby areas within a 250-metre radius of the relevant locations to kill adult mosquitoes;
- carrying out inspection of the locations, removing stagnant water, applying insecticides and disposing of abandoned water containers every week with a view to preventing mosquito breeding; and
- enhancing public education efforts through organising health talks, setting up mobile education stations, and distributing publicity leaflets.
The CHP's Port Health Division continues to step up inspections at boundary control points and to remind cross-boundary public transport operators and other relevant parties to ensure good environmental hygiene and effective implementation of anti-mosquito measures. Furthermore, staff members of the Port Health Division distribute leaflets to travellers, conduct temperature screenings for inbound travellers, conduct health assessments for travellers with fever or related symptoms, and refer them to hospitals for follow-ups when necessary.
To raise awareness among the elderly about preventing mosquito-borne diseases, the Visiting Health Teams under the Elderly Health Service of the DH have been advising the elderly on mosquito-borne diseases prevention and tips on travel health at health talks conducted at District Elderly Community Centres and Neighbourhood Elderly Centres. Besides, the Visiting Health Teams have also reminded all residential care homes for the elderly in Hong Kong to enhance mosquito control measures. The DH's Maternal and Child Health Centres, Student Health Service Centres and Special Assessment Centres also advise pregnant women, infant carers and students on symptoms and preventive measures of the mosquito-borne diseases.
Dr Tsui reminded members of the public that those returning to Hong Kong from areas affected by mosquito-borne diseases should continue to apply insect repellent and closely monitor their personal health condition. If they feel unwell, they should seek medical attention immediately and inform their doctors of their travel history. The public should avoid using non-steroidal anti-inflammatory drugs (such as ibuprofen), to prevent aggravating the risk of haemorrhage. In general, children should not take medications containing aspirin to relieve fever or other symptoms because it may lead to Reye's syndrome, a serious and potentially fatal complication.
Members of the public should also adopt anti-mosquito measures during the rainy season against mosquito-borne diseases. Proper use of DEET-containing insect repellents or other effective active ingredients can prevent mosquito bites, but the following precautions should be taken when using them:
- read the label instructions carefully first;
- apply right before entering an area with a risk of mosquito bites;
- apply on exposed skin and clothing;
- use DEET of up to 30 per cent for pregnant women and up to 10 per cent for children (For children who travel to countries or areas where mosquito-borne diseases are endemic or epidemic and where exposure is likely, those aged 2 months or above can use DEET-containing insect repellents with a DEET concentration of up to 30 per cent);
- apply sunscreen first, then insect repellent;
- reapply only when needed and follow the instructions; and
- in addition to DEET, there are other insect repellents available on the market containing different active ingredients, such as IR3535 and picaridin. When using any insect repellent, the public should follow the usage instructions and precautions on the product label.
In addition, the FEHD appeals to members of the public to continue to stay alert and work together to carry out mosquito prevention and control measures early, including inspecting their homes and surroundings to remove potential breeding grounds, changing water in vases and scrubbing their inner surfaces, removing water in saucers under potted plants at least once a week, and properly disposing of containers such as soft drink cans and lunch boxes. The FEHD also advises members of the public and estate management bodies to keep drains free of blockage and level all defective ground surfaces to prevent the accumulation of water. They should also scrub all drains and surface sewers with an alkaline detergent at least once a week to remove any mosquito eggs.
The public should call 1823 in case of mosquito problems and may visit the following pages for more information: the CF page of the CHP and the Travel Health Service, the latest Travel Health News, tips for using insect repellents, and the CHP Facebook Page, Instagram Account and YouTube Channel, and also the Mosquito Prevention and Control dedicated page of the FEHD.
Ends/Friday, August 22, 2025
Issued at HKT 19:02
Issued at HKT 19:02
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