Lassa Fever: An Old World Arenavirus


ABSTRACT

A brief summary of lassa fever, its history, pathology and effects on the
indigenous populations. Also, lassa fever in the context of newly emerging
diseases.

LASSA FEVER

On January 12, 1969, a missionary nun, working in the small town of
Lassa, Nigeria, began complaining of a backache. Thinking she had merely pulled
a muscle, she ignored the pain and went on about her business. After a week,
however, the nurse had a throat so sore and so filled with ulcers, she couldn\'t
swallow. Thinking she was suffering from one of the many bacterial diseases
endemic to the area, her sisters administered every antibiotic they had on store
in the town\'s Church of the Brethren Mission Hospital. But, the antibiotics did
nothing. Her fever escalated, she was severely dehydrated and blotches,
hemorrhages, were appearing on her skin. She began to swell and became delirious,
so they shipped her to a larger hospital, where one day later she went into
convulsions and died. After a nurse who was tending to the sister came down with
the same symptoms and died, the doctors in the hospital began to suspect it was
a disease heretofore unseen by any of them. Autopsy on the nurse showed
significant damage to every organ in the body, the heart was stopped up, with
loads of blood cells and platelets piled well into the arteries and veins.
Fluids and blood filled the lungs. Dead cells and lipids clogged the liver and
spleen. The kidneys were so congested with dead cells and free proteins they had
ceased to function. Dissecting the lymph nodes, they discovered that they were
completely empty; every white blood cell had been utilized in a futile attempt
to stave off the unknown microbe. A few days later, a prominent western viral
researcher contracted the unknown disease and the hunt for the microbe that
caused lassa fever, began in earnest.(Garrett, 1994)
Lassa fever is a virus belonging to the family Arenaviridae. Genus
Arenavirus, although being around for about 60 years in the form of lymphocytic
choriomeningitis, has recently been brought to the public\'s attention because of
the large number of species known as "emerging viruses" in the genera. The
genera consists mostly of new world viruses, among them the Junin, Machupo and
Guanarito viruses, which cause, respectively, Argentine, Bolivian and
Venezuelan hemorrhagic fevers along with a few other non - pathogenic viruses.
These viruses, long hidden in the deepest recesses of rain forests, are making
their presence felt as much of the rain forest and other isolated areas become
more and more accessible. Lassa fever is mostly on the rise as its main vector,
the rodent Mastomys natalensis, is increasing in numbers due (indirectly) to an
increase in poverty and scarcity of food.(Garrett, 1994) To be specific, when
the endemic region has a scarcity of food, the villagers kill and eat the larger
rat, Rattus ra ttus, which is a main competitor of the Mastomys natalensis,
thereby allowing the smaller Mastomys to flourish. The disease mainly effects
the areas of western Africa, from Senegal to, of course, Zaire, although it has
been exported to the United States (about 115 cases). (Southern, 1996)
Lassa fever consists of two single strands of RNA enclosed within a
spherical protein coat. The RNA exists as two strands designated L (for long)
and S (for short). The S segment is the more abundant of the two as it codes for
the major structural components such as the internal proteins and the
glycoproteins, while the L segment codes for RNA polymerase and perhaps a few
structural proteins. The protein coat has a number of T-shaped glycoproteins
protruding from it, composed of GP (glycoprotein)2 which is the base and GP1
which is the T-bar. (Southern, 1996) This structure is what inserts itself into
the receptors on the host cell. When the virus first gains entry into the cell,
it quickly takes over the mechanisms of the cell to its own purpose. First it
creates clones of its RNA strands, then directs the cell to make the
glycoproteins on the host cell membrane. The virions bud from the cell membrane,
leaving the cell intact until, finally, the production of virions exceeds the
cells capabilities and the c ell lyses.
Infection with Lassa virus leads, after a 10 day incubation period, to a
gradual onset of fever, then full blown Lassa fever begins. First, the throat
gets exceedingly sore, even to point of severe ulceration and inability to
swallow or drink. In the first week anorexia, vomiting and chest pains are also
common. The second week is worse. The chest pains move to the abdominal