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
Roles of the the CDC Epidemiological studies the MMWR Notafiable diseases (see tables 15.3 & 15.4) Recommendations: antibiotics drugs vaccine The WHO based in Geneva, Switzerland
What are disease ‘Reservoirs’? Nonliving (usually noncommunicable, opportunistic) tetanus fungi Living Animal (‘zoonotic’) (generally noncommunicable) rabies anthrax lyme disease Human (may be ‘contagious’) cholera leprosy HIV ‘ Carriers’ (read essay about Typhoid Mary, p 376) Nosocomial
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, dust cholera, salmonellosis C. Vector transmission Reservoirs, Vehicles and Vectors are not the same!
Case study: Lyme disease An “Emerging Disease” New Lyme, Conn, 1982 Borrellia burgdoferi White-tailed deer & mice Ixodes complex life cycle
Patterns of disease occurrence epidemic pandemic endemic sporadic cyclic
Case study: Tuberculosis -- A ‘reemerging’ disease Mycobacterium tuberculosis Intracellular pathogen lungs WBCs immune response granulomas Spread/control linked to clinical and social factors: 1) Diagnosis and treatment difficult 2) Slow growth 3) Poverty -- developed & developing nations 4) AIDS
What are the stages of an infection? Adherence Colonization Invasion 1. Adherence glycocalyx fimbriae receptors
Case study: Helicobacter pylori causes peptic ulcers Only discovered 1982 Dimorphic causes 60-80% of stomach ulcers 90% doudenal ulcers Stomach cancers Immune response plays important roles Good news: treatable Bad news: 25% in U.S. infected More bad news: antibiotic resistance is spreading
Gonorrhea agent Neiserria gonorrhoeae -- Gram-negative dipplococcus -- attaches via fimbriae Endotoxin Infection in males “ thick, copious & yellowish” pus
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
What are the clinical stages of a disease? Incubation Prodromal Invasive Acme Decline Convalescence Infections can be: Acute Chronic latent
What causes the symptoms of infection? Altered physiology e.g., fever; hormones; blood chemistry Damage to cells, tissues and organs e.g., respiratory infections, syphilis, etc Damaging immune responses e.g., many diseases; tuberculosis, leprosy rheumatic fever, etc Toxins exotoxins Gram-Positive sp. proteins Secreted from cells Highly toxic, specific effects endotoxins Gram-negative Lipopolysacchrarides Less toxic, more general effects pyrogenic hypotension Syphilis lesions in liver
What causes the symptoms of Syphilis? Agent Treponema pallidum spirochete Stages of the infection Incubation Primary (1 O ) syphilis chancre (clinical latency) Secondary (2 O ) syphilis immune hypersensitivity (clinical latency/ recurrent 2 O ) Tertiary syphilis gumma lesions
Syphilis, con’t. Tertiary syphilis gumma lesions autoimmunity? Treatment Congenital syphilis Saddle nose Notched teeth Saber shin nose
A Souvenir of London Bought a souvenir in London got 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
<ul><ul><ul><li>Toxicity of Some Exotoxins Toxicity compared with: </li></ul></ul></ul><ul><ul><ul><li>Toxin Lethal Dose (mg) Strychnine Snake Venom </li></ul></ul></ul><ul><ul><ul><ul><li>Botulism Type D 0.8 x10 -8 (mouse) 3x10 6 times 3x10 5 X </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Tetanus 4 x10 -8 (mouse) 1x10 6 X 1x10 5 X </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Shigella Neurotoxin 2.3 x10 -6 (rabbit) 1x10 6 X 1x10 5 X </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Diphtheria 6 x10 -5 (guinea pig) 2x10 3 X 2x10 2 X </li></ul></ul></ul></ul>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
Botulism and Tetanus Clostridium botulinum vs C. tetani obligate anaerobes Botulism food borne flaccid paralysis Tetanus soil borne rigid paralysis
A Botulism Case History Food risks Antitoxins Birds, Botox and Bioweapons…
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