16: Zoonosis Flashcards
bats do not have more viruses than all other mammalian orders
viruses growing in mammals have a higher chance of spreading in other mammals because the jump isn’t that far
closer to mammals than other organisms so the virus has less evolution to do
bats, primates and rodents have a higher proportion of observed zoonotic viruses compared to other groups of mammals
bats, primates and rodents as the ones where most of the viruses are homologous to humans
not just that they carry more viruses but viruses they carry jump more easily
other factors involved in spillover risks
opportunity for contact with humans
- close contact with humans necessary
propensity to exhibit clinical signs that exacerbate viral shedding
other ecological, behavioural factors
life-history differences
phylogenetic proximity to humans
what’s so special about bats?
second most diverse mammalian order on earth after rodents
facilitate rapid transmission of pathogens
gregarious - like to live with each other in big groups of 50,000 or more
- large population sizes sustain ague-immunising infections
interaction with humans is frequent
- peri-domestic habits since they like to live in old houses in proximity with humans
- bushmeat so exposure to saliva, bodies, etc.
- deforestation for mining industries will displace bat populations and viruses they carry to new environments, potentially closer to us
relatively long lifespan for their body size (3-10x longer than equivalently-sized mammals)
- if they carry a virus, they carry it for a very long time
- facilitate viral pestilence for chronic infections since there are mutations from selective pressures
fly long distances
- allow dispersal over long distances (not localised to a particular place)
- flight mimic fever (fever as a mechanism to dampen the ability of viruses to replicate so it allows them to control and dampen viruses)
classic pathology caused by strong activation of the immune system in response to viral infection seen in humans (cytokine storm) which does not occur in bats
- weakened DNA sensing due to the high metabolic requirement of flight
- loss of genes involved in the innate response
bats are not our enemies
provide considerable ecosystem services across a vast range of regions and habitats
pollination
arthropod suppression
- need less insecticide on crops
seed dispersal
- fruit bats eat fruits/seeds, fly away and excrete seeds
replication in a new host for viruses as extremely difficult
first line of defense since they have to be in contact with the pathogen
- pathogen needs to be able to enter the human body
viral replication
- once in, it has to enter cells, force them to replicate and break open the cell
most animal viruses unable to replicate in the human body
virus first needs to replicate in humans and be transmissible
ones that are transmissible can also evolve and become human exclusive
- no need for animal reservoirs anymore
- not talking about zoonoses anymore
2 main obstacles to overcome to replicate in a new host
virus needs to interact with many different cellular proteins to enter a new cell and replicate
- wants to be able to replicate and assemble new cells
- need to stop defences in cells, and to be released efficiently by cells so they can infect other cells
- needs to do this with very little genetic material
- once in the host cells, needs to interact with a myriad of proteins to remodel the host environment
virus needs to evade immune responses of the host
viruses exploit host cell machinery for all aspects of their multiplication
animal viruses will replicate in humans only if they can interact with all useful proteins they need
clone viral proteins one by one and introduce them in new cells
interfere pathway as a critical role in the control of viral infections
when a cell is infected, viral PAMPs recognised by specific receptors
- virus interacts with a number of host cells and delivers the genome inside the cells
- DNA in the cytosome unusual so every cell recognises it as a virus
initiates cascade of events that results in infects cells releasing a small set of molecules called interferon/IFN for short (cytokines)
cells exposed to interferon start making proteins to combat viral infection
- every cell in our body has receptors for IFN
sometimes cells get destroyed in the process but the cell will be replenished and the virus doesn’t transmit
what do viruses need to do to replicate in a host?
need to inhibit the IFN response
interferons are powerful so if they’re working, there are few viruses that survive
- any virus that makes us sick is able to replicate for at least 5-10 days in our bodies and have learned to grow and amplify despite the existence of IFNs
how can viruses evade interferons but not CD-4 or CD-8 T-cell responses?
T-cells activated when cytokines are released but it takes 5-7 days
virus is free during thes period and only have to evade IFN
- replicate to amplify and transmit to a new host within 5-7 days before numbers decrease because T-cells are unleashed
disproportionate number of new zoonosis being caused by RNA viruses
RNA viruses most likely to be associated with spillover events since they adapt better
high mutation rates
high multiplication rates
smaller and don’t have to evade T-cell responses with proteins so they manipulate the system to replica to a high level in the first -7 days to transmit the disease to new hosts
