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Bio-Terror
A bioterrorism attack is the
deliberate release of viruses, bacteria, or other germs (agents) used to cause
illness or death in people, animals, or plants. These agents are typically found
in nature, but it is possible that they could be changed to increase their
ability to cause disease, make them resistant to current medicines, or to
increase their ability to be spread into the environment. Biological agents can
be spread through the air, through water, or in food. Terrorists may use
biological agents because they can be extremely difficult to detect and do not
cause illness for several hours to several days. Some bioterrorism agents, like
the smallpox virus, can be spread from person to person and some, like anthrax,
can not.
Bioterrorism Agent Categories
Bioterrorism agents can be
separated into three categories, depending on how easily they can be spread and
the severity of illness or death they cause. Category A agents are considered
the highest risk and Category C agents are those that are considered emerging
threats for disease.
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Category A
These high-priority agents
include organisms or toxins that pose the highest risk to the public and
national security because:
- They can be easily spread
or transmitted from person to person
- They result in high death
rates and have the potential for major public health impact
- They might cause public
panic and social disruption
- They require special
action for public health preparedness.
-
Anthrax (Bacillus
anthracis)
-
Botulism
(Clostridium botulinum toxin)
-
Plague (Yersinia
pestis)
-
Smallpox(variola
major)
-
Tularemia(Francisella
tularensis)
-
Viral hemorrhagic
fevers(filoviruses [e.g., Ebola, Marburg] and arenaviruses [e.g.,
Lassa, Machupo])
-
Category B
These agents are the second
highest priority because:
- They are moderately easy
to spread
- They result in moderate
illness rates and low death rates
- They require specific
enhancements of CDC's laboratory capacity and enhanced disease
monitoring.
-
Brucellosis (Brucella
species)
-
Epsilon toxin of Clostridium
perfringens
-
Food safety threats
(e.g., Salmonella species, Escherichia coli O157:H7, Shigella)
-
Glanders (Burkholderia
mallei)
-
Melioidosis(Burkholderia
pseudomallei)
-
Psittacosis (Chlamydia
psittaci)
-
Q fever (Coxiella
burnetii)
-
Ricin toxin from Ricinus
communis (castor beans)
-
Staphylococcal
enterotoxin B
-
Typhus fever (Rickettsia
prowazekii)
-
Viral encephalitis (alphaviruses
[e.g., Venezuelan equine encephalitis, eastern equine encephalitis,
western equine encephalitis])
-
Water safety threats
(e.g., Vibrio cholerae, Cryptosporidium parvum)
-
Category C
These third highest priority
agents include emerging pathogens that could be engineered for mass spread
in the future because:
- They are easily available
- They are easily produced
and spread
- They have potential for
high morbidity and mortality rates and major health impact.
-
Emerging infectious
diseases such as Nipah virus and hantavirus
Scientists are most concerned
about smallpox and anthrax. Both are bacteria that can spread through the air in
a powder and cause swift, deadly diseases. Smallpox could be even more lethal
because it's easily spread from one person to another. Also worrisome are the
bubonic plague, botulism, tularemia and ebola.
There is no real preventative
measures other than stopping the initial introduction of the bio-terror
substance. It would not be apparent that a biological agent has been
dispersed until people begin falling ill several days later. For most biological
agents, the initial symptoms would resemble a flu-like malaise.
Anthrax
Anthrax
is an acute infectious disease caused by the spore-forming bacterium Bacillus
anthracis. Anthrax most commonly occurs in wild and domestic lower
vertebrates (cattle, sheep, goats, camels, antelopes, and other herbivores), but
it can also occur in humans when they are exposed to infected animals or tissue
from infected animals
Given appropriate weather and
wind conditions, 50 kilograms of anthrax released from an aircraft along a 2
kilometer line could create a lethal cloud of anthrax spores that would extend
beyond 20 kilometers downwind. The aerosol cloud would be colorless, odorless
and invisible following its release. Given the small size of the spores, people
indoors would receive the same amount of exposure as people on the street.
There are currently no
atmospheric warning systems to detect an aerosol cloud of anthrax spores. The
first sign of a bioterrorist attack would most likely be patients presenting
with symptoms of inhalation anthrax.
Symptoms of disease
vary depending on how the disease was contracted, but symptoms usually occur
within 7 days.
