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On Watch for West Nile Virus in Oklahoma

• Kristy K. Bradley, DVM, MPH, Dipl. ACVPM
• State Public Health Veterinarian/
• Assistant State Epidemiologist
• Oklahoma State Department of Health
• [phone]
• kristyb_at_health.state.ok.us

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West Nile Virus Background

• Family Flaviviridae
• Genus Flavivirus
• Japanese Encephalitis Antigenic Complex
• Complex includes Alfuy, Japanese encephalitis,
  Kokobera, Koutango, Kunjin, Murray Valley
  encephalitis, St. Louis encephalitis, Stratford,
  Usutu, and West Nile viruses.
• All are transmissible by mosquitoes, many can
  cause febrile, sometimes fatal, illnesses in
  humans.

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West Nile Virus Transmission Cycle
Mosquito vector
Incidental infections
West Nile virus
West Nile virus
Incidental infections
Bird reservoir hosts
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West Nile Virus Background

• First isolated in 1937 from the blood of a woman
  in Uganda
• First recorded epidemic in Israel in 1950s.
• Soon recognized as one of the most widespread
  Flaviviruses.
• Distributed through Africa, West Asia, Europe and
  the Middle East.

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West Nile Virus Enters the U.S.
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West Nile Virus in the US -Some Possible
Pathways of Introduction

• Infected human host
• Human-transported vertebrate host
• Legal importation of birds
• Illegal smuggling of infected birds
• Human-transported vector(s)
• Storm-transported vertebrate host (bird)
• Intentional introduction (terrorist event)

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Media West Nile Frenzy
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West Nile Virus in North AmericaHuman Case
Summary 1999 - 2001

• 1999 thru 2000
• 83 confirmed human cases
• All from greater NYC metro area
• 9 deaths (11)
• 85 of confirmed cases gt 50 yrs old
• 2001
• 66 confirmed human cases from 10 states
• 9 fatalities (14) median age 69 yrs.

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Number of WNV-Infected Crows Reported from the
North Central and South Central Regions,by Week,
2001
As of 2/1/02
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WNV Vertebrate Health Impacts 1999-2001

• Birds-101 species 11,640 99.9
• Horse 673
• Cat 1
• Dog 0 ----
• Dom. Rabbit 1
• Raccoon 1
• Gray Squirrel 1
• Eastern Chipmunk 1
• Striped Skunk 1
• Big Brown Bat 1
• Keens Bat 1

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WNV Impact on Pets

• Horses and pet birds of most concern
• vaccine for horses
• avoid mosquito exposure for pet birds
• Dogs and Cats resistant to disease
• no special preventative measures needed
• Pocket pets may be vulnerable
• more research needed

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2002 National WNV Surveillance (Final ArboNet
Report)

• 16,739 avian infections reported from 44 states
  (439 in Oklahoma)
• 14,571 equine infections confirmed in 40 states
  ( 965 in Oklahoma)
• 6,604 WNV-positive mosquito pools from 36 states
  ( 18 in Oklahoma)
• 4,156 human cases from 40 states (21 in OK)
• 284 human deaths (2 in OK)

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WNV Surveillance in Oklahoma

• FUNDING AND COLLABORATION
• Supplemental Epidemiologic and Laboratory
  Capacity Grant from CDC with activities beginning
  November 2000
• Formation of InterAgency Zoonotic Disease
  Working Group
• OK Dept. of Agriculture, OK Dept. of Wildlife
  Conservation, OK Animal Disease Diagnostic
  Laboratory, and USDA Veterinary Services and
  Wildlife Services

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WNV Surveillance in Oklahoma

• OBJECTIVES
• 1. Early detection of WNV epizootic
• activity so intervention is
  possible to
• prevent human illness.
• 2. Obtain good baseline epidemiologic
• data on incidence of other
• arboviral infections (SLE, WEE,
• LaCrosse)

