SPREAD OF DISEASE

Te Awamutu Courier, Volume 55, Issue 3938, 11 August 1937, Page 9

SPREAD OF DISEASE

THE PART THE INSECT PLAYS. WHAT SCIENTIFIC RESEARCH REVEALS. In New Zealand and the southern parts of Australia, insect borne diseases are fortunately few. We have malaria, even though an anopheline mosquito capable of conveying this disease is widely distributed. The dengue conveying mosquito does not extend so far south, though recent surveys show that this insect may be met with in the interior towns in New South Wales, much further south than Sydney, and it seems to be extending along the coast towards Sydney itself. As we know, the role that flies play, especially the domestic fly, in the spread of typhoid fever is an Indirect tut important one. Fortunately, adequate sanitary control has greatly reduced the incidence of this disease.

In warm climates where there is a native population living under insanitary conditions and only slightly clothed, various kinds of flies may visit in number any open sore. They may thus convey infection from these to trifling abrasions and cuts on other people. In this way the skin lesions of jaws in Jamaica, fed upon by flies of the genius Hippelates, readily lead to further cases.

Yaws occurs among the natives in nerthern Australia, and doubtless our bush flies arc one of the ways in which native children contract the disease. Yaws is related to a much more serious disease, and it has been recently discovered that in Arabia a mild form of this latter is widely prevalent and is, like some cases of yaws, spread by the agency of flies. Flies, also, in Central Australia, have probably been responsible for the ready dispersal of a serious purulent infection of the eyes, an aphthalmia responsible sometimes for subsequent blindness.

Apart from typhoid fever and its related intestinal diseases, the only important condition in the southern parts of Australia, spread or .almost certainly spread, by some kind of insect or mite is an endemic and usually mild form of typhus fever. The true, often epidemic, typhus fever is a very severe disease nearly always conveyed by body lico. This constituted one of the gaol fevers of a century or so ago. When prisoners were brought into court for trial, the . infection, presumably from body lice, though possibly in some other unknown way, was sometimes conveyed to those in attendance, not even the bench and the bar escaping. TYPHUS EPIDEMICS. These typhus epidemics constitute some of the Black Assizes. During the Western Circuit of 1730, the infection was apparently contracted from the Bridewell at Taunton, which had been filled by drafts of prisoners from other neighbouring gaols, more than a hundred being tried. Creighton, in his history of Epidemics in Britain, states that as the circuit was continued through Devon and Dorset, various members—the high sheriff, a sergeant at law, the crier of the court, and two of the jurge’s servants, and finally the judge himself, Chief Baron Pengeiley, and another sergeant at law—all sickened of the disease and died. The reference to the judge’s servants preceding the judge in the onset of their illnesses indicates that the latter was probably infected from them, they in their turn being more likely to come in close contact with those who handled the infected and doubless lice infected prisoners. The most notorious of these eighteenth centurc Black Assizes was that of the Old Bailey Sessions in London in April, 1750, when the Lord Mayor of the year, one of the Justices of the Common Pleas, Baron of the Exchequer, and an Aiderman, all simlarly succumbed.

Nosegays, in the form of sweet smelling posies, were carried or placed in proximity to the officials of the court, under the idea that the infection was air borne; and possibly herbs, such as rosemary and lavender did play some slight part in repelling the advance of lice. The Australian form of typhus is not louse borne, but the exact means of spread remains to be determined. It is probable that the conveyer is some insect or mite associated with rats or mice. A rat Lea is known elsewhere to convey a similar form of typhus and certain nrites and ticks are responsible for other kinds of the disease. THE RAT BLAMED. A close study has been made of the ecto-parasitcs of rats and mice in

