Control Unit of the Urban Services Department and to Hei Ling Chau Leprosarium. Lectures are given on malaria and allied subjects to various groups of health personnel under training.
Control operations
183. The important malaria vectors are A. minintus and A. jey- portensis var, candidiensis, while A, maculanus and A. hyrcanus have also been proved to be potential carriers. For control purposes the Colony is divided into "protected" and non-protected areas.
184. The whole of the urban area comprising Hong Kong Island, Kowloon, and New Kowloon is a protected area. In addition there are relatively small zones in the New Territories, at Rennie's Mill Camp. Kau Wa Keng, Chi Ma Wan Prison and the township on Cheung Chau Island, where control measures are maintained. Since the 1st April, 1959, similar measures have also been instituted at the new Shek Pik Reservoir site for the protection of workers engaged in the construction of the dam.
185. The extension of the control programme to Rennie's Mill and Kau Wa Keng only commenced in 1950, to Cheung Chau Island in 1951 and to Chi Ma Wan in 1955. From 1952 onwards, in the face of progressive urban development, protection has been gradually extended to the Ngau Tau Kok, Kwun Tong, Cha Kwo Ling and Lei Yue Mun arcas in New Kowloon,
186. The method of control of malaria is based predominantly on anti-larval measures consisting of the rough training of streams, ditching and larviciding. Anti-malaria oil was a first employed as the main larvicide but, starting in 1950, Gammexane dispersible powder was used instead of oil. This continued satisfactorily until 1957 but, on account of development of resistance on the part of malaria vectors elsewhere against chlorinated hydrocarbon insecticides after prolonged use and in order to delay the possibility of the development as long as possible, it was considered advisable to reintroduce the use of oil, except in agricul- tural lands where its application would be unsuitable. Under local conditions this use of oil has proved to be safe and economical.
187. In certain instances, the Bureau also undertakes the control of culicine mosquito breeding. Against Culex farigans, which has shown definite resistance to Gammexane, Diazinon dispersible powder has been found very useful, particularly when breeding takes place in sumps. For Aedes rogoi which breeds profusely in brackish water in numerous rock
pools along the shore. Gammezane bricks' have continued to prove their effectiveness without any sign of resistance developing.
IER.
Results of the malaria control work in the urban areas have so far been satisfactory and the incidence of natural malaria transmis- sion has virtually been reduced to zero. Routine adult mosquito catches and larval surveys were carried out in the protected areas of Kowloon and Hong Kong throughout the year. Except in one or two instances when young larvae of A. maculanus and A. Ayrcanus were detected, all the other findings were negative. However vector mosquitoes abound just outside the protected areas and, given a favourable opportunity, can regain a foothold at any time. Therefore constant vigilance is neces- sary and there is no room for complacency or relaxation of the control
measures.
189. In the New Territories, except in the few selected areas as mentioned above, there is as yet no overall vector control programme. In the rural districts, where the population is scattered and wet cultiva- tion is traditional, to adopt anti-larval measures as currently practised in the urban areas would not yet be feasible owing to the agricultural practices in use. Further, comprehensive anti-aduh mosquito measures. once instituted, would have to be continued as long as unprotected con- tiguous borders are present, with a grave risk of resistance developing. 190. Police personnel and troops stationed in the New Territories continue to depend on paludrine prophylaxis as their main line of defence against malaria.
191. In the Sai Kung district, in the eastern part of the New Terri- tories where the majority of malaria notifications originate, chemopro- phylaxis by weekly distribution of paludrine tablets was started towards the end of March 1959 in the two comparatively small villages of Pak Kong and Pak Sha Wan. This was designed as a pilot experiment in contrat by chemoprophylaxis but, unfortunately, the experiment had to be discontinued in January 1960 as the necessary co-operation from the public began to dwindle. The initial results of the scheme were however encouraging, since not a single case of fresh infection had been reparted in either of these two villages throughout the period of medication: indeed, up to time of writing this report, although cases continued to appear in neighbouring villages, no fresh infections have been reported from the two villages concerned,
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