Infection: A state of tissue destruction resulting from invasion of microorganisms
Communicable: transferred from one person to another
1.Contact Transmission: is the spread of pathogens from one host to another by direct contact
(touching), indirect contact (thru fomites, which are inanimate objects that transfer pathogen), and
respiratory droplets (less than 1 meter is contact transmission, more than 1 meter is airborne transmission
= vehicle transmission)
2. Vehicle Transmission: is the spread of pathogens via airborne transmission (more than 1 meter
travelled via aerosol, cloud of droplets), waterborne transmission, and foodborne transmission as well
as bodily fluid transmission being handled outside the body.
3. Vector Transmission: are animals that transmit diseases from one host to another.
1. Biological vectors (which not only transmit pathogens but also serve as hosts)
2. Mechanical vectors (which do not serve as hosts but as simple transportation
to new hosts, on their feet or other body parts).
Non-communicable: Caused by genetics/environment
Bacteria: Can survive without the host, aerobic/anaerobic (survives best in deep tissue, makes it
harder to treat).
Cocci (sphere), bacilli (rods)
-nucleus does not have a CM, not separate from cytoplasm
- rigid cell wall
Gram positive = Release exotoxins (exo = outside, result in host cell dysfunction/lysis)
Gram negative = Release toxins in the cell (endo = inside, the LPS)
Pyogenic bacteria- fever inducing
Virus: Can’t survive without the host (obligate)
- If viral infection sparks an strong immune response, it can lead to neutralization of the virus
and control the infection. Infection will cease after a definite period.
- If not strong enough, can lead to chronic infection
Fungi: have a nuclear membrane. Unicellular= yeasts, Multicellular= molds, replicate by
- are common resident microbes, which are also opportunistic.
Mycoses/ Mycotic: refer to infections with fungi Chain of Infection
1. Infectious Agent/ Pathogen
2. Reservoir- need
antimicrobials to break the
3. Portal of Exit- wear mask,
4. Means of transmission-
direct, droplet, airborne,
5. Portal of Entry- cover and
protect entry points (gloves,
6. Susceptible Host
Types of Infection:
Pathogenicity: qualities that promote production of the disease. Includes: potency, invasiveness,
ability to evade immune system, spread of disease, production of toxins, tissue damage it elicits
Virulence: the potency of the pathogen, which is indicated by the ratio of the number of cases of
disease in a population compared to the number of people exposed. (Most virulent= causes
disease in most of those exposed).
Infectivity: proportion of exposures needed to cause infection. (Most infective= exposure=
Toxigenicity: ability of pathogen to produce toxins that cause tissue damange
Antigenicity: level to which a pathogen is see as foreign. Elicits immune response
Antigenic variability: eluding detection by altering antigens present (responsible for variation
Facultative parasite: may live on a host, but can survive independently. Bacteraemia: when septicemia is caused by bacteria.
Maceration: a softening and breakdown of tissues, often related to excessive moisture
Phases of Acute Infection
1. Exposure- any contact to pathogen
2. Incubation- once infected, but don’t realize you are sick (most contagious)
3. Prodrome- feeling of under the weather
4. Clinical illness- signs + symptoms, leads to diagnosis
5. Convalescence- return to normal.
Complications of Infection
1. Septicemia- Widespread infection that enters the bloodstream
- causes increased blood flow, increased vasodilation, increased capilliary permeability.
Eventually blood flow slows down, organs shut down, fever and low BP
Treatment: IV therapy to correct the fluid distribution, antibiotics, oxygen to correct
hypoxia. Draw blood to get an indication of cause
2. Chronic Infection- Immune response is always going on
Manifestations of Infection
incapacitation- affects the fx
lymphadenitis- inflamed lymph nodes
purulent exudates- can use charcoal dressings to help with odor