Chapter 14 Flashcards
1
Q
Reservoirs of Infectious Diseases of Humans
A
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Animal Reservoirs
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Zoonoses:
- Diseases that naturally spread from animal host to humans
- Acquire zoonoses through various routes:
- Direct contact with animal or its waste
- Eating animals
- Bloodsucking arthropods
- Humans are usually dead-end host to zoonotic pathogens
- Generally speaking, it is an one-way street; animals don’t consume humans and they don’t get too much contact with us.
- Humans pick up diseases from animals way more often whereas vice versa isn’t necessarily true.
- Emergent diseases tend to be zoonoses e.g. AIDS
- Bushmeat - consuming all kinds of wildlife animals.
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Zoonoses:
- **Human Carriers **– Infected individuals who are asymptomatic but infective to others. Ex: Typhoid Mary
- Some individuals eventually develop illness while others never get sick
- Healthy carriers may have defense systems that protect them
- e.g. Typhoid Mary - people around her started to get typhoid although she was asymptomatic herself
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Nonliving Reservoirs:
- Soil, water, and food can be reservoirs of infection
- Presence of microorganisms often due to contamination by feces or urine
- Also involve droplets in the air
- Biological Vector - animal that participates in lifecycle of pathogen. Ex: malira and mosquito via direct contact
- Mechanical Vector - contacts the pathogen but isn’t affected, carrier of the pathogen. Ex: cockroaches via indirect contact - no direct penetration or invasion
2
Q
Exposure to Microbes: Contamination and Infection
A
- Exposure to Microbes: Contamination and Infection
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Contamination
- The mere presence of microbes in or on the body
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Infection
- When organism evades body’s external defenses, multiplies, and becomes established in the body
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Contamination
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Portals of Entry
- Sites through which pathogens enter the body
- Four major pathways
– Skin
– Mucous membranes
– Placenta
– Parenteral route“not the gut” ex: wounds, broken skin, IV infection
- Routes of Entry for Invading Pathogens
- Ear, Conjunctiva of Eye, Nose, Mouth, Placenta, Vagina/Penis, Urethra, Anus, Insect Bite, Broken Skin
3
Q
Portals of Entry
A
- Portals of Entry
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Skin
- Outer layer of dead skin cells acts as a barrier to pathogens - Constantly shedding skin cells, can also transmit disease
- Some pathogens can enter through openings or cuts
- Others enter by burrowing into or digesting outer layers of skin
- Fomite - object with germs on its surface
- Outer layer of dead skin cells acts as a barrier to pathogens - Constantly shedding skin cells, can also transmit disease
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Mucous membranes
- Line the body cavities that are open to the environment
- Provide a moist, warm environment hospitable to pathogens
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Respiratory tract is the most common site of entry
- Entry is through the nose, mouth, or eyes
- Gastrointestinal tract may be route of entry
- Must survive the acidic pH of the stomach
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Placenta
- Typically forms effective barrier to pathogen
- Pathogens may cross the placenta and infect the fetus
- Can cause spontaneous abortion, birth defects, premature birth, congenital abnormalities
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Infections of the Fetus and Neonate
- T = Toxoplasmosis (Protozoa)
- O = Other
- R = Rubella
- C = Cytomegalo Virus
- H = Herpes Simplex
- Lead to congenital abnormalities, spontaneous abortions, prematurity
- Enterocyte - having to do with gut
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Parenteral route
- Not a true portal of entry
- Means by which the portal of entry can be circumvented
- Pathogens deposited directly into tissues beneath the skin or mucous membranes
- Not the gut, but different kinds of wounds or abrasions or even nosocomial from IV i.e. via open wounds on skin
- A “Catch-all” phrase
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Skin
4
Q
The Role of Adhesion in Infection
A
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The Role of Adhesion in Infection
- Process by which microorganisms attach themselves to cells
- Required to successfully establish colonies within the host
- Uses adhesion factors:
- Specialized structures
- Attachment proteins
- Adhesion = can be specific to species or tissues; adherence to glycoproteins on the cell; located on outer cell membrane, pili, fimbraie; Ex: slime layer, capsid proteins, viral spike, lipotechoic layer (cell wall associated) –> associated with adhesins glycoproteins
5
Q
Factors that Affect Disease Transmission
A
Factors that Affect Disease Transmission
- Just because you came in contact with germ does NOT necessarily mean you will automatically get infected:
