Causes, symptoms, prevention, and treatment of various animal diseases introduction

CAUSES OF DISEASES

Disease causes body functions to disfunction or function improperly. Three principal reasons most often

cited for the spread of diseases are poor sanitation, improper management, and introduction of new ani-

mals into a herd.

One or more of the following defects cause diseases.

Nutritional defects - An imbalance of required food nutrients in the ration is the cause of nutritional defects.

Animals receiving inadequate amounts of vitamins, minerals, fats, carbohydrates, and protein cannot produce

efficiently. Therefore, their levels of resistance to disease are lowered.

Physiological defects - These defects cause an improper functioning of glands, organs, or body systems. The

relationship between the diet and the proper functioning of body parts is directly related. For example, the

thyroid gland regulates the rate of body metabolism and depends upon an adequate supply of iodine to

function properly. An improperly functioning thyroid gland may increase the nutritive requirements of animals

to the point that very few nutrients are available for growth or production.

* Underlined words are defined in the Glossary of Terms.

---

- 2 -

Morphological defects (physical defects) - An accident or negligence is responsible for physical defects. Cuts,

scrapes, scratches, bruises, and broken bones are examples of morphological defects. Any one of these can

temporarily or permanently reduce the efficiency of an animal. Good management practices help eliminate

defects of this nature.

Pathogenic defects - Certain organisms produce toxins or poisons that upset the normal metabolic activity of

the animal. Viruses and bacteria are the most common disease-causing pathogens. They are microscopic in

size and capable of multiplying rapidly under ideal environmental conditions. Other pathogens are fungi and

protozoans. A discussion of each type follows.

Viral diseases are the most difficult to control because viruses closely resemble the chemical compounds

that make up a cell. Another problem in controlling viruses is that the chemicals capable of killing or control-

ling them also kill or destroy the host cell. Preventive vaccinations are the most successful method of

controlling viral diseases.

Bacteria are microscopic in size, produce powerful toxins, and multiply rapidly. Many bacteria are capable

of forming spores, resistant forms of bacterial cells able to withstand severe environmental conditions.

These spores are difficult to control and may lie dormant for years before being provided with the opportu-

nity to cause disease. Antibiotics are used successfully to control bacteria.

Fungal diseases are caused by fungi, which are small organisms. Many disease-producing fungi live in the

soil. It is often difficult to determine the cause of fungal diseases, because bacteria cause a secondary

infection and are often erroneously identified as fungi.

Protozoa are one celled and the simplest form of animal life. Some protozoa cannot move themselves and

must be transported by other means. Some move by making whip-like lashes or vibrating projections. A

number of different kinds of protozoa prey upon animals and cause disease.