Scythian archers in 400 BC and Hannibal in 190 BC were probably the first to "weaponize" biological agents. The former did it by dipping their arrowheads in feces or decaying cadavers; the latter, by launching pottery filled with poisonous snakes onto the ships of King Eumenes during the Second Macedonian War. Plague-infected cadavers were hurled into the fortifications of adversaries during medieval battles and during the famous Mongol siege of the Ukrainian city of Kaffa (now Feodosiya) in 1347.And consider the horrible Dr. Ishii:
Later, the development of the trebuchet, an enhanced catapult, made it possible to accurately launch several-hundred-pound loads of manure or large piles of bodies that previously had been too heavy. Although some authors believe cadavers were not competent plague vectors, the prevailing scientific establishment of those times lacked the epidemiologic sophistication to realize this. Biological projectiles had some strategic value--if only psychological--because their use persisted into the 20th century during the Russian Revolution, various European conflicts, and the South African Boer wars.
Shiro Ishii, a Japanese Army physician who rose to the rank of general, epitomized physician involvement in the biological war effort. Ishii dreamt of "doctors in combat alongside the glorious infantry." "Alongside" implied offensively using biological agents, not caring for the wounded. Dr Ishii is reported to have offered chocolates filled with anthrax bacteria to children in the Chinese town of Nanking (Nanjing).... Authors credit Dr Ishii with having launched perhaps the most gruesome series of biological weapon experiments in history.
As many as 10,000 prisoners died as a result of having been fed, sprayed, injected, or bombed with a long list of biological and chemical agents, including but not limited to plague, glanders, anthrax, dengue, cholera, and tularemia. Prisoners were given seawater intravenously or horse blood in plasma exchange replacements or deliberately frozen to death to ascertain the effect of temperature on the various pathogens. To determine the effects of barotrauma, they were pressurized until, as one eyewitness put it, "their eyes ruptured and bled." At specifically designated research facilities under Ishii's purview, no prisoners were allowed to survive. If they survived the initial series of experiments, they were then "sacrificed" to determine the progress of the iatrogenesis.
Plague fascinated Ishii. He believed it held great strategic potential and so masterminded the flea bomb, a porcelain structure filled with plague-infected fleas and oxygen. Oxygen sustained the fleas during high-altitude releases, whereas porcelain required less heat and force to shatter during detonation, allowing more fleas to survive. The brittleness of porcelain and a secondary charge ensured that the shell turned to dust, leaving no physical evidence of spent munitions. About 15 million fleas were released per attack. Previously classified documents revealed that at least 11 Chinese cities were attacked with plague, anthrax, and paratyphoid.
From 1940 to 1942, as many as 700 Chinese civilians died because of direct attacks. More than 120 deaths resulted from the aerial dissemination of plague-infected fleas over the cities of Ch'u-hsien (Qu Xian) and Ning-po (Ning-hsien). Because of the indiscriminate nature of biological weapons and the limited experience militaries had in using such weapons, aggressors occasionally succumbed to the diseases that they were trying to inflict on their enemy. During a Japanese assault on the Chinese city of Ch'ang-te in 1941, Japanese forces incurred 10,000 casualties and 1,700 deaths as a result of biological agents.
ADDED: I've inserted some paragraphs into the text above. And let me connect those historical tales to the recent news that about al Qaeda and the plague.