The Food and Environmental Hygiene Department (FEHD) announced on 16 June that the monthly gravidtrap index for Aedes albopictus (MGI) in May rose to a new high for the year, mainly in the New Territories.
Among the 57 survey areas in May, the area gravidtrap index (AGI) in four areas exceeded the alert level of 20 per cent. They were Ma Wan (27.1 per cent), Sai Kung Town (21.3 per cent), Lai King (21 per cent) and Sha Tin East (20.2 per cent). The FEHD has collaborated with relevant government departments to strengthen mosquito prevention and control work in the above-mentioned areas immediately. The FEHD reminded the public to carry out effective prevention and control measures against mosquitoes as the hot and rainy weather of summer is favourable for massive mosquito breeding within a short period of time. Relevant government departments have enhanced co-operation and commenced the All-out Anti-mosquito Operations in April to conduct fogging operations specifically at high-risk areas to eradicate adult mosquitoes.
The FEHD is very concerned about mosquito infestation and has conducted anti-mosquito operations at all respective locations. An inter-departmental anti-mosquito response mechanism has also been activated in the four districts where the AGI reached the alert level for co-ordinating relevant departments and stakeholders to carry out effective mosquito prevention and control measures. Relevant departments have also individually notified the groups under the survey areas concerned that had voluntarily subscribed to the gravidtrap rapid alert system when the AGI reached the alert level of 20 per cent. Subscribers have been invited to post specially designed alert notices in the common parts of their premises to remind occupants and staff to carry out anti-mosquito measures promptly.
Since April this year, the FEHD has put in place newly designed gravidtraps as a replacement for the ovitraps previously used to directly count the number of adult mosquitoes to enumerate the gravidtrap index and the new density index. The function of the new gravidtrap index is similar to that of the ovitrap index previously used in reflecting the extensiveness of distribution of Aedes albopictus in the survey area. The new density index indicates the average number of adult Aedes albopictus collected in each Aedes-positive gravidtrap in the survey area in order to better quantify the activity level of Aedes albopictus.
The gravidtrap index for Aedes albopictus is divided into four levels, reflecting the infestation level of Aedes albopictus. Level 1 (less than 5 per cent) indicates that infestation of the mosquito is not extensive in the area surveyed. Level 2 (5 per cent to less than 20 per cent) indicates that infestation of the mosquito is slightly more extensive in the area surveyed. Level 3 (20 per cent to less than 40 per cent) indicates that infestation of the mosquito exceeds one-fifth of the area surveyed. Level 4 (40 per cent or above) indicates that almost half of the area surveyed is infested with the mosquito. Specific preventive and control measures will be initiated accordingly.
The FEHD will collect the data of the density index this year to evaluate the effectiveness of mosquito control work. After sufficient data has been collected, the FEHD will establish a reference level for the corresponding prevention and control measures for the density index.
In order to enhance dengue vector surveillance, the FEHD will increase the number of survey areas from 57 to 62 from June this year. The five additional survey areas are Wong Tai Sin West, Tseung Kwan O East, Ngau Liu and Muk Min Shan, Ki Lun Shan and Cheung Chau North.
Aedes albopictus is a kind of mosquito that can transmit dengue fever (DF) as well as Zika virus infection. DF is commonly found in tropical and subtropical regions of the world, and has become endemic in many countries in Southeast Asia. The World Health Organization also issued warnings that the number of DF cases recorded in Asia last year was higher than before. As Hong Kong has recorded this year’s first local DF case in April and the dengue activity in neighbouring areas has remained high, and Hong Kong’s hot and rainy summer is conducive to the proliferation of mosquitoes, the community must stay vigilant and work with the Government to carry out effective mosquito control measures.
The spokesman added that as Aedes albopictus breeds in small water bodies, members of the public should carry out effective mosquito prevention and control measures including inspecting their homes and surroundings to remove potential breeding grounds, changing the water in vases and scrubbing the inner surfaces, removing the water in saucers under potted plants at least once a week, properly disposing of containers such as soft drink cans and lunch boxes, and drilling large holes in unused tyres. He also advised public and estate management bodies to keep drains free of blockage and level all defective ground surfaces to prevent 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.
In addition, rural areas and the vicinity of shrubby areas are natural habitats for mosquitoes, other insects and animals. Members of the public living in rural areas may install mosquito screens on windows and doors if necessary. Those staying in the natural environment should take appropriate personal protective measures against mosquitoes, such as avoiding staying in the vicinity of shrubby areas for a long time, wearing light-coloured long-sleeved clothes and trousers and applying DEET-containing insect repellent. Members of the public are reminded to make reports to relevant government departments via 1823 if mosquito problems are detected.
The gravidtrap and density indices for Aedes albopictus in different areas and information on mosquito prevention and control measures are available on the department’s website at www.fehd.gov.hk.
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