Fighting Malaria In New Guinea.

Health Authorities Have Remarkable Success With Larvæ-Eating Fish.

By Gordon Thomas.

SEVERAL articles which have ap peared recently in Sydney papers give one the impression that the Pub lic Health Department of New Guinea is not doing all it could in its anti-malaria campaign. It has been suggested that the “mosquito parasite” is not being used to its fullest capacity, and, as a result of Mr. W. R. Carpenter’s remarks, Mr. F. H. Taylor, lecturer on entomology at the Sydney University, has proceeded to the Territory with the idea, appar ently, of speeding up the work.

The “mosquito parasite” is known as Megarhinus inornatus, or the cannibal mosquito, and was given some publicity by a Mr. Pemberton, from Hawaii, in 1929. In some quarters the Hawaiian gentleman is given the credit of having “discovered” the parasite. This, however, is not the case. The species was named by Walker in 1865, and confirmed by Edwards (British Museum) in 1923. In the Administration’s Report to the League of Nations, 1929/30, the follow ing reference was made to this interest ing parasite: “An authority in Hawaii has become interested in the possibilities of propagating the local Megarhinus inornatus (Walker), the larvæ of which are active cannibals, as a check to the culicid populations of that country, and the re sults of his work are awaited with interest. The species was first described by Hill in this Ter ritory some years ago and its habits are well known, but, so far as can be discovered, it exerts no check on larvæ breeding in local natural con ditions. Samples are frequently found in the jungle and especially hollow paw-paw trees at the foot of the hills surrounding Rabaul."

In a more recent report, Dr. T. Clive Backhouse, of Rabaul, states that ex periments with Megarhinus inornatus have been carried on in the Territory since 1924 and the species are found in pot-holes but not in ground water; also they exercise no effect whatever on the local species of anopheline (A. punctala tus (Donitz) —2 var.) which are exclu sively a ground water breeder. There is, however, the possibility, after genera tions of breeding, that M. inornatus might become effective as a means of destroying the anopheline larvæ.

A means of combating the anopheline species which is being encouraged by the Public Health Department, and widely distributed throughout the Ter ritory to outstations and on private plantations is the Gambusia affinis, a mosquito-larvæ-eating fish which was imported from Sydney in March, 1930, and was successfully propagated in a pond of the Botanic Gardens in Rabaul.

The fish are surface feeders and, under experimental conditions, devour all culi cid larvæ, showing a distinct preference tor those of the anopheline.

Recently the Medical Officer at Kavi eng prepared an exhaustive report on his observations regarding Gambusia

affinis and the benefits derived from its introduction to his district. Malaria fever has been greatly reduced, the mor tality rate decreased and a great reduc tion in the spleen-rate amongst native children.

“In February, 1931,” says the report, “about 100 Gambusia affinis were re ceived from Rabaul —half were liberated in the drains and half in the muddy, buffalo-disturbed ponds outside the town. The Gambusia began to multiply immediately in the drains and in a few weeks the mosquito nuisance was abated. In the ponds the fish did not do so well and in November only one was found to contain Gambusia. They were restocked from the drains and in a short time the mosquitoes breeding there were controlled. Drains and ponds were alive with Gambusia and mosquitoes were rare.”

A summary of the report brings out these salient features: 1. In New Ireland Tertian and Sub tertian Malaria are endemic, the spleen rate for the whole district in 6,084 chil dren of age 1-12 being 30.4. 2. The town of Kavieng was in 1930 badly infested with anopheline and other mosquitoes breeding in drains and ponds. Measures of control proved in effectual until Gambusia affinis was in troduced in February, 1931, when the town was quickly freed of mosquitoes. 3. As an experiment Gambusia affinis was, between May and December, 1931, introduced into all known breeding places of anopheli over an area of coastal villages 72 miles long containing 32 villages. 4. Subsequent examinations of the na tive population show that the spleen rate in the 32 villages treated has fallen from 24.6 in August, 1930, to 16.8 in February, 1931; 12.8 in October, 1931, and 4.2 in July, 1932; while in the re mainder of the subdivision the spleen rate in 35 villages has been 47.1, 23.9, 24.7 and 28.8 in the same months. More over, in the area treated there has been an excess of births over deaths for the first time on record.

It is but fair to the Public Health authorities in New Guinea that their untiring efforts in combating malaria should be placed on record. There is not sufficient publicity given to work of this nature in the Territory, and the public are often prone to interpret official silence as official ineptitude. Such an opinion is entirely erroneous where the Territory’s Public Health Department is