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Disease Epidemiology > Disease Emergence > Flashcards

Disease Emergence Flashcards

1
Q

ProMED

A
  • International society for infectious diseases
  • Website/email list- staff gather information on diseases affecting humans, animals, plants, taking a Onehealth approach to share with whoever is interested
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2
Q

Where do new infections come from?

A

More than 70% of newly emerging infections are derived from animals and wildlife

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3
Q

What kind of viruses are largely known to be causing new emerging diseases?

A

Proportionally large number of RNA viruses
- Ex. Coronaviruses (SARS, MERS, COVID19, Porcine epidemic diarrhea virus)
- Ex. Filoviridae (Ebola virus, Marburg virus)
- Ex. Flaviviridae (West Nile virus)
- Ex. Bunyaviridae (hantavirus)
- Ex. Paramyxovirus (Nipah virus)

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4
Q

How many viruses are humans currently susceptible to?

A
  • 1400 infections
  • 61% of these were derived from animals and wildlife
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5
Q

What is the most intimate relationship between humans and animals?

A

The animals that we choose to eat

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6
Q

Bats and Viruses

A
  • Study states that of 12,333 bats from Latin America, Africa, and Asia, approximately 9% carried at least one of 91 distinct coronaviruses
  • It is believed that there are at least 3200 coronaviruses that infect bats
  • There are many other zoonotic diseases that are believed to be linked to bat-borne virus (Hendra or nipah virus)
  • These viruses can be passed to an intermediate host before making it into humans, but it is not always necessary
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7
Q

Why are bats so good at leading to zoonotic disease outbreaks?

A

Studies indicate that bats are exceptional at acting as a natural reservoir for viruses because their immune system is great at fighting of the disease but keeping a very low level of infectivity which they can pass on while living out their lives.

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8
Q

SARS

A
  • Cluster of cases in 2002 and 2003, a doctor that had worked with these patients stayed at a hotel and passed on the virus to hotel guests. One women from Canada staying at hotel returned home, got ill and ended up in hospital, further passing on the virus.
  • Outbreak spread across 30 countries and regions, infected more than 8000 people, killing 775 people
  • 10% fatality rate in Canada; Toronto residents placed in quarantine
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9
Q

MERS

A
  • First reported in Saudi Arabia in Sept 2012; later identified first known cases occurred in Jordan in April 2012
  • All cases have been linked to travel through the Arabian Peninsula
  • Largest outbreak outside this area occurred in Korea in 2015 (traveller from Arabian peninsula)
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10
Q

Wild animal markets in Asia

A

Plays quite a large role in the emergence of zoonotic diseases

  • Bats infect animals that end up in these markets
    Ex. Palm civet cat (intermediate host of SARS coronavirus)
    Ex. Debate with COVID 19 between pangolin or other small mammals that have been known to pass on other coronaviruses
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11
Q

Components of transmission at Wild animal markets

A
  • Scavengers and wildlife (bugs, mice, dogs, bats, birds)
  • Retailers and customers
  • Animal-sourced foods
  • Wild and domestic animals for sale
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12
Q

What is a zoonosis?

A

Any disease or infection that is naturally transmissible from vertebrate animals to humans
- May be bacterial, viral, parasitic or may involve unconventional agents
- Effects public health, efficient animal food production, international trade of animal products
- Huge impact on poor livestock keepers that rely on the industry for their livelihood

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13
Q

What is an emerging infectious diseases (EID)?

A
  • Diseases that have newly appeared in a population or that have existed and are rapidly increasing in incidence
  • Many of these pathogens are not NEW, but they have simply emerged in a new host or found a new ecological niche and spilled over into a naïve species
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14
Q

Where did the phrase emerging infectious disease come from?

A

Came to prominence in the 80’s with the emergence of AIDS

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15
Q

HIV

A
  • Lentivirus
  • Currently affects 30 million people in the world
  • More than 1 million deaths/year
  • First clinically diagnosed in 1981
  • Spilled over from chimpanzees to humans (may have also been from bats originally)
    Multiple cross species “spillover” events of Simian immunodeficiency virus from chimps to humans, and now it has become well established and persistent in the human population
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16
Q

What is a spillover?

A

A single event during which a pathogen from one species (reservoir host) moves into another species; the movement may result in an outbreak

  • May occur often but we don’t notice it as it does not affect us or become well established within the host
  • May occur and result in multiplication and establishment within a new host and be successfully transmitted resulting in an outbreak
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17
Q

When do Pathogen spillover events occur?

