DISEASE E&E (Disease Emergence 1) Flashcards
ProMED:
-international society for infectious diseases
-staff around the world collect reports of disease and outbreaks
-have a one health approach
> 70% of newly emerging infections:
-derived from animals and wildlife
-proportionally large numbers are RNA viruses (ex. coronavirus, WNV, Ebola)
-humans are susceptible to 1400 infections (61% were derived from animals and wildlife)
Bats and viruses:
-almost 1400 different species of bats with different susceptibilities
-intermediate hosts are often involved in leap from bats to humans, but not needed
-exceptional in ability to act as natural reservoir of viruses
>immune system allows low level of infectivity
SARS (Severe Acute Respiratory Syndrome):
-spread across 30 countries and regions
-2 ways in Toronto 2003
Nosocomial:
-transmitted within hospital
MERS CoV (Middle East Respiratory Syndrome):
-first reported in 2012
-all cases linked to travel through the Arabian peninsula
-largest outbreak outside this area occurred in Republic of Korea
SARS-CoV-2:
-started from wild animal markets in Asia
-palm civet cat?
-pangolin?
Transmission of pathogens within markets:
-contribute to viral emergence
-just have live butchering happen
-mixture of wild and domestic animals
Zoonosis:
-any disease or infection that is naturally transmissible from vertebrate animals to humans
-bacterial, viral, parasitic or involve unconventional agents
-major health problem
-many prevent the efficient production of food or animal origin
-create obstacles to international trade in animal products
Emerging infectious diseases:
-diseases that have newly appeared in a population or that have existed and are rapidly increasing in incidence (Re-emerging)
-many of these pathogens are not ‘new’, they’ve just emerged in a new host or found a new ecological niche
Human immunodeficiency virus (HIV):
-lentivirus
-over 1 million deaths/year
-spilled over from chimpanzees to humans
-multiple cross species ‘spillover’ events
-has become well established and persistent in the human population
Spillover:
-a single event where a pathogen from 1 species (reservoir host) moves into another species
>such a movement may result in an outbreak
-may occur with us knowing or not become well established in new host OR
>can result in multiplication and establishment in new out and successfully be transmitted resulting in outbreak
*complex interactions between multiple species in dynamic environments
Pathogen spillover:
-occurs when epidemics in host population are not driven by transmission within that population, but transmission from a reservoir populations
5 steps for spillover to occur:
- A source (or reservoir) host of the pathogen must exist
- Host needs to be infected
- Pathogen must be released from the source host into an environment that allows its transmission to a spillover
- Spillover host must be exposed to sufficient quantity of viable pathogen to allow for an effective exposure
- Spillover host must be susceptible to the pathogen
Basic reproduction number (R0):
-number of secondary cases expected from one primary case in a completely susceptible population
-estimate of potential spread under a specific circumstance
Factors R0 depends on:
-transmission route (aerosol, sexual, etc.)
-density
-climate
-ventilation
-infectiousness
R0=0
-no further transmission
Ex. Lyme’s disease, rabies (in people)
R0=1
- Reservoir
- Spillover
- Stuttering chain
R0>1
-can result in an epidemic outbreak
-sustainability of outbreak depends on supply of susceptible hosts
Ex. Ebola virus spills over, spreads rapidly but then burns out and disappears
>too virulent to sustain an epidemic over the long term
R0>1 steps:
- Reservoir
- Spillover
- Stuttering chain
- Sustained transmission
- Epidemics OR spillover
R or Re:
-effective reproductive number
-population now has some immunity or interventions have been implemented
-population averaged value over a specific epidemic period
Rt:
-reproduction number at a given time
*will change over time depending on:
>immunity in population
>behaviour of hosts
>disease control interventions
>changes/mutations in the pathogen, etc.
Monkeypox:
-transmitted from infected animals to humans primarily through bushmeat hunting
>rope squirrels
Factors contributing to disease emergence:
- Environmental changes
- Human demographics/behaviour
- Internal travel and commerce
- Technology and industry
- Microbial adaption and change
- Breakdown in public health measures
Environmental changes:
-habitat destruction may cause animal populations to cluster allowing for spread of new pathogens
-agricultural expansion into various ecosystems
-climate change
Nipah virus emergence in Malaysia:
-emerged as respiratory and neurological disease
-spread rapidly through Malaysia and Singapore
-misdiagnosed at first
-people were infected by close contact with pigs
-eventually pig culling helped to stop the outbreak
-40% mortality in humans
Nipah virus emergence good example of:
-‘density-dependent’ pathogen requiring a ‘threshold’ density of susceptible individuals to persist within a population
>most farms were small
>emerged on a new large pig farm
Nipah virus reservoir:
-flying foxes
>suffered from some loss of habitat due to several factors (fruiting failure in forest due to El Nino, anthropogenic fires)
-index farm had large fruit orchards, and the tress grew over open pig enclosures
-bats fed in trees and dropped pieces of fruit covered in saliva
*pigs amplified and aerosolized the virus!