Cutaneous:
Most (about 95%) anthrax infections occur when the bacterium enters a cut or
abrasion on the skin, such as when handling contaminated wool, hides, leather or
hair products (especially goat hair) of infected animals. Skin infection begins
as a raised itchy bump that resembles an insect bite but within 1-2 days
develops into a vesicle and then a painless ulcer, usually 1-3 cm in diameter,
with a characteristic black necrotic (dying) area in the center. Lymph glands in
the adjacent area may swell. About 20% of untreated cases of cutaneous anthrax
will result in death. Deaths are rare with appropriate antimicrobial therapy.
Inhalation:
Initial symptoms may resemble a common cold. After several days, the symptoms
may progress to severe breathing problems and shock. Inhalation anthrax is
usually fatal.
Intestinal:
The intestinal disease form of anthrax may follow the consumption of
contaminated meat and is characterized by an acute inflammation of the
intestinal tract. Initial signs of nausea, loss of appetite, vomiting, fever are
followed by abdominal pain, vomiting of blood, and severe diarrhea. Intestinal
anthrax results in death in 25% to 60% of cases.
A 1970 analysis by the World
Health Organization concluded that the release of aerosolized anthrax upwind of
a population of 5,000,000 could lead to an estimated 250,000 casualties, of whom
as many as 100,000 could be expected to die.
A later analysis, by the Office
of Technology Assessment of the U.S. Congress, estimated that 130,000 to 3
million deaths could occur following the release of 100 kilograms of aerosolized
anthrax over Washington D.C., making such an attack as lethal as a hydrogen
bomb.
Vaccine supplies are limited and
U.S. production capacity is modest. There is no vaccine available for civilian
use. Incubation (the time from exposure to symptoms) 2-60 days.
Smallpox
The disease is at
least 3000 years old. Smallpox is caused by the virus variola. Smallpox is a
poxvirus, characterized by a brick-shape, containing linear double stranded DNA,
a disk-shaped core within a double membrane, and a lipoprotein envelope. The
virion contains a DNA-dependant RNA polymerase. This enzyme is required because
the virus replicates in the cytoplasm and does not have access to the cellular
RNA polymerase, which is located in the nucleus.
An aerosol release
of smallpox virus would disseminate readily given its considerable stability in
aerosol form and epidemiological evidence suggesting the infectious dose is very
small. Even as few as 50-100 cases would likely generate widespread concern or
panic and a need to invoke large-scale, perhaps national emergency control
measures.
Some of the reasons
bioterrorists prefer smallpox are its high fatality rates – it kills some 30
percent of its victims – and its long incubation periods – up to 14 days.
Symptoms: There may be no symptoms for first two weeks after infection. About
two weeks after infection, the victim may develop high fever, malaise, headache
and backache. Two days after symptoms start, a rash develops, spreading all over
the body.
Several factors fuel the concern: the disease has historically been
feared as one of the most serious of all pestilential diseases; it is physically
disfiguring; it bears a 30 percent case-fatality rate; there is no treatment; it
is communicable from person to person; and no one in the U.S. has been
vaccinated during the past 25 years.
The United States
currently has a limited supply of smallpox vaccine (approximately 15 million
doses) available for emergency use, if needed. New methods for the production of
additional smallpox vaccine in large quantities are being explored. At this
time, no preventive vaccination program is planned.
Ebola
Ebola hemorrhagic fever (Ebola HF)
is a severe, often-fatal disease in humans and nonhuman primates (monkeys and
chimpanzees) that has appeared sporadically since its initial recognition in
1976.
The disease is caused by
infection with Ebola virus, named after a river in the Democratic Republic of
the Congo (formerly Zaire) in Africa, where it was first recognized. The virus
is one of two members of a family of RNA viruses called the Filoviridae. Three
of the four species of Ebola virus identified so far have caused disease in
humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The fourth,
Ebola-Reston, has caused disease in nonhuman primates, but not in humans.
Infection with Ebola virus in
humans is incidental -- humans do not "carry" the virus. Because the
natural reservoir of the virus is unknown, the manner in which the virus first
appears in a human at the start of an outbreak has not been determined. However,
researchers have hypothesized that the first patient becomes infected through
contact with an infected animal.
After the first case-patient in
an outbreak setting (often called the index case) is infected, humans can
transmit the virus in several ways. People can be exposed to Ebola virus from
direct contact with the blood and/or secretions of an infected person. This is
why the virus has often been spread through the families and friends of infected
persons: in the course of feeding, holding, or otherwise caring for them, family
members and friends would come into close contact with such secretions. People
can also be exposed to Ebola virus through contact with objects, such as
needles, that have been contaminated with infected.
