Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Smallpox

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from people ill with smallpox (e.g., fluid or pus from the

papules) was scratched into the skin of those who had never

had the illness, in an attempt to produce a mild reaction and its

accompanying protective effect. These efforts often resulted in

full-fledged smallpox, and sometimes served only to effec-

tively spread the infection throughout the community. In

Colonial America, such crude vaccinations against smallpox

were outlawed because of the dangers.

In 1798, Edward Jenner(1749–1823) published a paper

in which he discussed an important observation that milk-

maids who contracted a mild infection of the hands (caused by

vaccinia virus, a relative of variola) appeared to be immune to

smallpox. He created an immunizationagainst smallpox that

used the pus material found in the lesions of cowpoxinfection.

Jenner’s paper, although severely criticized at first, later led to

much work in the area of vaccinations. Vaccination using

Jenner’s method proved instrumental in decreasing the num-

ber of smallpox deaths.

Smallpox is dangerous only to human beings. Animals

and insects can neither be infected by smallpox, nor carry the

virus in any form. Humans also cannot carry the virus unless

they are symptomatic. These important facts entered into the

decision by the WHO to attempt worldwide eradication of the

smallpox virus. The methods used in the WHO eradication

program were simple and included the careful surveillance of

all smallpox infections worldwide to allow for quick diagno-

sis and immediate quarantine of patients. It also included the

immediate vaccination of all contacts of any patient diagnosed

with smallpox infection. The WHO program was extremely

successful, and the virus was declared eradicated worldwide in

May of 1980. Two laboratories (in Atlanta, Georgia and in

Koltsovo, Russia) retain samples of the smallpox virus,

because some level of concern exists that another poxvirus

could mutate (undergo genetic changes) and cause human

infection. Other areas of concern include the possibility of

smallpox virus being utilized in a situation of biological war-

fare, or the remote chance that the smallpox virus could some-

how escape from the laboratories where it is being stored. For

these reasons, large quantities of vaccineare stored in differ-

ent countries around the world, so that response to any future

threat by the smallpox virus can be prompt.

See alsoSmallpox, eradication, storage, and potential use as a

bacteriological weapon; Vaccine

SMALLPOX: ERADICATION, STORAGE,

AND POTENTIAL USE AS A BACTERIO-

LOGICAL WEAPONSmallpox, eradication, storage and potential use as a bacteriological weapon

Historically, smallpoxwas one of the most feared diseases in

the ancient world. After an extensive and successful eradica-

tion program, the World Health Organization(WHO) certified

the global eradication of smallpox infection in 1980. There has

not been a single reported case of smallpox infection in over 20

years. However, smallpox was once a deadly disease with the

power to decimate populations. Successful efforts to prevent

the spread of smallpox through vaccinationchanged the course

of Western medicine and indeed, the history of smallpox is a

fascinating testament to the effect of health and disease on the

development of modern civilization. Today it is difficult to

imagine the devastating effects of the disease on the human

population. In 1981, smallpox was removed from the WHO list

of diseases covered under the International Health Regulations,

which detail notification requirements and measures that

should be taken to contain an outbreak. The last reported case

of smallpox occurred in Somalia in 1977, and on May 8, 1980,

the WHO declared the global eradication of smallpox. This

meant that smallpox vaccination was no longer required and

the WHO indicated that only “investigators at special risk”

should have the vaccine. It was also decided that seed lots of

vaccinia virus would be maintained as well as stocks of 200

million doses of prepared vaccine in case of an accidental out-

break. There is a 30% case-fatality rate associated with small-

pox infections among unvaccinated individuals and routine

vaccinations have now not been performed in the United States

in over 25 years. The fact that stocks of smallpox still exist

means that an accidental or deliberate release of the virus could

occur. Smallpox, if used as a biological weapon, clearly pres-

ents a threat to both civilian and military populations. Thus,

although there is little risk of naturally occurring smallpox

infections at this time, there is a significant potential for a

smallpox epidemic of manmade origin.

The concept of using the variola (smallpox) virus in

warfare is an old one. During the French and Indian Wars

(1754–1767), British colonial commanders distributed blan-

kets that were used by smallpox victims in order to initiate an

epidemic among Native Americans. The mortality rate associ-

ated with these outbreaks was as high as 50% in certain tribes.

More recently, in the years leading up to World War II, the

Japanese military explored smallpox weaponization during

operations of Unit 731 in Mongolia and China.

There are a number of characteristics that make the var-

iola virus an excellent candidate for use as a biological

weapon. An aerosol suspension of variola can spread widely

and have a very low infectious dosage. In general, the dissem-

ination of a pathogen by aerosol droplets is the preferred

deployment method for biological weapons. Smallpox is

highly contagious and is spread through droplet inhalation or

ingestion. As there are no civilian or military smallpox vacci-

nation requirements at this time, a large susceptible population

is at risk from the infection. The incubation period in naturally

occurring cases averages seven to 14 days. However, the

period could be shortened to three to seven days, especially in

the cases of aerosol application. People who have contracted

the disease are contagious during the late stages of the incu-

bation period, even though they remain asymptomatic. Thus,

transmission of the disease can occur as early as two days after

exposure to the virus. Depending on the climate, corpses of

smallpox victims remain infectious for days to months. The

duration of the disease is long and coupled with the complex

isolation and protection requirements of smallpox treatment,

each infected person would require the efforts of several med-

ical support personnel.

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