Essentials of Anatomy and Physiology

be wasted but would be applicable to the emerging
diseases as well. Unfortunately, that has not proven
true, because as of 2006 most nations were not at all
prepared for a possible pandemic of avian flu.
Avian influenza A (H5N1) is truly an emerging dis-
ease. The virus is a natural parasite of wild birds
and has infected domestic flocks in Asia, Europe, and
Africa. Although not a frequent event, people have
caught the virus from infected chickens or ducks,
and the human mortality rate has been 50% (though
with a relatively small number of cases, fewer than 500,
this may not be accurate). The great concern is that
the virus will mutate and become contagious for peo-
ple, that is, easily transmissible from person to person.
By way of plane travel, the virus could be spread
throughout the world in a matter of weeks. The avian
flu virus H5N1 may never mutate into a “people”
virus, but we have to be prepared for just that. As of
2006 we have no vaccine for this virus (some are in the
testing stages) and only one antiviral medication that is
even somewhat effective. Because this would be a
“new” disease for people, it is possible that no group of
people will have evolved any kind of resistance to it.

Bird flu may be for us what measles was to the

Hawaiian islanders in the 18th and 19th centuries. The

measles virus was brought to the islands by Europeans

(for whom it was usually not fatal, reflecting thousands

of years of coexistence) and nearly wiped out the native

population, for whom it was a new virus.

However, this is by no means certain. It may be that

milder cases of human avian flu have been overlooked

thus far, that H5N1 causes a wide spectrum of disease

in people, from mild to fatal. It may even be possible

that some human cases are asymptomatic (antibody

studies would be needed to determine that). We have

much to learn.

See also Box 22–3: Microbiology in the 21st

Century; you may be able to add to it.

THE PATHOGENS

In the sections that follow, each group of pathogens

will be described with a summary of important char-

acteristics. Examples of specific pathogens will be

given to help you become familiar with them. Tables

An Introduction to Microbiology and Human Disease 507

BOX22–3 MICROBIOLOGY IN THE 21ST CENTURY

2004 SARS vaccines are tested, but the human

SARS virus seems to disappear.

Avian influenza A (H5N1) causes sporadic

cases in people in East Asia.

A vaccine for the human papillomaviruses

that cause most cases of cervical cancer

proves to be very effective.

The incidence of whooping cough in the

United States rises markedly.

2005 A U.S. teenager becomes the first person to

survive rabies without having received the

rabies vaccine.

Avian flu is recognized as a pathogen with

the potential to cause a human pandemic.

Vaccines for the Ebola and Marburg viruses

are successful in monkeys.

A vaccine for shingles is effective in adults.

A more effective tuberculosis vaccine is in the

testing stages.

The 21st century has just begun; here is a micro-

biological perspective.

2001 In sub-Saharan Africa, more than 25 million

people have AIDS or are HIV positive.

Anthrax spores are sent through the U.S.

mail, causing 22 cases of the disease, with 5

fatalities.

2002 In China, the number of AIDS cases increases

ever more rapidly.

Multidrug-resistant strains of Mycobacterium

tuberculosisproliferate throughout the world.

A strain of Staphylococcus aureusis found that

is fully resistant to the antibiotic vancomycin.

2003 Cases of SARS are reported by China (after a

delay of 4 months—the disease was first

found in November 2002), and the disease

spreads to Europe and North America, affect-

ing more than 8000 people.

The first cases of mad cow disease are

reported in Canada and the United States.

In the United States, 35 human cases of

monkeypox are acquired from prairie dogs.

Donated blood and organs are screened for

the West Nile virus.