Chapter 14: Pathogenesis of Infectious Disease

Virulence (Structure)

-Capsules: have polysaccharide coating lack surface receptors for phagocytes to bind and adhere cannot ingest/kill Ex: Streptococcuspneumoniae, Klebsiella pneumoniae, Haemophilis influenzae, Neisseria meningitis -Flagella: enable flagellated bacteria to invade aqueous areas of the body, may also help in mobility to help bacterium to escape phagocytosis

path-

"Prefix meaning ""disease"""

Virulence (Attachment)

-Adhesins (ligands): molecules on surface of pathogens enable pathogens to recognize and bind to particular host cell receptors -Pili (bacterial fimbriae): enable bacteria to attach to surfaces, such as tissues in the human body

How pathogens escape Immune Responses

-Antigenic Variation: pathogens changing surface antigens to avoid antibodies -Camouflage and Molecular Mimicry: some organisms conceal their foreign nature by coating themselves with host proteins, surface antigens closely resemble host antigens -Destruction of Antibodies: Some pathogens produce IgA protease an enzyme that destroys some of the host's antibodies Ex: Haemophilus Influenzae

Virulence Factors

-Attributes that enable pathogens to escape host, use defense mechanisms and cause destruction/disease

Reasons infection may not occur?

-Microbe may land at anatomic site where it is unable to multiply (pH levels, moisture, unsuitable environment) -Some must attach to specific receptor sites before multiplication to start damage -Antibacterial factors may be present at site (lysozyme in tears, saliva, sweat) -Indigenous microflora may inhibit growth (microbial antagonism) by absorbing nutrients, occupying space -Indigenous microflora may produce antibacterial factors like bacteriocins that destroy pathogen (microbial antagonism) -Individual's overall health/nutritional status -Immunity to pathogen (vaccine, re-exposure) -Phagocytes (white blood cells) present in blood/tissue may destroy pathogen

Exoenzymes released by bacteria:

-Necrotizing Enzymes -Kinases -Collagenase -Lecithinase -Coagulase -Hyaluronidase -Hemolysins

Virulence (cont'd)

-Sometimes used to express measure/degree of pathogenicity Ex: it takes 10 Shigella cells to cause shigellosis, but 100-1000 salmonella cells to cause salmonellosis Shigella is MORE VIRULENT than Salmonella

Infection

-Synonym for infectious disease -Microbiologists reserve it to mean colonization of pathogen; may or may not go on to cause disease

Virulence

-used as synonym for pathogenic may be virulent (pathogenic disease causing) or avirulent strains (nonpathogenic no disease) of a species Ex: Toxigenic (toxin-producing) strains of Corynebacterium diphtheriae can cause diphtheria, but nontoxigenic strains of C. diphtheriae cannot

Steps in Pathogenesis (6)

1. Entry of pathogen into body 2. Attachment of the pathogen to some tissue(s) within the body 3. Multiplication of the pathogen 4. Invasion or spread of the pathogen 5. Evasion of host defenses 6. Damage to host tissue(s)

4 Phases of Infectious Disease (IPIC)

1. Incubation Period 2. Prodromal Period 3. Period of Illness 4. Convalescent Period

Infectious Disease

A disease caused by a microbe, and the microbes that cause infectious diseases are referred to as pathogens

Infection vs. Infectious Disease

A person can be infected with a pathogen, but not have an infectious disease; colonization

Pathogenicity

Ability to cause disease

Subacute Disease

Comes on faster than chronic disease, and slower than acute diseaseEx: bacterial endocarditis (SBE)

2. Prodromal Period

First signs/symptoms of disease (not specific); general feeling of sickness; unwell, off

Latent Infections

Infectious diseases that go from being symptomatic to asymptomatic and then later symptomatic Ex: Syphilis, herpes virus infections (cold sores, genetical herpes, shingles)

Localized Infections

Once infected; disease remains localized in one area Ex: pimples, boils, abscesses

Primary vs. Secondary Infections

One infectious disease follows another -first disease: primary -second disease: secondary Ex: bacterial pneumonia caused by viral respiratory infection -Mechanism: primary infection virus damages cilitated epithelial cells of respiratory tract; unable to clear opportunistic bacterial pathogens from respiratory tract, leading to secondary infection (bacterial pneumonia)

Endotoxins

Part of the cell wall structure of Gram-negative bacteria-cause serious adverse physiologic effects such as fever and shock

1. Incubation Period

Pathogen is multiplying, period from arrival of pathogen to onset of symptoms

4. Convalescent Period

Period of recovery; could result in normalcy, disability, or death :(

Exotoxins

Poisonous proteins secreted by a variety of pathogensEx: Neurotoxins, enterotoxins, exfoliative toxin, erythrogenic toxin, leukocidins*major mechanism by which pathogens cause disease

Toxins

Poisonous substances released by various pathogens 2 types:

Acute Disease

Rapid onset, followed by rapid recovery Ex: Measles, mumps, influenza

Chronic Disease

Slow onset and lasts a long time Ex: Tuberculosis, leprosy, syphilis

3. Period of Illness

Specific signs/symptoms of disease--communicable diseases most easily transmitted during this phase

Pathogenesis

Steps involved in the development of disease

Symptoms vs. Signs of Disease

Symptoms:-subjective (aches, pains, ringing, blurred vision, nausea) told by patient-symptomatic vs. asymptomatic diseases Signs:-objective evidence (high BP, abnormal heart rhythm, lab results)

Systemic Infections (generalized infection)

When the infection spreads throughout the body Ex: TB spreads to many organs