Biological weapons

Biological and toxin weapons are either microorganisms like virus,
bacteria or fungi, or toxic substances produced by living organisms that
are produced and released deliberately to cause disease and death in
humans, animals or plants. 

Biological agents like anthrax,
botulinum toxin and plague can pose a difficult public health challenge
causing large numbers of deaths in a short amount of time. Biological
agents which are capable of secondary transmission can lead to
epidemics. An attack involving a biological agent may mimic a natural
event, which may complicate the public health assessment and response.
In case of war and conflict, high-threat pathogens laboratories can be
targeted, which might lead to serious public health consequences.

Biological
weapons form a subset of a larger class of weapons sometimes referred
to as unconventional weapons or weapons of mass destruction, which also
includes chemical, nuclear and radiological weapons. The use of
biological agents is a serious concern, and the risk of using these
agents in a terrorist attack is thought to be increasing.