IAI - diagnosis and control of infection

Question 1

What is epidemiology?

Answer 1

Science that studies when and where diseases occur and how they are transmitted in a population.

Question 2

what concept is used to explain how a patient can acquire an infection from another person

Answer 2

Chain of infection

Question 3

What two main factors affect the spread of infection?

Answer 3

• 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

Question 4

What are reservoirs?

Answer 4

Habitat in which an infectious agent normally lives, grows,
and multiplies.

Question 5

What are the 3 main modes transmission?

Answer 5

• Contact transmission
• Indirect transmission – vehicle or vector
• Horizontal (vs vertical)

Question 6

Describe contact transmission.

Answer 6

A healthy person is exposed to pathogens by either touching or being close to an infected person or object.

Question 7

What is direct contact transmission?

Answer 7

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.

Question 8

What is indirect contact transmission?

Answer 8

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

Question 9

What is droplet transmission?

Answer 9

• 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.

Question 10

What is vehicle transmission?

Answer 10

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

Question 11

What is vector transmission?

Answer 11

Transmission of disease via animals that carry disease from one host to another. Insects are most important animal vectors.

Question 12

What is mechanical transmission?

Answer 12

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)

Question 13

What is biological transmission?

Answer 13

• 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

Question 14

What is the difference between horizontal vs vertical transmission?

Answer 14

• 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

Question 15

What are Koch’s 4 postulates?

Answer 15

• 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.

Question 16

whats the exception for kochs first postulate?

Answer 16

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

Question 17

whats the exception for kochs second postulate?

Answer 17

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

Question 18

whats the exception for kochs third postulate?

Answer 18

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.

Question 19

What two methods are used in a diagnostic laboratory to confirm infection?

Answer 19

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

Question 20

What are the 3 different types of mediums in bacteria culturing?

Answer 20

• 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).

Question 21

what is Multiplicity of infection (MOI)

Answer 21

refers to the number of virions that are added per cell during infection.

Question 22

What is selective toxicity?

Answer 22

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.

Question 23

What are antibacterial agents?

Answer 23

• Type of antimicrobial drug used in the treatment and prevention of bacterial infections.

Question 24

what 2 things can antibacterial agents do?

Answer 24

• They may either kill (bactericidal) or inhibit the growth of bacteria (bacteriostatic)

Question 25

What are 4 bacterial resistance strategies?

Answer 25

• By preventing drug from reaching its target by reducing its ability to penetrate the cell
• By inactivation of drug via modification or degradation
• By expulsion of the drug from the cell via general or specific efflux pumps
• By modification of the drug’s target site within the bacteria

Question 26

What are 5 viral resistance strategies?

Answer 26

• Results from spontaneous mutations in the viral genome during viral replication
• Mutations are within the target of the antiviral drug
• The error-prone polymerase enzyme in RNA viruses cause these viruses to develop resistance more frequently than DNA viruses
• Special concern during extended therapy for chronic infections (e.g. HIV, HBV and HCV)
• Combination therapy with more than one agent is commonly used to delay appearance of resistance.

Question 27

What are the types of adaptive immunity?

Answer 27

Question 28

What are the requirements of an effective vaccine?

Answer 28

• Safe, with no or few side effects – it must not cause disease!!
• Give long lasting, appropriate protection against the natural form of the pathogen
• Stimulate both a humoral and cell-mediated immune response and the production of memory cells.
• Low in cost
• Stable with long shelf life and no special storage requirements
• Easy to administer

Question 29

do keats quiz on diagnosis and control of infection

Answer 29

https://keats.kcl.ac.uk/mod/lesson/view.php?id=6620874

Question 30

what kind of immunity is ‘exposure to infectious agent’

Answer 30

active - natural

Question 31

what kind of immunity is ‘vaccination’

Answer 31

active - artificial

Question 32

what kind of immunity is ‘maternal antibodies’

Answer 32

passive - natural

Question 33

what kind of immunity is ‘injected antibodies’

Answer 33

passive - artificial

Question 34

why are viruses difficult to treat

Answer 34

because they rely upon their host cells for the majority of
their metabolic functions and selective toxicity is difficult to achieve.

Question 35

There are 6 links in the chain of infection and only eliminating the reservoir for the infectious agent can stop the transmission of infection

true or false

Answer 35

false. breaking any link in the chain of infection can stop the transmission of infection