Smallpox
Submitted by Michael G. Holland, MD, FACMT, FACOEM,
FACEP
What is it?
Smallpox
is a viral infection that is highly contagious,
and historically has been associated with
widespread epidemics among susceptible
populations. It is one of the pestilent diseases
that have been feared by mankind since antiquity.
The fatality rate is 30% or higher in persons with
a normal immune system, and survivors often are
permanently disfigured due to extensive scarring.
Case fatality rates would be much higher in people
with weakened immune systems (ie, those with HIV,
cancer, chemotherapy).
What are the symptoms?
Smallpox
has an incubation period of about 12-14 days from
the time of exposure to the onset of symptoms. The
initial stage of the disease, the prodrome,
consists of a high fever, severe body aches,
headache and backache, as well as a generalized
ill feeling that usually confines victims to bed.
In a few days a characteristic rash appears in the
mouth and throat, that quickly spreads to the face
and arms, and then the legs and trunk. Initially
the rash is maculopapular (red, raised bumps) that
in 1-2 days becomes small, clear, fluid-filled
blister-like lesions (vesicles). The fluid in the
lesions eventually becomes cloudy (pustular), and
then after about 8 or 9 days of the rash, the
lesions become crusted over and scabs form. The
scabs eventually separate, and pitted scars
remain. A person is contagious from the onset of
the rash until all lesions have scabbed over, but
especially contagious for the first 7-10 days of
the rash. Rarely, exposure to scabs that have
fallen off can cause infection, as evidenced by
the fact that British soldiers gave blankets from
smallpox patients to American Indians during the
French and Indian War (see below).
Are
there any common diseases that can be mistaken for
smallpox?
The
rash has some characteristics that are very
similar to chickenpox, and indeed prior to
eradication of the disease, cases of chicken pox
were misdiagnosed as Smallpox. The rash is
distinguished from chicken pox by the fact that
all lesions tend to be at the same stage (i.e.,
vesicular, pustular or scabbed) at the same time;
whereas in chicken pox, the rash comes in various
“crops”, so that the same person will have
lesions in all three stages widely distributed.
Also, the smallpox rash is more prominent in the
face and extremities, and less so on the trunk
(centripetal distribution), whereas chicken pox is
more concentrated on the trunk. The severity of
the illness is also much higher in smallpox. A
much rarer disease, monkeypox, is related to
smallpox and can appear identical, but is
restricted to isolated areas in Africa, is not as
contagious, and does not carry the same morbidity
or mortality.
Who is at risk of smallpox infection?
Patients with weak immune systems, such as those with
HIV, organ transplant recipients, etc, are at risk for
severe cases and would have a higher mortality rate.
Anyone born after 1971 probably did not receive primary
immunization, and therefore would be highly susceptible to
having a full –blown case of the disease (nearly 50% of
US population). Older people with prior immunization would
have a less severe form and a lower mortality rate, but
would nonetheless be susceptible to the disease, and would
be just as contagious if they contract smallpox as those
who had never been vaccinated.
Why is smallpox so feared as a biological warfare
agent?
Smallpox is an extremely infectious disease, with
severe morbidity, and a mortality rate of at least 30%.
Since contact within 30 feet of a case will cause
infection, a biowarfare release causing only a small
number of initial infections would rapidly spread within a
few weeks to an epidemic. There is historical evidence of
its lethality as a biowarfare agent. During the French and
Indian Wars, blankets from smallpox patients were given to
native Indian populations by British soldiers, with
subsequent epidemics killing up to 50% of affected tribes.
A former Soviet Union civilian bioweapons program
director claims that the USSR had produced smallpox in
huge quantities in the 1980’s, as well as successfully
adapted them for use in missiles and bombs. Since the
Soviet breakup, funding for this program was severely cut
and security lapsed. The fear is that
investigators/scientists could have left the program with
a supply of smallpox virus and may now be working for
another.
What is the treatment of smallpox?
Treatment historically has been immunization to prevent
infection, and strict isolation of active cases and their
contacts, with rapid immunization of all exposed persons.
Vaccination within 3 days of exposure to a known case
would prevent or significantly modify the course of
disease. Vaccination within 4-7 days after exposure would
likely offer some protection
and lessen the severity of disease. In this way, the World
Health Organization was able to successfully eradicate
smallpox in 1977, which lead to cessation of virtually all
vaccination programs in 1980 (the US stopped requiring
smallpox vaccinations in 1972). There are no drugs or
antibiotics proven effective in treating smallpox
infection. Some newer antiviral agents may theoretically
help in the event of a smallpox outbreak, but these are
untested.
Doesn’t immunization (smallpox vaccination) protect
you from smallpox?
Vaccination against smallpox has been practiced for
centuries. High rates of smallpox vaccination in the USA
made this a rare disease in the twentieth century. Since
the rate of vaccine adverse reactions exceeded the natural
incidence of the disease by the 1950’s, recommendations
to stop routine vaccination appeared in the 1960’s, and
all vaccinations in the USA ceased in 1972.
