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