“On Watch” for West Nile Virus in Oklahoma

1. “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 (405) 271-4060 kristyb@health.state.ok.us

2. 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.

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

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

6. West Nile Virus Enters the U.S.

7. 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)

8. Media “West Nile Frenzy”

9. 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 > 50 yrs old • 2001 • 66 confirmed human cases from 10 states • 9 fatalities (14%); median age = 69 yrs.

10. 1st U.S. crow Last crow Number of WNV-Infected Crows Reported from the North Central and South Central Regions,by Week, 2001 *As of 2/1/02

11. 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 Keen’s Bat 1

12. 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

14. 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)

15. 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

16. 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)

17. Distribution of Important Arboviruses in the U. S. Eastern Equine Encephalitis California serogroup viruses Western Equine Encephalitis St. Louis Encephalitis Probably Highlands J

18. 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

19. 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)

20. WNV Surveillance in Oklahoma • Dead Wild Bird Surveillance and Testing • Equine Encephalitides Monitoring and Testing • Enhanced Passive Surveillance for Human Meningoencephalitis • Mosquito Trapping & Testing

21. 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 densities> 1/sq. mi. provided an early warning for a human outbreak First Positive Bird 11/13/00

22. 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

23. 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) untiltransported to laboratory or pick-up point.

24. Number of Calls to 1-800-990-CROW

25. Number of Birds Tested for WNV by Week; Oklahoma-2002

26. Distribution of WNV+ Birds by Species, Oklahoma-2002 Total Birds = 438

28. 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) 

29. 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

30. 2001 U.S. Avian Surveillance Data

32. West Nile Disease in U.S. Horses; 1999-2001 Data from USDA/APHIS

33. 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.

34. West Nile Virus Surveillance in Oklahoma:Veterinary • 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.

35. 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 > 2 years.

36. WNV Equine Vaccine • Conditional license approved August 1, 2001to 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

37. WNV Equine Vaccine • Ft. Dodge Labs estimates 35% of nation’s 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.

38. West Nile Virus Surveillance in Oklahoma:Preliminary 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.

39. 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 Number of Equine West Nile Cases by State, 2002

40. Distribution of Oklahoma Equine WNV Cases, Aug. 9 - 23, 2002

42. Distribution of Oklahoma Equine WNV Cases, Aug. 24 - Sept 6, 2002

43. Distribution of Oklahoma Equine WNV Cases, Sept. 7 - Sept. 19, 2002

44. Distribution of Oklahoma Equine WNV Cases, Sept. 20 - Oct 4, 2002

46. 2002 National Equine Surveillance Data

47. 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.

48. 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

49. 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

50. 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.