IAI - diagnosis and control of infection Flashcards
What is epidemiology?
Science that studies when and where diseases occur and how they are transmitted in a population.
what concept is used to explain how a patient can acquire an infection from another person
Chain of infection
What two main factors affect the spread of infection?
- Reservoirs of infectious organisms-places where pathogens can grow and accumulate
- Modes of transmission – the various ways in which pathogens move from place to place
What are reservoirs?
Habitat in which an infectious agent normally lives, grows,
and multiplies.
What are the 3 main modes transmission?
- Contact transmission
- Indirect transmission – vehicle or vector
- Horizontal (vs vertical)
Describe contact transmission.
A healthy person is exposed to pathogens by either touching or being close to an infected person or object.
What is direct contact transmission?
Person-to-person transmission (touching, kissing, sexual intercourse). No intermediate object is involved
Examples: Hepatitis A, Smallpox, Staphylococcal infections,
mononucleosis, sexually transmitted diseases such as syphilis or HIV/AIDS.
What is indirect contact transmission?
The microbe is transferred via a nonliving object or fomite, such as towels, eating utensils, thermometers, stethoscopes, bedding, clothes, money, and needles.
Examples: Herpes simplex virus, Cytomegalovirus, Giardia, Impetigo
What is droplet transmission?
- Microbes are spread in mucus droplets that travel short distances (less than 1 meter). It can occur through sneezing, coughing, or talking.
- Typical of respiratory viruses (e.g., influenza, adenovirus, respiratory syncytial virus, human metapneumovirus), Bordetella pertussis, Pneumococci, Diphtheria and Rubella.
What is vehicle transmission?
Transmission of disease via medium such as water, food, air, blood, body fluids, and intravenous fluids.
- Waterborne Transmission: Usually caused by water contaminated with sewage.
- Airborne Transmission: Not to be confused with droplet transmission, is due to inhalation of small pathogens and particles (e.g. bacterial and fungal spores) that are suspended in air and can travel long distances.
- Foodborne Transmission: Typically due to bad sanitation practices leading to contamination of food with pathogens
Examples: Anthrax, tuberculosis, salmonella, cholera, typhoid, legionella
What is vector transmission?
Transmission of disease via animals that carry disease from one host to another. Insects are most important animal vectors.
What is mechanical transmission?
Mechanical Transmission: Passive transport of pathogens on vector’s body.
- Flies are the most common vector. Most of the diseases can also be contracted more directly through contaminated food, water, air, hands and person-to-person contact
- Examples include enteric infections (dysentery, diarrhoea, typhoid or cholera) and eye infections (trachoma and conjunctivitis)
What is biological transmission?
- Biological Transmission: Pathogen spends part of its life cycle in the vector and transmission to the host is through a bite.
- Examples include malaria, Zika virus, Dengue fever, schistosomiasis and rabies
What is the difference between horizontal vs vertical transmission?
- Transmission from mother to child is called vertical transmission and can occur in utero across placenta, at the time of delivery or during breast feeding.
- Person-to-person transmission that is not between mother and offspring is called horizontal transmission.
- Examples include HIV, Rubella and toxoplasmosis
What are Koch’s 4 postulates?
- The microorganism must be found in abundance in all organisms suffering from the disease, but not in healthy organisms.
- The microorganism must be isolated from a diseased organism and grow in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
whats the exception for kochs first postulate?
Koch says “The microorganism must be found in abundance in all organisms suffering from the disease, but not in healthy organisms.”
Exceptions to the first postulate: Asymptomatic or
infectious diseases
- e.g. cholera or typhoid fever and viral infections such as polio, herpes simplex, HIV and hepatitis C
whats the exception for kochs second postulate?
Koch says “The microorganism must be isolated from a diseased organism and grow in pure culture.”
Exceptions to the second postulate: Some microbes cannot be grown in vitro or there are no susceptible animal species
- e.g. Treponema pallidum (syphillis), Mycobacterium leprae (leprosy) and wart viruses
whats the exception for kochs third postulate?
Koch says “The cultured microorganism should cause disease when introduced into a healthy organism.”
Exceptions to the third postulate: not all organisms exposed
to an infectious agent will acquire the infection
- e.g. resistance to malaria conferred by possessing at least one sickle cell allele.
What two methods are used in a diagnostic laboratory to confirm infection?
Direct detection methods:
clinical specimen is examined for the presence of a microbe or its products. ie:
- culture of bacteria
- culture of viruses
- microscopy
- detection of nucleic acids
Indirect detection:
- blood and other body fluids examined for antibody presence against pathogen
- serological test
What are the 3 different types of mediums in bacteria culturing?
- Defined medium: if the exact chemical composition is known.
- Enrichment medium: contains some component that permits the growth of specific types or species of bacteria, usually because they alone can utilise the component from their environment.
- Selective medium: Culture media designed to support the growth of only specific microorganisms (e.g. selection done by adding antibiotics or lacking amino acids).
what is Multiplicity of infection (MOI)
refers to the number of virions that are added per cell during infection.
What is selective toxicity?
selectively toxic substance is one that is harmful to the target organism but harmless to the host organism.
Achieved by exploiting the differences between the
metabolism and structure of microorganisms and the
human cells they infect.
What are antibacterial agents?
- Type of antimicrobial drug used in the treatment and prevention of bacterial infections.
what 2 things can antibacterial agents do?
- They may either kill (bactericidal) or inhibit the growth of bacteria (bacteriostatic)
