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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
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