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Diagnosis of WNV

• SEROLOGY
• 1. IgM-capture ELISA (serum or CSF)
• Diagnostic if CSF-positive IgM
  antibodies
• usually present in serum by
  8th day of illness
• 2. ELISA, IFA, HI
• Need four-fold rise in
  paired titers for case
• confirmation postive tests
  need confirmation by
• PRNT

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Diagnosis of WNV

• PCR (polymerase chain reaction)
• CSF, brain
• Not sensitive enough to test serum or blood
• Viral Isolation (requires BSL-3 lab)
• blood, brain, CSF
• Immunohistochemistry
• brain tissue (autopsy)

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WNV Surveillance in Oklahoma

• Dead Wild Bird Surveillance and
• Testing
• Equine Encephalitides Monitoring
• and Testing
• Enhanced Passive Surveillance for
• Human Meningoencephalitis
• Mosquito Trapping Testing

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Dead crows per square mile vs. human cases,
Staten Island 2000
Ref Eidson. Emerg. Inf. Dis. 7(4)662-4 2001
Conclusion Weekly dead crow densitiesgt 1/sq.
mi. provided an early warning for a human outbreak
First Positive Bird
11/13/00
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WNV Surveillance in Oklahoma Avian

• Established dead bird reporting hotline --
• 1-800-990-CROW
• Dept of Ag triages phone reports OSHD and
  local county health departments used as drop-off
  sites
• Developed testing capabilities at Oklahoma
  Animal Disease Diagnostic Lab
• Necropsy, RT-PCR test for WNV,toxicology screen
• Success depends on many community partners
• Animal control, zoos, bird watchers, parks
  workers

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Instructions on Submission of Freshly Dead Birds

• Wear gloves or cover hand with plastic bag when
  collecting bird.
• Double bag in small garbage bag or other plastic
  bag.
• Keep at refrigeration temperature - not
  frozen-(place in cool location, refrigerator, or
  bucket with ice) until transported to laboratory
  or pick-up point.

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Number of Calls to 1-800-990-CROW
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Number of Birds Tested for WNV by Week
Oklahoma-2002
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Distribution of WNV Birds by Species,
Oklahoma-2002
Total Birds 438
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Avian WNV Positivity Rates by County Oklahoma

• Range 2 (Canadian) - 100 (Grant)
• Wagoner 53.3 (32/60)
• Ottawa 39.5 (32/81) ?
• Muskogee 38.2 (63/165) ??
• Haskell 37.5 (3/8)
• McCurtain 35.7 (10/28)
• LeFlore 30 (6/20)
• Tulsa 28.4 (151/531) ???
• Beckham 25 (3/12) .
• Oklahoma 15.5 (51/329) ???

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WNV Surveillance in Oklahoma Avian

• 3,481 dead wild birds submitted for testing
• 438 positive (28 different species)
• Ceased bird testing October 15 due to depletion
  of resources
• 38 counties origin of WNV birds
• 10/13 counties with human cases had positive
  bird as first indicator

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2001 U.S. Avian Surveillance Data
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West Nile Disease in U.S. Horses 1999-2001
Data from USDA/APHIS
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Symptomatology of West Nile Disease in Horses

• Spectrum of illness
• Ataxia, limb weakness, and muscle fasiculations
  commonly reported
• Sometimes progression to down in rear or
  complete recumbency very rapid (hours)
• Recovery not always complete.

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West Nile Virus Surveillance in
OklahomaVeterinary

• Oklahoma ranked 2 in no. of horses/capita
• Equine owners and veterinarians urged to report
  suspect equine encephalitis cases to OSDH, ODA,
  or USDA.
• Blood test or testing of brain tissue performed
  at OADDL.
• All dead or euthanized horses first examined
  for rabies at State Public Health Laboratory.

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West Nile Virus Diagnosis by IgM Capture ELISA

• Can provide diagnosis on single specimen (serum
  or CSF)
• IgM antibodies detectable by 8-10 days
  post-infection.
• Sera collected prior to 8 days with equivocal
  results should be retested a few days later.
• Cross reaction with other flaviviruses PRNT
  confirmatory.
• IgM antibodies generally persist 2-3 months
  IgG gt 2 years.

