Transcript WNV: Veterinary Medicine and Public Health

West Nile virus on the
Prairies
Tasha Epp, DVM, PhD
October 5, 2010
WNV 1999, New York
Spread across USA - 1999
Spread across USA - 2000
Spread across USA - 2001
Spread across USA – 2002
Spread across USA - 2003
Great Plains and WNv
Birds and WNv
Virus
 Family: Flaviviridae
 Genus: Flavivirus Japanese Encephalitis
Antigenic complex
– Includes JE, WNV, Kunjin, Murray Valley
encephalitis, SLE, etc
– RNA, single stranded
Natural Cycle
Species affected
 Birds
 Mosquitoes
 Humans, horses
 alpacas, camels,
sheep, squirrels,
reptiles, etc
Clinical Disease
 Humans
– Asymptomatic
– WNV Fever
– WNV neuro-invasive
 Other mammals or birds
– Neurological symptoms (mild to severe)
– Death
Long Term Outcomes - Humans
 Symptoms reported “post-recovery”
– Self-reported fatigue
– Memory problems
– Extremity weakness
– Word-finding difficulty
– Headaches
– Depression
– Attention deficits
Surveillance in Prairies from 20022010
 2002
– Humans, horses and birds in Manitoba
– first bird and clinical horses reported in SK
 2003
– epidemic (birds, horses, humans, etc) in SK and MB
– First cases in AB
 2004 – 2006
– Mild years, very few cases
 2007
– epidemic returns in full force on prairies
 2008-2010
– Few cases reported
2003: Horse, bird, human and mosq.
Five Hills Health Region
 Highest reported number of cases in SK
 Seroprevalence
– Overall 9.8% (7.4, 12.6)
– Rural only 16.8%
– Urban only 3.2%
 Rural versus urban:
– 6 times more likely to be positive (95% CI: 3,
13)
Present Surveillance in SK
Minimal
Few West Nile Virus mosquitoes present. Minimal
risk does not mean no risk; take precautions
against mosquito bites.
Low
WNV mosquito development. Take precautions
against mosquito bites.
Moderate
The mosquito species that carries West Nile Virus
has been recorded in numbers that warrant extra
precautions.
High
WNV-positive mosquitoes identified in significant
numbers. Precautions against mosquito bites
should be taken at all times.
Regardless of the risk rating for your region, remember that there is no such thing as
"risk-free". If you can be bitten by a mosquito, you can contract West Nile Virus.
Source: Saskatchewan Ministry of Health, Population Health Branch
Occupational Data
 Mosquito exposure
– Rural residents or workers
 Farmers
 Outdoor jobs or recreation
 Tissue or fluid exposure
– Laboratory, field or clinical workers
 People involved in dead bird collection
 Veterinarians
 Pathologists
Precautions for workers
http://www.cdc.gov/niosh/docs/2005-155/
http://www.phac-aspc.gc.ca/ols-bsl/wnvbio-eng.php
Using an effective insect
repellent helps prevent
mosquito bites.
Photograph courtesy of
CDC/PHPPO/DPDE/CAB/Ph
otoServices.
Long-sleeved shirts, long
pants, and socks will help
prevent mosquito bites.
Photograph courtesy of
Joe Larson, USDA.
Control Measures:
 Source reduction
– Remove standing water, etc
 Mosquito control
– Personnel protection
– Larviciding
– Adulticiding
 Vaccination
 Behavior modification
Mosquito Control
 Preferred
method for
surveillance in
SK
 Best prevention
of infection in
people?
Vaccination?
 Is this feasible?
 Who would get vaccinated?
 Cost-benefit analysis?
Human Behavior?
 DEET
 Drain
 Dress
 Dusk to dawn
Northern Colorado study
 Loveland and Fort Collins
 Similar ecology, demographics
– High plains ecoregion
– 90% white, around 10% >65 yrs
 Loveland had mosquito control program
– Less WNV-infected mosquitoes than Fort
Collins
Northern Colorado study
 Loveland had higher neuroinvasive disease rate
– Loveland = 38.6/100,000
– Fort Collins = 15.9/100,000
Northern Colorado study
 Loveland residents
– reported less use of DEET
 Most influenced by age
 Second influenced by risk perception
– more likely to spend time outdoors at
dusk and dawn
 both weekdays and weekends
– Long clothes not important
First Nations and WNv
 Identified many activities resulting in
exposure
 Identified features of homes or yards
resulting in exposure
 Control measures
– Smoke or Mosquito coils
– DEET based products
– Clothing (children versus adults)
Communicating Risk
 When?
 How?
 What?
Future of WNv
 What should we expect?
 Is WNv here to stay?
 Can we predict WNv years before they
occur?
Questions?