Microbiology and Immunology

Hershey, Alfred Day WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Herpes simplex virus types 1 and 2 appear identical

when examined using the high magnification power of the

electron microscope. Both types are icosahedral in shape; that

is, their surface consists of twenty equal-sized and equilateral

triangles.

The oral form of herpes is manifest as cold sores or so-

called fever blisters, and is common in young children. The

virus can be passed from person to person very easily. Only a

brief contact is needed for transmission. Cold sores are

innocuous in children and adults. However, they can be a very

serious health threat in newborns.

The genital form can be apparent as genital sores. These

appear as clustered blistery-appearing sores on the vagina,

vulva, cervix, penis, buttocks, or the anus. Pain, itching, and a

burning feeling during urination can accompany the sores. In

more severe cases, the lymph glands can be swollen, with a

number of flu-like symptoms evident. These symptoms of

what is referred to as primary herpes persist for several weeks

then disappear. They can return, usually to a lesser extent, in

anywhere from a few weeks to years later. Others who are

infected may not display any symptoms whatsoever.

Diagnosis of infection in asymptomatic people can still be

made, based on the detection of viral antibodies in the blood.

Herpes affects some 80 million people in the United

States alone, with one in six of these people having genital

herpes. Herpes is spread by human contact. Typically this

involves kissing, touching, or sexual contact. Typically, a per-

son is contagious when he or she has open sores. Because of

this, contact with others can be minimized when sores are

present, thus minimizing the chance of spread. However, it has

been proven that genital herpes can be spread even when no

symptoms or sores are evident. The chance of this happening

is about 10 percent. The spread of herpes via wet toilet seats

and the like is now considered to be unlikely.

Studies have shown that the chances of pregnant women

passing either herpes simplex virus to the developing fetus are

rare. Transfer can occur during childbirth. If open sores are

evident at this time, a caesarean section may be considered to

avoid the chance of infection.

Herpes simplex virus replicates insides cells of the host.

An association between a virus particle and the surface of the

host cell starts this process. The host cell is typically that in

nerves. This association is specific, involving the recognition

of a host surface molecule. Another viral protein then associ-

ates with several of the host cell molecules that are collec-

tively termed the herpes virus entry mediators. This second

association leads to the fusion of the host and the viral mem-

branes. The contents of the virus can then be emptied into the

host cell.

Once in the host cell, the viral deoxyribonucleic acid

genetic material somehow enters the nucleus. The viral DNA

is then replicated using the transcriptionmachinery of the

host. The viral transcription process occurs immediately with

certain stretches of the viral DNA and a bit later with other

stretches of the DNA. The early geneproducts participate in

the replication of the later regions of the viral DNA.

New virus particles can be produced very soon after

infection. Or, alternatively, the infection may become what is

described as latent. In a latent infection, no viral particles are

produced. Viral DNA continues to be replicated along with

host DNA until such time as a signal stimulates the transcrip-

tion of viral genes that are involved in the assembly of new

virus particles. Stress, surgery, menstruation, and skin infec-

tionssuch as sunburn are known to be signals, although the

molecular nature of these stimuli is unclear.

Recurrence of symptoms can be more frequent with

people whose immune systems are compromised, such as

those with leukemia or acquired immunodeficiencysyndrome

(AIDS). Currently there is no cure for herpes. Physicians can

prescribe one of three medications to treat genital herpes.

These are acyclovir, famciclovir, and valacyclovir. With or

without medication, in general the recurrences become fewer

with the passage of time, often ending after five to six years.

Despite this fading of symptoms, the herpes simplex

virusescan be debilitating aside from their direct affects. They

can deplete the body’s immune resources, leaving someone

more vulnerable to infection by another microbial agent.

See alsoLatent viruses and diseases; Virus replication

HHershey, Alfred DayERSHEY, ALFREDDAY (1908-1997)

American microbiologist

By seeking to understand the reproduction of viruses, Alfred

Day Hershey made important discoveries about the nature of

deoxyribonucleic acid(DNA) and laid the groundwork for

modern molecular genetics. Highly regarded as an experi-

mental scientist, Hershey is perhaps best known for the 1952

“blender experiment” that he and Martha Chase conducted to

demonstrate that DNA, not protein, was the genetic material

of life. This discovery stimulated further research into DNA,

including the discovery by James Watsonand Francis Crickof

the double-helix structure of DNA the following year.

Hershey’s work with bacteriophages, the viruses that prey on

bacteria, was often carried out in loose collaboration with

other scientists working with bacteriophages. Hershey shared

the Nobel Prize in Physiology or Medicine in 1969 with Max

Delbrück and Salvador Edward Luria. The Nobel Committee

praised the three scientists for their contributions to molecular

biology. Their basic research into viruses also helped others

develop vaccines against viral diseases such as polio.

Hershey was born in Owosso, Michigan, to Robert Day

Hershey and Alma Wilbur Hershey. Hershey’s father worked

for an auto manufacturer. Alfred attended public schools in

Owosso and nearby Lansing. He received his B.S. in bacteri-

ology from Michigan State College (now Michigan State

University) in 1930 and his Ph.D. in chemistry from the same

school in 1934. Hershey’s interest in bacteriology and the bio-

chemistryof life was already evident when he was a graduate

student. His doctoral dissertation was on the chemistry of

Brucella,the bacteria responsible for brucellosis, also known

as undulant fever. After receiving his Ph.D., Hershey took a

position as a research assistant in the Department of

Bacteriology at the Washington University School of

Medicine in St. Louis. There, he worked with Jacques Jacob

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