Transcript Variola Virus - Penn State York

Variola Virus
Presented by Megan Eline
Orthopox Characteristics

Belongs to Orthopoxidae Family

Very large, brick-shaped virus.

300 X 200 nm in size.

dsDNA genome (200 kbp).

Virus particle is enveloped and contains
filamentous nucleocapsid
What is Smallpox?

A serious,
contagious, often
fatal disease
caused by the
variola virus.

2 Clinical forms:
– Variola major
– Variola minor
Pustules
Early History of Smallpox

Origin is uncertain, but believed to have
originated in Africa, which then spread to India
and China.

Smallpox reached Europe between the 5th and
7th centuries

Epidemics occurred in the North American
colonies in the 17th and 18th centuries
Epidemiology





The first recorded smallpox epidemic was in 1350
BC during the Egyptian-Hittite war.
In the London epidemic of 1857-1859, there were
14,244 deaths; in the 1863-1865 outbreak - 20,059
deaths.
Japan-1892 their records showed 165,774 cases with
29,979 deaths.
In the Philippines between 1917 and 1919, 162,503
reported cases and 71,453 deaths.
In the 20th century alone, an estimated 300 million
people died from the disease.
Smallpox gets defeated

Last known case in the United States was in
1949.

Last known naturally occurring case in the world
was in Somalia in 1977.

Except for laboratory stockpiles, the virus has
been eliminated.
Dr. Edward Jenner

Observed that farmers
who caught cowpox
never caught smallpox.

1798 he introduced
cowpox vaccination for
smallpox.

James Phipps was the
first person to receive the
vaccine and he did not
become infected.
Symptoms

Fever (101°-104°F)

Occasional vomiting

Malaise

Rashes

Head and body aches

Pustules
Transmission





Humans are the only natural hosts.
To survive, the virus must pass from
person to person.
Inhaled droplets of air or aerosols enters
through respiratory mucosal route.
Direct or prolonged face-to-face contact
required with infected person.
Bodily fluids or contaminated objects.
Replication Process
(Lytic Cycle)






Binding to cell receptors and penetration of host
cell.
Uncoating of protein coat.
Gene expression and transcription.
Genome replication (occurs in the cytoplasm).
Assembly and release of new virions.
Replication occurs in ~12 hours.
Variola Virus Replication
Infection Process

Incubation Period (7-17 days)
– No symptoms occurring.

– Virus replicates in lymph nodes.
– Not contagious.
Prodrome Period (2-4 days)
– Initial symptoms occurring.
– Virus replicates in spleen, bone marrow, &
lymph nodes.
– Sometimes contagious.

Early Rash (4 days)
– Small red spots on tongue and in mouth.
– Spots develop into sores.
– Most contagious phase!!!
– Rash appears on skin & spreads over body
within 24 hours.
– Fever develops.

Third day - raised bumps appear.

Fourth day bumps fill up with a thick,
opaque fluid.
– Fever increases and remains high until scabs
form.

Pustular Rash (5 days)
– Pustules form.
– Contagious.



Pustules and Scabs (~5 days)
–
Pustules form a crust and scab
–
By the end of second week after rash appears, most sores
are scabbed over.
–
Contagious.
Resolving Scabs (~6 days)
–
Scabs fall off and leave scars.
–
Contagious.
Scabs Resolved
– Once the last scab has fallen off, the person is no longer
contagious.
Diagnostic Tests

Routine viral cultures.

Variola PCR targets the hemagglutin gene.

Electron Microscopy.
Prognosis

Variola major fatality rate is 30%.
– Hemorrhagic & flat smallpox have >90%
fatality rate.

Variola minor fatality rate is <1%.
Preventative Measures

Smallpox vaccine provides
a high level of protection
against the disease for
about five years. Without
the vaccine, it is nearly
impossible to prevent
infection.

Contains live vaccina
virus.

Does not contain smallpox
and does not cause
smallpox.
More Preventative Measures
•Good hand hygiene.
•Isolation of suspected smallpox patients.
•Keep sites covered with gauze.
Smallpox as a Biological
Weapon

Smallpox was used as a biological weapon during the
French-Indian wars in the United States (1754-1767),
when British soldiers gave the Indians blankets that had
been used by smallpox patients.

Japan considered the use of smallpox as a biological
weapon in World War II.

Smallpox is currently contained in two high security labs
(United States and Russia).

Rated among the most dangerous of all potential
biological weapons.
Shared modes of protection against poxvirus infection by
attenuated and conventional smallpox vaccine viruses




Trying to develop a safer vaccine due to a more
immunocompromised population of individuals (ie.
AIDS, chemotherapy for cancer, organ transplant).
Used modified vaccinia Ankara and NYVAC
replication-deficient vaccinia viruses
If vaccine is present at time of virulent strain, then the
antibody is sufficient to protect the host and T cells are
not necessary.
If no prior immunity, then T cells and antibodies must
both respond. T cells are more efficient & clear infection
better than antibodies.
QUIZ!!!!

When is smallpox the most contagious?

Name 3 symtoms of smallpox.
T or F Humans are not the only natural
hosts of the variola virus.
When was the last known case of smallpox
in the United States?


Resources






www.cdc.gov.
The New Mexico Epidemiology Report,Volume
2003, Number 4.
Ward, Brian., Epidemic. New York, Dorling
Kindersley Publishing, Inc., 2000
Prescott, Lansing M., John P. Harley, Donald A.
Klein, Microbiology, New York, McGraw-Hill
2002
http://dermatology.about.com/cs/smallpox/a/smal
lpoxhx.htm
www.aafp.org/afp/ 20030901/889.html
Resources Continued






http://www.whale.to/v/smallpox1.html
http://www.cnn.com/HEALTH/library/DS/00424
.html
cidrap.umn.edu/cidrap/content/bt/smallpox/bi
ofacts/smllpx-summary.html
www.pnas.org.
http://dermatology.about.com/cs/smallpox/a/smal
lpoxhx.htm
www.aafp.org/afp/ 20030901/889.html