Microbiology and Immunology

Variola virus WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Naturally acquired immunity to chickenpox does not

prevent individuals from contracting shingles years, even

decades later. Shingles occurs in between 10% and 20% of

those who have had chickenpox. In the United States, upwards

of 800,000 people are afflicted with shingles each year. The

annual number of shingles sufferers worldwide is in the mil-

lions. The disease occurs most commonly in those who are

over 50 years of age.

As the symptoms of chickenpox fade, varicella zoster

virus is not eliminated from the body. Rather, the virus lies

dormant in nerve tissue, particularly in the face and the body.

The roots of sensory nerves in the spinal cord are also a site of

virus hibernation. The virus is stirred to replicate by triggers

that are as yet unclear. Impairment of the immune system

seems to be involved, whether from immunodeficiency dis-

easesor from cancers, the effect of drugs, or a generalized

debilitation of the body with age. Whatever forces of the

immune system that normally operate to hold the hibernating

virus in check are abrogated.

Reactivation of the virus causes pain and a rash in the

region that is served by the affected nerves. The affected areas

are referred to as dermatomes. These areas appear as a rash or

blistering of the skin. This can be quite painful during the one

to two weeks they persist. Other complications can develop.

For example, shingles on the face can lead to an eye infection

causing temporary or even permanent blindness. A condition of

muscle weakness or paralysis, known as Guillan-Barre

Syndrome, can last for months after a bout of shingles. Another

condition known as postherpetic neuralgia can extend the pain

of shingles long after the visible symptoms have abated.

See alsoImmunity, active, passive and delayed; Infection and

resistance; Latent viruses and diseases

VVariola virusARIOLA VIRUS

Variola virus (or variola major virus) is the virus that causes

smallpox. The virus is one of the members of the poxvirus

group (Family Poxviridae). The virus particle is brick shaped

and contains a double strand of deoxyribonucleic acid. The

variola virus is among the most dangerous of all the potential

biological weapons.

Variola virus infects only humans. The virus can be eas-

ily transmitted from person to person via the air. Inhalation of

only a few virus particles is sufficient to establish an infection.

Transmission of the virus is also possible if items such as con-

taminated linen are handled. The various common symptoms

of smallpox include chills, high fever, extreme tiredness,

headache, backache, vomiting, sore throat with a cough, and

sores on mucus membranes and on the skin. As the sores burst

and release pus, the afflicted person can experience great pain.

Males and females of all ages are equally susceptible to infec-

tion. At the time of smallpox eradication approximately one

third of patients died—usually within a period of two to three

weeks following appearance of symptoms.

The origin of the variola virus in not clear. However, the

similarity of the virus and cowpoxvirus has prompted the sug-

gestion that the variola virus is a mutated version of the cow-

pox virus. The mutation allowed to virus to infect humans. If

such a mutation did occur, then the adoption of farming activ-

ities by people, instead of the formally nomadic existence,

would have been a selective pressure for a virus to adopt the

capability to infect humans.

Vaccinationto prevent infection with the variola virus is

long established. In the 1700s, English socialite and public

healthadvocate Lady Mary Wortley Montaguepopularized the

practice of injection with the pus obtained from smallpox

sores as a protection against the disease. This technique

became known as variolation. Late in the same century,

Edward Jenner successfully prevented the occurrence of

smallpox by an injection of pus from cowpox sores. This rep-

resented the start of vaccination.

Vaccination has been very successful in dealing with

variola virus outbreaks of smallpox. Indeed, after two decades

of worldwide vaccination programs, the virus has been virtu-

ally eliminated from the natural environment. The last

recorded case of smallpox infection was in 1977 and vaccina-

tion against smallpox is not practiced anymore.

In the late 1990s, a resolution was passed at the World

Health Assembly that the remaining stocks of variola virus be

destroyed, to prevent the re-emergence of smallpox and the

misuse of the virus as a biological weapon. At the time only

two high-security laboratories were thought to contain variola

virus stock (Centers for Disease Controland Prevention in

Atlanta, Georgia, and the Russian State Centre for Research

on Virologyand Biotechnology, Koltsovo, Russia). However,

this decision was postponed until 2002, and now the United

States government has indicated its unwillingness to comply

with the resolution for security issues related to potential

bioterrorism. Destruction of the stocks of variola virus would

deprive countries of the material needed to prepare vaccinein

the event of the deliberate use of the virus as a biological

weapon. This scenario has gained more credence in the past

decade, as terrorist groups have demonstrated the resolve to

use biological weapons, including smallpox. In addition, intel-

ligence agencies in several Western European countries issued

opinions that additional stocks of the variola virus exist in

other than the previously authorized locations.

See also Bioterrorism, protective measures; Bioterrorism;

Centers for Disease Control (CDC); Smallpox, eradication,

storage, and potential use as a bacteriological weapon; Viral

genetics; Virology; Virus replication; Viruses and responses to

viral infection

VVenter, John CraigENTER, JOHNCRAIG(1946- )

American molecular biologist

John Craig Venter, who until January 2002 was the President

and Chief Executive Officer of Celera Genomics, is one of the

central figures in the Human Genome Project. Venter co-

founded Celera in 1998, and he directed its research and oper-

ations while he and the company’s other scientists completed

a draft of the human genome. Using a fast sequencing tech-

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