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Advice on prevention and control of Japanese Encephalitis Vector

Japanese encephalitis (JE), a mosquito-borne viral disease in humans and animals, is a major public health problem in east and southeastern Asia. People get JE by the bite of mosquitoes infected with the virus. Mosquitoes become infected when feeding on infected animals, in most cases domestic pigs and wild birds, and then transmit the disease to humans and other animals during the feeding process. Sporadic cases of JE occurred locally very infrequently in past decades.

Vector

The vectors responsible for the transmission of JE are mainly Culex mosquitoes including Culex tritaeniorhynchus, Culex gelidus and Culex fuscocephala. In China and many endemic areas in Asia, Culex tritaeniorhynchus is the principal vector. This species feeds outdoors beginning at dusk and during evening hours until dawn. Larvae are mostly found in flooded rice fields, water-lodged abandoned fields, marshes and small stable collections of water around cultivated fields. The other two species are also known to occur in Hong Kong. Their local favourable breeding habitats are weedy grounds with moderate degree of pollution for Culex gelidus and water storage pits, irrigation ditches and rice fields for Culex fuscocephala.

FEHD had carried out a territory-wide survey on Japanese Encephalitis vector in 2005 to update the information on their distribution. Adult trappings were conducted in areas within 2km radius from pig farms, slaughter houses and sites with aggregation of migratory birds. Larval surveys were also conducted in illegal cultivation and vacant sites.

The following map shows the findings of Japanese Encephalitis vector in October 2005

(Map)

Please click here for information on the findings of Japanese Encephalitis vector since October 2004.

Preventive measures

1. Source reduction / Elimination of breeding place

  • Illegal cultivation on government land should be avoided
  • Device such as water pump / water gate should be installed in drainage system of water-lodged field such as paddy field and Sai Yeung Choi field to ensure continuous water flow or complete removal of stagnant water regularly;
  • Inspection programme for mosquito control should be implemented in water-cultivation areas and animal farms
  • Stagnant water in surface drainage channels including those around houses and sheds should be eliminated
  • Water in containers for feeding animals should be removed after feeding and the containers should be well covered after use.

2. Larviciding

  • Larvicides such as temephos and B.t.i. (Bacillus thuringiensis israelensis ) should be applied according to the instruction label to any breeding places that cannot be eliminated within one week; and
  • For large areas such as water ponds, larvivorous fishes or shrimps can be applied as a measure of biological control.

3. Personal protection

  • Mosquito screen should be installed at windows / louvers (14 - 16 mesh: 14 x 14 - 16 x 16 holes / square inch);
  • Mosquito net should be used in bedroom when necessary;
  • Mosquito net should be used to protect bird-cage from dusk to midnight;
  • Repellent which contains 10 -30 % concentration of DEET (N, N-diethyl-meta-toluamide) should be applied on clothing / uncovered areas of body, while performing outdoor activities;
  • Long sleeved clothes and long trousers should be worn during outdoor activities;
  • Mosquito trapping device using chemical such as octanol and carbon dioxide as attractant could be installed at outdoor areas; and
  • Application of odor-producing cosmetic such as perfume / body lotion should be avoided for outdoor activities

 

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