There are two classes of biological agents: pathogens and toxins. Pathogens cause illness and/or death among people, plants, and animals. Biological agents may be delivered by aircraft, artillery and rockets. They may also be delivered in the form of insect vectors. Toxins, which are poisonous substances produced during the metabolism and growth of certain microorganisms and some higher plant and animal species, may as well be delivered by aircraft, artillery and rockets. Unlike nuclear, chemical and most toxin weapons, the transport and effects of pathogens are very unpredictable. Germs are effective in low concentrations and wide dispersal might take place. Due to the great breakthroughs in genetic engineering the potential is indeed great for the creation of toxins and other biological products which may be employed as weapons of mass destruction and, indeed, unsuspected substances to be employed in warfare may exists in several countries's arsenals.

PATHOGENS

Pathogens are living organisms that cause disease in man, animals or plants. They include bacteria, rickettsia (any of a group of parasitic bacteria that live in arthropods (as ticks and mites) and can cause disease if transmitted to human beings), viruses and fungi. These are commonly referred to as germs and, while estimates differ, there are about one hundred naturally occurring pathogens that could be used as biological warfare agents. Pathogens cause disease (infection) by entering the body through the lings, digestive tract, and through lesions in the skin and mucous membranes of body openings. Then, after a variable incubation period they may reproduce and overcome the body's defenses and cause illnesses. The consequences - hours may pass before the effects of pathogens become apparent - can range from incapacitation to death. Disease signs and symptoms, which generally get progressively worse in the individual, can include upper respiratory flu or cold like symptoms, vomiting, diarrhea, pneumonia, ar skin lesions (spots or rashes). Some pathogens even cause nervous system damage resulting in paralyses, convulsions, and coma prior to death. Incapacitation and death may result within days or weeks. Since several factors affect the production of disease in the individual, i.e., the body's resistance (the readiness of the immune system); virulence (severity) of the pathogen; dose or number of pathogens received by the individual; means of entry (infection through the lungs generally lessens the incubation time compared to infection through breaks in the skin - the skin itself is a protection barrier), not everyone will get ill or simultaneously display the same signs and symptoms.
Many of the pathogens have very low infective doses (some as low as 1 to 20 microorganisms) and billions of pathogen cells can be packed in 1 gram of agent. The pathogens's light weight and small size allow them to spread easily in all areas not airtight; they can sail with the wind and travel extensive downwind distances, Because of this they can be easily disseminated by aerosol. Many of the pathogens are contagious. Food and water supplies are easily contaminated.
Pathogens are living microorganisms whose span of life may be measured from hours to days, and they are sensible to environmental conditions, i.e., sunlight, humidity, wind, temperature gradient and temperature.
• Sunlight - Most biological pathogens are sensitive to the effects of solar radiation (UV, or Radiation lying in the ultraviolet range) but not all are affected by sunlight. Some natural and some man-made pathogens are encapsulated (protective coverings). Also, many bacterial an fungal spores and biologically altered pathogens can resist or extend agent life in sunlight.
•Humidity -dehydration spreads the death of the pathogen while, on the other hand, a low relative humidity is favorable for the employment of dry agents. Additional moisture in the air during high humidity actually increases the decay and death rate of pathogens in dry form. Humid condition may also promote an aggregation of particles causing them to fall out more rapidly. Moderate to heavy rainfall will tend to wash out the pathogen agent cloud from the air.
•Wind - Wind increases the dispersal of the pathogen agent cloud and it increases dehydration of the agent.
•Temperature gradient - Under lapse and neutral conditions, more atmospheric mixing occurs and this leads to lower agent concentration. A stable atmosphere or inversion results in greater agent concentration and area coverage.
•Temperature - Pathogens can be selected, treated (encapsulated), or biologically altered. Then they can be dispersed even in extreme temperature ares such as the arctic and desert regions.