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Infectious Dose - unique to each pathogen, amount required to be infectious
- Some only require a single bacteria, some require thousands
- the lower the infectious dose the easier it is to get the disease
- Does NOT tell how sick you will get
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Virulence - how easily it can get you sick
- high virulence doesn’t mean you get sicker, just means it is easier to get you sick
- minimal level of disease required to get you minimally sick
- Portal of Entry - needs to be the right portal for the germ
- Immune System of the Host - related to genetics of immune system like specific (T, B cells) and non-specific (mucus, stomach acid) factors
- **Environment and Exposure **- exposure to pathogen or vaccination
- **General Level of Health of the Host (Consitution) **- determined by diet (wholistic), age, immuno compromised (surgery, AIDS), stress
6
Q
The Role of Adhesion in Infection
A
The Role of Adhesion in Infection
- Attachment proteins help in adhesion
- Found on viruses and many bacteria
- Viral or bacterial ligands bind host cell receptors
- Interaction can determine host cell specificity
- Changing/blocking a ligand or its receptor can prevent infection (some medications do this)
- Inability to make attachment proteins or adhesins renders microorganisms avirulent
- Some bacterial pathogens attach to each other to form a biofilm
7
Q
Manifestations of Disease
A
- Infection is the invasion of the host by a pathogen
- Disease results if the invading pathogen alters normal body functions
- Disease is also referred to as morbidity
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Comorbidity - occurs together with a disease
- Ex: karposi sarcome is comorbidity of AIDS
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Comorbidity - occurs together with a disease
- Manifestations of Disease: Symptoms, Signs, and Syndromes
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Symptoms
– Subjective characteristics of disease felt only by the patient; what a person reports and feels e.g. malaise (not feeling good), cramps, chills. -
Signs
– Objective manifestations of disease observed or measured by others; anything that doctor can measure and observe (some can be both symptom and signs) -
Syndrome
– Symptoms AND signs that characterize a disease or abnormal condition (ex: AIDS, marphan’s, down’s) - Asymptomatic, or subclinical - infections lack symptoms but may still have signs of infection
- Acute - at that moment, rapid
- Sub-acute - between acute and chronic
- Chronic - over time, long lasting
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Symptoms
8
Q
Virulence Factors (Terminology)
A
- Virulence Factors of Infectious Agents
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Pathogenicity
- Ability of a microorganism to cause disease
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Virulence
- Degree of pathogenicity
- Virulence factors contribute to virulence
- Adhesion factors
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factor
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Pathogenicity
9
Q
Virulence Factors
A
Extracellular enzymes (Exozymes)
- Secreted by the pathogen
- Dissolve structural chemicals in the body
- Help pathogen maintain infection, invade, and avoid body defenses
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Hyaluronidase and Collagenase
- Helps bacteria spread more rapidly
- Collagenase - in the extracellular matrix; secreted by bacteria; destroys collagen in ECM
- Hyaluronidase - a GAG; destroys hyaluronic acid and lets the bacteria spread
- Bacteria also make hyaluronic acid, is on outside of bacteria. Because of this the host may not recognize the bacteria and not generate immune response
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Coagulase and Kinase
- Coagulation is clot formation
- Coagulase reacts with clotting protein and can coat its surface of the bacterium with fibrin upon contact with blood. The fibrin clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host
- Bacteria coagulate blood so it can hide in clots
- Kinase later dissolves clots and helps the bacteria spread
- Streptokinase - clot buster, produced by bacteria and has medical applications
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Mucinase (Mucin = glycoprotein, gives mucus it’s slimy character); exoenzyme
- Degrades mucin, can help pathogen like an ameoba spread through digestive tract since mucus has a lot of antimicrobial content
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Keratinase (keratin = found in skin and hair)
- Degrades keratin, can help pathogens like ringworm spread on skin
10
Q
Virulence Factors (Toxins)
A
Toxins
– Chemicals that harm tissues or trigger host immune
responses that cause damage
– Toxemia refers to toxins in the bloodstream that are carried beyond the site of infection
– Two types
- **Exotoxins **- target specific cells. The more specific the more toxic the agent. Typically a small protein.
- **Endotoxins **- lipids from Gram Neg bacteria
- Toxinosis - suffering from disease caused by presence of a toxin. Viruses don’t produce toxins but bacteria can.
