Smallpox lecture.docx

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17 Mar 2012
Smallpox lecture
Disease origins
Old world disease and it’s an indiscriminate disease and doesn’t discriminate against age,
gender , sex, etc. anybody is equally susceptible to getting smallpox, a lot of people have the
tendency to get smallpox
Humans acquired this disease from other forms of pox like diseases in different animals and this
is how it crossed the species barrier
10,000 BC first agricultural settlements in NE Africa and spread to India by means of Ancient
Egyptian merchants.
Earliest evidence on Egyptian mummies (1570-1805 BC) Pharaoh Ramses V (died 1156 BC)
Described in 1122 BC in China and is mentioned in ancient texts of India
Known in Greece and Rome and wasn’t a major threat until 180 AD
During the plague of antoinine was believed that smallpox and malaria both contributed to the
decline of the Roman Empire
Introduced in Europe in the fifth century and was a frequent epidemic during the Middle Ages.
16th century became a serious disease in England and Europe.
There are pockmarks (cavities that are left over from the disease) this is evident in the
mummified head in Ramses V.
Effects of Smallpox
- Plague of antonine resulted in the decline of the Roman Empire in 1008 and started in
Mesopotamia when returning soldiers brought it back to Italy
- New world in the 16th century, introduced by the Spanish and Portuguese and lead to the
decimation of the population. Fall of the empires of the Aztecs and the Incas.
- Contributed to the settlement of the N America by French and English (1967) . In the eastern
coast of North America the disease was introduced by early settlers and declined native
population so it contributed to the settlement of North America by French and English, and
made the Indians a lot weaker to resist colonization.
- Smallpox was believed to be the first incidence of biological warfare.
- Commander of the British forces of North America suggested that the deliberate use of smallpox
to demolish the native population. They purposely infected blankets and gave it to the natives
and set up an epidemic along the Indians, and this was done to win the war and to gain control
of the den.
- Slave trade, bringing African people to contribute to the dwindling labour force. These are the
different elements involved in the spread of smallpox.
- Virus: Genus: Orthopoxvirus family Poxviridae. It has 200 genes that form this virus.
- Common name (variola virus)
- Variola major (more virulent) with a mortality of about 30 % , and variola minor (less virulent)
2% mortality rate.
- Other orthopox virus genus also include the monkeypox is virtually indistinguishable from
smallpox but slightly less , cowpox, camelpox, chickenpox, and ectrmedia (mousepox) viruses.
- Variola minor- mortality rate is less than 2% in unvaccinated persons
- Mortality rate for Variola major 3% in vaccinated individuals and 30-50% in unvaccinated
- Tends to be much higher in naive populations.
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- Hemorrhagic smallpox is known as black pox.
- Malignant and hemorrhagic forms of Variola major and occurs in approximately 5-10% of
infected people. Those that are exposed and have an infection due to Variola major may
develop the serious hemorrhagic form
- Almost always fatal, mortality rate of 95%, mortality is related to virulence and vaccination as
- Smallpox must be continuously transmitted from human and human in order to survive.
- Humans tend to be a short term carrier model and they may be able to transmit this disease for
a small period of time
- Smallpox doesn’t exist in animal reservoirs. There are other related orthopox viruses which are
different and manifest differently.
- Direct contact: inhalation of aerosols or contaminated formites. It multiplies in the mucus
membrane of the mouth and nose and moves to the lymph nodes and then to internal organs,
there it re-enters the bloodstream
- Eventually the virus multiplies and then it re-enters the bloodstream.
- Infectious virus remains present in oronasal secretions and in skin scabs
- If a person sneezes or residue from oronosal cavity a person can get infected if that contact
- Potential for long- distance aerosol spread is controversial.
- Transmission on formites possible for a short period of time.
- Virus only remains viable for up to 2 days outside human host.
Clinical Manifestation
- Acute disease, it can lead to death or some form of immunity
- Acute onset- fever, malaise, rigors, vomiting, headache, backache and occasionally delirium
- 2-3 days after the symptoms occur skin lesions appear on the body as well.
- Lesions tend to be very common on the face and extremities
- 8-14 days after symptoms appear; the pustules develop scabs and heal.
- The pustules dry up and scabs form, the dry skin falls off the body , and this also affects the
elasticity of the skin.
- Can lead to skin scarring.
- Infectious a day prior, to the appearance of the rash, and until the time the scabs have
- There may be complications from secondary infections, and it could be that other infections
occur as well, and it may also lead to the other forms such as the Variola major
- Pustules image: they become more severe, and more clustered pustules, by the third day,
measles form something similar, and as they become more severe and they convulge and
cluster around.
- They are mostly on the face and extremities, the pustules begin to touch one another, and they
are merging are into a confluent sheet. By the thirteenth day, you see some sign of the pustule
drying out, and there is some damage to the skin drying out.
- People who had smallpox were given a smallpox recognition card, it lead to a third of all the
blindness that occurred
- Spread of the disease spread to face and the extremeties, common on the face, palms and feet,
- Rnot value is from 5-10 and it depends on the virulence of the virus for epidemic smallpox.
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