Why Is There No Malaria In Fiji?

Interesting Discussion of a Subject Which Officialdom Ignores

Letter to the Editor.

Ab I have had considerable experience in health campaigns conducted by the various Governments of the Pacific and the Rockefeller Foundation of U.S.A.

I was interested in “Planes as Germ Carriers” and your editorial note in your journal of September.

Your conclusion that there are no dis eases endemic in New Guinea which dc not already exist in Australia, and that it is much more important to watch' care fully the airmail service between Asia and Australia, via Darwin, is correct in general.

But, although the Australian Medical Services have done wonderful work with the funds and equipment at their dis posal, complete medical surveys or ento mological surveys have not been per formed and there may be some diseases foreign to Australia still unrecognised.

Perhaps Dr. Torrance meant that New Guinea could be an intermediate country in the spread of yellow fever from America to Australia. This could easily occur, with the much more rapid transit by aeroplanes facilitating the transport of infected mosquitoes.

Yellow fever and malaria are similar diseases only insofar that they are both transmitted by mosquitoes. The life his tory and breeding habits of the vectors are entirely different. The vector of

yellow fever is hardy in comparison to the anophelines. The vector of yellow fever abounds throughout the Pacific and Australia, and (as can be deduced from Dr. Torrance’s statement): “Only one mosquito infected with yellow fever is necessary to create a reservoir of infec tion for the millions of the same type of mosquito to rapidly disseminate the dis ease.”

In the Pacific, yellow fever would be disastrous. The people have no immunity and it could be almost safely said that almost every home throughout the Pacific has its vectors of yellow fever. A person developing yellow fever soon after arrival in any Pacific port may be the commence ment of a disastrous outbreak of the disease, unless the disease was readily recognised and every precaution taken to prevent the vectors biting the person during the infective stage—which is only for a short period during an attack of yellow fever.

In the Pacific, though, the general rule is that medical practitioners have such large areas to control, and such poor means of co-operation, that they can see only a small proportion of people under their charge, and the possibilities are that yellow fever would be widespread and uncontrollable before it would be recognised.

Urgent Need For Survey

IN regard to your statement that Fiji 1 has the anopheles and material swamps, I should like to draw your atten tion to the following abstract from a report to the League of Nations com piled by Dr. R. W. Cilento and Dr. P.

Harmant in 1929: “Malaria is the next subject that demands attention, the disease which of all others definitely marks off North Melanesia from South Melanesia, and the possibility of the introduction of which into Fiji or New Caledonia is regarded with trepidation by the Administrations.

“Factors which have prevented up to the present the introduction of the dis ease into these Territories have not been definitely determined. It is considered that malaria does not exist in either Territory because anophelines have not been found, but there is no adequate evidence of the non-existence of anophel ines other than (1) the accepted fact of the absence of malaria; and (2) that anophelines have not been discovered by any entomological collector in the few investigations that have been made with regard to the mosquito population.

“Both for filariasis and malaria, it is most desirable that there should be a comprehensive entomological survey of the whole of Melanesia, extending over a considerable period, and dealing intim ately with the question of the vector or vectors of each disease in particular localities.

“Combined with such an investigation, there should be an examination of the whole of the literature which at present exists on the question of mosquito fauna

in Melanesia, the whole being finally tabulated in order that there might be produced as complete a picture as pos sible in a readily accessible form. It is considered that this is one of the most important features of co-ordinated re search that could be instituted at pre sent in the Pacific.”

Such a survey as recommended could also include a thorough survey of the vector of yellow fever, at least making possible rapid control measures in the event of yellow fever being introduced.

A valuable piece of educational work would also result. The vector of yellow fever is also the vector of dengue fever.

Transmission Of Malaria

are many kinds of anopheles * mosquitoes, but only a few of the species have so far proved to be capable of effectively transmitting malaria. Still, this does not mean that those anophel ines, which have been proved malaria carriers in the comparatively few investi gations are the only ones which can transmit malarial infection.

Personally, I have never seen anophel ines in Fiji, Tonga, or Rotuma. If any observer has ever reported them, care should be exercised to determine if they are of the type suitable for the trans mission of malaria.

