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New monitoring system to look for carriers of Japanese encephalitis

More than 300 pig farms in Hong Kong and the Mai Po wetland will be monitored  for Culex mosquitoes,  the carriers of deadly Japanese encephalitis.

The monitoring system, to be introduced by the Food and Environmental Hygiene Department in October, will cover other high-risk sites in the New Territories and parts of the urban area.

The department decided to strengthen its surveillance after three Japanese encephalitis cases were reported this year, consultant  Ho Yuk-yin  told the South China Morning Post.

The disease  killed an Indonesian domestic helper in June and made two men severely ill. Both  are still in stable condition in hospital.

The virus is transmitted to humans through the bite of the Culex mosquito, which carries the virus after feeding on infected pigs. Wild birds are also a reservoir of the virus.

Since 2000, the department has used an ovitrap system to monitor Aedes albopictus mosquitoes, which carry dengue fever.

There is no regular and systematic surveillance of Culex mosquitoes, although the department occasionally studies the distribution of the species as part of its programme to track down mosquitoes that carry malaria.

'We know that Culex mosquitoes are relatively active in the New Territories, including Yuen Long, Tin Shui Wai and the North District,' Dr Ho said.

'Starting from October, we want to monitor if there are any Culex in pig farms. The Mai Po  bird park is also a target. We will also look at sites across the city so we will know the general picture of the Culex distribution.'

The department will use light traps to collect the mosquitoes, and will also check if there are any larvae in stagnant water.

Concern about the city's mosquito problem has grown after the department's ovitrap index - a measure of mosquito eggs laid in special traps across  Hong Kong - rose sharply from 11.9 per cent in April to 31.6 per cent in May.

The figure dropped to 22 per cent in June after the government launched an  anti-mosquito campaign, including the setting up of district task forces and clearing of construction sites and illegal farms.

Dr Ho said the situation  last month was 'similar' to June, although the final result would not be released until mid-August.

'In some areas the situation has improved, while in some it has worsened,' he said.

The department had no plan to expand the ovitrap surveillance system.

'Currently, we put the traps in 38 locations and because of resource constraints, we have no plan to expand the surveillance further,' he said.

'The system has been running well. The index gives us a good idea of mosquito distribution. More importantly, the index has successfully raised public awareness about mosquito-borne diseases.'



Pig farms under the spotlight in mosquito hunt