Biomedical Engineering Reference
In-Depth Information
In 2004, rotaviruses were responsible for about half a million deaths, mostly in
developing countries [5].
Worldwide, about 350 million people are chronic carriers of hepatitis B,
and about 100 million people are chronic carriers of hepatitis C. In aggre-
gate, about one quarter (25 million) of the hepatitis C chronic carriers will
eventually die from ensuing liver diseases [4].
Infectious organisms can kill individuals through mechanisms other than
through the direct pathologic effects of growth, invasion, and inflammation.
Infectious organisms have been implicated in vascular disease. The organ-
isms implicated in coronary artery disease and stroke include Chlamydia
pneumoniae and Cytomegalovirus [6].
Infections caused by a wide variety of infectious organisms can result in
cancer. About 7.2 million deaths occur each year from cancer, worldwide. About
one-fifth of these cancer deaths are caused by infectious organisms [7]. In
Europe, 60
15%
of liver cancer is caused by hepatitis B infection [8]. Organisms contributing
to cancer deaths include bacteria (Helicobacter pylori), animal parasites
(schistosomes and liver flukes), and viruses (Herpesviruses, Papillomaviruses,
Hepadnaviruses, Flaviviruses, Retroviruses, Polyomaviruses). Though fungal and
plant organisms do not seem to cause cancer through human infection, they
produce a multitude of biologically active secondary metabolites (i.e., synthesized
molecules that are not directly involved in the growth of the organism), some
of which are potent carcinogens. For example, aflatoxin produced by Aspergillus
flavus, is possibly the most powerful carcinogen ever studied [9].
In summary, infectious diseases are the number one killer of humans
worldwide, and they contribute to vascular disease and cancer, the two lead-
ing causes of death in the most developed countries. These observations
clearly indicate that every healthcare professional, not just infectious disease
specialists, must understand the biology of infectious organisms. A listing of
the number of occurrences of some common infectious diseases is provided
in Appendix II.
70% of liver cancer cases are caused by hepatitis C virus; 10
ONLY A SMALL PERCENTAGE OF TERRESTRIAL ORGANISMS
ARE PATHOGENIC IN HUMANS
Given all the suffering caused by infectious organisms, you might begin
to wonder whether the majority of terrestrial life-forms are devoted to the
annihilation of the human species. Not to worry. Only a tiny fraction of the
life forms on earth are infectious to humans. The exact fraction is hard to
estimate because nobody knows the total number of terrestrial species. Most
taxonomists agree that the number is in the millions, but estimates range
from a few million up to several hundred million.
It is worth noting that species counts, even among the most closely
scrutinized classes of organisms, are prone to underestimation. In the past, the
