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Focus on Human Impact: A constant enemy: infectious
disease (ch. 9)
•
Direct contact with a pathogen, touching open sores or body fluids form
an infected person (contagious comes from the Latin contagio, meaning
contact or touch)
•
Indirect contact touching doorknobs, tissues, diapers, or other objects
previously in contact with an infected person
o Ex: Athletes foot
•
Contact with a vector such as a fly or mosquito, which carries a pathogen
from an infected person or contaminated material to new hosts
o In some cases, part of the pathogen’s life cycle occurs inside the
vector, which intermediate host
▪
Ex: mosquitoes are the intermediate host of the West Nile
virus
•
Inhaling pathogens such as cold and flu viruses, that have been spewed
into the air by uncovered coughs or sneezes
•
Nosocomial Infection- an infection that is acquired in a hospital, usually
by direct contact with a microbe
o Two of the most serious are MRSA infections and Colon
inflammation caused by Clostridium difficile bacteria
•
Epidemic- a disease outbreak in an area or population that occurs above
predicted or normal levels
o Ex: 2011 cholera epidemic in Haiti
•
Pandemic- A situation in which epidemics of a disease break out in
several countries around the world withing a given time span
o Ex: HIV/AIDS, H1N1 “swine flu” in 2009
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Sporadic Disease- A disease that breaks out irregularly and affects
relatively few people
o Ex: whooping cough
•
Endemic Disease- A disease that occurs more or less continuously in a
region
•
Worldwide, Diarrheal Diseases and Respiratory Infections Take more than
100 million lives each year
•
Virulence- The relative ability of a pathogen to cause serious disease
o Depends on how fast the pathogen can invade tissues, how
much damage it causes, and which tissues it targets
▪
Ex: a virus that can cause pneumonia is more virulent than
one that causes the sniffles
•
Ex: Rabies is extremely virulent because it targets the
brain
Disease
Diarrheas (includes amoebic
dysentery, cryptosporidiosis)
Type of
Pathogen
Protozoa,
virus, and
bacteria
Estimated
Deaths per
Year
31 million
Malaria
Protozoa
2.7 million
Hepatitis (includes A, B, C, D, E)
Virus
1–2 million
Schistosomiasis
Worm
200,000
Hookworm
Worm
50,000+
2
Whooping cough
Bacteria
100,000
Measles
Virus
220,000
Tuberculosis
Bacteria
2.4 million
Various respiratory infections
(pneumonia, viral influenza,
diphtheria, strep infections)
Virus,
bacteria
71 million