- Toxemia - toxin in the blood (Ex: tetanus)
- Intoxication - Presence of toxin inside of you, typically via food (Ex: food poisoning)
- Neurotoxin - nervous system affected
- **Enterotoxin **- intestines affected
- **Hemotoxin **- red blood cells affected
- Nephrotoxin - kidney affected
**Toxoid **- substance that is similar to a toxin, but isn’t really a toxin. Produced by humans to build immunity.
- Make toxoid from a toxin. Ex: denature exotoxin and produce a toxoid.
- When denatured the body will produce antibodies against it.
- Antibodies can react with the actual toxin.
Process:
Exotoxin (protein) => denatured => toxoid => antibodies created => antibodies will react with toxin
11
Q
Virulence Factors (Antiphagocytic Factors)
A
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Antiphagocytic factors
– Factors prevent phagocytosis by the host’s phagocytic cells-
Bacterial capsule
– Composed of chemicals not recognized as foreign
– Slippery; difficult for phagocytes to engulf bacteria
– e.g. hyaluronic acid -
Antiphagocytic chemicals
– Prevent fusion of lysosome and phagocytic vesicles into phagolysosomes
– Leukocidins (chemicals to kill leukocytes) directly destroy phagocytic white blood cells -
Antiphagocytic factors
- There are bacteria that live inside phagocytic cells e.g. Tuberculosis
- Again, evolution at work as bacteria evolve faster than humans do.
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Bacterial capsule
12
Q
Stages of Infectious Disease
A
- The Stages of Infectious Disease
– The disease process occurs following infection
– Many infectious diseases have five stages following infection:
- Incubation period = bacteria starts to grow inside;
- Prodromal period = period of malase (not feeling well); e.g. flu-like symptoms –> doesn’t mean its actually flu though.
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Illness = disease state
- In the US, # infections gone up but # death gone dramatically down.
- Decline/Death
- Convalescence = start to get better/stronger (unless you died, then you don’t usually get better)
- How basteria cause disease?
- toxins/virulence factors
- body has to compensate for presence of bateria, so it creates inflamation, which can hurt the body
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Emergent Diseases - long incubation is worse for host
- If you don’t know you have the disease it can be transmitted before symptoms are shown
- most of the common diseases have short incubation period
- this is not a predetermined number of days for every person, unique to each person
- e.g. Pneumonic plague - very short IP vs. Leprosis - years of IP
- What factors affect incubation period?
- virulence of bateria
- distance between portal of entry and target cell
13
Q
Portal of Exit
A
- Pathogens leave host through portals of exit
- Many portals of exit are the same as portals of entry
- Pathogens often leave hosts in materials the body secretes or excretes
- Examples: Eyes (tears), Noes (secretions), Mouth (saliva, sputum), Mammary glands (milk, secretions), Vagina (secretions, blood), Urethra (urine), Seminal vessicles (semen), Anus (feces), Skin (flakes), Broken skin (blood), Ear (earwax)
- **Fecal-Oral Route **- evolved because lack of water purification, affects water supply in many areas. Ex: polio virus
14
Q
Modes of Infectious Disease Transmission
A
- Transmission is from a reservoir or a portal of exit to another host’s portal of entry
- Three groups of transmission
- 1-Contact transmission
- Direct, indirect, or droplet
- 2-Vehicle transmission
- Airborne, waterborne, or foodborne
- 3-Vector transmission
- Biological or mechanical
- 1-Contact transmission
15
Q
Classification of Infectious Diseases
A
• Diseases can be classified in number of ways
– The body system they affect
– Taxonomic categories
– Their longevity and severity
– How they are spread to their host
– The effects they have on populations (rather than on individuals)
Don’t confuse disease with germ (germs cause disease)
• Terms used to classify infectious disease
– Acute disease
– Chronic disease
– Subacute disease
– Latent disease
– Communicable
– Contagious
16
Q
Epidemiology
A
- Epidemiology - study of where and when diseases occur and how they are transmitted
- Frequency of Disease
– Track occurrence of diseases using two measures-
Incidence
– Number of new cases of a disease in a given area during a given period of time -
Prevalence
– Number of total cases of a disease in a given area during a given period of time
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Incidence
- Occurrence also evaluated in terms of frequency and geographic distribution
17
Q
How Epidemiologists Report Data
A
18
Q
Terms of Occurance of Disease
A
- Endemic disease: found in certain level in regions in general, uniform distribution
- Sporadic: occasional cases
- Epidemic: beyond endemic - much higher level of cases concentrated in specific region (centralized)
- Pandemic: All over the world e.g. Spanish flu
