Introduction to Infectious diseases Flashcards
What are the 5 main groups of pathogens?
- Bacteria
- Viruses
- Protozoa
- Fungi
- Helminths
What is a manifested infection?
with typical clinical features
What is an asymptomatic/ subclinical infection?
without clinical and laboratory sign of infection but with molecular and pathophysiological changes
What is a persistent infection?
occurs after a microorganism has been dormant in the host, sometimes for years
What is an exogenous infection?
results from environmental pathogens
What is an endogenous infection?
results from the host’s normal flora (for instance, Escherichia coli displaced from the colon, which may cause urinary tract infection).
What is an acute infection?
is used to refer to microbe living inside a host for a limited period of time, typically less than three months.
If the microbe lives in a host between three and six month, we are talking about sub acute infection
What is a chronic infection?
infection that lasts longer than 6 months
What is a mixed infection?
is an infection by two and more infectious agents like Chickenpox and scarlet fever.
Coinfectionis the
What is a coinfection?
is the simultaneousinfectionof ahost by multiplepathogenspecies. For example the coinfection oflivercells withHepatitis B virusandHepatitis D virus.
What is a secondary infection?
is an infection by a microorganism that follows an initial infection by another kind of organism like Flu and Staphylococcus, Rickettsia and salmonella
What is a superinfection?
a second infection following the recovery of another infection
especially when caused by microorganisms that are resistant or have become resistant to the antibiotics used earlier.
What is a reinfection?
is a second infection that follows recovery from a previous infection by the same causative agent
What is a relapse?
The return of a disease or the signs and symptoms of a disease after a period of improvement.
What is a recidive?
Recurrence of clinical features even after apparent recovery
What is the definition of an infection?
When an infectious agent enters the body
An infection is not synonymous with an infectious disease
What is the infectious process?
interaction between the pathogenic microorganism, the environment, and the host.
What are the steps involved in the infectious process?
- Entry of pathogen into the host
- Local multiplication and spread
- Systemic spread and multiplication
- Exit of the pathogen from the host
How does the pathogen damage the host?
- Invasion and multiplication
- toxin production
- immunopathology
- combination of the above
What are the characteristics of infectious diseases? (6)
- caused by a specific agent
- specific agent enters through specific route
- periodicity and cyclic recurrence
- contagious disease/ communicable disease
- leads to immunity after recovery
How can we classify infectious diseases?
- By duration - acute vs chronic
- By burden - mild vs severe
- By nature - typical vs atypical (deleted, abortive, fulminant)
- By localization - local vs systemic
What are deleted atypical by nature infectious diseases?
- without a typical symptom or syndrome
What are abortive atypical infectious diseases?
- with typical onset and fast extinction of the symptoms
What is fulminant atypical infectious diseases?
- coming on suddenly with great severity
What are the phases of infectious disease?
- Incubation period
- Prodromal period
- Clinical phase
- Decline phase
- Recovery phase
What is involved in the incubation period?
time between infection and the appearance of signs and symptoms.
What is involved in the prodromal phase?
mild, nonspecific symptoms that signal onset of some diseases.
What is involved in the clinical phase?
a person experiences typical signs and symptoms of disease.
What is involved in the decline phase?
symptoms subside
What is involved in the recovery phase?
symptoms have disappeared, tissues heal, and the body regains strength
What is symbiosis?
interaction between two different organisms living in close physical association, typically to the advantage of both.
What are the three forms of symbiosis?
- Mutualism
- Commensalism
- Parasitism
What are the three forms of symbiosis?
- Mutualism
- Commensalism
- Parasitism
What are the three forms of symbiosis?
- Mutualism
- Commensalism
- Parasitism
What is mutualism?
- both the microorganism and the host work together.
What is commensalism?
either the body or the microorganism benefits, while the other is not affected negatively by the interaction
What is parasitism?
one organism benefits and at the expense of the other
What is a host defense?
Micro organism cannot invade unless it overcomes the host’s defenses
these may include:
- skin barrier, pH, mucous, non-specific inflammatory responses, specific immune responses
How can the pathogen overcome host defenses?
- A primary pathogen (causes disease in a healthy host)
- Opportunistic pathogen (causes disease in an immunocompromised host)
What are pathogen defenses?
contain virulence factors
- promote disease formation
- provide opportunity for the microbe to infect and cause disease
- adhere to host
- colonize host
- evade host defenses
How are pathogens transmitted?
