33: WNV and Chikungunya

Question 1

west nile virus characteristics

Answer 1

enveloped Flavivirus in the same family as dengue, zika, hep c

Question 2

WNV history

Answer 2

first identified in birds in 1937
- zoonosis

from 1950s-1980s, caused human outbreaks of mild febrile illnesses in Israel, Egypt, India, France and SA

in 1990s, triggered encephalitis
- mutations causing it to be more virulent

Question 3

WNV human disease statistics

Answer 3

80% of infected individuals have few or no symptoms
- high asymptomatic rate like zika

most symptomatic people recover but weakness can last for months

about 1 in 150 progress to severe disease

1 in 10 people with severe disease develop invasive neurological disease that can lead to death

Question 4

WNV symptoms

Answer 4

fever, headaches, joint pain, vomiting, diarrhoea, rash

severe disease
- headaches, stupor, coma, muscle weakness, vision loss, paralysis

no vaccine or specific antiviral treatments

Question 5

WNV mosquito vector

Answer 5

Culex species that lives in tropical and temperate zones of the world
- broader range than Aedes mosquitos

Question 6

WNV life cycle

Answer 6

true animal reservoir where specific bird species carry the virus

vertical transmission means it can be transmitted to mosquito offspring

zoonosis that causes disease in both bird and mammalian hosts

humans are accidental dead-end hosts who cannot transmit to the next mosquito

Question 7

dispersal of WNV lineages

Answer 7

1a as the lineage mutated to become more virulent in both birds and humans

Question 8

WNV in NA statistics

Answer 8

autochtonous/local outbreaks started in 1999
- infected birds and humans in NA localy

50k human clinical cases and 3-6M infections in the US since 1999

Question 9

burden of disease WNV in the US

Answer 9

now centred in the western US

bird reservoir shifted from east to west coast

Question 10

chikungunya virus characteristics

Answer 10

enveloped RNA virus (alpha virus)

transmitted primarily via Aedes aegypti and Aedes albopictus

causes a similar disease as dengue or zika but genetically very different

Question 11

chikungunya (and alphavirus) disease

Answer 11

causes encephalitis and arthritis as an alpha virus

Question 12

chikungunya (and alphavirus) disease

Answer 12

causes encephalitis and arthritis as an alpha virus

Question 13

Chikungunya transmission

Answer 13

sylvatic cycle in Africa
- enzootic
- between mosquitos and non-human primates/rodents/birds

urban cycle in Asia
- no syllabic cycle in Asia
- Aedes aegypti is the primary vector

Question 14

why did chikungunya spread in 2013/2014?

Answer 14

geographic ranges of Aedes mosquitos expanding
- consequence of climate change and globalisation

international travel

more genetic adaptation and mutation for better replication

Question 15

chikungunya in the Americas in 2013/2014

Answer 15

originally only spread by Aedes aegypti

starting in 2005, new viral mutations allowing infectivity in Aedes albopictus which are more widespread

Question 16

clinical symptoms of chikungunya infection

Answer 16

occur 4-7 days post-exposure

sudden onset of fever

rash

muscle aches

swollen/painful joints

<0.1% mortality but people can end up with arthritis for months/years

no specific treatment, vaccine or preventive drug

Question 17

acute stage of chikungunya disease

Answer 17

4-6 days after infection, 80%-90% of infected adults are symptomatic
- non-specific symptoms

typically resolve within 7-10 days but up to 40% may develop chronic infection

Question 18

chronic stage of chikungunya disease

Answer 18

18 months after acute disease, 40% of infected individuals still have IgM and many still have symptoms
- virus is still present

12% of long-term joint paints attributed to chikungunya

small number (<1%) develop guillain-barre or encephalitis but few deaths

Question 19

differences between chikungunya and WNV

Answer 19

diseases are difficult to distinguish
- both have fever, muscle aches and joint pain

onset of fever more abrupt/rapid with chikungunya