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Vector-borne diseases

Vector-borne diseases

12 May 2023

Vector-borne diseases

Vectors are living organisms such as mosquitoes, mites and ticks that can carry disease from one infected person (or animal) to another person. The diseases transmitted by vectors are called vector-borne diseases. They can be caused by parasites, bacteria or viruses.

In Hong Kong, there are several important vector-borne diseases including dengue fever, Japanese encephalitis, malaria, scrub typhus and spotted fever. Most dengue fever and malaria cases recorded are imported from endemic countries via international travel, while most cases of scrub typhus and spotted fever acquired the infection locally and had history of going to vegetated areas in Hong Kong, for example hiking areas, outdoor workplaces, vegetated areas near home or outdoor recreational areas.

Mosquitoes are responsible for transmitting dengue fever (Aedes mosquitoes), Japanese encephalitis (Culex mosquitoes) and malaria (Anopheles mosquitoes) while scrub typhus and spotted fever are transmitted by mites and ticks respectively.


To prevent vector-borne diseases, members of the public need to protect themselves from stings / bites of mosquitoes, mites and ticks, and prevent their proliferation.

Prevention of stings/bites

  • Wear loose, light-coloured long-sleeved tops and trousers
  • Use DEET-containing insect repellent on exposed parts of the body and clothing
    • Pregnant women and children of 6 months or older can use DEET-containing insect repellent. In general, use DEET of up to 30% for pregnant women and up to 10% for children
  • Take additional preventive measures when engaging in outdoor activities:
    • Avoid using fragrant cosmetics or skin care products
    • Re-apply insect repellents according to instructions
    • If both insect repellents and sunscreen are used, apply insect repellents after sunscreen

When members of the public go hiking or go to scrubby areas, here are some additional preventive measures:

  • Prepare for the visit
    • Wear shoes that cover the entire foot; avoid wearing sandals or open shoes
    • Tuck trousers into socks or boots to prevent arthropods from reaching the skin
  • During the visit
    • Stay on footpaths and avoid walking through vegetation. Do not brush along the vegetation at the sides of footpaths
    • Avoid resting on vegetation, or at humid and dark places
    • Do not hang clothing on trees or vegetation
    • Do not feed wild or stray animals
  • After the visit
    • Inspect body parts and clothing; clear any attached arthropods carefully
    • Take a soapy shower and wash the clothes
    • Inspect and clean the bodies of accompanying pets
  • If an attached tick is found on the body
    • Gently remove it by grasping its head with tweezers or fine-tipped forceps close to the skin, then disinfect the bite area and wash hands with soap and water
    • Do not crush or twist the tick during removal

Prevention of vector proliferation

  • Prevent accumulation of stagnant water
    • Change the water in vases once a week
    • Avoid using saucers underneath flower pots
    • Cover water containers tightly
    • Ensure air-conditioner drip trays are free of stagnant water
    • Put all used cans and bottles into covered dustbins
  • Control vectors and reservoir of the diseases
    • Inspect and disinfest pets and pet beddings regularly
    • Trim vegetation particularly the grass in your premises
    • Store food and dispose of garbage properly to prevent rat infestation. Holes at the wall and ceiling should be repaired and filled

Advice for travellers

  • Take preventive measures to avoid mosquito bites. For children who travel to countries or areas where mosquito-borne diseases are endemic or epidemic and where exposure is likely, children aged 2 months or above can use DEET-containing insect repellents with a concentration of DEET up to 30%. For details about the use of insect repellents and the key points to be observed, please refer to 'Tips for using insect repellents'.
  • If you are travelling to areas where vector-borne diseases are common, arrange travel health consultation with your doctor at least six weeks before the journey for risk assessment. During the consultation, the need for any vaccinations, chemoprophylaxis and vector preventive measures will be determined.
  • Vaccines for Japanese encephalitis are recommended for travellers who plan to stay one month or longer in Japanese encephalitis-endemic countries, particularly in rural areas, and for short-term (less than one month) travellers if they plan to have significant/ extensive outdoor or night-time exposure in rural areas during the transmission season of the disease.
  • There is no registered vaccine against malaria in Hong Kong. Travellers who plan to stay in malaria-endemic areas should consult their doctors beforehand to determine if anti-malarial prophylaxis is required. This medication should be taken before the trip, continued throughout the journey and until some time after leaving the area according to the instruction of the doctor.
  • If travelling in endemic rural areas, carry a portable bed net and apply permethrin (an insecticide) on it. Permethrin should NOT be applied to the skin. Seek medical attention promptly if feeling unwell.
  • If you feel unwell during your visit abroad or after return, seek medical advice immediately and provide travel details to the doctor. Urgent blood tests may be necessary and prompt treatment is vital.