#29 Viral outbreak Zika, VDPV, Ebola

Question 1

what are the 3 international health threats?

Answer 1

Zika, Ebola, Vaccine derived Polio

Question 2

how many times have each health threat been declared a PHEIC?

Answer 2

Ebola - twice
Zika - once
VdPV - twice

Question 3

what features does a virus need to have to be declared a PHEIC?

Answer 3

• sudden serious or unexpected
• global health risk
• may require international concern

Question 4

what were the features of the Ebola outbreak in 2014/2016

Answer 4

-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

Question 5

what is the cycle of Ebola virus

Answer 5

• 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

Question 6

how is ebola transmitted?

Answer 6

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

Question 7

how do humans shed ebola virus

Answer 7

• 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

Question 8

where can ebola persist in some patients?

Answer 8

can persist in immunopriveleged sites such as the eye

can persist in the semen for up to a year- can be transmitted via semen

Question 9

what are the features of the ebola outbreak in 2019?

Answer 9

• 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

Question 10

how is ebola diagnosed?

Answer 10

• 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

Question 11

what are some emerging ebola virus therapies?

Answer 11

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

Question 12

what are the features of Zika that make it hard to detect

Answer 12

• 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

Question 13

what is the cycle of Zika virus

Answer 13

it has a primate jungle cycle
it lives in Macaques and is transmitted by mosquitos
sometimes having spillovers into humans

Question 14

what lead to Zika infecting humans much more than usual?

Answer 14

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

Question 15

where was the outbreak of Zika?

Answer 15

South america

Question 16

how is Zika shed?

Answer 16

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

Question 17

how is the Zika virus transmitted amongst people

Answer 17

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

Question 18

what is the diagnostic challenge zika presents?

Answer 18

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

Question 19

how do you determine someone has Zika in late infection? what are the issues around this?

Answer 19

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

Question 20

how you diagnose early zika infection?

Answer 20

the virus will still be in the blood so test with RT-PCR for rapid diagnosis - strong diagnosis - reliable

Question 21

how many people present with illness from Zika?

Answer 21

only 20% of people get clinical illness

80% are asymptomatic

Question 22

where is zika shed for prolonged periods?

Answer 22

whole blood - up to 80 days

Question 23

what WT polio virus is circulating still?

Answer 23

type 1 has not been eradicated yet

Question 24

how does Vaccine derived polio revert to virulence?

what vaccine allows this

Answer 24

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

Question 25

where is VDPV common?

Answer 25

in western countries where immunocompromised people are common - they will become chronically infected with the virus in the vaccine as they cannot clear it
the virus will mutate in them continually until it reverts back to virulence

also common in places where vaccination levels are low - long transmission chains among unvaccinated people will occur until it reverts back to virulence - takes over a year

Question 26

what polio vaccine strain is responsible for most VDPV outbreaks

Answer 26

• the type 2 vaccine causes 80% of cases

Question 27

how have we gotten around the type 2 VDPV outbreak?

Answer 27

• we have started to use the polio type 2 inactivated vaccine - salk!

Question 28

what enabled a VDPV outbreak in PNG?

Answer 28

• they have very low vaccination levels
• they have poor surveillance of acute flaccid paralysis
• they have a weak health system

the virus was able to revert back to virulence through unvaccinated people

Question 29

what are the contributing factors to virus emergence?

Answer 29

• microbial adaptation
• changing human susceptibility
• climate and weather
• human travel
• public health breakdown
• war and famine
• bioterrorism
• poverty and social inequality