Pathology 1

Epidemiology and Disease Processes

Chapter 17, examples from Chapter 19

Fields of Microbiology

Epidemiology-- Population focus

-- disease spread & containment

Microbial pathology-- Disease focus

-- ‘etiology’ of disease-- Biology of pathogen & effects on host

Clinical Microbiology-- Patient focus

-- ID of pathogen and treatment

Germs

John Snow’s classic search for source of cholera – London, 1854

Pathology 2

Roles of the the CDC

Epidemiological studies

the MMWR

Notafiable diseases (see tables 15.3 & 15.4)

Recommendations:antibioticsdrugsvaccine

The WHO

based in Geneva, Switzerland

Pathology 3

What are disease ‘Reservoirs’?Nonliving (usually noncommunicable, opportunistic)

tetanusfungi

LivingAnimal (‘zoonotic’) (generally noncommunicable)

rabiesanthraxlyme disease

Human (may be ‘contagious’)choleraleprosyHIV

‘Carriers’ (read essay about Typhoid Mary, p 376)

Nosocomial

Pathology 4

What are “modes of transmission:”The “Five F’s”

A. Contact transmission

Direct Contact transmission-- includes ‘aerosols’-- respiratory infections

Indirect Contact transmission involves ‘fomites’Haemophilus

B. Vehicular transmission (disseminates)water, food, dustcholera, salmonellosis

C. Vector transmission

Reservoirs, Vehicles and Vectors are not the same!

Pathology 5

Case study: Lyme disease

An “Emerging Disease”

New Lyme, Conn, 1982

Borrellia burgdoferi

White-tailed deer & mice

Ixodescomplex life cycle

Pathology 6

Lyme disease, con’t

Distibution

Stages of disease

Acute symptoms:

“Bulls-eye rash”

flu-like symptoms

Chronic symptoms:

arthritis

neurological disorders

etc

Treatmentantibiotics (yes and no)

Pathology 7

Patterns of disease occurrenceepidemic

pandemic

endemic

sporadic

cyclic

Pathology 8

Case study: Tuberculosis -- A ‘reemerging’ disease

Mycobacterium tuberculosis

Intracellular pathogenlungsWBCsimmune responsegranulomas

Spread/control linked to clinical and social factors:

1) Diagnosis and treatment difficult

2) Slow growth

3) Poverty-- developed & developing nations

4) AIDS

Pathology 9

What are the stages of an infection?Adherence

Colonization

Invasion

1. Adherenceglycocalyx

fimbriae

receptors

Pathology 10

Case study:Helicobacter pylori causes peptic ulcers

Only discovered 1982

Dimorphic

causes60-80% of stomach ulcers90% doudenal ulcersStomach cancers

Immune response plays important roles

Good news: treatable

Bad news: 25% in U.S. infected

More bad news: antibiotic resistanceis spreading

Pathology 11

Gonorrhea

agent Neiserria gonorrhoeae-- Gram-negative dipplococcus-- attaches via fimbriae

Endotoxin

Infection in males

“thick, copious & yellowish” pus

Pathology 12

Infection in females

cervix

fallopian tubes

PID

ectopic pregnancy

neonatal prophylaxis

epidemiology

Pathology 13

Colonization and Invasion are often coupled

Many ‘strategies’

Enzymes (‘virulence factors’)collagenase

hemolysin

streptokinase

Phagocytosis

Intracellular and extracellular infections

Listeria and actin tails

collagenase hemolysin

Pathology 14

What are the clinical stages of a disease?

Incubation

Prodromal

Invasive

Acme

Decline

Convalescence

Infections can be:AcuteChroniclatent

Pathology 15

What causes the symptoms of infection?

Altered physiologye.g., fever; hormones; blood chemistry

Damage to cells, tissues and organse.g., respiratory infections, syphilis, etc

Damaging immune responsese.g., many diseases; tuberculosis, leprosy

rheumatic fever, etcToxins

exotoxinsGram-Positive sp.proteinsSecreted from cellsHighly toxic, specific effects

endotoxinsGram-negative LipopolysacchraridesLess toxic, more general effects

pyrogenic hypotension

Syphilis lesions in liver

Pathology 16

What causes the symptoms of Syphilis?

AgentTreponema pallidumspirochete

Stages of the infectionIncubation

Primary (1O) syphilischancre

(clinical latency)

Secondary (2O) syphilis

immune hypersensitivity

(clinical latency/ recurrent 2O)

Tertiary syphilisgumma lesions

Pathology 17

Syphilis, con’t.

Tertiary syphilisgumma lesions

autoimmunity?

Treatment

Congenital syphilis

Saddle nose

Notched teeth

Saber shin nose

Pathology 18

A Souvenir of London

Bought a souvenir in Londongot to hide it from my mum.

Can't declare it at the customs,but I'll have to take it home.Tried to keep it confidential,but the news is leaking out.Got a souvenir of London.There's a lot of it about.

Yes I've found a bit of London,and I'd like to lose it quick.Got to show it to my doctor,'cos it isn't going to shrink.

Want to keep it confidential,but the truth is leaking out.Got a souvenir of London.There's a lot of it about.

by Procol Harum, 1973 ASoL

Pathology 19

Toxicity of Some Exotoxins Toxicity compared with: Toxin Lethal Dose (mg) Strychnine Snake Venom

Botulism Type D 0.8 x10-8 (mouse) 3x106 times 3x105 X

Tetanus 4 x10-8 (mouse) 1x106 X 1x105 X

Shigella Neurotoxin 2.3 x10-6 (rabbit) 1x106 X 1x105 X

Diphtheria 6 x10-5 (guinea pig) 2x103 X 2x102 X

Some Effects of Exotoxins

1) Cell destruction (hemolysins)

2) Hemorrhaging (anthrax, Streptococus toxins)

3) Effect intestinal function (enterotoxins)water balance (cholera toxin)

4) Nerve function (botulism & tetanus toxins) Anthrax lesion

Pathology 20

Botulism and TetanusClostridium botulinum vs C. tetani

obligate anaerobes

Botulismfood borne

flaccid paralysis

Tetanussoil borne

rigid paralysis

Pathology 21

A Botulism Case History

Food risks

Antitoxins

Birds, Botox and Bioweapons…