By Shireen AbdulrahmanBiochemistry of viruses course [Biochemistry Department]
Could it not be contrived to send smallpox among these disaffected tribes of Indians? We must use every stratagem in our power to reduce them.‘Sir Jeffrey Amherst, the Commander-in-Chief of the British forces in North America 1763
I will try to inoculate the [Native American tribe] with some blankets that may fall in theirhands, and take care not to get the disease myself.‘ Colonel Henry Bouquet, British forces in North America 1763
Smallpox decimated the Native Americans, who had never been exposed to the disease before and had no immunity.
In the 1980s, the Soviet Union developed variola as an aerosol biological weapon and produced tons of virus-laden material annually intended for intercontinental ballistic missiles.
Smallpox is considered one of the most serious bioterrorist threats.
An estimated 300 million people died from smallpox in the20th century alone.As the worlds population grew, and travel increased, so thevirus that Edward Jenner called the "speckled monster"grasped every opportunity to colonize the world.People struggled to find ways to battle with smallpox.It was also potentially one of the most devastatingbiological weapons ever conceived
Smallpox is an acute, contagious disease unique to humans, caused byeither of two virus variants, Variola major and Variola minor.The disease is also known by the Latin names Variola or Variolavera, which is a derivative of the Latin varius, meaning"spotted", or varus, meaning "pimple".The term "smallpox" was first used in Europe in the 15th century todistinguish variola from the "great pox" (syphilis).
Smallpox is believed to have emerged in human populations about10,000 BC. The earliest physical evidence of smallpox is probably thepustular rash on the mummified body of Pharaoh Ramses V of Egypt.Traders carried the disease from Egypt to India during the 1stmillennium BC. From there it swept into China in the 1st century ADand reached Japan in the 6th centuryReturning crusaders provided a way for smallpox to spread throughEurope in the 11th and 12th centuries.
After vaccination campaigns throughout the 19th and 20thcenturies, the WHO certified the eradication of smallpox in 1979.The last naturally occurring case of smallpox (Variola minor) wasdiagnosed on 26 October 1977.Smallpox is one of the two infectious diseases to have beeneradicated, the other being rinderpest, which was declarederadicated in 2011.
Variola has 2 predominant variants, major and minor Variola major —is a serious illness with a mortality rate according to the CDC of 30% or more, in unvaccinated people, while Variola minor — is a milder infection with a mortality rate of less than 1% During the era of naturally occurring smallpox, several variations of variola major disease were recognized.
Smallpox Signs and SymptomsThe symptoms of smallpox begin with high fever, head and bodyaches, and sometimes vomiting.A rash follows that spreads and progresses to raised bumps and pus-filled blisters that crust, scab, and fall off after about threeweeks, leaving a pitted scar.
Transmission can happen in one of several ways: Face-to-face contact Direct contact with infected fluids and contaminated objects Through the air The virus can cross the placenta, but the incidence of congenital smallpox is relatively low. Smallpox transmission does not occur through animals or insects.
Physical exam for signs and symptoms of smallpox. This will include a skin and mouth exam to look for the smallpox rash. If there is a moderate or high suspicion of smallpox, the doctor may order certain lab tests. Tests may only be conducted in specially protected laboratories, known as "Biosafety Level 4" labs (BSL-4).
PCR and restriction fragment length polymorphism (RFLP) analysis are used to identify the specific strains ELISA and serologic tests measure the variola virus-specific immunoglobin and antigen to aid in the diagnosis of the virus. Immunohistochemistry and electron microscopy The origin of the virus may be traced by genome analysis of the virus.
In order to precisely diagnose a smallpox infection, virus must be grown on chorioallantoic membrane - a vascular membrane found in bird eggs - and then have the lesions examined. At the microscopic level, Poxviruses form cytoplasmic inclusions, such as Guarnieri bodies in virus-infected epidermal cells. The virus appears as pink blobs when stained with eosin and hematoxylin.
Figure : A photograph revealing smallpox virus pocks on the chorioallantoic membrane of a developing embryonic chick.
Before a smallpox diagnosis is made, your healthcareprovider will consider other illnesses that can mimic the signsand symptoms of smallpox. Some of these illnesses include: Chickenpox Monkeypox Herpes zoster (also called shingles) Adverse reaction to medications Contact dermatitis Erythema multiforme Hand, foot, and mouth disease
Figure: This is a chickenpox scab (left), and smallpox scab (right) viewed from above as a demonstration in comparative morphology.
Smallpox is caused by infection with variola virus, which belongs to the genus Orthopoxvirus. The organism got its name from the Latin word varius meaning spotted, or varus meaning “pimple”. Variola virus infects only humans in nature.
Both enveloped and unenveloped virions are infectious. Variola major causes smallpox and Variola minor causes alastrim. Infection with either variola major or variola minor confers immunity against the other.
Figure : Variola virus, the agent of human smallpox.