- direct contact - skin to skin, mucous to mucous, across placenta, breastmilk, sneeze, cough
- indirect contact - airborne, foodborne, waterborne, objects
- vectors - carriers of infectious agents
What factors influence disease transmission?
- Agent
- Host
- Environment
Which factors in relation to the agent influence the transmission of a disease?
Infectivity
Pathogenicity
Virulence
Antigenic stability
Survival
Which factors in relation to the host influence the transmission of a disease?
Age
Sex
Genetics
Behaviour
Nutritional status
Health status
Which factors in relation to the environment influence the transmission of a disease?
Weather
Housing
Geography
Occupational setting
Air quality
Food
What is adherence?
whether or not the microorganism can attach itself onto the host cell membrane.
If a microorganism cannot adhere to a host cell membrane, disease will not occur.
How do microbes attach themselves onto host tissue?
- They have ligands - projections that attach host receptors of surface proteins
- examples:
tissue tropism - pathogens prefer specific tissues over others
species specificity - pathogen that only infects certain species
genetic specificity
What is invasion?
Microorganisms are exposed to many barriers after introduction into the host.
Some bacteria are able to cause disease while remaining on the epithelial barriers, while many need to penetrate that barrier.
Once this barrier has been penetrated, these pathogens can multiply without competition.
What is colonisation?
multiplication of pathogenic organisms where toxins are produced and the normal flora are overcome
- host shows signs of septicemia
What is the infectious dose?
For infection to proceed an infectious dose should be determined.
This is the minimal number of microbes necessary to establish infection.
How do microorganisms evade host defenses?
- intracellular pathogens - live inside the cell
- produce capsules that prevent phagocytosis
- produce membrane damaging toxins which kill phagocytes
- interfere with complement activation
- survive in the phagocyte
- pathogens produce proteases (avoid antibodies) and catalases (prevents digestion of an engulfed pathogen)
- antigenic variation to later antigen structure
- can mimic host molecules - cause disease-related damage
How do microbes cause damage to host while avoiding host defenses?
direct and indirect methods
What are some direct methods by which pathogens cause harm to the host while avoiding host defense mechanisms?
- exotoxins
- Endotoxins
- exoenzymes
What are exotoxins?
- Proteins secreted by pathogens that cause damage to the host (botulinum toxin, tetanus toxin, hemolysin (ruptures red blood cells).
What are endotoxins?
- Toxic substances that are released when the bacterial cell is killed (Lipolysaccharides).
What are exoenzymes?
- Enzymes that function outside the host cells or tissues. These include coagulase (forms a fibrin clot that “hides” the microbe from phagocytosis), hyaluronidase (breaks connective tissues down), or fibrinase (breaks down blood clots to allow pathogens to continue spreading).
How does the pathogen exit the host?
- A pathogen must exit the body. This occurs through various routes.
Examples include sneezing, coughing, diarrhea, coitus, pus, blood, or insect bites.
How do pathogens survive outside of the host?
a pathogen must be able to survive in the environment long enough to be transmitted to another host.
Some are hardy and can survive for several weeks before a new host is found.
There are others that survive in animal reservoirs or require direct contact because they are fragile.
What is an emerging infectious disease?
Newly identified & previously unknown infectious agents that cause public health problems either locally or internationally
What are re-emerging infectious diseases?
- infectious agents that have been known for some time
- had fallen to such low levels that they were no longer considered public health problems
- now showing upward trends in incidence or prevalence around the world
what are some agent factors that contribute to emergence?
- evolution of pathogenic infectious agents (microbial adaptation)
- resistance to drugs
- resistance of vectors to pesticides
what are some agent factors that contribute to emergence?
- evolution of pathogenic infectious agents (microbial adaptation)
- resistance to drugs
- resistance of vectors to pesticides
What are host factors that contribute to emergence?
- mass migration of poeple
- Migration of labor population from rural to urban areas in unhygienic squatter settlements
- International travel as a result of trade and tourism contributing to global dispersion of disease agents, disease reservoirs and vectors
- Changes in lifestyle
- Declining immunity of as a result of HIV infection, which make him vulnerable to a host of infections.
What are the environmental factors that are contributing to emergence?
- Environmental sanitation characterized by unsafe water supply , improper disposal of solid and liquid waste, poor hygienic practices and congested living conditions all contribute to emergence of infection
- Climatic changes resulting from global warming inducing increased surface water evaporation , greater rainfall changes in the direction of bird migration and changes in the habitat of disease vectors are also contributory factors
