Notes

1.Chimera Viruses
Plague, smallpox, anthrax -- the world's deadliest biological agents aren't out to get you. Any harmful properties they possess are simply byproducts of their evolution
the chimera combined elements of lion, goat and serpent into one monstrous form
Geneticists have already discovered the means to increase the lethality of such bioweapons as smallpox and anthrax by tweaking their genetic structure. By combining genes, however, scientists could theoretically create a virus that triggered two diseases at once. During the late 1980s, the Soviet Union's Chimera Project studied the feasibility of combining smallpox and Ebola into one super virus
Other potential nightmare scenarios involve strains of viruses that require certain triggers. A stealth virus would remain dormant for an extended period until triggered by predetermined stimuli. Other possible chimeric bioweapons might require two components to become effective. Imagine a strain of botulinum toxin that, when combined with the botulinum toxin antidote, only becomes more lethal. Such a biological attack would not only result in a higher mortality rate
2.Nipah Virus
Viruses adapt and evolve over time. New strains emerge and, occasionally, close contact between humans and animals allow life-threatening diseases to leap to the top of the food chain. As human populations continue to swell, the emergence of new diseases is inevitable
Nipah virus is just such a disease
Nipah virus, along with a number of other emerging pathogens, is classified as a Category C biological weapon. While no country is known to have researched its weaponization, its potential for widespread use and 50 percent mortality rate make it a bioweapon to watch for
3.Rinderpest
When Genghis Khan invaded Europe in the 13th century, he inadvertently unleashed a fearsome biological weapon in the wake of his conquest.
Rinderpest is caused by a virus closely related to measles, and it affects cattle and other ruminant animals
rinderpest-infected animals to various corners of the globe, often resulting in millions of dead cattle, along with other livestock and wild animals
While Genghis Khan wielded rinderpest as a weapon by accident, many modern countries aren't as innocent. Canada and the United States have both researched use of the virus as an anti-livestock bioweapon
4.Rice Blast
A number of bacteria, viruses and toxins pose a significant threat to human beings, but plenty of the world's biological agents prefer different prey: cultivated food crops
Several countries, especially the United States and Russia, have devoted a great deal of research to diseases and even insects that target key food crops
One such bioweapon is rice blast, a crop disease caused by the fungus Pyricularia oryzae (also known as Magnaporthe grisea). The leaves of affected plants soon develop grayish lesions composed of thousands of fungal spores. These spores quickly multiply and spread from plant to plant, sapping the plants and leading to much lower crop production. While breeding resistant plants is a good defensive measure against some crop disease, rice blast presents a problem because you wouldn't have to breed resistance to one strain of fungus, but 219 different strains.
A number of countries have pursued rice blast as a biological weapon, including the United States. By the time the U.S. dismantled its anti-crop program, it had amassed nearly a ton of the harmful fungus for a potential attack on Asia
5.Botulinum Toxin
Take a deep breath. If the air you just inhaled contained botulinum toxin, you'd have no way of knowing. In weaponized airborne form, the deadly bacteria would be completely colorless and odorless
the o­rganism's deadly toxin rounds out the list of six Category A biological weapons.
Its power, availability and limited treatability have made botulinum toxin a favorite among several countries' bioweapons programs. Luckily, effectively using such a weapon can still provide challenges
C. botulinum occurs all over the world, especially in soil and marine sediments
6.Tularemia
While tularemia only claims an overall 5 percent mortality rate, the microorganism that causes it is one of the most infectious bacteria on Earth
Francisella tularensis occurs naturally in no more than 50 organisms and is especially prevalent in rodents, rabbits and hares. Humans typically acquire the disease through contact with infected animals, infected insect bites, the consumption of contaminated foods or the inhalation of the bacteria in aerosol form.
Tularemia doesn't transfer between human hosts and can be easily treated with antibiotics or prevented with a vaccine. It does, however, spread very rapidly between animal hosts and humans or when used in aerosol form. It is this factor, not its mortality rate, that earned F. tularensis a Category A biological weapon ranking. It is especially virile in aerosol form. Due to these factors, the United States, Britain, Canada and the Soviet Union all worked to create weaponized tularemia after the close of World War II
7.Plague
the term "plague" continues to cling to another long-standing suspect and current Category A biological weapon: the Yersinia pestis bacterium
Plague exists in two main strains: bubonic and pneumonic. Bubonic plague typically spreads by bites from infected fleas, but also can be transmitted from person to person through contact with infected bodily fluids. This strain is named for the swollen glands, or buboes, around the groin, armpit and neck
Pneumonic plague is less common and spreads through the air by coughs, sneezes and face-to-face contact. Its symptoms include high fever, cough, bloody mucus and difficulty breathing.
