Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Medawar, Peter Brian

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births) to maintain the virus within the population. Below that

level, the virus will eventually die out unless it is re-intro-

duced from an outside source. On the geological time-scale,

man has evolved recently and has only existed in large popu-

lations in comparatively modern times. In the past, when

human beings lived in small populations, it is concluded that

the measles virus could not exist in its present form. It may

have had another strategy of infection such as to persist in

some form and infect the occasional susceptible passer-by,

but this remains unproven. It has been suggested that the

modern measles virus evolved from an ancestral animal virus,

which is also common to the modern canine distemper and

the cattle disease rinderpest. This theory is based on the sim-

ilarities between these viruses, and on the fact that these ani-

mals have been commensal (living in close proximity) with

man since his nomadic days. The ancestral virus is thought to

have evolved into the modern measles virus when changes in

the social behavior of man gave rise to populations large

enough to maintain infection. This evolutionary event would

have occurred within the last 6000 years when the river val-

ley civilizations of the Tigris and Euphrates were established.

To our knowledge, measles was first described as a disease in

ninth century when a Persian physician, Rhazes, was the first

to differentiate between measles and smallpox. The physician

Rhazes also made the observation that the fever accompany-

ing the disease is a bodily defense and not the disease itself.

His writings on the subject were translated into English and

published in 1847.

The measles virus itself was first discovered in 1930,

and John F. Endersof the Children’s Hospital in Boston suc-

cessfully isolated the measles virus in 1954. Enders then

began looking for an attenuated strain, which might be suit-

able for a live-virus vaccine. A successful immunizationpro-

gram for measles was begun soon after. Today measles is

controlled in the United States with a vaccinationthat confers

immunity against measles, mumps, and rubella and is com-

monly called the MMR vaccine. Following a series of measles

epidemics occurring in the teenage population, a second

MMR shot is now sometimes required by many school-age

children as it was found that one vaccination appeared not to

confer life-long immunity.

In October 1978, the Department of Health, Education,

and Welfare announced their intention of eliminating the

measles virus from the U.S.A. This idea was inspired by the

apparently successful global elimination of smallpox by the

World Health Organization vaccination program, which

recorded its last smallpox case in 1977.

Death from measles due to respiratory or neurological

causes occurs in about 1 out of every 1000 cases and

encephalitis also occurs at this frequency, with survivors of the

latter often having permanent brain damage. Measles virus

meets all the currently held criteria for successful elimination.

It only multiplies in man; there is a good live vaccine (95 %

effective) and only one sero-type of the virus is known.

Usually measles virus causes an acute infection but, rarely (1

out of every million cases), the virus persists and reappears

some 2-6 years causing SSPE. However, measles virus can

only be recovered with difficulty from infected tissue and

SSPE is a non-transmissible disease. To successfully eliminate

measles, it would be necessary to achieve a high immunization

level, especially in children.

See alsoAntibody-antigen, biochemical and molecular reac-

tions; History of immunology; History of public health;

Immunity, active, passive and delayed; Immunology;

Varicella; Viruses and responses to viral infection

MMedawar, Peter BrianEDAWAR, PETERBRIAN(1915-1987)

English biologist

Peter Brian Medawar made major contributions to the study of

immunologyand was awarded the Nobel Prize in physiology

or medicine in 1960. Working extensively with skin grafts, he

and his collaborators proved that the immune systemlearns to

distinguish between “self” and “non-self.” During his career,

Medawar also became a prolific author, penning books such as

The Uniqueness of the Individualand Advice to a Young

Scientist.

Measles rash on a child’s back.

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