Lassa Fever: An Old World Arenavirus Essay, Research Paper

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 region

and intractable vomiting begins followed by severe edema of the throat and neck,

tinnitus (ringing in ears), bleeding from the gums and mouth, huge rashes,

coughing and dizziness. During this acute phase extremely low blood pressures of