Plague victims themselves -- both dead and alive -- have historically served as effective delivery vehicles for this biological weapon
Several countries have explored the use of plague as a bioweapon and, as the disease still occurs naturally throughout the world, copies of the bacterium are relatively easy to come by. With appropriate treatment, plague's mortality rate can dip as low as 5 percent
There is no vaccine.
8.Ebola Hemorrhagic Fever
scientists suspect the Ebola virus normally resides within a native, African animal host, but the exact origin and natural habitat of the disease remain a mystery. As such, we have only encountered the virus after it has successfully infected humans or nonhuman primates.
Once present in a host, the virus infects others through direct contact with blood or other bodily secretions
Doctors don't know why some patients are better able to recover than others. Nor do they how to treat it. And, as noted earlier, there's no Ebola vaccine. In fact, we only process a vaccine for one form of hemorrhagic fever: yellow fever.
While many medical professionals labored to better treat and prevent outbreaks of Ebola, a team of Soviet scientists set out to turn the virus into a weapon. They initially encountered difficulties cultivating Ebola in the laboratory, enjoying more success with the development of Marburg hemorrhagic fever.
While the virus normally spreads through physical contact with bodily secretions, researchers have observed it spread through the air under laboratory conditions. The possibility of a weaponized, aerosol form of the virus only further cements Ebola and related viral hemorrhagic fevers as permanent placeholders on the list of Category A agents.
9.Anthrax
its high mortality rate and environmental stability, the anthrax bacteria is also classified as a Category A biological weapon. The bacteria live in the soil, where grazing animals typically come into contact with spores while rooting around for food
People, however, may become infected with anthrax by touching the spores, inhaling them or ingesting them.
Most cases of anthrax are cutaneous, transmitted through skin contact with the spores. The most deadly form is inhalation anthrax, when the spores travel to the lungs and then the immune cells carry them to the lymph nodes
The disease isn't easy to catch under normal situations, and it can't be transmitted from person to person. Still, health workers, veterinarians and military personnel normally undergo vaccinations. The rest of us, however, remain at risk if someone were bent on another anthrax attack.
Along with the lack of widespread vaccination -- a common theme among our scary bioweapon nominees -- longevity is another point in anthrax's favor. Many harmful biological agents can only survive a short while under certain conditions. But hardy B. anthracis can sit on the shelf for 40 years or more and still pose a lethal threat.
These attributes helped to establish anthrax as a favorite among bioweapons programs throughout the world.
B. anthracis remains one of the most well-known and feared bioweapons. Numerous biological warfare programs have worked to produce anthrax over the years and while a vaccine exists, mass vaccination would only become viable if mass exposure occurred.
10.Smallpox
British forces infamously distributed smallpox-infected blankets to Native American tribes in Ottawa. The native inhabitants of the Americas were particularly susceptible to the illness since, unlike their European invaders, they hadn't encountered smallpox before and lacked any degree of immunity to it. The disease cut through the tribes like wildfire
Smallpox is caused by the variola virus. The most common form of the disease has a 30 percent mortality rate
the World Health Organization (WHO) spearheaded an effort to eradicate smallpox through mass vaccinations. As a result, 1977 marked the last naturally occurring case of smallpox. The disease was effectively eliminated from the natural world, but laboratory copies of smallpox still exist. Both Russia and the United States possess WHO-approved stores, but as smallpox played a role in several nations' bioweapons programs, it's unknown how many secret stockpiles still exist
T­­he CDC classifies smallpox as a Category A biological weapon due to its high mortality rate and the fact that it can be transmitted through the air. While a smallpox vaccine exists, typically only medical and military personnel undergo vaccination -- meaning the rest of the population is very much at risk if smallpox were unleashed as a weapon. How might the virus be released? Probably in aerosol form or even in the old-fashioned wa­y: by sending an infected individual directly into the target area.