Epidemiology: Chapter 13 ( Host Microe interactions and epidemiology)

True pathogens

causes disease in healthy persons with a normal/healthy immune defenses

(ex. Influenza virus, plague bacillus, malarial protozoan)  

Opportunisitic pathogens

causes disease when the host’s defenses are compromised or when they move from a harmless location into a part of the body where they don’t belong

• (ex. Pseudomonas sp and candida albicans)

Portal of entry

what are the two types?

• characteristic routes a microbe follows to enter the tissues of the body 

  • Exogenous agents originate from source outside the body 

  • Endogenous agents already exist on or in the body aka our normal flora 

The portals of entry include ….

Sam grew really red under Phillip

1. Skin > nicks, abrasion, punctures, incisions 

2. Gastrointestinal tract > food, drink, and other ingested materials 

3. Repiratiory tract > oral and nasal cavities 

4. reproductive tract

5. Urinary tract

6. Placenta > Transplacental > passes through placenta from mother to the fetus

Portal of exit

departure of pathogens by a specific avenue > influencing the spread of the infection

types of portal of entry….

1. Respiratory tract + salivary glands > mucus, sputum, nasal drainage, saliva 

2. Epithelial cells > skin and scalp 

3. Fecal exit 

4. Urogenital tract > urinary + reproductive systems 

5. Removal of blood or bleeding 

Endemic

• persistent in a specific geographic location but the severity + prevalence is low to not be consider a threat to public health

Sporadic

• not common as it can be rare and hard to predict when it occurs 

Epidemic

a sudden increase in cases in a population

Point-source epidemic

infectious agent from a single source

Common source epidemic

all cases are from an contagious inanimate object (fomite)

Propragated epidemic

 cases occur due to person-to-person contact resulting in a continuous increase over time 

Pandemic

worldwide across many continents 

Incidence

• new cases that occur in a specific time period in a population as compared to the general healthy population 

Prevalence

is the # of new and old cases with respect to the whole population represented by a percentage of the population

Nosocomial

• health-care associated infections that are acquired or developed during a hospital stay

• (ex. Surgical procedures, equipment, personnel, and exposure to drug resistant microorganisms) 

Most common noscomial sites

• surgical incisions, respiratiory tract, GI tract, Skin, urinary tratc, and blood (sepsis)

What type of bacteria are involved in nosocomial infections

1. gram-negative intestinal flora (E.coli, Klebsiella, Pseudomonas) 

2. Gram positive bacteria (staphyloccoci and streptococci) and yeast 

3. True pathogens (Tubercle bacillus, Salmonella, Hepatitis B, and Influenza virus) 

Zoonosis

infections in animals transmitted to humans > infection becomes dead-end host (pathogen infects organisms > infection in organisms can’t be transmitted further) 

Fomite

inanimate objects aka Vehicles (food, water, biological products) 

Vectors:

• live animals (other then human > include arthropods / some mammals, birds, lower vertebrates) that transmits an infectious agent from one host to another

Biological vectors

• actively participate in a pathogens life cycle (ex. Mosquito with malaria) 

Mechanical vector

• are not needed in the life cycle of an infections agent > they are transporters of the agent ONLY, they do not get infected (house fly spreading bacteria) 

Communicable infections

• when an infected host can transmit the infectous agent to anothe host and establish infection in the host

Non communicable infections

• infectious diseases does not arise through transmission from host to host but rather by a persons own normal microflora (opportunistic pathogen )

  OR

• contact with infectious organisms in natural, non-living reservoir

Direct contact

• physical contact or fine aerosol droplets (someone breaths, talks, coughs, or sneezes)

• within 6 feet

Indirect contact

• passes from infected host to intermediate conveyor  and then to another host

  examples

• vehicles

• airborne > droplets (larger) + aerosols (tiny) 

• more then 6 feet