Disease

EQ: How are diseases transmitted?

Definition of a Disease

• The growth of a pathogen that begins injuring cells and tissues

• Spread from contact with an infected person or surface

Germ Theory

• Old school – disease was caused by an evil spirit or by doing evil deeds

• Early Work – Pasteur and Koch showed disease was actually caused by microorganisms

• Koch’s Postulates– The microorganism is always found in the ill person– The microorganism can be isolated from the ill person

and grown in a growth medium outside the body– When the microorganism is then injected into a

healthy person that person gets sick with the illness– The microorganism can be isolated from the newly

sick person

Agents of Disease• Viruses

– Non-cellular particles that use the cell’s mechanisms to reproduce more viruses and then ruptures the cell to escape

– Examples: chicken pox, the common cold• Bacteria

– Infect tissue directly growing in infected cells killing them– Produce toxins– Examples: lime disease, TB, flesh eating bacteria

• Fungi– Rapid growth in skin tissues causing irritation and infections– Examples: ringworm, athletes foot

• Protozoans– Small microorganisms– Live in body and irritate body systems– Examples: malaria, Montezuma's revenge

Non-Specific Defenses

First Line of Defense

• Not specific to any one pathogen

• Primary source of preventing disease from infecting the body

Skin

– Acts as a barrier to prevent bacteria and viruses from entering the body

– Very few pathogens can enter through the skin

– Very effective if unbroken

• Bacteria and viruses will enter through the orifices like the nose, mouth, and eyes

Mucus / Cilia

– All natural orifices are protected from disease entering the body by tiny hairs and snot like material

– Mucus is the silvery excretion that traps particles

– Cilia are hairs that filter out disease particles– Many of the secretions contain lysozyme

which is an enzyme that breaks down the walls of bacteria

Phagocytes

• White blood cells that target and engulf the invading disease particles

• Not specific to any particular pathogen

• Produced in the lymph nodes of the body – this is why your lymph nodes swell when you

are sick

• Creates swelling at the site of a wound

• This is the pus when you pop a pimple

Fever

• A rise in the bodies temperature– Stimulates the white blood cells– Can kill some pathogens as they are taken

out of their ideal temperature range– Should not always be treated with a drug

• As long as it is low grade it is doing more good for your body than harm

• Only becomes harmful when it goes above 102

Interferon

• An enzyme produced by a virus infected cell that helps block viral reproduction

• Slows down the infection so that specific defenses can begin to work