The Lymphatic System
and
Immunity
I
nfluenza,whichcomes in many varieties, can be
devastating to the human population. In 1918,
the Spanish flu pandemic killed somewhere between
30 and 50 million people worldwide. In 1997 and
2004/2005, bird flu originated in Hong Kong and
spread quickly. Because the World Health Organiza-
tion (WHO) and many nations provided enormous
resources, these outbreaks were contained to
parts of Southeast Asia. In early 2009, a
strain of H1N1 influenza (swine flu) ap-
peared in Mexico City and spread
to many countries, mainly
through commercial air travel.
Some influenza virus-
es are “human” viruses
that are harbored in
other species,
. often causing
no harm
to that
NATIONAL
GEOGRAPHIC
species. The most common forms of influenza (such as
influenza A) are harbored in pigeons. Other forms of
influenza are really “animal” viruses that can occasion-
ally infect humans; thus many forms of influenza are
referred to as a particular “animal” flu. Initially, these
animal viruses can be passed only from the animal to
the human. Of greater concern is the ability of a virus
to be transmitted from one human to another, a trans-
formation that may take several years to occur.
Vaccinations are often used to reduce the inci-
dence of viral infections. Although researchers rushed
to develop a vaccine for the H1N1 strain to be distrib-
uted throughout the United States, vaccination did not
proceed as rapidly as the Centers for Disease Control
and Prevention wished because of lack of vaccine and
people’s resistance to it. Fortunately, by first targeting
those who were most susceptible, a full-blown epidemic
was avoided.
Regular vaccinations for seasonal flu and for other
childhood diseases (such as measles, mumps, rubella,
and chicken pox) are essential for maintaining good
health. But how do these vaccines protect your body
from disease? They work with a powerful assortment of
disease fighters collectively referred to as your
lym p h a tic
system .
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