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Disease Epidemiology #2 > Evolution and Ecology Part 2 > Flashcards

Evolution and Ecology Part 2 Flashcards

1
Q

SARS- CoV- 2 Delta Evolution

A
  • First detected in India Dec 2020
  • Case confirmed in UK Mar 2021
  • Delta replaced alpha from April to June, as it was better at transmission (70% higher; R0) and had a higher viral load over duration of infection and most people were not vaccinated
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2
Q

R0 evolution of delta Covid compared to alpha

A
  • Alpha had R0= 1-3
  • Delta had R0= 5-10
    o More competitive, transmissible and therefore causes ancestral strains to become extinct= evolution by natural selection
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3
Q

Evolution of antibiotic resistance (steps)

A

Occurs through natural selection
Steps:
1. Patient is infected with bacterial pathogen and treated with antibiotic drug

  1. Drug kills most bacteria but some mutants carry an antimicrobial resistance gene that protects them
  2. Mutants survive and pass on antimicrobial resistance gene to their offspring
  3. Patient now has a drug-resistant population of bacteria and cannot recover. This drug resistant bacteria can be passed on to other individuals
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4
Q

Study of antimicrobial resistance over 10 yrs

A
  • Saw Enterobacteriaceae strains become resistant to 10 antibiotics over the 10 year period
  • Shows that this evolution can occur very quickly
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5
Q

Penicillin resistance vs. usage

A
  • Penicillin resistance measured on pneumococci cultured from human patients from 11 EU countries
    o There are strict regulations of antibiotic prescriptions in northern EU compared to southern EU
    o Saw that there was greater resistance to penicillin in the bacteria from the southern EU patients compared to the northern EU
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6
Q

Superbugs

A

Very deadly; 700,000 people per year and expected to be 10 million by 2050

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7
Q

Discovery of new antibiotics

A
  • Antimicrobial resistant bacteria is evolving faster than science is inventing new antibiotics
  • There was a period 1920-1987 in which all of the major antimicrobial drug classes were discovered. The last marketable class discovered in 1987.
  • There is no treatment options for certain bacterial infections and bacterial infections in general are becoming harder to treat worldwide
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8
Q

Antimicrobial use in Canada (2016) in humans vs. animals

A
  • Canada is a major food producer
  • 19x more domestic animals (700 million) than humans (36.11 million)
  • In 2016, used 4x more antibiotics for animals than humans
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9
Q

Antimicrobial use in Canada breakdown

A
  • 20% in humans
  • 78% in production animals
  • 1% in companion animals
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10
Q

Antimicrobial classes used in Canada

A

Health Canada has 4 classes of importance: 1=very high, 2= high, 3= medium, 4= low

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11
Q

Class 1 antimicrobial drugs

A
  • Restricted to humans and domestic animals
  • Drugs that are considered more precious and they are trying to protect

Eg. Cephalosporins and fluroquinolones

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12
Q

Class 2 antimicrobial drugs

A
  • Used in all 3 sectors (humans, domestic, production animals)

Eg. Lincosamindes, macrolides, penicillins

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13
Q

Class 3 antimicrobial drugs

A
  • Used in food animals
  • Since not really used in human medicine, not thought to be causing antimicrobial resistance in humans

Eg. Tetracycline

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14
Q

Spread of antimicrobial resistance from food animals to humans

A
  1. Farm workers come into direct contact with animals carrying the antimicrobial bacteria
  2. Public eats animal food products containing antimicrobial resistant bacteria
  3. Animal waste is used to fertilize crops and contaminates water supplies
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15
Q

Evidence that evolution of antimicrobial resistance in agriculture influences human health

A
  1. Ceftiofur and salmonella in broilers
  2. MRSA in pigs being passed to people
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16
Q

