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Experiments were also carried out in order to determine whether malaria could be controlled in villages in the New Terri- tories by monthly fumigation of dwellings with Gammoxane, using Gammexane Smoke Generators.
The insecticidal action of Gammexane aunoke is by direct kill and by the effect of the residue deposited on walls and ceilings of rooins after fumigation,
The three villages of Shum Tseng, Pok Wai, and Chuk Yuen were selected for the experiments with Chuk Yuen acting as a control. The parasite rate was taken as an index of the degree of malaria infection in each of the three villages and was deter- mined at the ouset and termination of the experiments ie, in May and December. Mosquito catches were carried out each month in order to determine the vector species in the respective villages and the effect of Gammexane on the mosquito population.
The dosage of (ammexaue employed was a 2 oz. Generator per 4,000 cu. ft. of room space, but this dose was often exceeded; on the other hand, the proper sealing of rooms for 2 hours after fumigation could not always be ensured.
In view of the short period over which the experiments were conducted vix, one malarial season, it was decided to accept an significant only marked reductions in the parasite rates. Mosquito Catches,
A. hyrcanus var. sinensis was the predominant anopheline species in all these villages and was found mainly in pigsties. A. minimus and A. jeyporiensis var, audidiensis, the two important vector species in the Colony, were found in small numbers in Shum Tseng and Pok Wai but aut in Chuk Yuen. A few A. tessellatus were caught only in Pok Wai Villnge.
lok Wai Shum Taeng
Chuk Yuen
Malaria Pornsites.
Parasite rate
(May, 1948)
4.16%
16.6%
18.9 %
Parasite rate (Dec., 1948)
NIL. 31.2 % 9.12%
Plasmodium vivax was the only species of malarial parasite encountered in blood films when determining parasite rates.
Conclusion.
The conclusion drawn from the experiments is that the Gammexane Smoke Generator is unlikely to prove successful iu controlling Malaria in Malaria endemic areas unless supported by other control measures.
On the other hand, the experiments proved that flammexane Smoke is a powerful insecticide, although the residual effect after fumigation is not as lasting as that obtained by spraying with solutions of Gammexane or DDT. Bug infestations were eradicated and fly and mosquito nuisances were controlled for short periods in the two villages subjected to Gammexane fumigation.
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A larval survey carried out in November in hill-streams near the villages of Tau Yuen Wai and Foo Tou in the Ping Shan area gave the following result:-
A. byreanus var. sinensis 147. A. minimus 24. A.
maculatus 3.
The two villages combined showed spleen and parasite
rates of 31% and 20% respectively.
A larval survey carried out in December in the hill-streams near Chung Uk Village, gave the following result:
A. maculatus 98, A. karwari 66, A. hyrcanus var. sineusia 121, A. jeyporiensis var. candidiensia 4, and A. minimus 52.
The village showed a spleen and parasite rate of #17% and 0% respectively.
Teaching of Mosquitology.
A course of twenty Lectures on this subject was given to Public Health Inspectors together with Field and Laboratory Demonstrations. Personuel of the Army and Navy were also given a course of instruction in Anti-Malaria Work, and arrange- ments have been made with the University to recommence the course in Malariology for the M.B. CL.B.
Legal Action.
Sixty legal notices were served in the course of the year for mosquito" beceding, and two people were summoner).
Mosquito Nuisances.
Mosquito muisances were investigated on behalf of the Urban Council at Eastern District, Central District, Upper Level, Pokfulam, Aberdeen, Stanley, Shek 0. Tytam Tak, Shaukiwau. Kowloon City, Kowloon Tong, Kui Tak, Lai ('hi Kok, Hung Hom, Yaumati and Tsim Sha Tsui.
Syret. J. B. MACKIE, Government Mulaviologist.
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