#29 Viral outbreak Zika, VDPV, Ebola Flashcards
(29 cards)
what are the 3 international health threats?
Zika, Ebola, Vaccine derived Polio
how many times have each health threat been declared a PHEIC?
Ebola - twice
Zika - once
VdPV - twice
what features does a virus need to have to be declared a PHEIC?
- sudden serious or unexpected
- global health risk
- may require international concern
what were the features of the Ebola outbreak in 2014/2016
-the outbreak occurred in West Africa
- this is outside of Ebola’s geographic range which is central Africa
also spread to some places across the world via infected health care workers
what is the cycle of Ebola virus
- it has a jungle cycle
- it is contained in bats which dont get sick from the virus
- they shed the virus to primates and antelopes which experience high levels of mortality
- the virus is transmitted to humans as we eat the meat for bushmeat
- human to human transmission can occur
how is ebola transmitted?
humans eat bushmeat and become infected
human to human transmission can occur via entry of bodily fluids on mucous membranes or broken skin
transmission risk increases with intimate contact of someone who is infected
how do humans shed ebola virus
- it is found in bodily fluids such as semen, breastmilk, blood (very high titres in blood), tears, urine
it has a very low infectious dose - highly contagious
where can ebola persist in some patients?
can persist in immunopriveleged sites such as the eye
can persist in the semen for up to a year- can be transmitted via semen
what are the features of the ebola outbreak in 2019?
- occuring inside the geographic range of ebola - central africa
- the virus cannot be managed as the area is war torn recently
- currently trying to use ring vaccination with experimenal vaccine
how is ebola diagnosed?
- everyone who contracts ebola will get sick and present with acute clinical presentation
- they virus has a lengthy stage of viremia - around 3 weeks
- blood will be taken or oral fluid and diagnosed with PCR. RT-PCR is often used to test for the viral glycoprotein and nucleoprotein. if positive they will do strain differentiation and confirmation
- serology wont be used for diagnosis but can be done. those who die will die before they mount an immune response
what are some emerging ebola virus therapies?
2 Monoclonal Ab’s and 1 drug
very postitive results
overall mortality when treating with the Ab’s is down to 30% from 80%
when treated early the mortality is down to 5%! extremely low
MERCKs ebola vaccine is currently being used also in ring vaccination strategy
what are the features of Zika that make it hard to detect
- Zika causes mild symptoms and has low clinical expression - clinical symptoms are fever and rash which are very common to alot of diseases in south america
- it doesn’t cause any damage except to foetuses which was realised later on
what is the cycle of Zika virus
it has a primate jungle cycle
it lives in Macaques and is transmitted by mosquitos
sometimes having spillovers into humans
what lead to Zika infecting humans much more than usual?
during the war the African lineage (jungle cycle virus) of zika was able to enter Malaysia
in malaysia the lineage diverged and adapted to the Aedes aegypti mosquito which is a mosquito that hangs around humans - this enabled it to infect humans
where was the outbreak of Zika?
South america
how is Zika shed?
it is shed in the whole blood from the 1st day of infection for up to 80 days!! prolonged!!
shed in urine, saliva for 20 days
and semen
how is the Zika virus transmitted amongst people
mainly through the Aegypti mosquito vector
through perinatal (mother to baby) - biggest concern as it causes foetal abnormalities to baby - around 30%
through sexual contact - in semen for up
blood transfusion
what is the diagnostic challenge zika presents?
it is a clinical mild rash illness - confusing when dengue and chikungunya are very similar clinically
can cause foetal abnormalities
there is no way of determining what baby will be affected
30% will develop abnormalities
all you can do is monitor
it is also related very closely with Dengue - it is hard to distinguish them genetically
how do you determine someone has Zika in late infection? what are the issues around this?
Zika and Dengue are related very closely
travellers often present with a rash late in time
there is no way of knowing if their infection was dengue or Zika
if you test someone when they present late with a rash and it comes back negative this is expected - the viremic period will have passed - they still may have had an infection
therefore the tests have to be done with serology - testing antibodies. However this is also hard to determine dengue from Zika as the ab’s produced are highly cross reactive. they are hard to distinguish. need to try neutralisation assay or something quantitative and labor intensive
how you diagnose early zika infection?
the virus will still be in the blood so test with RT-PCR for rapid diagnosis - strong diagnosis - reliable
how many people present with illness from Zika?
only 20% of people get clinical illness
80% are asymptomatic
where is zika shed for prolonged periods?
whole blood - up to 80 days
what WT polio virus is circulating still?
type 1 has not been eradicated yet
how does Vaccine derived polio revert to virulence?
what vaccine allows this
the live attenuated sabin vaccine can revert back to virulence
when someone is vaccinated they will shed the virus from their faeces - it can be transmitted to others but most will be vaccinated
- it can infect those that are not vaccinated and transmit through unvaccinated people for years
- it takes 1 year for the virus to revert back to virulence through this method - creates VDPV
