BIOLOGY OF DISEASEBIOLOGY OF DISEASE

jrmg 2009jrmg 2009

any change (other than an injury) that any change (other than an injury) that interferes with the normal body functioninterferes with the normal body function

refers to conditions that impair normal refers to conditions that impair normal tissue functiontissue function

caused by infectious agentscaused by infectious agents

can be acquired: can be acquired: contact with someone carrying the contact with someone carrying the

infectious agentinfectious agent contaminated objects, food, air or contaminated objects, food, air or

waterwater

spread quickly or at a slow ratespread quickly or at a slow rate E.g. Polio virus E.g. Polio virus (contagious but not virulent)(contagious but not virulent)

Ebola hemorrhagic fever Ebola hemorrhagic fever (virulent but not contagious)(virulent but not contagious)

IS DISEASE IS DISEASE SYNONYMOUS SYNONYMOUS

WITH INFECTION?WITH INFECTION?

results from the results from the invasion and invasion and growth of a growth of a pathogenpathogen

tissue function is tissue function is impaired impaired

results when a results when a pathogen pathogen invades and invades and begins growing begins growing within a host within a host

bodily function: bodily function: normalnormal

TYPES OF DISEASETYPES OF DISEASE

Can be:Can be: GeneticGenetic

Cystic fibrosisCystic fibrosis HemophiliaHemophilia

TYPES OF DISEASETYPES OF DISEASE

Because of agingBecause of aging e.g. e.g.

Atherocslerosis, Atherocslerosis, osteoporosis osteoporosis

TYPES OF DISEASETYPES OF DISEASE

InfectiousInfectious German measlesGerman measles Chicken poxChicken pox MalariaMalaria

WHAT are Pathogens?WHAT are Pathogens?

Opportunistic PathogensOpportunistic Pathogens

potentially infectious potentially infectious agentsagents But….. But….. (healthy immune (healthy immune

systems)systems)

Found on…Found on… elderly elderly (immuno suppressed)(immuno suppressed)

cancer patients* cancer patients* (immuno- compromised)(immuno- compromised)

people who have people who have AIDS or are HIV-AIDS or are HIV-positive positive (immuno- (immuno- compromised)compromised)

Types of Infectious Types of Infectious AgentsAgents

Viral infectionsViral infections e.g. colds, influenza, measles, e.g. colds, influenza, measles,

chicken pox, West Nile virus, chicken pox, West Nile virus, hepatitis, AIDShepatitis, AIDS

Types of Infectious Types of Infectious AgentsAgents

Bacterial infectionBacterial infection e.g. pneumonia, strep throat, boils, e.g. pneumonia, strep throat, boils,

acne, streptococcal infection, bubonic acne, streptococcal infection, bubonic plague, and anthraxplague, and anthrax

OTHER EXAMPLESOTHER EXAMPLES Salmonella typhiSalmonella typhi - typhoid fever, and - typhoid fever, and

Yersinia pestisYersinia pestis- bubonic plague- bubonic plague Staphylococcus aureusStaphylococcus aureus-causes skin, -causes skin,

respiratory, and wound infectionsrespiratory, and wound infections Clostridium tetaniClostridium tetani, which produces a , which produces a

toxin that can be lethal for humanstoxin that can be lethal for humans Staphylococcus epidermidisStaphylococcus epidermidis- acne- acne

Types of Infectious Types of Infectious AgentsAgents

Protozoan infectionsProtozoan infections e.g. Malaria, amoebiasis and e.g. Malaria, amoebiasis and

DiarrheaDiarrhea

EXAMPLESEXAMPLES

Diarrhea: Giardia Diarrhea: Giardia lamblialamblia and and Cryptosporidium Cryptosporidium parvumparvum

Malaria: Plasmodium Malaria: Plasmodium vivaxvivax

Wuchereria bancroftiWuchereria bancrofti Brugia malayiBrugia malayi, or , or

Brugia timoriBrugia timori

Types of Infectious Types of Infectious AgentsAgents

Fungal infectionsFungal infections e.g.yeast e.g.yeast

infections, infections, ringworm and ringworm and athlete's foot athlete's foot

CandidaCandida genus genus opportunistic opportunistic

pathogens pathogens vaginal yeast vaginal yeast

infections and infections and thrush (a throat thrush (a throat infection) infection)

Types of Infectious Types of Infectious AgentsAgents

Helminthes Helminthes Infection Infection simple, simple,

invertebrate invertebrate animals, some of animals, some of which are which are infectious infectious parasitesparasites

e.g. e.g. Schistosomiasis Schistosomiasis Liver fluke Liver fluke disease disease

HOW DO THESE HOW DO THESE INFECTIOUS INFECTIOUS AGENTS HARM AGENTS HARM THE HOST???THE HOST???

