Archaea WORLD OF MICROBIOLOGY AND IMMUNOLOGY34•
This volume spread knowledge about canning around the
world and launched what would become a vast industry.
In 1812 Appert used his prize money to make his Massy
plant into the world’s first commercial cannery, which
remained in operation until 1933. Appert, who also invented
the bouillon cube, was financially ruined in 1814 when his
plant was destroyed during the Napoleonic wars. He died in
poverty in 1841.See alsoFood preservation; Food safetyAArchaeaRCHAEA
Genes that code for vital cellular functions are highly con-
served through evolutionary time, and because even these
genes experience random changes over time, the comparison
of such genes allows the relatedness of different organisms to
be assessed. American microbiologist Carl Woese and his col-
leagues obtained sequences of the genes coding for RNAin the
subunit of the ribosome from different organisms to argue that
life on Earth is comprised of three primary groups, or
domains. These domains are the Eukarya (which include
humans), Bacteria, and Archaea.
While Archae are microorganisms, they are no more
related to bacteria than to eukaryotes. They share some traits
with bacteria, such as having a single, circular molecule of
DNA, the presence of more mobile pieces of genetic material
called plasmids, similar enzymesfor producing copies of
DNA. However, their method of protein production and
organization of their genetic material bears more similarity to
eukaryotic cells.
The three domains are thought to have diverged from
one another from an extinct or as yet undiscovered ancestral
line. The archae and eukarya may have branched off from a
common ancestral line more recently than the divergence of
these two groups from bacteria. However, this view remains
controversial and provisional.
The domain Archae includes a relatively small number
of microoganisms. They inhabit environments which are too
harsh for other microbes. Such environments include hot,
molten vents at the bottom of the ocean, the highly salt water
of the Great Salt Lake and the Dead Sea, and in the hot sul-
furous springs of Yellowstone National Park. Very recently, it
has been shown that two specific archael groups, pelagic eur-
yarchaeota and pelagic crenarchaeota are one of the ocean’s
dominant cell types. Their dominance suggests that they have
a fundamentally important function in that ecosystem.See also Bacterial kingdoms; Evolution and evolutionary
mechanisms; Evolutionary origin of bacteria and virusesAArenavirusRENAVIRUS
Arenavirus is a virus that belongs in a viral family known as
Arenaviridae. The name arenavirus derives from the appear-
ance of the spherical virus particles when cut into thin sectionsand viewed using the transmission electron microscope. The
interior of the particles is grainy or sandy in appearance, due
to the presence of ribosomesthat have been acquired from the
host cell. The Latin designation “arena” means “sandy.”
Arenaviruses contain ribonucleic acid(RNA) as their
genetic material. The viral genome consists of two strands of
RNA, which are designated the L and S RNA. The ribosomes
of the host that are typically present inside the virus particle
are used in the manufacture of the components that will be
assembled to produce the new virus particles. Little is known
about the actual replication of new viral components or about
the assembly of these components to produce the new virus
particles. It is known that the new virus exits the host by “bud-
ding” off from the surface of the host cell. When the budding
occurs some of the lipid constituent from the membrane of the
host forms the envelope that surrounds the virus.
Those arenaviruses that are of concern to human health
are typically transmitted to humans from rats and mice. The
only known exception is an arenavirus called the Tacaribe
virus, which is resident in Artibeusbats. The association
between an arenavirus type and a particular species of rodent
is specific. Thus, a certain arenavirus will associate with only
one species of mouse or rat. There are 15 arenaviruses that are
known to infect animals. A hallmark of arenaviruses is that
the infections in these rodent hosts tend not to adversely
affect the rodent.
Of the fifteen virusesthat are resident in the animals,
five of these viruses are capable of being transmitted to
humans. When transmitted to humans, these arenaviruses can
cause illness. In contrast to the rodent hosts, the human illness
can be compromising.
Most arenavirus infections produce relatively mild
symptoms that are reminiscent of the flu, or produce no symp-
toms whatsoever. For example an arenavirus designated lym-
phocytic choriomeningitis virus, usually produces symptoms
that are mild and are often mistaken for gastrointestinal upset.
However, some infections with the same virus produce a
severe illness that characterized by an inflammationof the
sheath that surrounds nerve cells (meningitis). The reasons for
the different outcomes of an infection with the virus is yet to
be resolved.
A number of other arenaviruses are also of clinical con-
cern to humans. These viruses include the Lassa virus (the
cause of Lassa fever), Junin virus (the cause of Argentine
hemorrhagic fever), Machupo virus (the cause of Bolivian
hemorrhagic fever), and Guanarito virus (the cause of
Venezuelan hemorrhagic fever). Hemorrhagic feversare char-
acterized by copious bleeding, particularly of internal organs.
The death rate in an outbreak of these hemorrhagic fevers can
be extremely high.
An arenavirus is transmitted to a human via the urine
or feces of the infected rodent. The urine or feces may con-
taminate food or water, may accidentally contact a cut on the
skin, or the virus may be inhaled from dried feces. In addi-
tion, some arenaviruses can also be transmitted from one
infected person to another person. Examples of such viruses
are the Lassa virus and the Machupo virus. Person-to-person
transmission can involve direct contact or contact of anwomi_A 5/6/03 1:07 PM Page 34