RESULT OF CONTROL.
Anopheline Prevalence.
Numerous checking catches and surveys were made by the Malaria Bureau in the controlled area of Kowloon and Hong Kong, but no anophelines, either larvæ or adults could be found. Incoming air craft were similarly searched with negative results,
This does not mean that the larval control programme could be relaxed in any way, as Malaria Bureau checks have proved heavy vehicular traffic from the New Territories, and some 400 junks, are daily pouring their quota of mosquitoes into the controlled area. Complete permanent mosquito sterilization as reported from Cyprus would therefore be impossible.
Culicine Prevalence.
In the areas controlled by the Malaria Bureau, control of culicine mosquitoes was also undertaken.
The introduction of the Gammexane Brick much facilitated the control of rock pool, Aedes togoi breeding in nearby islands. These had formerly contributed to the mosquito nuisances on the south side of Hong Kong Island.
In the urban area where this work is done by the Urban Council, mosquito nuisances were investigated on their behalf at Shaukiwan, North Point, Happy Valley, Bowen Road, Wong Nei Chong, Mt. Parish, Queen's Road East, Caine Road, Queen Mary, Mt. Cameron, Aberdeen, Yaumati, Lai Chi Kok and Hung Hom,
MALARIA INCIDENCE.
Although some 412 cases of malaria were notified in the Colony from the civilian population, only 7 of these were European, and on investigation all seven of these proved to have been contracted in the New Territories outside the controlled areas, The European malaria rate is the only criterion of the effect of the control work on the Maleria incidence, and as this is nil, the present control programme would appear to be completely effective.
For the first time for twenty years no cases of malaria were reported from the Laichikok Hospital and Prison. This is due to the larval control of the paddy in that area made possible by the introduction of Water Miscible Gammexane.
The Chinese cases notified were relapses among the local inhabitants and the enormous transient population, who come from a territory where the principle carrier (A. mininus) has an infection rate of 12%.
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Notification of malaria was made compulsory in June of this year, since which time some 46 cases have been notified by private practitioners.
In the New Territories 106 cases of malaria were notified from a population of 200,000. This low rate taken in conjunction with the high village infection rate (12%) of A. mininus confirms previous observations that the native population have a high degree of immunity.
Total expenditure;
COSTS.
Insecticides-Gammoxane
Malariol
Supervising staff
Labour
Transportation
$ 36,051.00 36,180.00
166,933.00
342,173.00
9,000.00
$579,387.00
From an estimated population of 2,265,000, the expenditure per capita of approximately H.K. 20 cents is the cheapest rate so far reported in the world in Malaria control work.
OTHER WORK.
Fly Control Work.
Experiments were carried out at the Government Compositing Station Taun Wan, and the maturing tanks at San Hui to determine whether Gammexane could be used prophylactly to prevent fly breeding in nightsoil.
Experimental tanks and control pits were built by the Bureau at these centres and it was found that up to the time of writing, a dilution of 1-3,000 of water miscible Gammaxane was sufficient to inhibit com- pletely any fly breeding in nightsoil. A field trial was also undertaken at Fanling, New Territories from October to December to determine whether spraying of manure sumps by Gammexane could control the fly nuisance in that horticultural centre. This was also successful—a bi-weekly spray- ing of the sumps giving complete control of breeding. Detailed results of the experiments are given in Appendix A.
13th Aprü, 1951.
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J. B. MACKIE,
Malariologist.