Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Epidemics, bacterial

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EEpidemics, bacterialPIDEMICS, BACTERIAL

An epidemic is the occurrence of an illness among a large

number of people in the same geographical area at the same

time. Bacterial epidemicshave probably been part of the lives

of humans since the species evolved millions of years ago.

Certainly by the time humans were present, bacteriawere well

established.

On example of a bacterial epidemic is the plague.

Plague is caused by the bacterium Yersinia pestis. The bac-

terium lives in a type of rodent flea and is transmitted to peo-

ple typically via the bite of the flea. People who come into

contact with an infected animal or a flea-infested animals such

as a rat can also contract the disease.

Plague has been a scourge on human populations for

centuries. In the Middle Ages, the so-called Black Plague

(Bubonic plague) killed millions of people in Europe. The

crowded living conditions and poor sanitation that were typi-

cal of the disadvantaged populations of the large European

cities of that time were breeding grounds for the spread of

plague.

While often thought of as an epidemic of the past,

plague remains today. Indeed, in the United States the last epi-

demic of plague occurred as recently as 1924–1925 in Los

Angeles. The widespread use of antibioticshas greatly

reduced the incidence of plague. Nonetheless, the potential for

an epidemic remains.

As for plague, the use of antibiotics has reduced bacte-

rial epidemics. However, this reduction generally tends to be a

feature of developed regions of the world and regions that

have ready access to health care. In other less advantaged

areas of the globe, bacterial epidemics that have been largely

conquered in North America and Europe, for example, still

claim many lives.

An example is bacterial meningitis. The bacterial form

of meningitis (an infection of the fluid in the spinal cord and

surrounding the brain) is caused by Haemophilus influenzae

type b, Neisseria meningitides, and Streptococcus pneumo-

niae. Antibiotics that are routinely given to children as part of

Court held outside during an epidemic, to lessen the chance of spread of illness.

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