West Nile Virus. Lyndon Badcoe PhD Epidemiologist

Transcription

1 West Nile Virus Lyndon Badcoe PhD Epidemiologist

2 Outline Mapped Distribution Vector Borne Disease Plan WNV Biology Clinical Syndromes Modes of Transmission Prevention

3 WNV in North America 25 October 2002

4 USA WNV 1 October 2004

5 USA Human WNV Cases September 27, 2005

6 California Map Human and Animal Cases 7 September 2004

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9 Fresno WNV Map

10 Fresno WNV Cases Fresno WNV Cases = = = = 27 = 0 7/7/2005 7/9/2005 7/11/2005 7/13/2005 7/15/2005 7/17/2005 7/19/2005 7/21/2005 7/23/2005 7/25/2005 7/27/2005 7/29/2005 7/31/2005 8/2/2005 8/4/2005 8/6/2005 8/8/2005 8/10/2005 8/12/2005 8/14/2005 8/16/2005 8/18/2005 8/20/2005 8/22/2005 8/24/2005 8/26/2005 8/28/2005 8/30/2005 9/1/2005 9/3/2005 9/5/2005 9/7/2005 9/9/2005 9/11/2005 9/13/2005 Number of Cases Human Cases Birds Mosquito Pools Horses Sentinel Chickens Date of Onset = 31 = 76

11 Equine WNV Positive Cases 8 September 2005 Fresno = 32

12 West Nile Viremic Blood Donors 1 October 2004

13 USA WNV Positive Blood Donors September 27, 2005

14 History of West Nile Virus WNV first isolated in West Nile, Uganda 1937 Recent WNV encephalitis in people Algeria 1994 Czech Republic 1997 Democratic Republic of Congo 1998 Russia 1999 France & Israel 2000 Epizootics Birds: Israel 1997 to 2001 Horses: Morocco 1996; France 2000

15 Possible Modes of Introduction of West Nile Virus into the USA Infected human host Human-transported vertebrate host Legal Illegal Human-transported vector(s) Storm-transported vertebrate host (bird) Intentional introduction

16 West Nile Virus Epidemiology Transmission Mosquitoes, blood, transplant, transplacental, breast milk, renal hemodialysis Seasonality Age 28 March to 3 December in USA for 2003 Mostly June to October when mosquitoes most active Fatal encephalitis mainly in people over 50 years Reservoir hosts Birds Incidental Hosts Humans, horses, other mammals, amphibians

17 West Nile Virus Transmission Cycle Mosquito vector Bridge vector WNV Incidental hosts Bird reservoir host

18 WNV Risk Factors Human WNV Cases Sentinel Chickens WNV-positive Mosquito Pools WNV-positive Dead Birds WNV-positive Equine Cases WNV-positive Environmental Conditions Overall Risk Level Proximity of WNV to Humans Normal Season Emergency Planning Epidemic Conditions

19 West Nile Fever Symptoms Incubation Period 3-14 days after a bite from an infected mosquito Cohort study Colorado (40 cases) Body aches 98% Eye pain 63% Skin rash 63% Swollen lymph nodes 48% Nausea or vomiting 48% Duration of illness approximately 22 days Anecdotal reports Lingering fatigue Weakness Muscle fasciculations for weeks or longer

20 WNV Aseptic Meningitis Fever, headache, nuchal rigidity (100%) Nausea, vomiting, neck pain, myalgia (80%) Symptoms with variable frequency Low back pain Tremors Parkinsonism Myoclonus Flaccid paralysis of limb Cranial nerve palsies Cerebellar signs Outcome good

21 WNV Encephalitis Most common symptoms Fever, headache, altered mental status Variable symptoms Tremors Weakness Cerebellar signs/symptoms Nystagmus, dysphagia, decreased gag Locked-in syndrome Outcomes variable

22 Fresno 2004 WNV Epidemic WN Flaccid Paralysis 4.4/100,000 population Fresno ~ 37 people <1% CNS disease Worst case scenario Neuroinvasive WNV 4 ~20% West Nile Fever West Nile Fever 116 ~80% Asymptomatic Asymptomatic 467

