Pathogenesis of microbial Infection Flashcards
(46 cards)
Symbiosis definition
-The close and often long-term interaction between two different
biological species
What are the 3 types of symbiotic associations
Commensalism:
-one organism benefits and the other derives neither benefit nor
harm.
Mutualism:
-association which is beneficial to both organisms involved
Parasitism:
-one organism, the parasite, benefits at the expense of the other
Obligate intracellular vs facultative parasites
-Obligate intracellular parasites can only reproduce within host cells (e.g. intracellular bacteria like Chlamydia and all viruses)
-Facultative parasites do not rely on
the host to continue their life-cycle and can live/reproduce inside and outside cells (e.g. Salmonella)
Normal flora definition and functions
-Population of microorganisms that reside in the skin, mucous membranes and intestinal tract of human body
1. Helps development of mucosal immunity
2. Protects host from colonisation with pathogenic microbes
3. Aids in digestion of food
Human microbiome definition
-Collection of genes of all the
microbes in normal flora
Why is knowledge of the normal flora of the human body important?
-Allows prediction of the pathogens causing infection as bacteria tend to grow in specific body sites
e.g. Pneumococci frequently colonize the
upper respiratory tract, and are believed to act as a reservoir for infection of the lower respiratory tract
-Investigation for underlying abnormalities in specific areas of the body when bacteria are
isolated from normally sterile sites
e.g. alpha-hemolytic streptococci in the
throat is considered normal flora, whereas in the blood is likely the cause of bacterial endocarditis
Resident vs transient flora in hand hygiene
Why does flora change during hospitalisation?
-Exogenous environmental
infections (e.g. hospital
flora found on linen,
equipment, water supply)
-Invasive techniques
employed increase risk of
infection (e.g. urinary
catheters, I.V. lines)
-Use of antibiotics
What are opportunistic infections?
-Caused by non-pathogenic microorganisms that act as pathogens in certain circumstances:
-Normal flora moves to other parts of the body causing
infection (e.g. E coli can ascend urethra and cause UTIs)
-If host defence mechanisms are weakened (e.g. immunocompromised patients)
-Lack of competition from normal flora due to its loss from body (e.g. vaginal yeast infections due to use of
antibiotics)
Infection definition
The presence of microorganisms in the body
Colonisation definition
Describes when a new microorganism grows on superficial body sites
(skin, mucous membranes and GI tract) without invading the body
Carrier definition
A person who harbours a microorganism and can be a source of infection for others
Pathogen definition
A microorganism capable of causing disease
Microbial pathogenesis
The process by which infection leads to disease
What is the course of infectious diseases?
What does immunopathogenesis cause?
Immunopathogenesis is a primary cause of cell death in many infections is due to killing of infected cells by the host immune system:
-Cytotoxic T cell mediated attack (e.g. Hepatitis B virus and liver damage)
-Antibody-mediated damage to the host (e.g. Streptococcus pyogenes and rheumatic fever)
-Antibody-mediated complement fixation (e.g. Hepatitis C virus exploits the complement system to establish persistence)
Symptom vs Sign vs Syndrome
-Symptoms: Subjective features of
disease experienced only by the
patient. Infections can be
asymptomatic (sub-clinical) or
symptomatic
-Sign: Objective manifestations of
disease that can be observed and
measured by others
-Syndrome: Group of symptoms and
signs characteristic of a disease
Local effects vs systemic effects in response to infection
Local effects:
-Inflammation (swelling)
-Tissue necrosis
-Nasal congestion
Systemic effects:
-Fever
-Altered immune response
-Muscle pain (myalgia)
Obligatory steps for infectious agents
Stages of infectious disease progression
1) Incubation: Time between exposure and onset of a specific clinical sign.
2) Prodrome: Period during which non specific “constitutional” symptoms occur (e.g. fever, malaise, loss of appetite) Not all infectious diseases have a prodromal stage.
3) Illness: Period when clinical features of the infection are present
4) Recovery (convalescence): Period when the illness abates and patient
returns to healthy state
Communicable vs Non-communicable disease
Communicable: The infection can spread from host to host directly (e.g. HIV) or indirectly (e.g. noroviruses)
-The term contagious is applied to a highly communicable disease spread by contact
Non-communicable: The infection is non
transmissible between humans (e.g. botulism)
What are the types of infections based on occurrence?
-Sporadic: the disease occurs only occasionally (e.g. tetanus)
-Endemic: the disease is continously present in a population, community or country (e.g. TB and chickenpox)
-Epidemic: the disease has greater number of cases than normal in an area within a short period of time i.e. outbreaks occur (e.g. SARS in 2003)
-Pandemic: epidemic disease that has
worldwide distribution (e.g. flu pandemic in 1918 and 2009)
What are the types of infections based on site of infection?
Superficial:
-self limiting, microorganisms replicate in epithelium at the site of entry and local damage is caused (e.g. impetigo or folliculitis caused by Staph. aureus and
common cold caused by rhinovirus)
-immune response to superficial infections can give rise to constitutional
symptoms (e.g. cytokine storm and influenza)
Systemic:
-replication of microorganism at multiple sites due to infection of deeper tissues
-spread throughout the body primarily via lymph and blood (e.g. chickenpox, measles, Salmonella typhi)
What are the types of infections based on outcome?
Acute infection:
-Rapid onset of disease with relatively brief period of symptoms. The pathogen is cleared within days (e.g. influenza, poliovirus, measles)
Persistent infection:
-The pathogen is not cleared from the host following primary infection, but remains in tissues of infected
individuals
