Disease Ecology Flashcards
what is considered a disease?
an Atypical condition in living organism that causes some sort of physiological impairment
Zoonotic diseases
diseases that are transmitted from animals to humans
Nipah virus
Is an RNA virus
jumped from bats to pigs to humans
high fatality rate because we did not coevolve
Lyme disease
-white footed mice are reservoir for disease, spreading disease to many tics
-mice populations usually kept in check by predators but no forests for predators bc of deforestation
malaria
-transmitted via mosquito bites, in low latitudes
-hella fuckin cases
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disease ecology
host-pathogen interactions within the context of their environment and evolution
what are the goals of disease ecology? (2)
1) understand pathogen transmission and spread over time and space
2)impacts of host populations
all disease causing organisms are:
what does it do to donor and recipient
Selfish
donor: + fitness recipient: - fittness
exploitative
infectious diseases are not transmitted between hosts;
the pathogens/ parasites that cause diseases are
Direct transmission
direct contact between hosts
Indirect transmission
indirect transfer of infectious agent: fomites, airborne, animal vectors
Horizontal transmission
transmission within same generation
Vertical Transmission
parent to offspring before or during birth
how do viruses replicate inside cells (steps)
- virus binds to cell and enters
- virus delivers its genome to site where it can reproduce new copies of viral protein and RNA
- viral protiens and RNA burst through cell wall,
influenza horizontal or vertical?
horizontal
3 vertically transmitted diseases
zika, chickenpox, HIV
What is the RNA virus repsonsible for the disease COVID 19?
SARS-CoV-2
What transmission is relatively unaffected by host density?
frequency dependent transmission
The per capita rate at which susceptible individual becomes infected increases with
fraction of host pop that is infectious BUT DOES NOT INCREASE WITH OVERALL DENSITY
what is an example of a vector borne pathogen?
STDs
Endemic
constant presence, however low spread
Epidemic
High spread, only certain reasons
Pandemic
global epidemic
What is R0 in pathogens
the relative reproductive ratio of a pathogen
describes the initial growth of a pathogen in previously unexposed host population
beta=
transmission rate
probability for infection
N=
number of host available for infection
weird V- nu =
virulence- disease induced death rate of hosts
d=
natural death rate of host
r=
recovery of host
how do we interpret R0
the average number of people who will be infected by 1 person with a disease, has certain assumptions
assumptions for R0
-naiive population
-everyone is susceptible in pop
-no vaccinations- transmission interventions
when R0 > 1
disease is increasing
When R0< 1
disease in decline
What is a dimensionless metric? meaning it does not refer to a specific time window?
R0
What does R0 get replaced with once disease starts to spread?
Re and Rt
effective reproduction number
what does R0 inform us?
what does it not inform us of?
how much the disease spreads and how hard it is to contain
does not inform us of virulence: ability to damage host
are R0 Re and Rt constants?
no, they vary from place to place and vary from time to time
What are compartments?
subpopulations of the host
what do compartment models do?
help epidemologists stop the spread
can different diseases have different compartment models?
yes
How do we slow disease?
behavioural changes
herd immunity(vaccinations)
Behavioural changes: isolation vs quarantine
isolation: separate sick individuals from healthy
quarantine: separate individuals who have been exposed, even if not showing symptoms
when does herd immunity occur?
when immunity rates are high enough that pop growth rate (r) of pathogen is negative, it might go extinct
herd immunity threshold-
H miinimum percent of pop that must be immunized to reach herd immunity
what is the coorelation between R0 and H
the higher the R0- the higher the H must be- because higher contagious pathogens spread fast
why do pathogens hurt hosts? if they rely on them? (virulence)
because parasites that replicate too slowly do not produce sufficient transmission stage,
replicate too quickly will kill their host before transmission
selection favours pathogens with intermediate levels of within host transmission
strategies for combating infection: tolerance vs resistance
tolerance: ability for host to tolerate infection by minimizing damage done without impeding replication or transmission
resistance: reduce probability of infection, reduce replication, increase pathogen clearance.
why arent hosts more resistant to diseases
-trade-offs between resistance and fitness related traits
-pathogen evolution
-tradeoff between resistance and weakness to other diseases
host- parasite interactions ,may lead to
co evolutionary dynamics that increase genetic diversity of both host and parasite
Devil facial tumor
tasmanian devils
-non viral clonally transmissible cancer
chronic wasting disease
-elk and deer
-highly contagious
-caused by a prion
-fatal neurological disease
Sylvatic plague
prairy dogs
transmitted by fleas,
endangered black footed ferrets also at risk
whirling disease
caused by parasite causes young fish to die and older mfs to swim in tail chasing motion
Chytridiomycosis
causing major decline in amphibians
chytrid fungus responsible
inhibits ability to breathe
white nose syndrome (Pd)
-Ascomycete fungus
-bats
-attacks bare skin of hybernating bats
-causes them to be more active than normal, burning fat -stores and making them leave in the winter
-Huge decline in bats
