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Infectious disease
disease caused by a microbe
pathogens
microbes that cause infectious diseases are collectively referred to as
Infection
commonly used as a synonym for infectious disease (e.g. an ear infection is an infectious disease of the ear)
What do microbiologists reserve the word infection to mean?
colonization by a pathogen; the pathogen may or may not go on to cause disease
What happens when a person is infected by a pathogen?
they could be infected but not have an infectious disease
Why infection doesn’t always occur
microbe lands on anatomic site —> unable to multiply
pathogens aren’t able to attach to specific receptor sites before they are able to multiply and cause damage
indigenous microflora may inhibit growth of the foreign microbe
indigenous microflora may produce antibacterial factors (i.e., bacteriocins) that destroy the pathogen
the individuals nutritional and overall health status often influences the outcome of the pathogen-host encounter
the person may be immune to that particular pathogen
phagocytes present in the blood may destroy the pathogen
Four periods or Phases in the course of an infectious disease
the incubation period
the prodromal period (“maybe”) (i think, i might be sick)
the period of illness
the convalescent period
Localized Infection
once an infectious process is initiated, the disease may remain localized or it may spread
Examples of localized infections
pimples, boils, abscesses (skin)
Systemic or generalized infections
when the infection spreads throughout the body
Acute disease
rapid onset, and is usually followed by a relatively rapid recovery
Acute disease examples
measles, mumps, and influenza
Chronic disease
slow onset and lasts a long time
Chronic disease examples
tuberculosis, leprosy, syphilis
Subacute disease
comes on more suddenly than a chronic disease, but less suddenly than an acute disease
Subacute disease examples
bacterial endocarditis
Symptom of a disease
some evidence of a disease that is experienced by the patient; subjective
more difficult to assess —> further symptoms
“I saw the sign”
the symptomatic and asymptomatic
Example of symptoms
aches or pains, ringing in the ears, blurred vision, nausea, dizziness
Sign of a disease
some type of objective evidence of a disease
Examples of signs of a disease
elevated blood pressure, abnormal heart sounds, abnormal pulse rate abnormal laboratory results
Latent Infections
infectious diseases that go from being symptomatic to asymptomatic, and then later, go back to being symptomatic
Examples of latent infections
syphilis and herpes virus infections such as cold sores, genital herpes, and shingles
Primary infection
the first disease
Secondary infection
the second disease
Example of one infectious disease may commonly follow another
serious cases of bacterial pneumonia frequently follow mild viral respiratory infections
What happens during the primary infection?
the virus causes damage to the ciliated epithelial cells of the respiratory tract; these cells are then unable to clear opportunistic bacterial pathogens from the respiratory tract, leading to the secondary infection (easier to develop because already susceptible)(pneumonia)
Steps in the Pathogenesis of Infectious Diseases - EAM SED
entry of the pathogen into the body
attachment of the pathogen to some tissues within the body
multiplication of the pathogen
invasion or spread of the pathogen
evasion of host defenses
damage to the host tissue
EAM SED - “ eam sed (said) these are the steps”
1-5 is just infection, 6 damage
Virulent
synonym for pathogenic
Strain species
virulent (pathogenic) strains and avirulent (nonpathogenic) strains
Virulent strains VS Avirulent strains
virulent strains are capable of causing disease; avirulent strains are not
Example of virulent and avirulent strains
toxigenic strains of Corynebacterium diphtheriae can cause diphtheria, but nontoxigenic strains of C. diphtheriae cannot. Thus, the toxigenic strains are virulent, but the nontoxigenic strains are not
Virulence occasionally used to…
express the measure or degree of pathogenicity - how virulent something is
Example of virulence (degree of pathogenicity)
it only takes 10 shigella cells to cause shigellosis, but it takes between 100 and 1000 salmonella cells to cause salmonellosis. Thus, shigella is more virulent than Salmonella
some strains of streptococcus pyogenes (flesh eating strains) are more virulent than other strains of S. pyogenes
Virulence factors
attributes that enable pathogens to attach, escape, destruction, and cause disease
Examples of ways virulence factors attach
adhesins and pili
adhesins (ligands)
special molecules on the 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 within the human body
What are considered to be virulence factors
capsules and flagella
Examples of encapsulated bacteria
Streptococcus pneumoniae, Klebsiella pneumoniae, Haemophilus influencae, and Neisseria meningitidis
Why are flagella are virulence factors?
they enable flagellated bacteria to invade aqueous areas of the body; many also help the bacterium to escape phagocytosis
Toxins
poisonous substances released by various pathogens
2 types of toxins
endotoxins and exotoxins
endotoxins
parts of the cell wall structure of Gram-negative bacteria
can cause serious, adverse physiologic effects such as fever and shock
exotoxins
poisonous proteins secreted by a variety of pathogens
Examples of exotoxins
neurotoxins, enterotoxins, exfoliative toxin, erythrogenic toxin, leucocidins
Exfoliative toxin example
causes skin to peel off
scalded skin syndrome
Leukocidins example
destroy white blood cells —> evade immune system
Neurotoxin example
botulism
Exoenzymes released by bacteria include
necrotizing enzymes, kinases, collagenase, lecithinase, coagulase, hyaluronidase, hemolysins
Mechanisms by which pathogens escape immune response
antigenic variation, camouflage and molecular mimicry, destruction of antibodies
antigenic variation
changing their surface antigens
camouflage and molecular mimicry
some organisms conceal their foreign nature by coating themselves with host proteins
destruction of antibodies
some pathogens produce IgA protease an enzyme that destroys some of the hosts antibodies, ex. Haemophilus influenzae
Why do you need yearly vaccines sometimes?
influenza and covid very good at constantly changing