West Nile virus:

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West Nile virus Research challenges and
opportunities presented from this emerging
flavivirus ADED rounds, 1000-1100 PST, March
16, 2004

Harvey Artsob, PhD Director, Zoonotic Diseases
and Special Pathogens National Microbiology
Laboratory, Health Canada
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West Nile virus
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Family Flaviviridae Spherical enveloped viruses
with a ()-strand RNA genome of 10-11Kb
Genus - Pestiviruses Bovine Viral Diarrhea
Genus Hepaciviruses Hepatitis C
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Members of the Japanese encephalitis virus
serocomplex
Cacipacore virus
Japanese encephalitis virus
Koutango virus
Murray Valley encephalitis virus
Alfuy virus
St. Louis encephalitis virus
Rocio
Stratford
Usutu virus
West Nile encephalitis virus
Kunjin virus
Yaounde virus
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Flavivirus Genome
ns4a
NC
NC
ns2a
-3'
NS3
NS5
C
prM
E
NS1
5'-
ns4b
ns2b
furin
pr M
7 non-structural genes/proteins
3 structural Genes/proteins
From Roehig, Fourth National Conference on West
Nile Virus in the United States 2003.
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Egypt 1951
Phylogenetic Relationships among West Nile Viruses
France 1965
South Africa
Israel 1952
Romania 1996
Kenya 1998
Senegal 1993
Morocco 1996
Lineage 1 India, Australia, Europe Russia,
Middle East, North Africa, Africa (Senegal, C.
African Republic Ivory Coast) Lineage 2 Africa
(Central and Southern including Madagascar)
Italy 1998
Volgograd 1999
New York 1999
Israel 1998-A
NY2000 3282
NY2000 3356
NY 1999 equine
LIN-1
NY 1999 hum
Conn 1999
MD 2000
NJ 2000
Israel 1999 H
C.Afr.Rep 1989
Senegal 1979
Algeria 1968
Lanciotti et al. 2002. Virology 298,96-105
C.Afr.Rep 1967
Iv.Coast 1981
Kunjin 1960
Kunjin 1973
North American strain has not changed
significantly to date Davis et al 2003 (
abstract-ASTMH meeting) tested over 30 isolates
from 6 states and 5 provinces collected in
20012002 and found an average nucleotide
divergence of only 0.18 Ebel et al 2003 (
abstract-ASTMH meeting) showed isolates from NY
state from 2000-2002 remained relatively
genetically homogeneous with a mean genetic
distance of less than 0.002.. However strains
collected in 2002 were more genetically diverse.
Kunjin 1984b
Kunjin 1991
Kunjin 1984a
Kunjin 1966
Kunjin 1994
India 1955a
India 1980
India 1958
India 1955b
Kenya
Uganda
Senegal 1990
Uganda 1937
C.Afr.Rep 1972a
LIN-2
C.Afr.Rep 1983
Uganda 1959
C.Afr.Rep 1972b
Madagascar 1988
Madagascar 1986
Madagascar 1978
JE SA 14
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West Nile virus studies proposed or under
consideration Genotyping of WNV
isolates/specimens from divergent sources (human,
mosquito, bird) and different regions across
Canada comparisons with isolates from the United
States, Europe, and Africa Analysis of proteomic
changes in WNV infected cells Virulence
studies/host infection with multiple WNV strains
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West Nile human infections
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West Nile Virus Activity in the Continental US

• Year Human Horses States
• 1999 62 25 4
• 2000 21 63 12
• 2001 66 733 27
• 4156 14901 44
• 9377 4636 45

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West Nile Virus Activity in Canada

• Year Human Horses Provinces
• 1999 1(travel) 0 0
• 2000 0 0 0
• 2001 0 0 1
• 416 356 5
• 1335 445 7
• Several hundred additional suspect cases were
  identified

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Human infection with WNV in 2003 vs 2002
Province B.C. Alberta Saskatchewan Manitoba Ontari
o Quebec New Brunswick Nova Scotia Yukon
2003 20 272 792 (6 deaths) 141 (2 deaths) 89 (2
deaths) 17 1 2 1
2002 0 2 0 0 400 (17 deaths) 17 (3 deaths) 0 0 0
not locally acquired, travel history
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Patterns of WN activity in North America, 2002
versus 2003 Geographic patterns of human cases
north central Largest concentration of human
cases in 2002 seen within the geographically
contiguous areas of the United States north
central area (Illinois, Michigan, Indiana, etc)
and Ontario.Few cases in that geographic region
in 2003 Why? Climatic factors? Build up of
immunity? Education/avoidance? Larviciding?
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Patterns of WN activity in North America, 2002
versus 2003 Geographic patterns of human cases
- westLargest concentration of human cases in
2003 seen within the western part North America
where Culex tarsalis is the most important
mosquito vector species (Colorado, Nebraska,
South Dakota, Prairies). There is a significantly
greater number of cases than in 2002 with many
hot spots of human cases within these
states/provinces. Why? Can human serosurveys
help shed some light on the question?
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Is the WNV strain introduced into North America
more virulent than most WNV strains?
Humans Emerging clinical syndromes movement
disorders, Parkinsonism, - Flaccid paralysis,
Rhabdomyolysis Short and long term
sequelae Ratio of severe to mild and/or
inapparent illness (lt 1100?) Infections
associated with transplantation, transfusion,
breastfeeding, transplacental transmission
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WNV Human Infection Iceberg Revisited
10 fatal (lt0.1 of total infections)
1 CNS disease case 100 total infections
lt? CNS disease
Febrile illness alone less frequent?
? West Nile Fever
80 Asymptomatic
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Factors related to the West Nile virus
amplification cycle
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VECTOR
ENVIRONMENT
HOST
VIRUS
From Turell, Fourth National Conference on West
Nile Virus in the United States 2003.
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Mosquito field isolates (PCR-positive
pools) Isolates from more than 40 different
mosquito species in North America including 10
from Canada
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Potential vectors of West Nile virus based on
laboratory vector competence studies
Efficient Moderate Inefficient
Ae. albopictus Ae. aegypti Ps. ferox Cx.
salinarius Ae. vexans Cx. tarsalis Cx.
nigripalpus Cq. perturbans Oc. atropalpus Cx.
pipiens Oc. canadensis Oc. japonicus Cx.
quinquefasciatus Oc. cantator Cx.
restuans Oc. sollicitans Oc. triseriatus Oc.
taeniorhynchus
From Turell, Fourth National Conference on West
Nile Virus in the United States 2003.
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Bionomics of potential mosquito vectors