Since immunity from vaccination lasts only about 10
years, the entire US population is considered susceptible
to the disease. Previously vaccinated persons would have a
much lower mortality rate if they contracted the disease,
but would nonetheless be incapacitated by the illness for
several weeks, and would be highly contagious and able to
spread the disease to others. There is some evidence that
two vaccinations would confer permanent, lifelong
immunity.
Is smallpox vaccination available?
Until recently, there were very limited supplies of
smallpox vaccine under the control of the CDC, and they
were reserved for epidemic investigators and other special
populations, and were not available to the general public.
After the events of September and October 2001,
however, the U.S. government took further actions to
improve its level of preparedness against terrorism. One
of many such measures—designed specifically to prepare
for an intentional release of the smallpox
virus—included updating and releasing a smallpox
response plan. In addition, the U.S. government ordered
production of enough smallpox vaccine to immunize the
American public in the event of a smallpox outbreak. Right
now, the U.S. government has access to enough smallpox
vaccine to effectively respond to a smallpox outbreak in
the United States.
Most states, including Pennsylvania, have published
smallpox response and vaccination plans, which are
available at the CDC and state health department websites.
These plans call for key health care workers and emergency
responders to be vaccinated, thereby assuring that
immunized personnel would be available to treat smallpox
victims in the event of a bioterrorism event, as well as
enough people available to immunize the general public to
contain an outbreak. Most of these plans are scheduled to
begin in March 2003.
How
is the
vaccination
given?
The smallpox vaccine is not given with a hypodermic
needle. It is not a shot as most people have experienced.
The vaccine is given using a bifurcated (two-pronged)
needle that is dipped into the vaccine solution. When
removed, the needle retains a droplet of the vaccine. The
needle is used to prick the skin a number of times to
cause a sore spot and one or two droplets of blood to
form. The vaccine usually is given in the upper arm.
If the vaccination is successful, a red and itchy bump
develops at the vaccine site in three or four days. In the
first week, the bump becomes a large blister, fills with
pus, and begins to drain. During the second week, the
blister begins to dry up and a scab forms. The scab falls
off in the third week, leaving a small scar. People who
are being vaccinated for the first time have a stronger
reaction than those who are being revaccinated.
Is
the smallpox vaccine safe?
The smallpox vaccine is the best protection you can get
if you are exposed to the smallpox virus. Anyone directly
exposed to smallpox, regardless of health status, would be
offered the smallpox vaccine because the risks associated
with smallpox disease (where about one third of victims
die) are far greater than those posed by the vaccine (1 in
a million die).
Since the immunization involves administering the live
vaccinia virus, there are side effects and risks
associated with the smallpox vaccine. Most people
experience normal, usually mild, reactions that include a
sore arm, fever, and body aches. However, other people
experience reactions ranging from serious to life
threatening. In the past, about 1,000 people for every 1
million people vaccinated for the first time experienced
reactions that, while not life-threatening, were serious.
These reactions included a toxic or allergic reaction at
the site of the vaccination (erythema multiforme), spread
of the vaccinia virus to other parts of the body and to
other individuals (inadvertent inoculation), and spread of
the vaccinia virus to other parts of the body through the
blood (generalized vaccinia). These types of reactions may
require medical attention.
Who is at risk of developing complications from the
smallpox vaccine?
People most likely to have serious side effects are
those who have had skin conditions such as eczema or
atopic dermatitis, even if it was in the remote past and
has now healed. Also, anyone with a weakened immune
systems, such as those who have received a transplant, are
HIV positive, are receiving treatment for cancer, or are
currently taking medications (like steroids) that suppress
the immune system. These same people are at risk of
inadvertent vaccination and complications if they come in
contact with the vaccination site of a family member who
has recently been vaccinated. In addition, pregnant women
should not get the vaccine because of the risk it poses to
the fetus. Women who are breastfeeding should not get the
vaccine. Children younger than 12 months of age also
should not get the vaccine. The Advisory Committee on
Immunization Practices (ACIP) also advises against
non-emergency use of smallpox vaccine in children younger
than 18 years of age. In addition, those allergic to the
vaccine or any of its components should not receive the
vaccine.
In the past, between 14 and 52 people out of every 1
million people vaccinated for the first time experienced
potentially life-threatening reactions to the vaccine.
Based on past experience, it is estimated that 1 or 2
people in 1 million who receive the vaccine may die as a
result. The incidence of eczema and atopic dermatitis is
now much higher than during the earlier part of the
twentieth century when we gained most of our knowledge of
vaccine complications.
Likewise, there are many more immunocompromised
individuals than in the past, so complication rates could
be higher if the vaccine is administered inappropriately. Careful screening of potential
vaccine recipients is essential to ensure that those at
increased risk do not receive the vaccine.
Where can I obtain more information about the smallpox
vaccination program?
The
PA health department website, www.health.state.pa.us
has information about the state’s vaccination plan. The
US Center for Disease Control
and Prevention (CDC) website also has a wealth of
information regarding the smallpox immunization program: http://www.bt.cdc.gov/
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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