The Coastal Hills

In this chapter I deal with an area of hill land which is malarious when under jungle, or when the ravine streams are choked by weeds after the jungle has been felled. It is equally unhealthy when the jungle has been felled and the ravine streams are free from weeds, for a new malaria carrier appears, namely, A. maculatus. The conclusions reached ten years ago have been confirmed, and much additional evidence could be adduced were it necessary to do so. It will be sufficient, however, if I reproduce what was written in 1909, practically the only alteration being that Nyssorhynchus willmori now appears as A. maculatus.

1909

In the previous chapters I have shown how malaria has disappeared from certain portions of the coast districts of Malaya, as the land has been drained, and the jungle felled. That this often occurs is well known to all with tropical experience; and it is with the hope that this will occur that the pioneer battles with his troubles. The hope is so strongly implanted that he takes it as a matter of course that the health will improve as the land is opened up.

Figure 10.1: General view of hill land estate. The photograph is taken from an elevation of about 300 feet. The view shows a series of ridges of greater or less height planted with rubber. In the background is the jungle. Between each of the ridges is a stream such as seen in Figure 10.2.

We often hear of what a terrible place some spot was or is. We rarely hear that a place was abandoned on account of its ill-health. But we never seem to hear that a place always remains unhealthy, and never improves as time goes on. This is because after a time the population of an unhealthy place consists almost entirely of those who have acquired a certain amount of immunity. New people have practically ceased to come to it. And so the health seems to improve, and local experience seems to fall into line with the general experience of the tropics. Yet it only wants new arrivals to come in numbers to start a severe outbreak of malaria. I have now, however, to record that in certain portions of the district, there has not been the slightest improvement in the six years during which they have been under my observation, nor have I any reason to suppose they will improve as long as the present conditions favouring the mosquito persist.

The land to which I refer is the hilly land of the coast districts of Selangor, in the ravines of which run streams of water, often of very small size indeed. In this hill land the mosquitoes which are to be found are A. umbrosus as in the flat land, A. maculatus and A. karwari. Now the important point about these mosquitoes is that, if a ravine stream be kept free from grass and other weeds, A. karwari and A. umbrosus no longer breed in it, while A. maculatus will breed in streams which have been absolutely free from grass and weeds for three years to my knowledge. Extensive observation has shown that it is not in all ravines that A. maculatus can be found, nor is it always present in the same ravine. It is possible there may be some seasonal variation,14 but of this I am not yet warranted in making any definite statement. I can say, however, that no amount of weeding or other care of a mountain stream will abolish A. maculatus, which I have found to be a natural carrier of malaria.

Figure 10.2: Stream in hill land. Streams such as these run between the ridges of the hill land. A. maculatus is found in them. Large quantities of silt are deposited in these streams, and when cleaned out the silt is thrown on the bands of the stream, as will be seen from the photograph.

For some years malaria has formed a subject of anxiety to the managers of certain estates in the district, since their labour forces have been seriously crippled, apart from the fact that the Europeans have also suffered severely, and blackwater fever has occurred in one instance. It was always hoped that the general experience would hold good in these estates, and that, as they were more opened up, the health would improve. In the meantime there was nothing to do but to push on with the opening programme, and give quinine to the coolies systematically. This has been done, thereby reducing the death rate and improving the general health of the coolies. The arrival of any considerable number of new coolies was, however, always the signal for an outbreak of the disease, and the older coolies who were apparently becoming acclimatised appeared occasionally to suffer with the new ones.

In the middle of 1907, when my investigations on the estates had for certain reasons suffered interruption, the position was as follows. I had determined the percentage of infected children on many of the estates of the district. I had also determined the adult mosquitoes to be found in the coolie lines, and made certain observations on their breeding places. I had determined that the carrier of malaria on the hill land was A. maculatus, and that it was confined exclusively to the hill land. I had also observed on three estates that it was present when there was grass and other weeds in the drains, but not when these drains were clean. I attributed their absence to the freedom from weeds. I had also determined its absence from certain ravines altogether. I, therefore, concluded that when further opening had taken place, the health of the labour would improve on the hill land places, as it had already done on the flat land places to my knowledge.

In 1908 I was on leave in England, and on my return to Malaya was for several months fully occupied in administrative details of the hospital system, which I was organising for the estates. During this period I came to the conclusion from what I incidentally saw, that despite the lapse of two years and despite the greater areas opened, no improvement had taken place in the hill land estates.

I accordingly determined to investigate the matter de novo. I determined to examine every set of coolie lines in the district and particularly those on the hill land, with the object of ascertaining the exact condition of each. I also decided to make a fuller inquiry into the breeding places and habits of the anophelines. The result of this inquiry has been to show that A. maculatus cannot be exterminated as long as there is water in the ravines in which it can breed; secondly, that malaria is as prevalent in the hill land as before; and thirdly, that quinine in the therapeutic doses can hold in check, but cannot eradicate, malaria.

It will be unnecessary to enter into details of each of the hill land estates, but the following figures will show the general condition.

On one occasion I visited Lanadron Estate. On the flat river bank the spleen rate was low and the children were healthy. Further in, at the “Darat Lines”, no fewer than 17 out of 27 children (62%) born on the estate had enlarged spleen. The “Darat” is about 23 feet above the general level of the surrounding flat land, and might have been, at one time, a sand bank in the sea. Yet in the eyes of A. maculatus it has found favour, and to them, at least, it is a hill. At the time of my visit I searched for them in vain, but Dr. Rattray afterwards found them in abundance.