A

Occurs when epidemics in a host population are driven not by transmission within that population but by transmission from a reservoir population

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18
Q

5 steps for a spillover to occur

A
  1. A source (or reservoir) host of the pathogen must exist
  2. The host needs to be infected
  3. The pathogen must be released from the source host into an environment that allows its transmission to a spillover (or recipient host)
  4. The spillover host must be exposed to a sufficient quantity of viable pathogen to allow for an effective exposure
  5. The spillover host must be susceptible to the pathogen
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19
Q

Basic reproduction Number (R0)

A

The number of secondary cases expected from one primary case in a completely susceptible population

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20
Q

Some factors affecting R0

A
  • Susceptibility
  • Transmission routes
  • Density of room/area
  • How long is carrier able to be infectious
  • Climate, Ventilation
  • Virus survivability
  • Infectiousness of the virus
21
Q

R0= 0

A
  • No further transmission
  • Ex. Lymes disease, Rabies
  • Dead end host diseases
22
Q

R0 = 1

A
  • Stable level of infection
  • Often involves stuttering chains
  • Ex. Monkeypox virus- similar symptoms to smallpox. Cases occurred to humans near tropical rainforests and transmission was limited (stuttering chains). Smallpox vaccines provide a level of immunity for monkey pox.
23
Q

Stuttering Chains

A

Some transmission but the chains are broken and a limited number of cases occur

24
Q

R0 >1

A

Can result in an epidemic outbreak

Sustainability of outbreak depends on supply of susceptibility of the hosts!!
- Ex. Ebola virus spreads rapidly and then burns out and disappears. The virus is too virulent to sustain an epidemic over the long term

25
Q

Effective Reproduction number (R or RE)

A
  • The number/estimate of individuals that will become infected from a single infected individual while considering that the population now has some immunity or interventions that have been implemented to prevent the spread.
  • Population averaged value over a specific epidemic period
26
Q

Reproductive number at a given time (Rt)

A

The number/estimate of individuals that will become infected from a single infected individual at a specific time. (Ex. New COVID strain, group going to festival- they will have a higher Rt)

27
Q

Factors effecting Rt

A

Factors:
- Immunity in population- vaccinations, contacts/ personal immunity from the virus
- Behaviour of hosts- quarantine vs. lifting regulations
- Disease control interventions
- Changes/mutations in the pathogen

28
Q

Karl Johnson and WHO

A

After thousands of sampling, found that Machupo virus (BHF) was being carried by large vesper mouse. People had moved into the jungle, mice would come inside to eat the peoples stored corn. Mice urinate on floor, floors are swept, aerolizing the virus and people getting sick and died. Led to WHO for disease.

Great example of how disease can emerge based on an environmental change

29
Q

Factors contributing to disease emergence

A
  1. Environmental changes
  2. Human demographics/behaviour
  3. International travel and commerce
  4. Technology and industry
  5. Microbial adaptation and change
  6. Breakdown in public health measures
30
Q

Components of environmental change that can impact disease emergence

A
  • Habitat destruction may cause animal populations to cluster allowing for spread of new pathogens
  • Agricultural expansion into various ecosystems
  • Climate change may also contribute to disease emergence (change where animals and pathogens live and survive)
31
Q

Nipah Virus emergence in Malaysia

A
  • Emerged in 1998 as a respiratory and neurological disease in pigs. Spread rapidly through Malaysia and Singapore by movement of infected pigs
  • Initially misdiagnosed as Japanese excephalitis virus so focus was on insect control
  • People were infected by close contact with pigs (40% died)
  • Eventually pig culling helped to stop the outbreak (caused near collapse of pig farming industry)
32
Q

How did Nipah virus emerge and spread through pig population?

A

Pigs: Emerged with the production of large pig farms of over 30,000 head. Displayed a density-dependent pathogen which means it required a threshold density of susceptible individuals to actually persist within a population

Flying fox Bats (fruit bats): Suffered a loss of habitat due to fruiting failure from el nino related drought, and anthropogenic fires led to palm oil production increase. The large pig farm also had a large fruit orchard with fruit growing over the pig enclosures. Bats would feed on the fruit, dropping infected fruit and saliva down into the pig stalls. The pigs then amplified and aerosilized the virus.

33
Q

Human demographics/behaviour impact on disease emergence

A

Human behaviour in terms of how we interact with animals
o Ex. bush meat trade
o Ex. Animal markets in Asia
o Ex. import of exotic pets

34
Q

Monkeypox outbreak due to exotic pet import

A

Example of human behaviour causing disease emergence

  • Monkeypox typically in rope squirrels, poached rats, dormice, monkeys. Human-human transmission limited (stuttering chains)
  • Outbreak in US, none of the reservoir hosts present in the states, but everyone infected had contact with infected pet prairie dogs
  • Source of virus was imported exotic pets including rope squirrels, poached rats and dormice, who were housed near the prairie dogs before being sold to homes.
35
Q

