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Introduction:

The Bacillus Anthracis bacterium is commonly found in soil and infects
grazing animals such as cattle. The bacterium has the potential to cause
disease through the spores producing toxins. The zoonotic disease is called
Anthrax and is a virulent disease with the potential to be used in aerosol form
as a biological warfare.

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Characterization:

 

Bacillus anthracis is a gram-positive, rod-shaped bacterium1. It is a
non-motile, spore forming bacteria that is non-hemolytic on blood agar4.

It can be grown in aerobic and anaerobic conditions, making it a facultative
anaerobe. The bacterium is 1-1.2mm in width and 3-5mm in length4.There are two forms of cells
that Bacillus Anthracis exists in. The
vegetative cells which are inside of the host, and dormant, endospore form
cells4. The hard coating of the bacteria helps these spores survive
for long periods of time in harsh and extreme conditions. These spores are
extremely resistant to different outside factors such as UV radiation, nutrient
depletion, and extreme heat4. The ability of the spores to be protected
increases the survival of the spores for decades4.The more
infectious form of the bacteria is the spore form which can release toxins into
the body after germination2. Germination requires an abundance of
nutrients that is found in the tissue and blood of the host1.

The
Bacillus Anthracis bacterium has two
main virulence features, the poly-g-D-glutaminc acid capsule and tripartite toxin4.

The capsule is produced by the bacteria in order to mask itself from the
macrophages in order to invade the immune system4. The bacterium
produces three proteins that form the combination of toxins that causes the
dangerous effects of the disease1. Bacillus Anthracis has an A-B toxin in which the B, binding,
subunit binds to gain entrance for the A, active, subunit into the host cell6.

The protective antigen, also known as PA is the B subunit for the two different
types of active subunits. In the exotoxins, there is the Edema Factor(EF) and
the Lethal Factor(LF)6. The EF has adenylate cyclase activity which
causes the cells to secrete a large amount of fluid6. The LF has
protease activity that interferes with the immune system’s inflammatory system6.

The etiologic agent of the zoonotic disease anthrax, is a genetically monomorphic
species7. The first plasmid on the different strains is pX01 which
encodes the different toxins while the pX02 encodes the genes needed for capsule
synthesis4.

 Three of the most well known strains are the
Ames, Sterne, and Vollum4.  The
Ames strain carries both of the plasmids which makes it the most virulent
strain that’s known from the species4. The Sterne strain is less
virulent and lacks the plasmid pX02 which codes for the capsule for protection;
this strain is used for vaccine research and is from Canada4. The Vollum
strain is also used for research and lacks the pX01 which codes for the toxins4.

 

Clinical Description:

 

Bacillus
Anthracis is the agent responsible
for Anthrax which is a zoonotic disease that has been around for centuries4.

The typical symptoms of the Bacillus
anthracis usually appear between 1 day after infection to more than 2
months after. The severity of the symptoms depends on the ability to seek
treatment in a timely manner with the possibility of serious illness or death2.

The most common form of the disease is cutaneous anthrax and is also the least
dangerous. Cutaneous anthrax occurs when the spores enter the body through
broken skin and reproduce vegetative cells that release exotoxin6. Cutaneous
anthrax begins showing symptoms 2-5 days after the initial exposure10.

These symptoms typically include small itchy blisters or bumps, swelling around
the sore, and painless skin sores like an ulcer with a black center called a Eschar5.

The sores are found mostly on the hands, face, neck, or arms of the infected
individual2. These lesions tend to heal after weeks and end up
leaving scars10.

The different modes of transmission also affect the
type of symptoms that an infected patient will encounter. Another form of the
disease is inhalation anthrax. The most dangerous form and most fatal even if
treatment is provided in a timely manner8. The case-fatality is
67%-88% even when antibiotic treatment and infection typically develops in 1-7
days but can take up to 2 months after the exposure to appear2. This
form of anthrax is at risk of becoming a biological weapon because it causes
the most harm and would be easier to infect a larger group of people if made into
an aerosol. Inhalation anthrax, also known as woolsorters’ disease, occurs when
the Bacillus Anthracis produces
endospores and these spores are inhaled; attaching to the lung tissue and begin
germination8. The germination process destroys the lung tissue,
eventually entering the blood system and traveling to other vital organs8.

