Bacteriological or biological agents of warfare are living organisms (or infective material derived from them) which are intended to cause disease or death in animals, plants, or man, and which depend for their effects on their ability to multiply in the person, animal or plant attacked. Various living organisms (for example, rickettsiae, viruses and fungi), as well as bacteria, can be used as weapons. The use of epidemic warfare on a strategic scale is liable to lead to the infection of a very high proportion of the population attacked, and even if the attacking country were protected (by immunization) from some specific strain, changes to more virulent forms might overwhelm the level of immunity. The chief types of bacterial and viral agents developed or considered have included: anthrax (bacterial), which can cause death in 24 hours if lungs are attacked; brucellosis or undulant fever (bacterial), which is fatal in 5% of untreated cases; tick-borne encephalomyelitis and mosquito-borne equine encephalitis (viral), which have no effective treatment, can be fatal and can cripple the nervous systems of survivors; bubonic and pneumonic plagues (bacterial); psittacosis (viral) which can be fatal in up to 40% of cases; Rocky Mountain spotted fever (rickettsial) which can kill in 3 days; tularaemia (bacterial), for which the untreated rate of fatality is 5-8%; typhoid and cholera (bacterial) which is extremely contagious; Q-fever (rickettsial); and chikungunya and dengue fevers (viral). Smallpox is one of the deadliest epidemic viruses known, but has been exterminated in the wild; the only stocks are in high-security research establishments in the USA and Russia.
There is no admitted military experience of the use of biological agents in warfare. However, it is reported that during the 1980s, the Soviet Union used rudimentary genetic engineering to create incurable strains of Back Death (bubonic plague). This was loaded into missile warheads aimed at the USA (but never fired).
One field trial of the dissemination of biologically active agents showed that 200 kg could be distributed from a ship travelling at a distance of 260 kilometres parallel to a coastline leading to a coverage of 75,000 square kilometres. The strength of such agents is illustrated by the fact that a similar degree of poisoning could be achieved with 0.5 kilo of Salmonella culture, with 5 kilos of botulinum toxin, 7 kilos of staphylococcal enterotoxin or 50 kilos of V-nerve agent, or for comparison, with 10 tonnes of potassium cyanide.
A bacterium called Deinococcus radiodurans can survive exposure to gamma rays that exceeds by thousands the lethal human dose and cracks glass. The DNA from 100-year old spores of the bacterium recovered from Antarctica reassembled and proliferated in a nutrient bath.
In 1990 the USA was planning to introduce malumbia caterpillars, an indigenous pest of the coca plant, as part of a programme against producers of cocaine in Peru.
In Iraq, firm evidence of Saddam Hussein's interest in biological warfare was discovered by a United Nations inspection team in 1991. Iraq signed the 1972 Biological and Toxin Weapons Convention. Challenged by a UN special commission under Resolution 687 aimed at destroying Iraq's chemical, biological and long-range missile armoury, it denied having biological weapons. Yet when the inspection team arrived, the Iraqis admitted that they had in 1986 begun research in Salman Pak, involving anthrax, botulism and gas gangrene, and that this research could be used for defensive or offensive purposes. It found equipment for fermentation, production, aerosol testing and storage, but no actual weapons and no means of filling them. However, the report noted that, in addition to the evident damage caused by allied bombing, "key buildings" had been removed a short time before.
In 1950 a US Navy minesweeper sprayed a rare Serratia bacterium onto San Francisco, eventually putting 11 people in hospital and killing one. Members of the Serratia genus were once known as harmless organisms that produced a characteristic red pigment. Today, Serratia marcescens is considered a harmful human pathogen which has been known to cause urinary tract infections, wound infections, and pneumonia.
The course of an epidemic is not generally predictable and it would not be possible for a military commander to control its spread. Thus, although analogies are often drawn between the possible consequences of BW attack and the great pandemics of history, it is unlikely that any military commander in a rational state of mind would try to start an epidemic: once started (assuming that it could be started at will), it could well spread far beyond the confines of the target area, both in space and in time, and there would be little the commander could do to regulate it.