Lecture 11: Pathogenicity & Epidemiology Flashcards
What is the ability to cause disease
Pathogenicity
What is the extent of pathogeniciy?
Virulence
What are the virulence factors?
adhesion factors
extracellular enzymes
toxins
antiphagocytic factors
What are the exo enzymes/ secreted enzymes?
Coagulase: coagulate blood
Kinases: Digest fibrin clots
Hyaluronidase: Hydrolyses hyaluronic acid
Collagenase: Hydrolyzes collagen
IgA proteases: destroy IgA antibodies
Siderophores: take iron from host iron-binding proteins
Antigenic variation: alter surface proteins
What are the adhesion factors on microbes?
Surface lipoproteins or glycoproteins called ligands bind to receptors on host cells
Ability to change or block the ligand or its receptor can prevent infection
Inability to make attachment proteins or adhesions renders the microorganisms avirulent
What are substances that contribute to pathogenicity?
Toxin
Ability to produce a toxin
Toxigeniciity
Presences of toxin the host’s blood
Toxemia
Inactivated toxin used in a vaccine
Toxoid
Antibodies against a specific toxin
Antitoxin
What are the characteristics of exotoxins that are extracellular and secretal?
Source: mostly Gram+
Metabolic product: by-products of growing cell
Chemistry: protein
Fever?: No
Neutralized by antitotoxin: yes
LD50: Small
Where are exotoxins produced?
Inside mostly gram-positive bacteria as part of their growth and metabolism.
They are then secreted or released following lysis into the surrounding medium
Type I, type II, and type III toxins
Explain type 1 toxins: superantigens
Cause an intense immune response due to (overhwelming amount of) cytokine released by hosts
Fever, nausea, vomiting, diarrhea, shock, death
Explain II toxins
Membrane-disrupting toxins
Lyse host’s cells:
Makes protein channels in the plasma membrane (eg leukocidins, hemolysins)
Disrupts phospholipid bilayer
Explain III A-B toxins
- Bacterium produces and releases exotoxin
- B (binding) component of exotoxin binds to host cell receptor and exotoxin enters cell
- A (active) component of exotoxin alters cell function by inhibiting protein synthesis
Describe endotoxins characteristics
Source: Gram negative
Metabolic product: present in LPS of outer membrane
Chemistry: Lipid A
Fever?: Yes
Neutralized by antitoxin: no
LD50: relatively large
Describe endotoxins
Endotoxins are part of the outer portion of the cell wall of gram-negative bacteria. They are liberated when the bacteria die and the cell wall breaks apart
Describe antiphagocytic factors
Certain factors prevent phagocytosis by the host’s phagocytic cells
-Bacterial capsule: composed of same chemicals found in host’s body
-Slippery - difficult for phagocytes to engulf the bacteria
-Antiphagocytic chemicals
-some prevent fusion of lysosome and [phagocytic vesicles
-Leukocidins directly destroy phagocytic white blood cells
What are the cytopathic effects of viruses?
Pathogenic properties of fungi
Fungal waste products may cause symptoms
Chronic infections provoke an allergic response
some fungi have toxins called mycotoxins
can also have capsule that prevents phagocytosis
Pathogenic properties of protozoa
presence of protozoa
protozoan waste products may cause symptoms
avoid host defenses by
-growing in phagocytes
-antigenic variation
Pathogenic properties of helminths (parasites0
use host tissue
presence of parasite interferes with host function
parasites metabolic waste can cause symtoms
Principles of epidemiology
Pathology: study of disease
Etiology: study of the cause of a disease
-Pathogenesis: development of disease
-Infection: colonization of the body by pathogens
-Disease: an abnormal state in which the body is not functionally normal
Pathogenic properties of algae
neurotoxins produced by dinoflagellates
-saxitoxin
- paralytic shellfish poisoning
Normal microbiota or macrobiota
permanently colonize the host
Mechanisms of pathogenicity (chart)
Transient microbiota
present for hours, days, weeks, or months
-cannot persist in the body
-competition from other microorganism
-elimination by the body’s defenses cells
-chemical or physical changes in the body
can’t colonize in the body
Symbiosis
close, long-termed reactions between two organisms
Commensalism
one organism is benefited and the other is unaffected
Mutualism
both organisms benefit
Parasitism
one organism is benefited at the expense of the other
Relationship between normal microbiota and the host is an example of?
Mutualism
Probiotics
Living microbes applies to or ingested into the body intended to exert a beneficial effect
Normal microbiota and the host
Normal microbiota protect the host by:
-occupying niches that pathogens might occupy
-producing acids
-producing bacteriocins
Some normal microbiota are opportunistic pathogens
Microbial antagonism
Competition between microbes
Contamination vs infection
Contamination- mere presence of microbes in or on the body
Infection - an organism has evaded the body’s external defenses, multiplied, and become established in the body
Resident/normal/ permanent microbiota
see chart
Portals of entry
Sites through which pathogens enter the body
-skin (broken)
-mucous membranes (nose, eyes, ears, mouth, vagina, anus, penus, urethra)
-placenta
-parenteral route (insect bite, injection, needle)
Locations of normal microbiota in humans
chart
When does a person acquire normal flora?