Ceftiofur and salmonella in broilers

A
  • Ceftriofur is a class 1 cephalosporin that is approved for use in domestic animals and is used off label in the poultry industry (injected into eggs to control omphalitis)
  • Salmonella occurs in healthy chickens and can be passed on the humans from poultry or the eggs
  • Concern is that the use of ceftriofur in chickens can result in salmonella being resistant to drugs similar to ceftriofur such as the drugs ceftriaxone and cephamycins which are used to treat salmonella in children and pregnant women
17
Q

Centriofur-resistant salmonella

A
  • Sampled retail chickens and human cases and found a link between centriofur resistance in both humans and chickens
  • Study in Quebec reduced centriofur use and saw an 89% decrease in resistant bacteria and a 78% decrease in resistant bacteria in humans. After study, they begun using ceftiofur again and resistant bacteria emerged
18
Q

MRSA, pigs and people

A
  • Staphylococcus aureus causes disease in humans and pigs/livestock
    o Many different clonal complexes. Eg. CC398
  • Use methicillin (beta-lactam antibiotic of penicillin class) to treat gram positive bacteria
    o MRSA- resistant bacteria (present in CC398)
    o MSSA- sensitive bacteria (present in CC398)
19
Q

Evolution of CC398 MRSA

A

Sequenced genome and found 2 major clades: human associated (genes needed to infect humans) and livestock-associated (genes that were resistant to methicillin tetM and tetracycline tetK)

  • Provided evidence that resistance evolved in CC398 from farm animals
20
Q

Farm workers with livestock-associated MRSA

A
  • Widespread in pig farms in Netherlands
  • Accounted for 39% of all MRSA in human patients
  • Humans working more than 20hrs per week were 5x more likely to carry the MRSA compared to individuals working less than 20 hours per week
    »These infected workers were then able to pass on livestock-associated MRSA to larger community and hospitals
21
Q

Vaccine use rather than antimicrobials

A
  • Effectiveness of vaccines is much longer than antimicrobials
  • Provide us with the ability to force a pathogen to become extinct (eg. Smallpox)
  • Vaccines can be altered to keep immune response when the pathogen undergoes viral evolution
  • Some infectious diseases have vaccine escape mutants
22
Q

Pathogens and strain diversity

A
  • Many pathogens have multiple strains
  • Strains have distinct antigens recognized by immune system= strain-specific antibody responses
    » Antibody response against one strain is not protective against another strain
  • Makes vaccine development more difficult
23
Q

Pathogen strain example

A
  • Streptococcus pneumoniae- causes pneumonia
  • More than 90 strains world wide
24
Q

Streptococcus pneumonia causing Invasive pneumococcal disease (IPD)

A
  • Includes bacteremia, sepsis, meningitis, pneumonia
  • Vaccines include Prevenar 7 and Prevenar 13 which only target 7 and 13 common serotypes out of the total 90 serotypes
    o Vaccination has reduced IPD incidence
25
Q

What is the consequence of using a vaccine that only protects against a few of the total number of serotypes?

A

Can drive strain replacement. Strains that are targeted will disappear and strains that are not targeted will increase in frequency (due to evolution)

26
Q

Marek’s disease in chickens

A
  • Highly contagious viral neoplastic disease discovered in 1907
  • Due to alphaherpes virus
  • Symptoms: T cell lymphoma and infiltration of nerves and organs by lymphocytes
  • Infected birds can shed virus. Transmission by dander from feather follicles and by inhalation
27
Q

Marek’s disease vaccine

A
  • Reduced disease incidence
  • Is a leaky vaccine (so prevents symptoms but infection and transmission can still occur)
  • Works because otherwise mortality rate is 100%
28
Q

Marek’s disease vaccinated chickens

A
  • Vaccinated individuals had better survival rate and were still shedding the virus into the environment.
  • Saw that more Virulent strains actually did better in vaccinated chickens compared to unvaccinated ones. Better shedding and for longer period
    o Vaccination resulted in evolution of highly virulent strains

Disease Epidemiology #2 (11 decks)

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