MAN AND HIS ENEMIES.

New Zealand Herald, Volume LXVI, Issue 20172, 5 February 1929, Page 6

MAN AND HIS ENEMIES.

BY W. R. M'GItEGOR.

PARASITES OF THE BODY.

FLUKES OF THE PHAROAHS.

CAUSE OF MANY DISEASES

FRESH WATER MENACE.

No. XIX.

'Although from time to time cases Jiave been recorded, it is unusual for the liver fiukc of the sheep to infest the tiody of man. Unfortunately, however, there uro numerous parasitic flukes peculiar to the human kind As in the sheep, some of them are inhabitants of the liver, some of them prefer 'to live in the blood, .while others again settle themselves down iu the tissues of the lungs. It is always the adult, egg-laying generation that inhabits the human body, ■while the asexual phase of the life-cycle is passed in the body of some other host, usually a small, fresh-water snail. Some of these life-histories are exceedingly complicated, as frequently more than one intermediate host is involved. Of pre-eminent interest among human ilukcs is Schistosoma or, as it used to be called, Bilharzia, after the celebrated Bilharz, its discoverer. This is a blood fluko which inhabits certain of the larger veins of man. ' There are several species of Schistosoma ■widely distributed over the world. Their stronghold is in Africa, especially in Egypt, where peculiar diseases due to their activities have been known from very ancient times. 'lhe eggs of the •worm were detected in the body of one of the Pharoahs that was subjected to scientific examination. It is reliably estimated that even at the present time in some districts in Egypt as many as 90 per cent, of the population is infected, 'i'lio parasite ranges also into Asia, the disease being very prevalent in Persia, as well as in such distant countries as China. Japan and the Philippine Isles. At least one species occurs in the tropical parts of America and the West Indies. Modern Research.

Tlic necessity for protecting the health of tho /large bodies of European troops that moved in Egypt and other parts of the tropics during the Great War stimulated -researches which have greatly added to our knowledge of this and other kindred parasites. In Schistosoma the sexes arc separate, both males and females being found in large numbers in the veins of man.

The eggs cannot, develop until they reach fresh water. Here they soon hatch out and the active larva which emerges commences an urgent search for the tiny water snail, Bulinus. in the tissues of which numerous young flukes are produced by a process of budding. These, minute creatures with forked tails, swim actively about in the water for a time, but unless tney come into contact with n human being or other suitable warmblooded animal, in the veins of which development into the adult form can be completed, life is limited to about 40 hours. The mode of infection is curious. [When the tiny fluke comes into contact "with the skin it quickly bores its way through and, passing into the blood and lymph vessels beneath, is eventually carried by the circulating blood to the liver, where it settles down for a time to feed and grow. These facts immediately suggest pmtec'tive measures. Care must lie taken that infected waters do not come into contact with the skin. Even wetting the feet in infected swamp water is highlv dangerous, for the worms are quite capable of/ passing through wet clothing. In regions where the infection is rife all water used for drinking and bathing rmM be effectively sterilised, either bv boiling or by chemical treatment. Once admitted to the stomach it is highly probable that the parasites are killed by the digestive juices, but if the drinking water is contaminated there is a distinct possibility that - they will reach the blood stream through the mucous membrane of the mouth. But the fact that the infective organism cannot exist for more than 40 hours outside the body of a suitable host affords the most generally applicable measure of control. It is onlv necessary that the water used for drinking. and washing should be stored in tanks for 48 hours to be sure that it is quite innocuous. Through Flea and Fish.

Although so very different in outward

appearance, the tapeworms are closely

related to the flukes zoologically. The life-history is always complicated, being in. most species divided between two separate hosts, though the "broad" tapeworm, which often attains a length of thirty feet, has been traced through u scries of three hosts. The larva develops at first in the tissues of the minute Cyclops, a water flea, which, being swallowed by a fish, transfers the infection to the muscles of that animal. Human beings become infected in their turn when the flesh of such fishes is used for food.

Included in the general term Filariasis are a large number of diseased conditions that have been observed from very ancieut times, but have been given a variety of names according to the particular morbid conditions that characterise them. Among these are certain obscure fevers, Cbyluria, Barbadoes leg. Cochin leg, and Elephantiasis, the latter a very terrible affliction that was often confounded with tru« leprosy. Acute

infections result in the swelling of the

lower limbs, and sometimes the arms and other parts of the body, to such an extent. as to become gross deformities too horrible for detailed description. It has been left for modern science to make the discovery that all these diseases are caused by one and the same parasite, a lowly lilood-worm, Filaria bancrofti. Mosquito Once Again.

iWhcn tho blood of diseased persons was (examined microscopically a remarkable periodicity in the movements of the worms was observed. During the day time blood taken from the surface vessels contains no parasites at all. This apparent disappearance was very puzzling until it. was discovered that they migrate to the deeper vessels during the hours of ■"daylight. In the evening they reappear jri the surface capillaries, gradually increasing in number until two or three o'clock: This marked perodicity was at o-ico explained by the discovery that they no dependent upon the mosquito for transfer from one host to another. From the biological point of view this periodicity of movement is one of the most remarkable features of the case. It is clearly an adaptation facilitating distribution by mosquitoes. Unless the parasites crowd into the superficial vessels r.t night there is little prospect that . they will ever pass into the stomach of a mosquito, j In tropical West Africa and I!?., Uganda there is another species of JMlaria which'comes to the surface during the day. Curiously enough the carrier in this case is not a nocturnal mosquito, but a biting fly, which is active during

No instance illustrates the depredations of parasitic worms more strikingly than Hie case of the bookworm. In nine cases j?, °l 'n e( i' o, l takes l> lac « through - the skin. Tho Rockefeller Sanitary Commission which carried out searching investigations between the years 1909 and J914. concluded that "more than two million peopl? m the Southern States were infected with hookworm, involving vast..suffering, P nr tial arrest of mental physical and moral growth, great loss of lite and noticeable decrease in economic •fßciency over vast regions." c