TYPES OF BW AGENTS

Although biology deals with all living organisms, we are concerned here with military biology, which is only those organisms that will adversely affect man, animals, or plants. These organisms include the following: 

. Microorganisms (bacteria, viruses, rickettsiae, fungi, protozoa) 

. Vectors of disease (insects, acarids, such as ticks and mites, and animals) l Pests (of animals and plants)

Microorganisms

Microorganisms are minute living organisms, which can usually be seen only with the aid of a microscope. Each organism is composed of a single cell or a group of associated cells capable of carrying on all functions of life, including growth and reproduction. Microorganisms do not have a digestive tract, organs of sight, or a heatregulating system. Many of them resemble plant life and are regarded as being in the vegetable kingdom. Some microorganisms, such as the protozoa, have characteristics that place them in the animal kingdom.

Microorganisms are universally distributed in the air, water, and soil. Every cubic foot of topsoil provides a natural home for billions of soil organisms. The skin, hair, nose, mouth, and digestive tract of humans and other animals harbor a considerable variety of microbes in large numbers.

Microorganisms capable of producing disease are known as pathogens. Most of these pathogens are parasites and live on or within another living organism, called a host, which provides shelter and nourishment. Other microorganisms thrive on decaying or dead organic material, and are known as saprophytes. Most microorganisms are nonpathogenic; that is, they do not cause disease. In fact, many of them are beneficial to both man and plant life. Certain microorganisms are responsible for producing many antibiotics, such as penicillin and streptomycin. Others are important in the production of alcoholic beverages, manufacture of vinegar, leather making, and curing cheese and tobacco, as well as in the preparation of industrial solvents.

On the basis of structural and behavioral characteristics, microorganisms are divided into five distinct kinds: . Bacteria . Rickettsiae l Viruses . Fungi l Protozoa

These broad groups provide the following agents used in biological warfare.

BACTERIA are very small single-cell organisms. They may be spherical, rod-shaped, or spiral in form. They are visible through an ordinary microscope. They are present everywhere in nature, in air, soil, water, and animal and plant bodies, both living and dead. Many types of bacteria can cause infection. The powerful toxins produced by some could be used alone for biological warfare. (Toxins are discussed later in this chapter.) Examples of diseases caused by bacteria are typhoid fever, meningitis, and tuberculosis.

RICKETTSIAE are usually smaller than bacteria, but they are still visible through an ordinary microscope. They grow only within living cells, and they are potent disease producers in man and animals. Many of them are transmitted by insect bites. Examples of diseases caused by rickettsiae are Rocky Mountain spotted fever and typhus.

VIRUSES are even smaller than rickettsiae and are not visible with the ordinary microscope. Some have been photographed through the electron microscope. Like the rickettsiae, they will grow only within the living cell. Viruses and rickettsiae are probably less well distributed than bacteria because they are more particular in their growth requirements. However, it is known that they can survive for short periods of time in the air. Examples of virus diseases are mumps, smallpox, psittacosis (parrot fever), and influenza.

FUNGI include such plants as yeasts, molds, and mildews. These organisms are known for their ability to spoil foods and fabrics. Generally speaking, diseases caused by fungi in humans are less severe than those produced by other microorganisms. They usually produce low-grade, mild, and often chronic diseases. A few fungi are capable of producing serious diseases, such as blastomycosis (a chronic infection affecting the skin or the lungs, bones, liver, spleen, and kidneys). Several diseases of plants are caused by fungi. Examples are potato blight, cotton root rot, corn smut, and wheat rust. If an attack is made on food crops, the agents used might be in this class.

PROTOZOA are single-celled, animal-like forms that occur in a variety of shapes and often have complicated life cycles. Some protozoa cause diseases in both man and animals. Problems of production and transmission limit their application in biological warfare, but it must not be assumed that these problems could not be solved. Examples of protozoa infections of man are amoebic dysentery and malaria.