22. Emerging viruses Flashcards
what are the 4 states of host virus interactions?
stable
Evolving
dead end
resistent host
what is a stable virus host interaction?
the virus and human can survive
like herpes
herpes can only infect humans so would be bad if it killed them
what is an evolving host virus interaction?
virus moving to an immunologically naive population
- from animals
- from one part of the world to another
eg Ebola or SARS-CoV-2
What is a Dead-end virus host interaction?
spread by a vector but once it infects humans the human cannot transmit it on
what is a resistant host virus host interation?
the virus cannot infect the host and the infect is blocked
What is a reason we are having more emerging viruses?
improving diagnostics leads to more emerging infections but there is just more data not necessarily more viruses
what is a newly emerging viral disease?
it is completely new in the global human population
what leads to a re emerging viral disease?
a break down of normal control methods causing a virus to become more prevalent in a population
what was the point in history where generally disease started spreading rapidly?
when we started domesticating animals and moving into towns
transmission via water, air and direct contact
what are the convergent forces for disease emergence?
globalisation and air travel
mega-cities and the poverty in them
Deforestation
altered ecosystems
movement of people and goods
microbial evolution
how do we initially recognise new emerging diseases?
occurrence of a outbreak
development of diagnostic techniques like being able to detect viruses in sewage
what new viruses are more likely to be recognised?
clinically unique viruses that have distinct symptoms
why was zika virus so hard to identify?
very similar symptoms to dengue to malaria
what contributes to emergence of new viral diseases?
virological determinants
environmental factors
host determinants
host population determinants
new tech for viral diagnosis
what are the virological determinants?
mutation
recombination
reassortment
fitness
adaptation
what are environmental factors?
ecological and zoonotic influences
what are host determinants?
specific risk behaviours
innate resistence
acquired immunity
physiological factors
what are host population determinants?
behaviours
Social
transport
commercial
iatrogenic factors (caused by medical examination or treatment)
why do emerging RNA viruses evolve much faster then DNA viruses?
- RNA viruses use Viral RdRp with very higher error rates
- RdRp don’t have proof reading ability
- DNA viruses use host DdRp which are more accurate
what do high mutation rates in RNA viruses result in?
Quasispecies
what are Quasispecies?
all the viruses in one body will have slightly different genomes that make up the consensus genome for the virus
- minor population variants
what causes emergence of new viral phenotypes?
mutation and recombination
closely related segmented viruses reassort their genome in dual infections
both DNA and RNA viruses can undergo recombination with other closely related species like coronaviruses
what is a controversial method of creating emerging viruses?
genetic engineering in gain of function research with bird flu and ferrets
dangerous and was not done in proper containment
altering things to find out what makes a human infectious virus and made a human infecting virus
where do many emerging viruses come from?
zoonotic viruses
Especially bats
West African ebola outbreak 2014 determinants
viral: evolution of the viral genome possibly making enhanced transmission
environmental: zoonotic transmission so contact with wildlife
host: burial customs like touching the dead
host population: transport and outbreak along a trading route
what changed between the normal Ebola outbreaks and the 2014 Ebola outbreak?
most outbreaks were in isolated villages that could be easily contained but the 2014 outbreak happened in a village along a new major transport route.
the main change was the location
how are the current Ebola outbreaks contained?
mainly by quarantine and rapid testing
high success vaccine so introduced ring fence vaccination
what is the disadvantage of the Ebola vaccine?
it is only effective against 1 strain
Zoonotic transmission of Coronaviruses
they have intermediate reservoirs from bats
- MERS = camels
- SARS = civet cats
- SARS-CoV-2 = some wild animal
mostly respiratory but also infect other tissues
Airborne transmission in small and large droplets
what are most human coronavirus?
common colds
what is the biggest difference in epidemiology between SARS-CoV and SARS-CoV-2?
SARS-CoV is believed not to be spread until you have symptoms
SARS-CoV-2 can be transmitted asymptomatically so people can spread it without knowing
what is the interspecies transmission of SARS-CoV?
bats transmits to palm civet and some small evolution before passing on to humans
transmission can occur both ways between humans and civet cats as the viruses are very similar
why are bats big reservoirs for viruses?
they can persist without much harm to the bats
bats live in big flocks so lots to infect
who does MERS-CoV mostly infect and where do they acquire that infection?
People with co morbidities
and contact with camels for sport/eating/transport
what is the difference between SARS-Cov and SARS-CoV-2?
the furin cleavage site on the spike protein
how is the SARS-CoV-2 spike protein different?
part of the protein is cleaved by the host cell proteins before it leaves the cell
make it more pathogenic and transmissible
what was transmission pathway for SARS-CoV-2?
food markets to local humans
spread around the local city
international travel made it spread around the world
how has the disease SARS-CoV-2 changed over time?
newer variants are more transmissible but less virulent
latest varients don’t enter the lower respiratory tract
what changing ecological factors have been linked with emerging diseases?
installing dams or irrigation
rerouting wildlife migration patterns
wildlife smuggling
air conditioning
deforestation
Urbanisation
what increases human contact with arthropod/insect vectors?
movement to native habitats due to expanding population
increasing vector density and spread
- changing climate
how does Zika virus mostly exist?
in a stable life cycle in an arthropod vector and an animal
what happens when Zika virus jumps to humans?
evolve and create a new life cycle without the arthropods reservoir
what are the symptoms of Zika?
most people have no overt symptoms
in pregnant people it causes foetal abnormalities
what happens West Nile virus enter humans?
it is a dead end virus so can’t be transmitted on
how do Zika virus outbreaks occur?
Naive population is badly effected but develop immunity to protect against reinfection
the outbreaks occur in waves as immunity wanes and the virus can take over again
what are the 2 phases of prevention and control of emerging disease?
investigative phase
Interventional phase
what happens in the investigation phase of disease control?
- disease is characterised
- assess the risk to the population
- infectious agent must be identified and characterised
- Development of diagnostics
- develop integrated approach
what happens in the interventional phase of disease control?
- commnication with population
- Technology transfor to local agencies
- public health measures like vector and water management
- recognition of the effect of human activity on disease pattern
- global surbeillance and warning systems
