A field experiment on the value of plasmoquine in the prophylaxis of malaria

Abstract

1. 1. Plasmoquine was given in an adult dose of 0·04 g ammes (0·9 mg. per kilogram body weight) twice weekly to a population of about 330 on a Rubber Estate where the incidence of malaria had been high for many years. 2. 2. At regular intervals of three months surveys were carried out to determine the malaria parasite rate (thick film method), the spleen rate, and the average hæmoglobin value of the population on this Experimental Estate. Surveys of anopheline breeding places were also carried out at the same time. 3. 3. Similar surveys were carried out at the same times on two contiguous Control Estates with populations of 405 and 362. 4. 4. The experiment was continued for a period of twelve months. 5. 5. The effect of plasmoquine prophylaxis on the incidence of clinical malaria was marked. In the year preceding the experiment the subtertian and benign tertian cases numbered respectively 30·4 and 52·5 per cent. of the population. Throughout the experimental period of twelve months, the incidence was 7·0 and 8·7 per cent. for subtertian and benign tertian infections respectively. 6. 6. From the parasite rates alone, the results were somewhat inconclusive, since the Control Estates showed a fall in the number of blood infections equal to that found on the Experimental Estate. Towards the end of the experiment, no P. falciparum gametocyte carriers could be found on the Experimental Estate. 7. 7. From the parasite rates only, it appears that the method was perhaps less satisfactory for benign tertian than for sub-tertian infections. This may possibly be due to plasmoquine having a less marked gametocidal action on P. vivax. 8. 8. There was slight improvement in the splenic index and in the average hæmoglobin percentage, but the improvement in the general physical condition of the labourer was most satisfactory. This observation was confirmed by the sickness rate which fell by 51 per cent. on the Experimental Estate, as compared with the previous year. On Control Estate I, the sick rate fell by 11 per cent. during the same period, but there was an increase of 21 per cent. in the sick rate on Control Estate II. 9. 9. The cost of this method of prophylaxis is about $600 (Straits Settlements) or £70 per annum per 100 labourers, including treatment of the average number of dependents.