23 WNV Infection by Age Group & Clinical Category, USA 2003 West Nile Neuroinvasive Disease West Nile Fever Age group (yr) Incidence per 100,000

24 Treatment of People Infected With West Nile Virus No specific treatment for infection with WNV Treatment of encephalitis due to West Nile Virus Intensive supportive therapy may be required Hospitalization IV fluids Respiratory Support Prevention of secondary infections Good nursing care

25 Comparison Comparison of Human of WNV Cases and Deaths and USA Deaths from WNV USA Number of Human Cases and Deaths Human Cases Deaths Year

26 Animals Affected By WNV Birds 225 species affected Some show no illness Severe illness & death in crows, jays, ravens, magpies Horses Most infected horses recover Serious neurological disease & death Fort Dodge equine vaccine approved Other Animals Dogs, Cats Squirrels Reindeer Seals Alligators

27 Bird Identification, Family Corvidae American Crow Common Raven Stellar's Jay Western Scrub Jay Yellow-billed Magpie

28 Clinical Signs in Small Animals Dogs and Cats Rarely exhibit clinical illness Fever, depression Muscle weakness, spasms Seizures, paralysis, myocarditis Wolf- 1 case 3 months old, zoo animal, CNS signs Suspect WNV in animals exhibiting neurological and cardiac symptoms

29 Clinical Signs in Horses Paralysis of lips, facial muscles, or tongue Head tilt, difficulty swallowing Altered mentation Sound sensitive Blindness Flu-like, anorexia, depression Muscle and skin twitching Hyperesthesia Propulsive walking Weakness, ataxia, recumbency Seizures Troubling righting Drowsiness

30 WNV Vaccine for Horses Fully licensed vaccine Killed product 2 doses, 3-6 weeks apart Annual booster Restricted use to veterinarians only

31 Mosquito Biology Mosquito Flight Range 300 yards up to 40 miles Culex tarsalis traveled 6 miles in one night Life Cycle Adult > eggs > larva > pupa Adult lifespan from 2 weeks up to 3 months Culex tarsalis first eggs 4 days after emergence Culex female lays in rafts of up to 300 eggs Culex spp can overwinter as a mated female

32 Dead Bird Testing Primary interest in corvids and raptors Carcasses must be fresh Submit carcass within 48 hours of death Carcasses can be stored at -70 C Free testing if approved To submit a dead bird phone

33 Wash your hands with warm water and soap after disposal Disposing of a Dead Birds Avoid touching the dead bird with your bare hands Use gloves or multiple heavy-duty plastic bags to pick up dead birds Grasp the dead bird with your hand inside the plastic bags Turn the plastic bags inside-out over the dead bird so the dead bird is now inside the plastic bags and your hands are on the outside of the plastic bags Place bagged bird carcass in a leak-proof plastic bag and seal the bag Place the sealed bag in another leak-proof plastic bag and tightly seal Dispose of the "double-bagged" bird carcass in a trash container Ensure that the trash container is secure from children and animals

34 Mosquito Abatement Integrated Control Program Surveillance for mosquitoes and arboviral diseases Mosquito control Trapping mosquitoes Adult / larvae : ground fogging & aerial spraying Biological control : mosquito fish Water source reduction

35 WNV ground fogging & aerial spraying

36 Avoid Mosquito Bites! Personal Protection Wear long pants and long-sleeved shirt when outdoors Place mosquito netting over infant carriers if outdoors Mosquito Repellent DEET is the most effective mosquito repellant Concentration of DEET determines length of protection 23.8% DEET lasts 5 hours, 10% lasts 2 hours Children use up to 30% DEET Do NOT use DEET on babies under 2 months Apply DEET at dawn and dusk or when mosquitoes are observed

37 DEET OFF 10% DEET Repel 23% DEET Repel 100% DEET

38 Contacts and Reference Sites Fresno County Communicable Diseases Division Epidemiology phone , fax Lyndon Badcoe CommunicableDisease/WestNileVirus.htm California WNV Surveillance CDC