-essentially through birth
-food, people, environment - mature normal flora
How does a bacteria attach itself to the host?
-Capsule, fimbriae, etc.,
Opportunistic pathogens
Normal microbiota that can cause disease under certain circumstances
Conditions that provide opportunities for pathogens
-immune suppression
-Changes in the normal microbiota- changes in the relative abundance of normal microbiota may allow opportunity for a member to thrive and cause disease
-introduction of normal microbiota into unusual site in the body
Skin
outer layer of packed, dead, skin cells
usually a barrier to pathogens
pathogens can enter
-through opening or cuts
-some can burrow into or digest the outer layers of skin
Parenteral route
not a true portal of entry, since its via injection or insertion
pathogens deposited directly into tissues beneath the skin or mucous membranes
Mucous membrane
line the body cavities that are open to the environment
provides a moist, warm environment
respiratory tract is the most commonly used site of entry
- entry is through the nose, mouth or eyes
gastrointestinal tract
- pathogens must be able to survive the acidic pH of the stomach
Pathogenic organisms
portal of entry
attachment or adhesion to cause infection
- bacteria viruses, and protozoa (parasites)
Infection - the invasion of the host by a pathogen
Disease - results only if the invading pathogen alters the normal functions of the body, also referred to as morbidity
Koch’s postulates
see chart
used to prove the cause of an infectious disease
Sign
a change in a body that can be measured or observed as a result of disease
Exceptions to Koch’s postulates
Classifying infectious diseases
Symptom
a change in body function that is felt by a patient as a result of disease
Syndrome
a specific group of signs and symptoms tha accompany a disease
Communicable disease
a disease that is spread form one host to another (also contains contagious disease)
Contagious disease
a communicable disease that is easily spread
Non-communicable disease
a disease that is not transmitted from one host to another
Severity of duration of a disease
Acute disease
symptoms develop rapidly
Severity of duration of a disease
Chronic disease
disease develops slowly
Severity of duration of a disease
Subacute disease
Symptoms between acute and chronic
Severity of duration of a disease
Latent disease
disease with a period of no symptoms when the patient is inactive
Extent of host’s involvement:
Local infection
pathogens limited to a small area of the body
Extent of host’s involvement:
Systemic infection
an infection throughout the body
Extent of host’s involvement:
Focal infection
Systemic infection that began as a local infection
Extent of host’s involvement:
Bacteremia
Bacteria in the blood
Extent of host’s involvement:
Septiicemia
Growth of bacteria in the blood
Extent of host’s involvement:
Toxemia
toxins in the blood
Extent of host’s involvement:
Viremia
viruses in the blood
Extent of host’s involvement:
Primary infection
acute infection that causes the initial illness
Stages of infections
following infection, sequence of events called the disease process occurs
Many infectious diseases have five stages following infection:
- Incubation period: no signs or symptoms
- Prodromal period: vague, general symptoms
- Illness: most severe signs and symptoms
- Decline: declining signs and symptoms
- Convalescence: no signs or symptoms
Extent of host’s involvement:
Subclinical disease
No noticeable signs or symptoms (inapparent infection)
Extent of host’s involvement:
Secondary infection
Opportunistic infection after a primary (predisposing) infection
Predisposing factors
Make the body more susceptible to disease
-inherited traits such as the sickle-cell gene
-climate and weather
-fatigue
-age
-lifestyle
-male/female - short urethra in females
-chemotherapy
Movement of the pathogens out of the host
Pathogens leave host through portals of exit
see chart
Reservoirs of infections
continual sources of infection
humans: carriers may have inapparent infections or latent diseases
animals: some zoonoses may be transmitted to humans
nonliving things (soil)
Transmission of disease: contact
Directo contact: close association between infection and susceptible host
Indirect contact: spread\ by fomites (touching surface that is contaminated)
- or droplet transmission via airborne droplets
Relative frequency of nosomial infections
see pie chart
Nosocomial infections
Are acquired as a result of a hospital stay
5-15% of all hospital patients acquire nosocomial infections
see chart
Transmission of diseases: vehicle and vector
Vehicles: transmission by an inanimate reservoir (food, water)
Vectors: arthropods, especially fleas, ticks, and mosquitoes
- Mechanical arthropod carries pathogen on feet
-Biological pathogen reproduces in vector (intermediate hosts)
Transmission of disease
see chart
Occurrence of disease:
Prevalence
Fraction of a population having a specific disease at a given time
Epidemology
The study of where and when diseases occur and how they are transmitted in a population
Emerging new diseases and contributing factors
Occurrence of disease:
Incidence
fraction of a population that contracts a disease during a specific time period
Occurrence of disease:
Pandemic disease
worldwide epidemic -
disease that occur in a large area and also occur occasionally
Occurrence of disease:
Epidemic disease
disease that occur in a large area and also occur occasionally
Occurrence of disease:
Sporadic disease
disease that occurs occasionally in a population
Occurrence of disease:
Endemic disease
Disease constantly present in a population
Disease acquired by many hosts in a given area in a short time