Variola virus is a large brick shaped virus with a measurementof 302 to 350 nm by 244 to 277 nm, which consist of singlelinear double stranded DNA.Its genome consist of 186 kbp and contain a hairpin loop ateach end.The hairpin loop at each end consists of 530 bp fragments.
They have 187 closely spaced open reading frames specifyingputative major proteins contain more than or equal to 65amino acids.The complete DNA (deoxyribonucleic acid) sequence of twoclosely related variola virus (VARV) genomes was publishedin the early 1990s.
Figure : Variola virus genome bp, base pair; ORF, open reading frame; VARV, variola virus.
Variola viruses are DNA viruses with virions consist of a surface membrane, a core, and lateral bodies with or without an envelope. During their life cycles variola produces extracellular and intracellular particles. The infection is caused by the extracellular particles. The capsid of virus is enveloped and virons mature naturally by budding through the membrane of the host cell.
Poxviruses are unique among DNA viruses in that they replicate inthe cytoplasm of the cell rather than in the nucleus.In order to replicate, poxviruses produce a variety of specializedproteins not produced by other DNA viruses, the most important ofwhich is a viral-associated DNA-dependent RNA polymerase.
Virus particles land on the cell surface and are taken into the cell.The genetic information (DNA) of the virus is released into the cell and begins to make copies of itself.These new DNAs are taken into the developing spherical viral particles and the particles mature internally and in so doing adopt a more block like appearance.
Most will remain in the cell as Intracellular Mature Viruses, (IMV) and will be released when the cell bursts. However, some of the virus particles will obtain a second wrapping of host cell membrane and this occurs at the trans Golgi. These double wrapped particles are called Intracellular Enveloped Viruses (IEV).
Some IEVs push through the cells plasma membrane and remain attached to the cell surface. These are called Cell- associated Enveloped Viruses (CEVs). Others that push through the membrane are released and are called Extracellular Enveloped Viruses (EEVs).
This organism is transmitted among humans primarily by inhalation of virus or by droplets from oral, nasal or pharyngeal mucus of an infected person. After the virus enters in the human body through respiratory tract, it grows on the mucous membrane and then spreads to the lymph nodes where it multiplies and then finally enters the blood stream.
PathologyAfter entering the blood stream the virus invades internal organs andskin.The time frame for the incubation of small pox is 10 to 12 days.
There is no proven treatment for smallpox, but research to evaluate new antiviral agents is ongoing. Laboratory studies suggest that the drug cidofovir may fight against the smallpox virus. Patients with smallpox can benefit from supportive therapy such as wound care and infection control, fluid therapy, possible ventilator assistance and antibiotics for any secondary bacterial infections that may occur.
Vaccinia immune globulin (VIG) can be offered to persons exposed to smallpox as a prophylaxis. Vaccination within three days of exposure can aid in the treatment by preventing or significantly lessen the severity of smallpox symptoms in the vast majority of people.
Prevention of smallpox rests on two pillars: 1. Vaccination 2. Isolation of patients if they develop fever.
The smallpox vaccine is made from a virus called vaccinia which is a “pox”-type virus related to smallpox. The smallpox vaccine contains the “live” vaccinia virus—not dead virus like many other vaccines. Also, the vaccine can have side effects. The vaccine does not contain the smallpox virus and cannot give you smallpox.
The only smallpox vaccine currently licensed by the Food and Drug Administration is Dryvax. The vaccine was first approved in 1931, and the existing lots were manufactured in the 1970s and early 1980s and stored frozen
Smallpox vaccination provides high level immunity for 3 to 5 years and decreasing immunity thereafter. If a person is vaccinated again later, immunity lasts even longer. Historically, the vaccine has been effective in preventing smallpox infection in 95% of those vaccinated.
The vaccine is given using a bifurcated (two-pronged) needle that is dipped into the vaccine solution. The pricking of the skin will 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.
Figure: Smallpox vaccination site, Day 4 through 21.
After vaccination, it is important to follow care instructions for the site of the vaccine. Because the virus is live, it can spread to other parts of the body, or to other people. The vaccinia virus (the live virus in the smallpox vaccine) may cause rash, fever, and head and body aches. In certain groups of people, complications from the vaccinia virus can be severe.
Smallpox is considered one of the most serious bioterrorist threats. It was used as a biological weapon during the French and Indian Wars, (1754 to 1767) when British soldiers distributed smallpox-infected blankets to American Indians. In the 1980s, the Soviet Union developed variola as an aerosol biological weapon and produced tons of virus-laden material annually intended for intercontinental ballistic missiles.
Several factors contribute to the concern about the use of smallpox as a biological weapon: Variola can spread from person to person. There is no widely available or licensed treatment for the disease. It has a high fatality rate. Variola is relatively stable as an aerosol. The infectious dose is small.
Since routine smallpox immunization ceased in the United States in 1972 and in all other countries by 1983, the global population is extremely vulnerable to the disease. Most of the world’s population has never been vaccinated or was vaccinated so long ago that immunity to smallpox has waned. Because there are no symptoms at the time of exposure, a covert release of variola may not be detected until sick people begin showing up at doctors offices and hospitals.