KNOWLEDGE OF DISEASE

Waikato Times, Volume 124, Issue 20734, 18 February 1939, Page 26 (Supplement)

KNOWLEDGE OF DISEASE

PART OF PHOSPHATES Since the discovery that many diseases are caused by small parasites, our knowledge of disease has very greatly increased. Some of these parasites are so small as to be beyond the powers of the best microscopes. Such an organism is spoken of as a “virus.” Others may be visible microscopically but appear only as small rods or rings and are referred to by the man in the street as “microbes.” Others, such as many internal worms, are quite large and at least big enough for much detail of their structure to be visible to the naked eye. During the last few years particularly, we have made an intensive study of many of these organisms both inside and outside the animal’s body. By this means we have gained a wealth of information, though there are still some very serious gaps in our knowledge. Microbes Responsible. Microbes are certainly responsible ' for many of the diseases which occur ! to-day among domestic animals. If I an animal became violently ill and died, when it contracted a disease, . there would be no trouble as a rule I in detecting the cause, for many of I the common diseases produce characteristic symptoms and changes which are then seen at post-mortems. These are often so characteristic as to leave little doubt in one’s mind as to the cause. Acquirement of a disease, however, is not always noticed by the owner. An animal may contract a disease in a mild form and remain affected over a long period without any visible change in its outward appearance. All this time, however, it may have a diseased centre or focus somewhere within its body. From this centre, the microbes may be leaving the animal by one or other of the natural openings. Contamination of the surroundings thus occurs and so other animals are affected. Swine fever may be spread on one’s boot from an infected to a non-infected sty. Infection by means of instruments is not uncommon. Infected dehorning instruments have been responsible for the outbreak of a form of tick disease in cattle. Men engaged in the control of animal diseases are obliged to be particularly careful to prevent the unwilling transmission of disease from infected to healthy herds.

Diseases Transmitted. A very large number of diseases are i spread through the intermediary of I ticks, lice, biting flies, or other ex- | ternal parasites. With all these in-sect-transmitted diseases, the microbe or larger parasite is taken up directly or indirectly by the external parasite from an infected animal and then spread to a non-infected one at a later period. In these diseases the insect or transmitting agent is known as the “intermediate”—the host in which the microbe sojourns for a while when being transmitted from one animal to another. There are very many offending agents which cause diseases and which require intermediate hosts. The young sheep fluke cannot develop beyond a definite stage unless it reaches the body of a certain type of snail, hence, fluke disease only occurs in areas where these snails exist, and destruction of them causes fluke disease to disappear. The hydatid cyst of sheep and cattle is the intermediate stage of the tape worm of a dog. The number of diseases which depend entirely on intermediate hosts for their natural spread is enormous. Incidentally, their control can be attempted indirectly by destruction of the intermediate host where this is practicable. Thus destruction of the common fowl tick, which lives during the day in the cracks of the woodwork of fowlhouses and only attacks the bird at night when on the perch, removes the danger of tick fever.

The body is a very complicated organism consisting of many parts or organs which require certain elements in the foodstuffs for their proper maintenance. Whenever any of these elements are. lacking, disease may make its appearance. The food eaten by the average ruminant covers a wide range, so that any possible deficiency in one plant may be compensated by another. However, where there is a definite deficiency in the soil of certain essential elements these may be lacking in the plant food.