Infectious Diseases
Pathogens
• Several types of small
microscopic organisms
• Most are Parasites – organisms
that live in or on another
organism and derive nourishment
from it
• Forms – bacteria, viruses,
rickettsias, protozoans, and fungi
Bacteria
• Single-celled microorganism
• Live anywhere – air, soil, and water
• Some are harmful to humans and
some are good
• When enter the body they multiply at
a rapid rate
• If person is not immune – disease
results
Virus
• Smallest known type of infectious
agent
• One of our worst enemies
• Not living cells
• Entirely dependent on living cells
for survival
• Only attack specific types of cells
– called a host
Rickettsias
• Resemble small bacteria but like
viruses only able to multiply by
invading a cell
• Found in intestinal tracts of insects
– fleas
• Passed by bites or feces
deposited on the skin
• Typhus or rocky Mt. spotted fever
Protozoans
• Single celled organisms larger
than bacteria with a complex
structure
• Most are harmless
• Common in tropical areas with
poor sanitation
Fungi
• Simple organisms that cannot
make their own food
• Prefer dark, damp
environments – nails, hair, and
skin
• Ringworm and athlete’s foot
Direct contact
• When an uninfected person
comes in physical contact with
an infected person
• STD’s
• Bite
• Pregnant mother to unborn
child
Indirect contact
• Enter the body through the
lungs
• exhaled, coughed, or sneezed
out by infectious person
• Inhaled and entered through
eyes or nose
Animals or insects
• Infected dogs or other animals
can spread diseases – rabies
• Mosquitoes or other
bloodsucking insect can
spread pathogens from an
infected person to a uninfected
person – malaria
Contaminated Objects
• Pathogens are spread by
objects an uninfected
person may touch –
eating utensils, glasses,
toothbrush, hairbrush, or
needles
Environment
• Food – careless handling can lead
to food poisoning
• Water and soil – careless disposal
of infectious waste – toxic dumping
– can be deadly
• Air – toxic chemicals released from
factories
Immune Response
• Two main types of defenses
• Innate immune system – inborn
defenses – provides nonspecific
resistance
• Adaptive immune system – specific
resistance
• Both work together to protect against
pathogens
Nonspecific resistance
• Physical barriers – first line of
defense
• Main barrier is your skin
• Mucus membranes – the soft,
skinlike lining of many parts of the
body – mouth, nose, and
bronchial tubes produce mucus to
trap pathogens
• Chemical barriers – enzymes
in tears and saliva destroy
pathogens
• Acidic digestive juices of the
stomach destroy pathogens
swallowed with food
• Other chemicals cause body
changes to help cells fight
pathogens
•Body cells – When
pathogens reach
bloodsteam, certain
types of white blood cells
called phagocytes group
together and destroy
them
• Inflammatory response – body
goes into a “red alert”
• Chemical mediators are released,
blood vessels dilate and increase
blood flow, this allows phagocytes to
leave blood stream and enter body
tissues. This continues until the
pathogen is destroyed.
• Symptoms – heat, redness, and
swelling
Specific Resistance
• General response – not
always enough to protect you
from disease
• Lymphocytes – white blood
cells that fight pathogens
• B Cells – encounter a pathogen
they enlarge and multiply – turn
into plasma cells – produce
antibodies – proteins that
destroy or neutralize invading
pathogens
• Remain in blood to become
active when encounters the
pathogen again
• T cells – two main groups –
alerts B cells
• Killer T cells – multiply by
presence of abnormal body
cells – attach to cells and
release toxins to destroy
abnormal cells
• Helper T cells – aid the activity
of the B and T cells.
Respiratory infections
• Common Cold – viral
• Symptoms – stuffy, runny nose,
sneezing, sore throat, and
headache
• Contracted – breathing in
contaminated droplets, rubbing
eyes or nose
• Influenza – viral
• Symptoms – chills, fever,
headache, muscle ache, and
weakness
• Contamination – droplet coughed
or sneezed into the air
• Flu can develop into pneumonia –
serious inflammation of the lungs
• Tuberculosis – bacterial
• Infection that most often affects
the lungs
• Symptoms – coughing (sometime
blood), chest pain, shortness of
breath, fever, sweating, poor
appetite, and weight loss
• Contamination – airborn droplets
from coughing or sneezing
• Strep throat – bacterial
• Infection of the throat
• Symptoms – sore throat, fever,
general feeling of illness, and
enlarged lymph nodes in neck
• Contamination – droplets
coughed or breathed into the
air
Immunity
• Body’s natural resistance to
many pathogens
Active immunity
• Body develops to protect
you from disease
• Some last a life time and
some a short period
Passive immunity
• Temporary immunity that an
infant acquires from its mother
• Last for a few months until
baby can produce antibodies
on it own
Vaccination
• Causing the body to produce
antibodies against the pathogen
• Live-virus vaccines – weak virus
• Killed-virus vaccines – killed virus
• Toxoids – chemically treated bacteria
to stimulate production of antibodies
for active immunity