• Host preference
• Population density
• Biting behavior
• Longevity
• Feeding time
• Seasonallity

From Turell, Fourth National Conference on West
Nile Virus in the United States 2003.
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Interpretation of mosquito data in relation to
human risk - relevance of infection rate in
different species with regard to risk for human
disease - importance of bridging vectors - what
are the important bridging vectors? - efficacy
of control measures


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Birds as reservoir hosts

• There is currently evidence for infection of over
  200 species of birds .
• The reservoir potential of these birds varies
  greatly and is dependent upon
• the competency (days and level of viremia) and
• relative number of infections (amount of birds
  in a given area, amount of infected mosquitoes
  feeding on these birds) of each bird species

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Birds as reservoir hosts

• 1. Very competent species (viremia 3-5 days,
  peak viremia 8.5-11.0 logs per ml serum)
• e.g. blue jay, house sparrow, american crow
• 2. Moderately competent species (viremia 2.8-4.5
  days, peak viremia 6.8-8.7 logs per ml serum)
• e.g. black billed magpie, American robbin
• 3. Weakly competent species (viremia 0.3-3.0
  days, peak viremia 4.7-6.7 logs per ml serum)
• e.g. mallard, Canada goose, mourning dove
• 4. Non-competent species (viremia transient, lt
  4.6 logs per ml serum)
• e.g. chicken, rock dove

From Komar, Fourth National Conference on West
Nile Virus in the United States 2003.
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Dead bird surveillance in Canada

• What worked?
• Timely early warning on temporal spatial
  distribution of WNV activity
• Used to inform the public
• Action point for intensified mosquito
  surveillance control?

• What needs to be addressed?
• Continuous testing of corvids after widespread
  virus activity observed
• Utility of dead bird sightings data or cluster
  analysis to predict human risk unknown

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Non Avian animals shown to be infected in the
United States, 1999-2002

• Alpaca
• Horses
• Big Brown Bat
• Little Brown Bat
• Cat
• Dog
• Grey Squirrel
• Llama
• Alligator

• Wolf
• Fox Squirrel
• Sheep
• Eastern Chipmunk
• Rocky Mountain Goat
• Striped Skunk
• Reindeer
• Domestic Rabbit
• Harbor Seal

From Bunning, Fourth National Conference on West
Nile Virus in the United States 2003.
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Is the WNV strain introduced into North America
more virulent than most WNV strains?

• Animals
• gt200 spp of birds susceptible
• Significant mortality in some e.g. American crow
• Mammals squirrels, dog, wolf, reindeer,
  mountain goat, etc
• Reptiles farmed alligators
• Implications for wildlife populations, zoos and
  endangered species

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Questions pertaining to natural cycle and ecology
of West Nile virus

• Will WNV spread to British Columbia?
• Will WNV gain a foothold in Atlantic Canada?
• What are the northern limits to the spread of
  WNV?
• (Presumed limitations to northern spread include
  a lack of Culex species to drive the cycles and
  degree day temperature limitations)

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Most positive birds been found in the
southernmost parts of Canadian provinces
(Limitations around 55N latitude?)
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Questions pertaining to natural cycle and ecology
of West Nile virus

• What are the relative roles of overwintering
  versus virus introduction via migratory birds for
  risk for recurrence of West Nile in a given
  region of Canada?

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Dissemination of WNV by migratory birds?
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Questions pertaining to natural cycle and ecology
of West Nile virus

• Overwintering mechanisms
• Mosquitoes hibernating adult Culex
• - in mosquito larvae?
• Other arthropods?
• Vertebrate hosts?

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ST LOUIS ENCEPHALITIS ACTIVITY 1975 WEST NILE
VIRUS ACTIVITY 2001, IN ONTARIO
Why is WNV so much more successful
than SLE in temperate areas of North America?

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Questions pertaining to natural cycle and ecology
of West Nile virus

• Will West Nile virus become endemic in certain
  parts of Canada? If so, which parts?
• Will immunity gradually build up in the bird and
  human populations in areas of continuous activity
  sufficient to limit WNV activity? Has this
  already started to happen in certain parts of
  North America?

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Questions/Discussion
Fight the bug