In regard to your comparison between yellow fever and malaria, it may be safely stated that in the few mosquito investi gations that have been conducted in Southern Melanesia and Polynesia ma larial anophelines have not been reported whereas aedesaegypti and its kindred, the proved vector of yellow fever, is widespread.

Fiji certainly has swamps which should be ideal for anopheles, right in the vicin ity of the chief ports of entry. Of recent times, all boats arriving in Fiji from malarious areas are adequately fumi gated. In the early days, transport was slow and mosquitoes probably succumbed before reaching Fiji.

VOUR queries in regard to the regional distribution of malaria are certainly questions which malariologists would like to be able to answer. Funds and facilities alone have* prevented definite answers to your questions.

Mystery Of Regional Malaria

A S to -why malaria is regional, I would like to draw your attention to the following: (1) Besides only a few types of anophelines being able to transmit malaria, there must also be a reservoir of infection, and the transmission of malaria by anophelines is complicated. (2) The regular North-east trades ex tend to and include the New Hebrides. (3) The distances between the islands in the chain of islands from New Guinea to the New Hebrides is comparatively small. Not that anophelines would fly from island to island along the archi pelago, but gradual extension from island to island would be possible by migration. This would also make sure of a reservoir of infection being migrated at the same time as the anophelines. (4) Of comparatively recent times immigration has been from Polynesia to

Melanesia. The South-east trades have helped this.

Anopheles are not found on all islands or areas of Northern Melanesia. I have good reasons to believe that generally speaking anopheles can breed only in a few places on the lowlands, or valleys and plains of the highlands. Of course, exceptions occur.

Insofar as Europeans are concerned they have settled on the lowlands and the general impression is formed that malaria is widespread. This is not the case, and is readily demonstrated by the fact that when natives from highlands, small islands, and natives of Polynesian extraction are brought to the plantations and missions on the coastal plains, they suffer much from acute malaria. This is because they have no immunity to malaria and multiple infections take

place, and not because they have brought malaria with them.

In the New Hebrides, it might be said that malarial areas are very small in comparison to the area of the New Hebrides. The Europeans were sold ‘Tabu” land by the natives and in almost all cases malaria was the primary cause of the “tabu.” Filariasis, another mosquito-borne disease, has also played a minor part in this direction, The general impression is that lowered temperature is the reason for lack of malaria on the small islands and high lands. In the New Hebrides, none of the hills or mountains are high enough (un less on Santo) for any extreme change of temperature. The chief reason for the absence of malaria on most of the small islands and highlands is: There is. a t the most, only a very small coastal

plain on the small islands; and ridges constitute the highlands where natives dwell. Consequently, rapid drainage is assured. Anophelines have to deposit eggs on the water, from which develop larvae, then pupaq, and then the mos quito.

While in certain countries eggs and larvae have been found in back eddies, they cannot be expected to remain long enough for complete development in tor rents which rush down steeply inclined hills to the sea. Any eggs deposited by migratory anophelines on the sides would be washed down to the coastal flats.

This also applies to New Guinea, Papua and the Solomons. Of course irrigation on the sides of hills has to be taken into consideration in some areas.

The natives of Maewo, New Hebrides, believed that “big legs” (elephantiasis) was caused through eating too much wet taro. This could not be; but a little con sideration showed that in growing wet taro an ideal breeding ground for the vector of filariasis would result.

There is much medical and entomo logical work necessary in the Pacific. 1 believe that the breeding grounds of mosquitoes capable of transmitting dis

eases in the Pacific are comparatively small. A thorough co-ordinated investi gation would define breeding places of the vectors of malaria, filariasis, yellow fever and dengue fever, and in most instances would determine control mea sures at a moderate cost.

Infective yellow fever mosquitoes have been kept alive from seven weeks to three months. There are authentic records of yellow fever developing on boats some considerable time after leav ing infected ports, through infected mos quitos making the ship their habitat.

Yellow fever has been transferred from country to country by experimental transportation of infected mosquitoes.

Precautionary measures recommended all depend upon local peculiarities and com plete mosquito control at airports and vicinity.

I am, etc.,

William J. Tully.

16 Bridge Street, Sydney.