One complication that can arise from all forms but especially inhalation is the
development of anthrax meningitis; this factor also affects the type of antibiotics
and antitoxin prescribed2. For inhalation anthrax, some symptoms
include common flu-like symptoms such as fever, shortness of breath, headache,
confusion/ dizziness, and vomiting2. As the disease progresses, life
threatening symptoms include septic shock, breathing difficulties, and
meningitis- inflammation of the brain and spinal cords8.

The third form of the disease is gastrointestinal
anthrax which is obtained from ingesting uncooked meat that is infected with
spores from cattle and other herbivore animals. Typically, symptoms appear 1-7
days after the exposure. Gastrointestinal symptoms include sore throat, bloody
vomiting, stomach pain, severe, bloody diarrhea, swelling of the abdomen,
fainting, and red eyes2. Once inside the body, the spores can reach
the blood stream, making the mortality rate around 50%6. Lastly, the
more recent form is injection anthrax, which is only found in Europe and
associated with heroin drug users2. Injection of anthrax can cause
fever, groups of small blisters from the injection, swelling around the sore,
and abscesses that are deep under the skin near and around the injection site2.

Cutaneous and injection anthrax display similar symptoms but the injection
anthrax can be more dangerous since it spreads faster and it more difficult to
treat2. 

There
are a variety of treatments for the anthrax disease depending on the type of
illness. The first for cutaneous anthrax includes a skin testing from a fluid
sample of a lesion or small tissue sample8. A blood sample will also
be taken and tested in a special lab8. After the identification of
anthrax, the patient begins a 60-day antibiotic course using ciprofloxacin,
etc.8. When a person is suspected of being exposed to the spores,
they are put on a post- exposure prophylaxis before symptoms are even shown in
order to prevent the progression of disease2. The sooner the
infected person receives medical treatment, the increased chance of a better
recovery9. The spread of activated spores throughout the body is
responsible for the produced toxins and poisons that cause illness9.

Once the toxins have spread throughout the body; the only treatment is an
antitoxin9. While the spores cause great harm to the body,
especially if left untreated, it is not contagious, meaning it can’t be passed
from person to person contact2.

The
infectious dose for inhalation anthrax is very high due to the clearing of
microbes from the various mechanisms of respiratory deposition. The average
infective dose is estimated to be between 8,000-50,000 spores6. From
current search by the Department of defense, in order to make an aerosol
capable of causing inhalation anthrax, 2,500-55,000 spores are needed for the
lethal dose6. Portals of entry include the respiratory,
gastrointestinal tracts, mucous membranes, and the skin.

 

Epidemiology and transmission:

 

The
bacteria were first made known through the work from Robert Koch who discovered
the spores and benefits that are provided to the bacteria in survival3.

He was able to grow and isolate a pure culture of the bacteria and then
proceeded to inject it into an animal3. Through his research, he
developed the research that described the relationship between the anthrax
disease and bacillus anthracis
bacterium. This research method became known as Koch’s postulates3.

After
studying the research of Koch, Louis Pasteur worked to develop a vaccine from
his own research of injecting the vaccine and then exposing the animals to the
bacterium and recording the results3. The effects of the vaccine
helped lower the rate of infection in United States, specifically the
vaccination of animals to prevent transmission to humans. After developing a
vaccine for animals, the 1950s saw the first human vaccine that created 92.5% effective
rate in preventing cutaneous anthrax3. This vaccine was then
replaced with the current one that is given to military personal from a limited
supply3. A majority of the cases of anthrax has come from people who
are handling animal skins such as drum makers. The ability to spread the
bacillus spores through inhalation has created the potential to become a
biological weapon. In a recent attack, 2001, letters were sent to U.S.

Senators’ offices and media agencies that contained Bacillus Anthracis spores3. The route of transmission, inhalation,
allowed it to spread before being identified, a total of 22 people got sick
from the bacteria and 43 people tested positive from being exposed to the
spores3. The Ames strain of the spores was used and it highlighted
the ability of the pathogen to be used as a biological weapon1. The
British in the 1940s worked to develop a type of bomb that could release an
aerosol of Bacillus Anthracis spores
and they tested it on islands near Scotland1. They also worked to
produce cattle cakes that were infected with the spores in order to decrease
the meat supply in Germany during the war1.

