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