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 has been carrying out a
territory-wide survey on local Japanese Encephalitis vectors since
late October 2004 to update the information on their distribution.
Adult trapping would be conducted in areas within 2km radius from
pig farms, slaughter houses and sites with aggregation of migratory
birds. Larval survey would also be conducted in illegal cultivation
and vacant sites.
The following
map shows the findings of Japanese Encephalitis vector
in October 2005
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 ¡V 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