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WNV Equine Vaccine

• Conditional license approved August 1, 2001 to
  Fort Dodge Laboratories, Inc.
• Two dose series given 3 -6 weeks apart
• Blood test (IgM capture ELISA) will distinguish
  between acute disease and vaccination antibody
  response
• Full vaccine licensure approved February, 2003

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WNV Equine Vaccine

• Ft. Dodge Labs estimates 35 of nations horse
  population (6.9 million) have been vaccinated.
• In highly enzootic areas, more than one annual
  booster may be necessary to provide protective
  immunity.
• Very good safety and efficacy record.

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West Nile Virus Surveillance in
OklahomaPreliminary Equine Findings

• 964 (1 zebra) laboratory-confirmed cases
• Majority of cases had onsets after Sept. 30
• 13.4 mortality rate
  (grossly underreported)
• Twenty-eight horses (2.9) had received 2 dose
  primary series within 9 months of disease onset.

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Number of Equine West Nile Cases by State, 2002

• THE TOP FIVE
• Texas 1,598
• Illinois 1,120
• Nebraska 1,092
• Minnesota 992
• Oklahoma 964
• Neighboring States
• Kansas 792
• Missouri 662
• Colorado 376
• Arkansas 73

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Distribution of Oklahoma Equine WNV Cases, Aug. 9
- 23, 2002
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Distribution of Oklahoma Equine WNV Cases, Aug.
24 - Sept 6, 2002
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Distribution of Oklahoma Equine WNV Cases, Sept.
7 - Sept. 19, 2002
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Distribution of Oklahoma Equine WNV Cases, Sept.
20 - Oct 4, 2002
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2002 National Equine Surveillance Data
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Summary of Equine Surveillance

• Complement to avian surveillance
• First indicator of transmission risk in western
  OK
• Funding depleted October 15, 2002
• Payment for equine testing in 2003 will be
  responsibility of animal owner.

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Culex Mosquitoes as Primary WNV Vectors

• Over 36 different types of mosquitoes have
  tested positive for WNV, but Culex species of
  mosquitoes are most involved with transmission.
• Culex characteristics
• prefer to feed on birds
• most prevalent July- Oct
• weak fliers
• breed in small areas of standing water
• adults live 3 weeks
• can overwinter and harbor
• WNV
  

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Culex tarsalis

• Most abundant in western agroecosystems and
  wetlands
• types of habitat vary from peridomestic sources
  to pasture and other flood irrigated crops to
  wetlands.
• Feeds most frequently on upland birds that roost
  and nest at elevated vegetative ecotones
• house finches, house sparrows, doves, quail
• Competent vector of SLE and WEE and WNV
• suitable bridge vector to horses or humans

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Other Animals Affected by West Nile Virus??

• Dogs and cats rarely develop illness after
  infection with the virus
• Sheep and goats may be more susceptible
• Documented outbreaks in squirrels in several
  states
• 25 squirrels tested in Oklahoma were positive
• More research needed in this area.

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Epidemic WNME, United States, 2002

• Western hemispheres largest arboviral ME
  epidemic
• 2,946 WNME cases
• 1,300 WNF / unspecified
• 284 deaths
• 39 states D.C.
• Largest WNME epidemic EVER
• Spread to Pacific coast
• New clinical syndromes
• Acute flaccid paralysis (West Nile polio)
• Five new transmission modes

4,156 illnesses
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New Transmission Modes

• Transplantation
• Transfusion
• Breast Milk
• Congenital
• Occupational

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West Nile Fever Human Disease

• Incubation period 3 - 15 days
• About 20 of those infected develop a mild
  illness (West Nile Fever)
• Acute aseptic meningitis or encephalitis develops
  in 1 out of every 150 infections.
• Most fatal cases gt50 years old majority of
  surviving patients suffer memory loss and marked
  muscle weakness