International wildlife trade

A

Huge impact on disease emergence due to human behaviour

  • Millions of exotics exported from Asia
  • Largest illegitimate business after narcotics
  • Conceal wildlife in normal household items
  • Huge threat to wildlife species persistence and greatest risk factors for emerging infectious disease since animals often carrying disease that can be passed on and spread in new places
36
Q

International travel and commerce impact on disease emergence

A
  • Hugely impacted by increase in airlines/airline passengers

Includes:
1. International travel of humans
- General travel
- Human migrants
- Ex. 1918 influenza due to soldiers returning from war

  1. International travel of animals
    - Animal and plant trade
    - Transport of vectors
    - Animal and animal product movement across trans-boundary diseases
    Ex. Foot and mouth disease in UK: Pig and sheep farm, pigs gone to slaughter, sheep sold off at market. Pig being fed illegal restaurant food waste (most likely importing illegal meat from Asia)
37
Q

Technology and industry impact on disease emergence

A

Industry: Selling products!! Very easy to sell all over the world but very hard to know exactly where it all came from.

  1. Food production is on a global scale; very complex and we have little understanding
  2. Food production systems have their own ecology
    - Feed lots: each pen probably represents 100-150 farms due to sorting
    - Feed Truck: 80-90 cattle, represents 30 different farms
    - Meat at grocery store: All different products coming from all over the world
38
Q

Emergence of Bovine Spongiform Encephlopathy

A
  • Similar diseases: Creutzfeldt Jakob Disease, Kuru, Scrapie
  • Caused by Prions (proteinaceous infectious particles)
  • First identified in small dairy farm 1985; believed to be due to the feeding of meat and bone meal
  • Believed to have started in 1970s prior to identification but disease takes a long time to present itself

**Spread all over the world because of MBM industry (being sold all over the world or feed to cattle being sold all over the world)

39
Q

Meat and Bone Meal Hypothesis

A
  • Feeding of contaminated meat and bone meal to cows lead to BSE
  • Higher incidence in dairy cows because it was more likely to feed them a dairy protein supplement. Therefore, higher incidence in areas in UK with dairy cows
  • Lower exposure in calves compared to adults
40
Q

Why was meat and bone meal used at the time?

A
  • It was freely available. Large amounts of sheep being culled at the time due to there being no market for them.
  • It was needed. There was no other effective source of protein feed in the UK
  • Commonly used in protein source in calf starter rations
41
Q

Origins of BSE

A
  • Three theories but answer is unknown
    1. Originated from scrapie-like agent from sheep
    2. Caused by spontaneous genetic mutation of the PRP gene of cattle
    3. Originated from another mammalian species with a TSE (African ungulate, cetacean or felidae
42
Q

Prions

A
  • Proteinaceous infectious particles
  • Natural uninfectious prion proteins are found in the cells of normal animals
  • Infectious prion proteins are folded into a different shape making it unstable and causing disease
43
Q

Steps taken by UK to deal with BSE epidemic

A
  • Feed Ban
  • SBO Ban (couldn’t use spinal cord, brain for bone meal)
  • Mammalian Meat Bone Meal ban
44
Q

How was BSE spread around the world?

A
  1. Shipped/imported cattle from UK
  2. Imported meat and bone meal- most likely came from UK, imported to other countries and then passed further on
45
Q

How did BSE get into Canada?

A

Cow imported from UK in 1987.

CFIA found and culled all UK imports into Canada after first case but some of these animals had already died and gone to rendering plants and been used to make MBM

46
Q

What steps did Canada do to deal with BSE?

A
  1. Ruminant MBM Ban to Ruminants 1997
  2. SRM (specific risk material) Removal 2003- similar to SBO from UK
    –> Included ensuring SRM wasn’t used in human food products or MBM products
47
Q

MBM Movement and impact

A

MBM is a commodity, used in industry to make money. Sold all over the world and eventually caused a spread of BSE. When it moves into different countries, the product loses its identity and it is very difficult to track

48
Q

Microbial Adaptation and change’s impact on disease emergence

A
  1. Emergence of antimicrobial resistant bacteria as a result of human usage of antimicrobial drugs in both people and animals

Ex. MRSA in humans, horses, pigs: Humans have both community and hospital MRSA. Horses have same community MRSA as humans. Pigs have specific MRSA strain and can pass that strain on to people.

  1. Antigenic drift of various influenza strains
49
Q

Breakdown in public health measures impact on disease emergence

A

Huge issue in developing countries, but occurs worldwide

Many possibilities:
1. Outbreaks after natural disaster due to damage to infrastructure

  1. Outbreaks due to incomplete or unsatisfactory completion of public health matters.

Ex. Community Well not chlorinated to proper levels because employees got lazy and did not maintain proper levels. Drinking water contaminated causing thousands of gastroenteritis cases

  1. Outbreaks due to lack of vaccination.

Ex. Mumps outbreak in university students

Disease Epidemiology (9 decks)

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