221. The population at risk is approximately 2,748,000 and the cost of control operations during 1959, including action against nuisance mosquitoes in certain restricted areas, was forty cents, or sixpence per head. This takes into account the emoluments of all staff and the expenditure on malaria oil, insecticides and equipment.
222. Malaria is a notifiable disease in the Colony. The main mosquito vector is A. minimus but A. jeyporiensis var candidiensis is also a known vector, A. maculatus and A. hyrcanus are also potential vectors. The predominant parasite is P. vivax which accounts for an average of 92% of the infections notified while P. falciparum and P. malariae account for an average of 5% and 3% respectively.
223. The total number of cases notified was 659, an increase of 212 cases over the 1957 total and Appendix 4 shows the source of origin of new and recurrent cases and the type of parasite identified. 224. One death from malaria was recorded. This occurred in a patient suffering from cancer who had had a series of emergency blood transfusions which were believed to be the source of the infection. Emergency transfusions, when blood cannot be obtained from the Blood Bank, are an infrequent cause of malaria and 2 other cases were thought to be infected in this way. At Appendix 5 is an analysis of new cases notified from protected areas.
225. The whole of the urban area is protected. This includes Hong Kong Island, Kowloon and New Kowloon. In addition there are relatively small zones in the New Territories, at Rennies Mill Camp. Chi Ma Wan Prison, the township on Cheung Chau Island and the Hei Ling Chau Leprosarium, where control measures are maintained,
226. The control of malaria is based mainly on anti-larval methods and anti-malaria oil, re-introduced in 1957, continues to be employed as the main larvicide. The use of Gammexane Dispersible Powder is now confined to agricultural lands where the application of oil is contra- indicated. In areas where insecticides are used, a close watch is main- tained for the emergence of resistant strains of vectors and so far there has not been any significant indication that this may be taking place. Routine adult mosquito catches and larval surveys made during the year in the protected areas were negative with one exception when larvae of A. maculatus were found in a portion of one stream which inadvertently had been left unsprayed for a short period. Ninety five
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percent of all cases of malaria notified emanate from the New Territories and of these 85% occur in the Sai Kung District.
227. Chemoprophylaxis using paludrine twice weekly continues to be the main defence in the unprotected areas of the New Territories and is used largely for the protection of the Armed Forces and the Police.
228. In the Sai Kung district a pilot experiment in the issue of paludrine to the inhabitants of two villages is now under way. The administrative arrangements are in the hands of the Medical Officer of Health, New Territories, and the stall of the Malaria Bureau is carrying out the assessment of the results. Here a considerable propor- tion of the cases occur in the floating population living in junks and sampans which ply between the mainland of China and the eastern sea board of the New Territories. The remaining cases are scattered amongst the 44 small villages of the Sai Kung District.
229, In certain instances the Burcau also undertakes the control of culicine mosquito breeding. Diazinon Dispersible Powder has proved to be valuable for the control of breeding of Culex fatigans in sumps. For Aedes logi, which breeds profusely in brackish water in the numerous rock pools along the shore, the use of gammexane bricks still proves effective after seven years of continuous use.
230. In the Bureau laboratory, work continued on the routine identification of mosquitoes and mosquito larvae, the dissection of mosquitoes and the staining and examination of blood smears. Malaria surveys were carried out at eight villages in the New Territories and field tests were undertaken to determine the efficacy of various insecticides, including the susceptibility of anophelines to these insecticides.
231. Other activities include lectures and demonstrations to medical students, to Health Inspectors, to Health Visitors and to Pest Control staff of the Urban Services Department. Advisory services were also provided for the Army and the Royal Air Force.
SOCIAL HYGIENE
232. Under the direction of the Social Hygiene Specialist this division provides specialist services in connexion with venereal dis- eases, leprosy and dermatology. The Specialist is the Government
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