Plague
Plague, caused by a bacterium
called Yersinia pestis, is transmitted from rodent to rodent by infected
fleas.
Plague is characterized by
periodic disease outbreaks in rodent populations, some of which have a high
death rate. During these outbreaks, hungry infected fleas that have lost their
normal hosts seek other sources of blood, thus increasing the increased risk to
humans and other animals frequenting the area.
Plague is transmitted from animal
to animal and from animal to human by the bites of infective fleas. Less
frequently, the organism enters through a break in the skin by direct contact
with tissue or body fluids of a plague-infected animal, for instance, in the
process of skinning a rabbit or other animal. Plague is also transmitted by
inhaling infected droplets expelled by coughing, by a person or animal,
especially domestic cats, with pneumonic plague. Transmission of plague from
person to person is uncommon and has not been observed in the United States
since 1924 but does occur as an important factor in plague epidemics in some
developing countries.
Epidemics of plague in humans
usually involve house rats and their fleas. Rat-borne epidemics continue to
occur in some developing countries, particularly in rural areas. The last
rat-borne epidemic in the United States occurred in Los Angeles in 1924-25.
Since then, all human plague cases in the U.S. have been sporadic cases acquired
from wild rodents or their fleas or from direct contact with plague-infected
animals.
Rock squirrels and their fleas
are the most frequent sources of human infection in the southwestern states. For
the Pacific states, the California ground squirrel and its fleas are the most
common source. Many other rodent species, for instance, prairie dogs, wood rats,
chipmunks, and other ground squirrels and their fleas, suffer plague outbreaks
and some of these occasionally serve as sources of human infection. Deer mice
and voles are thought to maintain the disease in animal populations but are less
important as sources of human infection. Other less frequent sources of
infection include wild rabbits, and wild carnivores that pick up their
infections from wild rodent outbreaks. Domestic cats (and sometimes dogs) are
readily infected by fleas or from eating infected wild rodents. Cats may serve
as a source of infection to persons exposed to them. Pets may also bring
plague-infected fleas into the home.
Botulism
Botulism is a rare but serious
paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium
botulinum. There are three main kinds of botulism. Foodborne botulism is
caused by eating foods that contain the botulism toxin. Wound botulism is caused
by toxin produced from a wound infected with Clostridium botulinum.
Infant botulism is caused by consuming the spores of the botulinum bacteria,
which then grow in the intestines and release toxin. All forms of botulism can
be fatal and are considered medical emergencies. Foodborne botulism can be
especially dangerous because many people can be poisoned by eating a
contaminated food.
The classic symptoms of botulism
include double vision, blurred vision, drooping eyelids, slurred speech,
difficulty swallowing, dry mouth, and muscle weakness. Infants with botulism
appear lethargic, feed poorly, are constipated, and have a weak cry and poor
muscle tone. These are all symptoms of the muscle paralysis caused by the
bacterial toxin. If untreated, these symptoms may progress to cause paralysis of
the arms, legs, trunk and respiratory muscles. In foodborne botulism, symptoms
generally begin 18 to 36 hours after eating a contaminated food, but they can
occur as early as 6 hours or as late as 10 days.
Tularemia
Tularemia, a disease that can
affect both animals and humans, is caused by a bacteria, Francisella
tularemsis. Although many wild animals are infected, (hares, rabbits,
squirrels, muskrats, beavers, deer), occasionally certain domestic animals can
be infected (sheep and cats). The rabbit is the species most often involved in
disease outbreaks. The bacteria can also be found in ticks and deerflies.
Many routes of human exposure to
the tularemia bacteria are known to exist. The common routes include inoculation
of the skin or mucous membranes with blood or tissue while handling infected
animals, the bite of an infected tick, contact with fluids from infected deer
flies or ticks, or handling or eating insufficiently cooked rabbit meat. Less
common means of spread are drinking contaminated water, inhaling dust from
contaminated soil or handling contaminated pelts or paws of animals. Tularemia
is not spread from person to person.
Tularemia is usually recognized
by the presence of a skin lesion and swollen glands. Ingestion of the organism
may produce a throat infection, intestinal pain, diarrhea and vomiting.
Inhalation of the organism may produce a fever alone or combined with a
pneumonia-like illness.
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