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Viruses are the simplest type of microorganisms and the smallest of all living things. They are much smaller than bacteria and range in size from 0.02 to 1 micron (one micron equals 1,000 millimeters). One drop of blood can contain over 6 billion viruses! Viruses were discovered in 1898 and observed for the first time in 1939. Virus is a Latin word meaning "poisonous slime."
Every living entity is composed of cells, except for viruses, which are totally inert until they come in contact with a living host cell. Hosts can include humans, animals, plants or bacteria. The infection point created from the virus occurs at the cellular level. There must be an exact fit between the virus and the cell or the invasion of the cell cannot occur.
Viruses are unable to exist by themselves; they must find a suitable host cell in order to attach and thrive. After a virus attaches to a cell, the virus begins to reproduce itself, resulting in an acute viral infection. Viruses can also be cultivated on chorioallantoic membranes (fetal membrane) from fertilized eggs. Cultivating viruses in this manner is very expensive and time consuming. Once a virus takes hold of the cell, it can cause the host cell to die.
Photo by Robert Burke
Special protective equipment is required for personnel responding to incidents suspected of involving viral agents.
Common examples of viral agents include measles, mumps, meningitis, influenza and the common cold. Viruses that most people are familiar with today are HIV (the virus that causes AIDS) and HBV (the virus that causes hepatitis B). Neither would be very effective terrorist agents because of the long incubation period and contraction methods required of AIDS, and the low lethality of the HBV virus. These viruses are not airborne and are usually very difficult to transmit. Very specific actions have to take place to transmit the viruses. HIV and HBV are transmitted by contact with blood and body fluids. They are more commonly referred to as bloodborne pathogens.
More likely virus candidates for terrorist agents would include Venezuelan equine encephalitis (VEE), smallpox and those that cause hemorrhagic fevers. Viral hemorrhagic fevers are a group of viruses that include Ebola, Marburg, Arenaviridae, Lassa fever, Argentine and Bolivian, Congo-Crimean, Rift Valley, Hantavirus, yellow fever and dengue.
Smallpox is a lethal infection caused by the variola virus, which has at least two strains, variola major and variola minor. Cases of smallpox date back over 2,000 years, and it is the oldest known human pathogen. Conquistadors brought the disease from Spain to the New World in the 1700s and it was transmitted to the Native Americans, which wiped out over 90% of that population over the next 100 years. It is believed that Ramses V, the Egyptian pharaoh who died in 1157 BC may have had smallpox pockmarks on his mummified face.
Naturally occurring smallpox was declared eradicated from the earth in 1980 by the World Health Organization (WHO), a branch of the United Nations. The last reported case in the world occurred in Somalia in 1977. Two laboratories hold the last known stocks of variola virus, the U.S.Centers For Disease Control (CDC) in Atlanta and VECTOR in Novizbersk, Russia. Clandestine stocks could exist in other parts of the World, but are as yet unknown. If they do exist, smallpox could come into the hands of terrorists and be used as a biological weapon. The WHO's governing body has recommended destruction of the remaining stockpiles.
An effective vaccination is available for smallpox and has been used for years for the general population. Since it is primarily a children's disease, vaccinations were given during early childhood and were effective for only about 10 years. Vaccination of civilians in the United States was discontinued in the early 1980s, although some military forces vaccinated until 1989 and members may still retain some immunity. Children, who are no longer vaccinated, would be at great risk from exposure to smallpox. Monkey pox and cowpox are closely related to variola and might be genetically manipulated to produce a smallpox-like virus.