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MICR 201 Microbiology for Health Related Sciences . Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010 Chapter 7: Principles of disease. Why is this chapter important?.
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MICR 201 Microbiology for Health Related Sciences Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010 Chapter 7: Principles of disease
Why is this chapter important? • How diseases are caused (etiology), how they can be characterized, and the concepts of sepsis and shock are important for developing an in-depth understanding of infections. • It is important to understand the differences between normal microbial flora and abnormal or infectious microbial organisms.
Useful definitions • A disease is any negative change in a person’s health. • What is health? • Etiology is the cause of a disease. • Normal microbiota consists of useful microorganisms colonizing our external and internal body surfaces. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2080455/ Health is the absence of any disease or impairment. Health is a state that allows the individual to adequately cope with all demands of daily life . Health is a state of balance, an equilibrium that an individual has established within himself and between himself and his social and physical environment.
Common terms for describing infections and causing organ damage
Normal microbiota and many anaerobic bacteria and many gram negative anaerobic bacteria
Normal microbiota • Can protect us through microbial antagonism • Many bacteria produce bacteriocins which are localized bacterial antibiotics. • Bacteriocins can kill invading organisms but do not affect the bacteria that produce them. • Produces vitamins (Vit K and B) • Stimulates and trains our immune system • Can become pathogenic • In an immunocompromised host • When inoculated at a different body site • E. coli is part of the normal flora of the digestive tract but can cause infection if it enters the urinary tract.
The etiology of disease and Koch’s postulates • Etiology is the cause of disease. • Proof of etiology of infectious diseases can be found using Koch’s postulates. • 1: The same pathogen must be present in every case of the disease and absent in the healthy. • 2: The pathogen must be isolated and grown in pure culture. • 3: When inoculated into a healthy new host the pure pathogen must cause the same disease. • 4: The pathogen must be re-isolated from these newly infected hosts.
Limitations of Koch’s postulates • In some cases, Koch’s postulates cannot be used. • Some microorganisms cannot be grown in pure culture on agar media in the laboratory: • Treponemapallidum (syphilis) • Mycobacterium leprae (leprosy) • Viruses and rickettsial organisms • Polymicrobial infections • One microorganism can cause multiple diseases.
Etiology refers to • Viral infection • The results seen after a disease occurs. • The cause of the disease. • The portal of exit. • None of the above.
If pathogens spread to the bloodstream or lymphatics and disseminate to other parts of the body, a(n) _____ occurs. • Acute disease • Latent disease • Chronic disease • Secondary infection • Systemic infection
The course of a disease • There are five specific phases • Incubation period – the time between the initial infection and the first symptoms. The more virulent the pathogen, the shorter the incubation time. • Prodromal period – when the first mild and rather general symptoms appear. • Period of illness-most severe signs and symptoms and rather specific • Period of decline- symptoms and signs decline, secondary infections may arise. • Period convalescence- no signs or symptoms but patient is not yet fully restored.
Communicable and contagious diseases • Some diseases are communicable. • They can spread from one person to another. • Some diseases are not communicable. • They cannot spread from one person to another and simply remain within the infected host. • Some communicable diseases are easily spread from person to person and these are referred to as being contagious. • They spread very easily through contact with an infected person.
Communicable and contagious diseases: methods of control • Isolation: • It prevents an infected individual from having contact with the general population • Patients are usually isolated in the hospital • Can be difficult to achieve as it cannot be imposed until firm diagnosis • Quarantine: • Exposed humans or animals are separated from the general population while they still appear healthy. • Lasts as long as the incubation period for the disease in question • If there are no longer any symptoms, the quarantine is lifted • Rarely used today because it is difficult to enforce • Vector control: • It is used to control the population of vectors, such as mosquitoes, that carry pathogens.
Herd immunity • Herd immunity is an important concept in limiting the spread of infection. • It is conferred to people through vaccination or if they are naturally exposed to the infection and prevents re-infection by the same pathogen. • When a majority of a population (herd) is immune to an infection there are very few potential hosts and the disease essentially disappears. • Good examples of herd immunity are polio and smallpox.
Herd immunity • Current herd immunity for polio is high. • The polio vaccine is routinely administered to children so there are few targets available for infection. • Current herd immunity for smallpox is low. • Smallpox has been putatively wiped out worldwide. • As a result, no one is vaccinated for this infection anymore except for the military. • Since vaccinations have ceased, the number of people immune to small-pox is low and there are many potential targets available for infection.
Duration of disease • Disease duration can vary depending on the overall health of the host. • There are four categories of disease duration: • Acute diseases develop quickly and last only a short time e.g. measles. • Chronic diseases develop slowly but last for a long time e.g. tuberculosis, hepatitis B. • Sub-acute diseases have an gradual onset (usually 6 to 12 months) and are almost always fatal e.g. sclerosing pan-encephalitis. • Latent diseases remain in the host after the symptoms disappear and can become reactivated years later e.g. chicken pox/shingles.
Persistent bacterial infections • Some pathogenic bacteria are capable of maintaining infections in hosts, even in the presence of inflammatory and specific antimicrobial mechanisms as well as a perfectly good immune response. • Persistent bacterial infections are treated with specific antimicrobial therapy. • Examples of persistent bacterial infections include: • Mycobacterium tuberculosis (causes tuberculosis) • Salmonella entericaserovarTyphi (causes typhoid fever)
The scope of infection • Infections can be localized. • A local infection is contained (walled off) such as a boil or an abscess. • Local infections are the easiest to deal with medically. • Infections can be systemic. • Systemic infections occur when pathogens move away from the initial infection location (also known as the focus of infection). • This movement is usually associated with the blood or the lymphatic system.
Terms related to systemic infections • Bacteremia – bacteria present in the blood • Septicemia – bacteria multiplying in the blood with organ spread and organs dysfunction • Toxemia – toxins in the blood • Viremia – viruses in the blood howshealth.com
Primary, subclinical, and secondary infections • Primary – the initial infection which has acute onset of symptoms. • Subclinical – no symptoms are visible even though the person is infected • These people are carriers of the disease and can infect others. • Secondary – seen in people that are already weakened from a primary infection. Secondary infections are caused by another microorganism and can be more dangerous. • Example: Influenza virus causing flu and subsequent infection with Haemophilusinfluenzae
Chapter 7 key concepts • Normal microbiota helps to protect against opportunistic pathogens. • Etiology is defined as the cause of a disease. • Koch’s postulates can be used to evaluate and identify the etiology of a disease. • Disease can be acute, chronic, sub-acute, or latent/ persistent. • Examples for infections that may become latent and persistent are tuberculosis (Mycobacterium tuberculosis) and typhoid fever (Salmonella entericaserovarTyphi). • Infection can be local or systemic, primary or secondary
To prevent that a patient with reactivated tuberculosis further spreads the disease you would intervene with the following method: • Quarantine • Isolation • Herd immunity • Treat with antibiotics. • None of the above.
An example of mutualism is _____. • Mycobacterium tuberculosis in the lungs • Salmonella entericaserovarTyphi surviving in the gallbladder • Saprophytic bacteria surviving on sloughed cells of the ear • Chlamydia species surviving in epithelial cells of the genital tract • Bacteria in the colon providing vitamins K and B
Quiz 1 – Wednesday, April 17 • 11:45pm – 1:20pm • Chapters 1 thru 6: Lecture, Reading, Chapter End Self Study Questions • Twenty-five Multiple Choice Questions = 50 points • Please bring: • Scantron (form No. 882-E for the Quiz – available at no cost at the Student Bookstore) • No. 2 pencil only
