#28 Flaviviruses - Dengue, Japanese Encephalitis, Yellow Fever, Zika Flashcards
name all the Flaviviruses
Zika, Hep. C, Japanese Encephalitis, Dengue, Yellow fever
what are the chances of developing clinical disease for Dengue, JE and Zika
Zika: 1 in 5 chance of developing clinical disease
Dengue: 1 in 10 chance of developing clinical disease
JE: 1 in 25 to 1000 chance of developing clinical disease
how are the Flavi’s spread
mosquitos
what serotypes of dengue circulate in endemic areas
all serotypes of dengue - serotype 1, 2, 3, 4 circulate at the same time
how is dengue spread?
mosquitos
what are clinical symptoms of dengue?
macropapular rash fever very severe pain in joints and muscles some people develop warning signs includes increased vascular permeability
what are the warning signs of dengue and what do they cause and why
warning signs develop when the disease becomes more serious
includes:
- clinical accumulation in the tissues and spaces of the body as they have developed capillary leak syndrome. leakage of plasma
- severe thrombocytopenia bad!!!
- can have a petechial rash where blood leaks from capiliaries - can cause BP to drop and organ failure
what occurs when water is given to someone with dengue why?
- as they have increased vascular permeability water will cause more fluid to leak into the tissues and can make situation worse
treatment is to not give fluids for dengue
how common is dengue infection - where is it most common in australia
- we dont have dengue in aus
but we do have it in return travellers
dengue is as common than flu infection in travellers
its more common than Hep. A
how many vaccines are there for Dengue
what is it
what does it cover
how effective is it
only 1 vaccine - only vaccine on the market
Chimerivax
it is a chimeric, quadrivalent vaccine
covers all 4 antigens for the 4 serotypes
not very good efficacy - 60%
what is the effect of the dengue vaccine in seropositive and seronegative patients
- in seropositive patients that have previously had dengue the vaccine prevents them from infection and prevents them from getting severe disease
- in those that are seronegative patients the vaccine lost protection from infection and there was an increased risk of developing severe disease
what is the recommendations for the dengue vaccine
- as the vaccine works best for those that are seropositive they only recommend to use the vaccine in places where the virus is endemic
- as these people have most likely been infected, and be seropositive
- therefore the benefits outweigh the cons in these areas
what is the transmission cycle of JE
- it is a virus that is transmitted through animals
- pigs and birds act as amplifiers of the virus
- mosquitos transmit the virus and humans are accidentally infected by mosquitos - we are not apart of the cycle
humans become infected when they are in animal/mosquito environments
what are the symptoms of JE and how long do they take to appear
ranges from febrille illness - headache fever and rigor to aseptic meningitis to encephalitis
incubation is 5-15 days
what age group is at risk of developing neurological illness from JE?
who normally gets JE?
there is age specific outcomes for JE infection - the older you are the more likely you are to develop neurological illness (5-10x more likely)
those at high risk are over 50 years old
younger people are not as at risk of developing neurological disease
although most JE infections occur in young children
how is JE diagnosed?
collect blood and do RT-PCR to diagnose infection when patient is viraemic - would allow diagnosis within days
serology can be taken later once they seroconvert to confirm the diagnosis
MRI can also be used in early infection to see brain changes and diagnose severe JE - water accumulation in the brain indicates inflammation
what is the prognosis of JE?
who dies
who survives?
20-30% of people will die from JE
70-80% will survive from JE infection:
out of the surviving 50% will have a severe disability including paralysis, movement disorder etc
the other 50% will have a mild disability - learning disorder, seizures etc.
what is the risk for JE for travellers?
1 in 250,000 travellers will get a clinical JE infection in endemic areas
dont have to travel for over a month to be at risk - most people who get sick were there for less than a month
what time of the year does most disease transmission of JE occur
may to october
how is JE treated?
it cant be treated
how many vaccines for JE are there?
what are they named and what are their features?
2 vaccines available - both good vaccines!
IMOJEV
- live attenuated chimeric vaccine that uses the internal structure of yellow fever virus and uses the JE envelope
- high efficacy
- rapid immune response
- one dose needed
- no safety concerns
JESPECT
- inactivated vaccine
- high conversion rates but Ab titres wane quickly hence need a booster every 2 years
- no safety concerns
where is yellow fever found
africa and south america
how is yellow fever spread
by mosquitos
what transmission cycles does yellow fever have
it has a urban cycle and a city cycle
urban cycle: the virus is transmitted in urban areas
jungle cycle: the virus is amplified in primates and by mosquitos - this is an issue as the virus cant be eradicated unless the primate population is eliminated
hence virus is maintained in the jungle cycle
what are the clinical features of yellow fever
first signs: fever, chills, back pain
virus will attack the liver and cause hepatitis
more severe symptoms will include abdominal pain, vomiting, jaundice
leads to multi-organ failure
how do you diagnose yellow fever?
why is it difficult?
yellow fever looks alot like other diseases / infections such as malaria, typhoid, etc. and they all circulate in the same areas
PCR is used to diagnose the virus first
then serology will be used once the patient has seroconverted to confirm diagnosis
how is yellow fever prevented?
yellow fever vaccine
- live attenuated vaccine
- induces neutralising ab’s
- very effective
what should you consider before giving the yellow fever vaccine?
yellow fever vaccine
should not be given to those allergic to eggs
should not be given to immunocompromised, children/infants, or pregnant women
there are adverse events that can occur from giving the vaccine such as post vaccination encephalitis and viscerotropic disease
what are the adverse event of yellow fever vaccine and who should you avoid giving the vaccine to
avoid giving vaccine to immunocompromised, infants and pregnant women
adverse events from the vaccine include:
Post vaccination encephalitis
- most cases of this are in children this is why we dont vaccinate the kids
Viscerotropic disease
- yellow fever like illness- its actually just yellow fever disease!!
- risk if youre over 65
- experience organ failure
- treatable if caught early
- other wise risk of death 60%
how is zika kept alive?
zika is kept alive in primates and spread by mosquitos
humans are accidentally infected by zika
how can zika be transmitted
blood, breast milk, saliva, semen
can cross the placenta from mother to baby - biggest issue
what are the symptoms of Zika?
how many people develop symptoms?
Zika causes mild fever / rash that lasts a week
the disease is self limiting
only 20% of people develop symptoms! 80% of cases are asymptomatic
what is the issue with Zika
causes foetal abnormalities - microencephaly
how is zika diagnosed?
PCR of blood to diagnose Zika infection
can confirm diagnosis with serology once patient has seroconverted
how do you manage pregnant women diagnosed with Zika
- confirm diagnosis using PCR and serology
- can scan baby every so on to see if changes has occured
can zika be sexually transmitted?
yes. zika is present in the semen for up to 90 days post infection