Flaviviruses Flashcards
Incubation period of Dengue?
4-6 days
Transmission vector and amplifying host of Dengue?
Aedes aegypti/albopictus and humans/non human primates
Indicators of severe Dengue?
Positive tourniquet sign
Narrowing pulse pressure with rising haematocrit
Bleeding
Second infection >18/12 from first
Dengue vaccine.
- Name
- Type
- Schedule
- Who gets it?
- How good is it?
- Contraindications
Qdenga (NB - remember to get QDENGA you need to Query if they’ve had DENGA (dengue))
Live vaccine
2 doses 3 months apart
People travelling to high risk areas who have evidence of previous Dengue infection
86% effective against hospitalisation and 65% effective against viraemia in those who have had primary Dengue
Contraindicated - children under 4, pregnancy, immuncomp
Japanese encephalitis vaccine:
Name?
What type?
Indications?
Schedule?
IXIARO
Inactivated verocell
2 doses 1 month apart
offered to those at high risk from travel (who will spend >1 month in area of high endemicity) or those travelling for a shorter time but who will do high risk activities (pig/rice farms)
Vector and amplifying host of japenese encephalitis?
Culex mosquito and pigs/wading birds.
Name the main flaviviruses and their vector?
Ticks
- TBE
- Powassan
- Omsk
- Louping Ill
Culex
- WNV
- Japanese encephalitis
- St Louis encephalitis
- Usutu
Aedes
- Yellow fever
- Dengue
- Zika
Yellow fever vaccine: Type and schedule?
Live vaccine with 17D strain of Yellow fever
One dose (100% effective) with boosters required if given to pregnant women/breastfeeding women.
Yellow fever vaccine contraindications?
- Contraindicated
○ <6 months
○ >60 (generally not recommended)
○ Immunosuppressed
○ Thymus disorders/removal
§ Including those with cardiac surgery pre 2000 as the thymus may have been removed
1st degree relative with YEL-AVD/YEL-AND
Describe YEL - AND
- YEL-AND
○ Yellow fever associated neurological disease
○ 2-56 days post vaccine
○ Fever, headache, focal neurological deficits, GBS
○ CSF demonstrates IgM
○ Usually complete recovery
Incidence - 0.8/100,000 vaccines given
Describe YEL - AVD
- YEL-AVD
○ Yellow fever vaccine associated viscerotropic disease
○ 1-18 days post vaccine
○ Fever and multiorgan failure that resembles yellow fever
○ 60% mortality
0.3/100,000 vaccines given
How long should couples abstain from unprotected sex if returning from a zika infected country?
3 months
Present in sperm for 3 months and vaginal tract for 2. Only 2 months required if only female partner travelled.
Subtypes of TBE?
European, transmitted by Ixodes ricinus ticks, and endemic in rural and forested areas of central, eastern and northern Europe
Far-Eastern, transmitted mainly by Ixodes persulcatus, and endemic in far-eastern Russia and in forested regions of China and Japan
Siberian, transmitted by Ixodes persulcatus, and endemic in Urals region, Siberia and far-eastern Russia, and some areas in north-eastern Europe
European subtype has a biphasic illness and tends to have better outcomes. The other two are more likely to have a monophasic illness with worse neuro outcomes.
TBE vaccine. Type, schedule and indications?
Tico-Vac - it is produced from virus grown in chick fibroblasts and then inactivated by formaldehyde
3 doses
0, 1-3 and 12 months
Indications
- TBE vaccine is used for the protection of individuals at high risk of exposure to the virus through travel or employment.
TBE transmission?
TBE is transmitted to humans by the bite of an infected tick or, less commonly, by ingestion of unpasteurised milk from infected animals, especially goats.
Amplifying hosts of culex transmitted flaviviruses?
Mostly birds (+pigs in Japanese encephalitis)
Amplifying host of aedes transmitted flaviviruses?
Non human primates (Dengue, Zika, Yellow)
Gold standard test for differentiating flavivirus infections?
PRNT - plaque reduction neutralisation test
How does the plaque reduction neutralisation test and what is a positive?
The basic design of the PRNT allows for virus-antibody
interaction to occur in a test tube or microtiter plate, and then measuring antibody effects on viral infectivity by plating the mixture on virus-susceptible cells. The cells are overlaid with a semi-solid media that restricts spread of progeny virus. Each virus that initiates a productive infection produces a localized area of infection (a plaque), that can be detected in a variety of ways. Plaques are counted and
compared back to the starting concentration of virus to determine the percent reduction in total virus infectivity. In the PRNT, the serum specimen being tested is usually subjected to serial dilutions prior to mixing with a standardized amount of virus. The concentration of virus is held constant such that, when added to susceptible cells and overlaid with semi-solid media, individual plaques can be discerned and counted. In this way, PRNT end-point titres can be calculated for each serum specimen at any selected percent reduction of virus activity.
Neutralising abs measured against a range of flaviviruses and a >4x change in specific quantitative antibody titres in paired sera, 10 days apart, is diagnostic.
