Sessional_Paper_1903 — Page 454

367

it to say that up to the present no competent observer has brought forward a single fact inexplicable by mosquito transmission or suggesting any other channel of infection.

2. Regarding other hosts of the malarial parasite than man, no one has found any other animal than man infected with the organism of human malaria. The supposition that monkeys may be the means of infecting anopheles in the jungle is made Lighly improbable by Koch's researches. We may point out, too, that such a supposition is in no way needed to explain malaria contracted in the jungle, the real mode of infection in such conditions being now quite well understood.

3. All recent research confirms the view that malaria is always derived from malaria pre-existing in others. It is as important to recognise that malaria is only derived from man as it is to appreciate that it is only transmitted by the mosquito (Anopheles). In other words malaria is as much an infectious disease as scarlet fever, the only difference being that it is not conveyed by contact, but only by the Anopheles mosquito.

Malaria then is an infectious disease--the infection or malaria parasite being conveyed from one person to another by the bite of Anopheles. An Anopheles mosquito, per se, is harmless; it is only an Anopheles containing parasites, or in other words an infected Anopheles, that can transmit malaria, and the only way by which an Anopheles can become infected is by "biting" some person who has the parasite in his or her blood.

It at first sight seems strange that the infective character of malaria has been and is still so overlooked by the general public. The actual mode of infection, however, has lately been made clear. Malaria is not in the tropics usually contracted from "fever' cases, but almost always from "latent" malaria in the native population.

Native Malaria.

1. Koch, in the East Indies, almost everywhere found malaria in the children though adults were free from infection. He commonly found malarial infection only on micros- copical examination of the blood. In some of the villages examined by him every child had malaria, in others a smaller proportion. He came to the conclusion that the degree of infection he found in these children was a test of the intensity of malaria.

2. We ourselves, finding that Anopheles caught in native villages always contained a considerable percentage of infected specimens, were led to the discovery that this was dependent upon a general infection of the native children of Africa who, although apparently in good health, had almost always the malaria parasite in their blood. We were thus able to show that the home of malaria is in native huts, hamlets, villages, and towns, and that European malaria is a mere resulting sign of the vast degree of indigenous latent malaria.

This has been amply confirmed subsequently by other observers, notably by Anuett and Dutton in Nigeria, Žiemann in the Cameroons, and again by ourselves in India.

:

The infection of Anopheles.

Where human infection is so general we should expect also to find Anopheles infected, and, indeed, in any batch of Anopheles caught in native huts a greater or less proportion always contain sporozoits, i.e., the malarial parasite in a condition ready for infecting man. The number of Anopheles infected is a variable one. As a rule in Africa it is from 5 per cent. to 10 per cent., but reached in some villages 50 per cent. Aro, on the Lagos railway, was an instance where the sporozoit rate in Anopheles caught in native huts was 50 per cent. Obviously it would be as difficult to avoid malaria in such a place as small-pox in a small-pox hospital.

We have said before the Anopheles are only capable of giving rise to malaria when they have previously fed upon blood containing malarial parasites, but a curious fact, and one of great importance, may be here noted. Anopheles are mainly to be found in association with native dwellings. One has not long to do with Anopheles without