many parts of the world. This study originated when it was discovered that our two common species of rat were responsible for outbreaks of plague in human beings. For more than thirty years a record has been kept in New South Wales of the species of fleas infesting rats and the numbers of these during the various months of the year. The kinds of fleas that infest rats vary in different places and at different times of the year. The mites also differ in different parts. As certain fleas are more liable to convey plague than other kinds, this distribution of rat fleas is of considerable importance. It will thus be seen that the study of the natural history of various kinds of insects, mites and even mammals, may help materially in finding out ways of controlling human diseases, which may be spread by these various hosts. THE TSETSE FLY. The tse-tse fly of East Africa has played a very important part in the occupation of this area by man and his cattle. The Royal Entomological Society of London has just published a large work on the ecology of these flies, by Mr C. F. M. Soynnerton. He has made a close study of the habits of the species of the tse-tse fly that occur in Tanganyika, and finds that each requires a different kind-of vegetation in which to flourish. By a modification of this vegetation to a required degree, or by its destruction, that species of tse-tse fly requiring such habitat vzill no longer be a menace to that region. The famous tsetse fly, Glossina morsitans, actually inhabits seven different types of country, and in controlling this pest each of these has to be separately considered. A close study has had to be made of the environment of these flies in all its many respects, including the consideration of man and the effect of his operations on the fly in question and the associations with domestic animals, soil conditions, climate, and so on.

Though complete clearance of the bush might eliminate a tse-tse fly, such clearing may lead to erosion of tlie country, and this has to be guarded against by barriers of vegetation, for instance, evergreen thickets. It is obvious that the control of a pest like the tse-tse fly opens up wide fields for consideration, and necessitates the careful exploration of all the aspects of any means of control selected before such a scheme is set in operation. It would be disastrous if, in getting lid of the pest, the country was made uninhabitable. STUDY OF ECOLOGY IMPORTANT. The study of ecology, that is, of the surroundings, literally of the home, of various species of insects that come into relationship with man, is proving year by year of more and more importance. In some countries it is found that certain strains of malarial mosquitos prefer to feed on domestic animals, such as cattle, in preference to man. Obviously here the villagers who lived in close propinquity to their domestic animals might escape infection, whereas those superior houses where the stables were remote might expose their inhabitants to a greater risk. It is unkind to suggest tiiat a juicy infant might protect its parents from the attentions of fleas and mosquitoes. It may be that the infant has fewer means of escaping from these pests, and so presents a more accessible source of food.

In controlling disease every possible avenue of attack has thus to be explored, and sometimes success may come from some very unexpected direction. Though in their native habitat the balance of nature has resulted in pests being, on the whole, more or less under control, their dispersal to new countries with new environments may enable them to spread widely and do much damage. How insidious the spread may be in other instances is shown by the case of the “stick fast” iiet, which has recently been reported ar, being attached to sparrows. We can understand how sparrows have become infested by the way they visit the fowl runs in search of food. If these fleas are now conveyed to sparrows’ nests in buildings we may anticipate that they will eventually attach themselves to starlings, and this will again open up further means ot spreading. The introduced dove is now plentiful around Adelaide, and is also likely to visit a fowl run. To prerent infestation of clean fowl runs it. may soon be necessary to see that the wire netting used for enclosing them is of a sufficiently small mesh to keep out sparrows.

Efforts have recently been made again to bring racehorses over from India to compete in Australia. Permission for this to be done has been very wisely refused. A trypanosome infection of horses, known as surra, is widely distributed in India. The infection may be latent over long periods. Various biting flies are believed to be the transmitters of these blood parasites from one animal to another. No guarantee can be given that a horse leaving India is unquestionably free from infestation by these blood parasites unless extraordinary precautions are taken. The accidental introduction of one such animal might lead to the establishment of surra in Australia, with disastrous results to horses and cattle. We have in the past taken too many risks, and too many diseases and pests have consequently become established in Australia. With the development of air transport dangers have increased very much in certain ways, so that the utmost watchfulness in all directions is very necessary, and no liberties can . ba. ,taken.—J.B.X!....Jii..Melbourne Age.