Manner of Inflicting/ Manner of Inflicting/ Causing Harm to the Causing Harm to the

HOST HOST entrance the host body entrance the host body

adhere to specific host cellsadhere to specific host cells invade and colonizeinvade and colonize

multiply between host cells or within multiply between host cells or within body fluids body fluids cause tissue damage cause tissue damage

production of toxins or destructive production of toxins or destructive enzymesenzymes

SO… Infectious agents SO… Infectious agents work…work…

By…By…1. become so numerous that they 1. become so numerous that they

interfere with normal bodily interfere with normal bodily functionsfunctions

2. destroys body cells and tissues2. destroys body cells and tissues

3. produce toxins3. produce toxins

HOW DID THEY HOW DID THEY FIND OUT THE FIND OUT THE CAUSE OF THE CAUSE OF THE DISEASE???? DISEASE????

Studying Infectious Studying Infectious Disease Disease

GERM THEORYGERM THEORY states that microorganisms can cause states that microorganisms can cause

diseasesdiseases infectious disease is caused by an infectious disease is caused by an

infectious agentinfectious agent

Studying Infectious Studying Infectious Disease Disease

ROBERT KOCHROBERT KOCH discovered:discovered:

Bacillus anthracis, Mycobacterium tuberculosis , Vibrio choleraBacillus anthracis, Mycobacterium tuberculosis , Vibrio cholera

Developed: Developed: use of agar as solid medium. use of agar as solid medium. invented nutrient broth and nutrient agar invented nutrient broth and nutrient agar

KOCH’s POSTULATEKOCH’s POSTULATE sequence of experimental steps for sequence of experimental steps for

directly relating a specific microbe directly relating a specific microbe to a specific disease to a specific disease

KOCH’s POSTULATEKOCH’s POSTULATE

suspected pathogenic organism suspected pathogenic organism present in all cases of diseasepresent in all cases of disease absent for healthy animalsabsent for healthy animals

suspected organism should be grown in suspected organism should be grown in cultures, cultures, in vitro in vitro but can also be but can also be in vivo in vivo (in (in animals)animals)

cells from a culture of suspected organism cells from a culture of suspected organism should cause disease in healthy animalsshould cause disease in healthy animals

organisms should be re-isolated and shown to organisms should be re-isolated and shown to be the same as originalbe the same as original

Modes of Infection Modes of Infection

Modes of InfectionModes of Infection

Indirect contactIndirect contact when a pathogen can withstand the when a pathogen can withstand the

environment outside its host for a long environment outside its host for a long period of time before infecting another period of time before infecting another individualindividual

Inanimate objects that are contaminated Inanimate objects that are contaminated by direct contact with the reservoirby direct contact with the reservoir

The fecal-oral route of transmission The fecal-oral route of transmission

Modes of InfectionModes of Infection

2. Air- borne (droplet infection)2. Air- borne (droplet infection) e.g. colds, flu, sinus infections, e.g. colds, flu, sinus infections,

German measles, pneumonia, German measles, pneumonia, meningitis, TB and SARSmeningitis, TB and SARS

Modes of InfectionModes of Infection

3. Contact3. Contact e.g. chicken pox, small pox, e.g. chicken pox, small pox,

syphilis, gonorrheasyphilis, gonorrhea

Modes of InfectionModes of Infection

4. Vectors- carry disease through 4. Vectors- carry disease through other animals (e.g. insect bites)other animals (e.g. insect bites) e.g. typhus, rabies, H- fever, e.g. typhus, rabies, H- fever,

malaria, denguemalaria, dengue

How do our body defend How do our body defend us from diseases?us from diseases?

Nonspecific mechanismsNonspecific mechanismsA. Structural DefenseA. Structural Defense

Skin, mucous membranesSkin, mucous membranes perspiration (salts and fatty acids)perspiration (salts and fatty acids) tears (contain lysozyme which can break tears (contain lysozyme which can break

down bacterial cell wall)down bacterial cell wall) acid secretion in stomach (HCl)acid secretion in stomach (HCl)

B.CellularB.Cellular PhagocytosisPhagocytosis

e.g. leucocytes in WBCe.g. leucocytes in WBC FEVERFEVER

How do our body defend How do our body defend us from diseases?us from diseases?

Specific mechanisms of host Specific mechanisms of host resistanceresistance

white blood cells called lymphocytes:white blood cells called lymphocytes: T-cells (produced from lymphocytes that T-cells (produced from lymphocytes that

matured in the thymus gland)matured in the thymus gland) B-cells (produced from lymphocytes that B-cells (produced from lymphocytes that

matured in the bone marrow). matured in the bone marrow).