IMMUNOLOGY
THE NATURE
OF
INFECTIOUS DISEASE
How Are Diseases Caused?
diseases are caused by disease-
Infectious
producing agents called Pathogens.
Bacteria, Protists, Fungi, and Viruses
Not all microorganism are pathogenic
disease – Any disease caused by
Infectious
the presence of pathogens in the body.
Where do diseases come from?
Themain source of human disease
pathogens is the human body itself.
People can be carriers.
They do not have the disease but act as a
reservoir and can spread the disease.
Carriers
Carrierscan pass on the disease during
the incubation period.
Incubationperiod – A symptom-free
period, while cells are multiplying within
the body.
Ex. Common cold, HIV
Other Reservoirs
Animals can also serve as reservoirs for
microorganisms that cause disease in
humans.
Rabies
Soil and Water can be reservoirs for
infectious disease.
Soils can contain pathogens such as fungi
and a type of bacterium that causes botulism.
Water may be contaminated by feces
Transmission
4 ways for pathogens can be transmitted
from reservoirs to humans.
Direct contact, by an object, through air or by
a vector
1.Direct contact – Common cold, Flu,
STDs and HIV
2.An object – Food poisoning, food is
contaminated by a food handler
Transmission
3. Vectors – An intermediate organism
Insects and ticks:
Malaria is transmitted by mosquitoes
Lyme disease is transmitted by ticks
Fleas helped transmit the bubonic plague
from rats to humans.
Causes of Symptoms of Disease
Viruses take over a host cell’s genetic
material and may cause death to the cells
they invade
Bacteria release toxins, which cause damage
to the host.
Toxins can produce fever, inhibit protein
synthesis, destroy blood cells, or cause spasms
Some toxins can be deadly.
What makes us FEEL sick (fever, sore throat)
are symptoms from our fight against the disease!
Patterns of Disease
Diseases are able to spread rapidly in
today’s highly mobile world.
Endemic – a disease that is always
present in a population. Ex. Common Cold
Epidemic – occurs when many people in a
given area are afflicted with the same
disease at the same time.
Ex. Flu, Polio
Treating Disease
Antibioticsare often used to kill or inhibit
the growth and reproduction of bacteria
Produced naturally by various species of
bacteria and fungi.
Do not affect viruses.
Problems with Antibiotics
Bacteria can often become genetically resistant
to antibiotics. (This involves plasmid transfer)
Resistance is caused by continued use of
antibiotics.
Penicillin first used in the 1940s but now after
about 60 years of use, types of bacteria have
evolved a resistance.
The bacteria produce an enzyme that breaks down
the antibiotic. Ex. Gonorrhea