The
bacterium and the disease it causes are more common in larger, warmer
agricultural areas such as Africa, southern Asia, southern Europe, and Central
America2. Other outbreaks occur sporadically in other parts of the
world with only a few in the last couple decades in the United States. Since
the 1960’s in the United States, there have been less than 10 cases of anthrax
reported each year, with 95% of them being the cutaneous form and the other 5%
being inhalation6. The majority of cases are naturally causing from
agricultural workers and a couple from laboratory infections. In previous
research, strains have been isolated from dead animals after reports of them
consuming other infected animals6. The prevalence in the United
States is extremely small, only limited to periodic outbreaks in areas of
cattle6. People who work in these areas and agricultural workers are
at an increased risk of coming in contact with the bacteria through
occupational exposure2. The risk of contracting the bacteria and
develop the disease also increases when contacting products from infected
animals2. 

The
main modes of transmission revolve around contact with infected animals or
products. Exposures such as contact with infected tissues of dead animals,
consumption of contaminated uncooked meat, contact with hides, or wool from
infected animals, and consumption of illegal drugs that have been contaminated
with the bacterium increase an individual’s risk of becoming infected with the
pathogen in one of the four different forms6. The main reservoirs of
the bacterium are farm and herbivorous animals. Some examples include cattle,
deer, sheep, and even goats. The main hosts include humans and mammals7.

 

 

Environmental:

 

The bacterium are normally found in the soil, living
in inactive spore forms4. The inactive form lives in the ground
undisturbed but regularly infects wild animals after ingestion of the spores.

The spores can be transported by different herbivores and domestic farm animals
such as cattle, goats, and deer4. In areas of common infection, animals
have regular vaccination to prevent outbreaks and there is an increased risk of
transmission between the people that encounter these animals along with the
skins, mead, and bones of the animals4. In order for the cells to
germinate without a host, it needs optimal conditions such as alkaline pH, high
organic and moisture levels in addition to warmer tmeperatures4.

 Different factors can enhance the density of
spores in a particular area. Some factors include increased rainfall, and
warmer temperatures. Increased rainfall after a drought in particular increases
the movement of the bacteria and can deposit the Bacillus Anthracis spores into a new area such as a pasture for
cattle or sheep. Vultures are also known to carry the spores after harvesting
on an infected carcass and help spread the endospores to other parts of the
world. The spores can live in the soil for decades and once they have become established
in an area, its almost impossible to remove them1. The bacterium
have become resistant to different types of disinfectants which increases the
risk of coming in contact with a herbivorous animal or occupational worker. The
bacteria usually live in the endospore form when exposed to different
environmental elements until they find a host that provided them with optimal
conditions. A temperature between 8 and 45 degrees Celsius, pH of 5-9,
increased humidity and adequate nutrients will begin the germination process of
the spores6. There has been increasing amounts of research regarding
the survival of anthrax spore in the permafrost in Artic regions from centuries
ago as the increase in climate change thaws the regions, unveiling new possible
outbreaks.

            The main preventative measure is a vaccine that is
not available to the public. The vaccine is given to military personnel in the
United States only with some exceptions for medical officials in the time of an
anthrax emergency6. There is a pre-exposure vaccination that is
recommended for agricultural workers with risk of coming in contact with
contaminated animals. The vaccination is also recommended for workers in
laboratories that are concentrating on the strains in a BSL 2 or higher lab,
and veterinarians that are at a high risk of being infected through
occupational exposures in various countries6.

If
there was a health hazard bioterrorist threat in the form of inhalation
anthrax, the Center of Disease Control has plans of action to isolate the
infected and prevent additional infections. The use of monitoring systems
throughout the United States would be one of the first methods of detecting the
spores after the release2. The other method of surveillance would be
the reporting by doctors when patients start exhibiting symptoms and lab
testing is ordered. The response would be to send the sample through the
Laboratory Response network and educating other health care professionals on
the issue along with the general public2. Once confirmed, medicine
and additional supplies from the Strategic National Stockpile would be
dispersed in the designated locations2. These preventative steps
would prevent further infections from the virulent bacteria and protect the at
risk populations.

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