DiseaseDisease - Any change, other than an injury,

that interferes with normal functioning of the body

Pathogen – a disease-causing microorganism Infection – when a body is successfully

invaded by a pathogenInfectious disease – a disease that can be

transmitted from person to person, or animal to person, or insect to person, etc.

How do diseases spread?It depends on the diseaseAir, wounds, contaminated water, food,

infected animals, insects, sex, etc.

Germ TheoryBefore the theory (mid-1800s), people

believed that disease was caused by bad luck or evil spirits

Germ theory states that microorganisms cause disease

Louis Pasteur – first scientist to create a vaccine

Anton VanLeeuenhook – invented the microscope, could see microscopic organisms for the first time

VirusesVirus – non-cellular,

non-livingInvade the host cells

(humans) and use those cells to reproduce themselves – CANNOT do this without the host

Hard to “cure”, but vaccines help to prevent the disease

BacteriaSingle cellsProkaryotesMost bacteria are

harmlessCan cause disease

by killing your cells, producing toxins, or invading your cells like a virus

Many can be killed with antibiotics

FungusMushrooms and molds are harmless

examplesMost fungi are harmlessAthlete’s foot, ring worm and San Joaquin

Valley Fever are examples of fungal diseases

ProtozoaSingle celled

eukaryotesMost common in

humid regions of the world

Malaria – caused by Plasmodium (infects red blood cells)

Hard to cure because protozoa are similar to our cells, so drugs that kill them, also kill our own cells

Helminths (worms)Enter through human digestive tract or skinCan be ingested: trichinosis (under cooked

pork), guinea worm disease (contaminated water),

Can enter through skin: schistosoma (schistosomiasis) – through snail infested water, Filaria worms cause elephantiasis – from mosquito bites

Classifying diseaseEmerging –

apparently “new” diseases

Re-emerging – diseases that have recently increased in incidence after a period of decline

Endemic – diseases that have remained relatively constant in incidence throughout recorded history

Emerging diseases

Re-emerging diseases

Endemic Diseases

AIDS, Cholera, Ebola, influenza, legionnaire disease, lyme disease

Tuberculosis, malaria, schistosomiasis

Pneumonia, polio, guinea worm disease, plague, strep throat