Japanese encephalitis vectors have been found in the vicinity of Shek Wu Wai and Shan Pui Tsuen in Yuen Long, according to results of a survey by the Food & Environmental Hygiene Department.

The department's Community Medicine Consultant Dr Ho Yuk-yin said the survey, started in late October, aims to get a better picture on the distribution of Japanese encephalitis vectors.

"Laboratory test results confirmed yesterday the presence of Japanese encephalitis virus in specimens collected from adult Culex tritaeniorhynchus, a known JE vector commonly found in Hong Kong in the vicinity of Shek Wu Wai and Shan Pui Tseun in Yuen Long," said Dr Ho.

"The result is not unexpected as JE is an endemic disease of local pigs. In fact, during case investigation of past JE cases, the presence of JE virus on Culex tritaeniorhynchus has also been detected. Mosquitoes may acquire the virus from birds and pigs which are known as the reservoir and amplifying host of the disease."

The survey has so far revealed the presence of Culex tritaeniorhynchus in an illegal cultivation site in Lam Tin and a stream in Tsuen Wan. Similar findings were made earlier this year in illegal cultivation sites in Sham Shui Po and Tsing Yi.

Dr Ho said: "We will strengthen mosquito control actions in the areas concerned and provide technical support to other departments and organisations involved in operations against mosquito breeding."

Anti-mosquito efforts underway in Ap Lei Chau

As regards the vector survey concerning the recent local JE case in Ap Lei Chau, Dr Ho said only one adult Culex tritaeniorhynchus was found in Ap Lei Chau in a light trap set by the department and none in other areas surveyed.

Intensive anti-mosquito operations are being conducted in Ap Lei Chau, including larviciding and fogging.

November ovitrap index stood at 2.4% 

On the index reflecting the distribution of Aedes albopictus, the mosquito vector for Dengue fever transmission, Dr Ho noted the November figure dropped steadily to 2.4% from a peak of 31.6% in May and 5.2% in October.

At the district level, none of the locations surveyed last month recorded an area ovitrap index exceeding 20%, a level that calls for more intensive action, same as October.

For port areas, the ovitrap index also dropped from 1.5% in October to 0.4% in November.