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West Nile Virus Mild Infection

• Lasts 3-6 days
• Febrile illness of sudden onset often accompanied
  by
• Tiredness Muscles aches and pains
• Loss of appetite Rash
• Nausea Swollen lymph glands
• Vomiting Headache
• Sensitivity of eyes when looking at light

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West Nile Virus Severe Infection

• Less than 1 of persons bitten by an infected
  mosquito progress to severe neurologic disease.
• Encephalitis more commonly reported than
  meningitis.
• Hospitalized for supportive care no specific
  treatment.
• Several patients experience severe muscle
  weakness and flaccid paralysis.

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Arboviral Surveillance in Oklahoma Human

• Free testing available at State Public Health
  Laboratory
• WNV and SLE
• Request must be made through a health care
  provider

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Temporal Relationship of Avian, Equine, and Human
WNV Events Oklahoma-2002
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Symptom Onset Dates of Human Cases of West Nile
disease in Oklahoma 2002
N 20 cases of probable or
confirmed WNV infection by detection of IgM
antibodies in CSF or serum.
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OK WNV Human Case Summary

• Sum of 21 Cases
• Eighteen patients over 50 years of age
• 1 exposure in D.C. 2 transfusion-related
• Majority of cases had onset of illness during
  October
• Counties of residence Muskogee (2), Tulsa (3),
  Oklahoma (3), Canadian (3), Washington, Rogers,
  Ottawa, Okmulgee, Pushmataha, Caddo, Kay, Beaver,
  and Osage.

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Mosquito Life Cycle

• Most eggs hatch within 48 hours.
• Larvae must breathe feed on organic matter.
• Pupae tumblers
• Only adult female mosquitoes need a blood meal.

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Mosquito Prevention Measures

• Personal Protection
• Avoid times and places where mosquitoes active.
• Cover exposed skin.
• Apply DEET-based repellant (10-30) to exposed
  skin and clothing.
• Mosquito Source Reduction
• Dispose of trash piles
• Mow tall weeds
• Drain rain barrels, plant containers, child
  wading pools, etc.
• Clean roof gutters of leaves and other debris.
  
  

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Tires as Mosquito Breeding Source
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Mosquito Abatement Measures

• Stock Tanks, Ornamental Water Gardens
• Apply mosquito larvacide (BTI).
• Stock with fish.
• Put in aerator pump.
• DO NOT treat with insecticides.
• Keep window and door screens in good repair.
  
  

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Larvicides

• Interrupt mosquito life cycle
• Most very environmentally safe
• microbial (Aquabac, Vectobac)
• Bacillus thuringiensis israelensis
• chemicals
• methoprene, oils,
• mononuclear films
  

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Adulticides

• Last resort
• Requirements for successful application
• spray when target species active
• low wind
• dispersal of ultra-low volume droplet size
• Bacillus thuringiensis israelensis,
  Bacillus sphaericus
• chemicals
• synthetic pyrethroids (resmethrin,
  sumethrin), inorganic phosphates (malathion)
  
  

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Oklahoma West Nile Virus Preparedness and Response

• Response will focus on public health messages
• Encourage cities with adulticide applicators to
  have public health licenses
• Costly to purchase equipment
• (ULV foggers chemicals)
• May need to address
• ordinances dealing with
• public health nuisances
  

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Changes in Surveillance Procedures for 2003

• Universal dead bird reporting hotline will not
  be used this year.
• Bird testing will only be done in communities
  with some mosquito control capabilities, e.g.
  Tulsa, Norman, Muskogee, Wagoner, Ponca City,
  etc.

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Changes in Surveillance Procedures for 2003

• State Public Health Lab will expect to test
  more human specimens with broader clinical
  presentations.
• Will try to enhance physician education.
• Will no longer pay for equine testing.
• Will attempt to enhance mosquito collections
  and testing.
• State Public Health Lab will test mosquito
  pools collected at 6-7 trapping locations across
  the state.

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What can we expect in 2003??
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RememberFight the Bite