Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Appert, Nicolas François

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AAntiviral drugsNTIVIRAL DRUGS

Antiviral drugs are compounds that are used to prevent or treat

viral infections, via the disruption of an infectious mechanism

used by the virus, or to treat the symptoms of an infection.

Different types of antiviral drugs have different modes

of operation. For example, acyclovir is a drug that is used to

treat the symptoms of the infections arising from the herpes

virus family. Such infection includes lesions on the genitals,

oral region, or in the brain. Acyclovir is also an antiviral agent

in the treatment of chickenpox in children and adults, and

shingles in adults caused by the reactivation of the chickenpox

virus after a period of latency. Shingles symptoms can also be

treated by the administration of valacyclovir and famciclovir.

Eye infections caused by cytomegalovirus can be

treated with the antiviral agent known as ganciclovir. The drug

acts to lessen the further development and discomfort of the

eye irritation. But, the drug may be used as a preventative

agent in those people whose immune systemwill be compro-

mised by the use of an immunosupressant.

Another category of antiviral drugs is known as the anti-

retroviral drugs. These drugs target those virusesof clinical

significance called retrovirusesthat use the mechanism of

reverse transcription to manufacture the genetic material

needed for their replication. The prime example of a retrovirus

is the Human immunodeficiency virus(HIV), which is the viral

agent of acquired immunodeficiencysyndrome (AIDS). The

development of antiviral drugs has been stimulated by the

efforts to combat HIV. Some anti-HIV drugs have shown

promise against hepatitisB virus, herpessimplex virus, and

varicella-zoster virus.

The various antiviral agents are designed to thwart the

replication of whatever virus they are directed against. One

means to achieve this is by blocking the virus from comman-

deering the host cell’s nuclear replication machinery in order

to have its genetic material replicated along with the host’s

genetic material. The virus is not killed directly. But the pre-

vention of replication will prevent the numbers of viruses

from increasing, giving the host’s immune system time to deal

with the stranded viruses.

The incorporation of the nucleotide building blocks into

deoxyribonucleic acid(DNA) can be blocked using the drug

idoxuridine or trifluridine. Both drugs replace the nucleoside

thymidine, and its incorporation produces a nonfunctional

DNA. However, the same thing happens to the host DNA. So,

this antiviral drug is also an anti-host drug. Vidarabine is

another drug that acts in a similar fashion. The drug is incor-

porated into DNA in place of adenine. Other drugs that mimic

other DNA building blocks.

Blockage of the viral replicative pathway by mimicking

nucleosides can be successful. But, because the virus utilizes

the host’s genetic machinery, stopping the viral replication

usually affects the host cell.

Another tact for antiviral drugs is to block a viral

enzyme whose activity is crucial for replication of the viral

genetic material. This approach has been successfully

exploited by the drug acyclovir. The drug is converted in the

host cell to a compound that can out compete another com-

pound for the binding of the viral enzyme, DNA polymerase,

which is responsible for building DNA. The incorporation of

the acyclovir derivative exclusively into the viral DNA stops

the formation of the DNA. Acyclovir has success against her-

pes simplex viruses, and Epstein-Barr virus. Another drug that

acts in a similar fashion is famiciclovir.

Other antiviral drugs are directed at the translation

process, whereby the information from the viral genome that

has been made into a template is read to produce the protein

product. For example, the drug ribavirin inhibits the formation

of messenger ribonucleic acid.

Still other antiviral drugs are directed at earlier steps in

the viral replication pathway. Amantadine and rimantadine

block the influenzaA virus from penetrating into the host cell

and releasing the nuclear material.

Antiviral therapy also includes molecular approaches.

The best example is the use of oligonucleotides. These are

sequences of nucleotides that are specifically synthesized to be

complimentary with a target sequence of viral ribonucleic acid.

By binding to the viral RNA, the oligonucleotide blocks the

RNA from being used as a template to manufacture protein.

The use of antiviral drugs is not without risk. Host cell

damage and other adverse host reactions can occur. Thus, the

use of antiviral drugs is routinely accompanied by close clini-

cal observation.

See alsoImmunodeficiency diseases; Viruses and responses to

viral infection

AAppert, Nicolas FrançoisPPERT, NICOLASFRANÇOIS(1750-1841)

French chef

Nicolas Appert gave rise to the food canning industry. Born in

Châlons-sur-Marne, France, around 1750, young Appert

worked at his father’s inn and for a noble family as a chef and

wine steward. By 1780 he had set up a confectionery shop in

Paris, France.

Appert became interested in food preservationwhen the

French government offered a 12,000-franc prize in 1795 to the

person who could find a way to keep provisions for

Napoleon’s armies from spoiling in transit and storage. After

years of experimentation Appert devised a method of putting

food in glass bottles that were then loosely corked and

immersed in boiling water for lengths of time that varied with

the particular food; after boiling, the corks were sealed down

tightly with wire. In an age before bacteriology, Appert did not

comprehend the fact that the heat destroyed microorganisms

in the food, but he could see that his method—which became

known as appertization—preserved the food. Appert later set

up his first bottling plant at Massy, south of Paris, in 1804.

The French navy successfully used Appert’s products in

1807, and in 1809 Appert was awarded the 12,000-franc prize.

A condition of the award was that Appert make public his dis-

covery, which he did in his 1810 work The Art of Preserving

Animal and Vegetable Substances for Several Years,which

gave specific directions for canning over fifty different foods.

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