West Nile Virus July 12, 2005

1. West Nile VirusJuly 12, 2005 Theresa Smith, MD Emily Zielinski-Gutierrez, DrPH Division of Vector Borne Infectious Diseases (DVBID) National Center for Infectious Diseases Centers for Disease Control and Prevention Fort Collins, Colorado

2. WNV is an Arthropod-Borne virus First discovered in 1937 in the West Nile district of Uganda Until 1999 only found in Asia, Southern Europe, Africa Flavivirus, in the Japanese Encephalitis Antigenic Complex –similar family to Yellow Fever, St. Louis encephalitis virus Transmitted by mosquitoes

3. Starting with some of the background: WN virus is a zoonotic flavivirus transmitted by mosquitoes, and uses birds as amplifier hosts. Because of this, we can expect many similarities between West Nile virus and St. Louis encephalitis virus, our domestic zoonotic flavivirus. ?The core of the cycle is enzootic transmission – or maintenance and amplification – in which mosquitoes and birds cycle the virus. Under permissive conditions, this amplification cycle can dramatically increase the number of infected birds and mosquitoes in an area through the course of the summer. ? Very intense transmission may produce avian epizootics, mammalian epizootics, or epidemics. Epizootic and epidemic transmission may involve the same vector species as enzootic transmission, or may involve other species that are susceptible to the virus and feed on a wider variety of hosts. These species are usually referred to as Accessory vectors or Bridge vectors because they bridge transmission from the maintenance cycles to incidental hosts like horses or humans.Starting with some of the background: WN virus is a zoonotic flavivirus transmitted by mosquitoes, and uses birds as amplifier hosts. Because of this, we can expect many similarities between West Nile virus and St. Louis encephalitis virus, our domestic zoonotic flavivirus. ?The core of the cycle is enzootic transmission – or maintenance and amplification – in which mosquitoes and birds cycle the virus. Under permissive conditions, this amplification cycle can dramatically increase the number of infected birds and mosquitoes in an area through the course of the summer. ? Very intense transmission may produce avian epizootics, mammalian epizootics, or epidemics. Epizootic and epidemic transmission may involve the same vector species as enzootic transmission, or may involve other species that are susceptible to the virus and feed on a wider variety of hosts. These species are usually referred to as Accessory vectors or Bridge vectors because they bridge transmission from the maintenance cycles to incidental hosts like horses or humans.

4. WNV Prevention Based on Transmission Personal-emphasize at times of high mosquito activity (dawn/dusk) or stay indoors Use mosquito repellent Wear long sleeves, pants Household Use/ fix screens Air-conditioning Empty standing water Community / environmental Empty standing water

5. Repellent Guidance Skin DEET still “gold standard” Both new additions good for shorter term protection Picaridin Roughly equivalent to DEET at same concentration Only a 7% product currently sold in US Oil of lemon eucalyptus Plant based 30% product similar to low concentration DEET Not for kids <3 years old Clothing Permethrin

6. Transmission The most common route of infection is bite of infectious mosquito 2002 revealed other modes Blood Transfusion Organ Transplantation Intrauterine Percutaneous exposure (occ. exposure) Breastmilk (probable)

7. Screening of Blood Supply As of July 2003, all blood donated in US is screened for WNV using nucleic acid amplification testing (NAT) Platform under IND Use of NAT continues to be refined Transfusion-associated risk very, very low In 2004, 224 PVDs identified One transfusion-associated transmission associated with a change in use of NAT

8. Presumptively Viremic Blood Donors, 2004

9. Presumptively Viremic Blood Donors, 2005

10. WNV and Pregnancy One confirmed intrauterine WNV infection (2002) Zero cases of WNV intrauterine transmission detected in 79 pregnancies (2003-4) Three cases of early post-natal WNV infection Transplacentally transmitted?

11. WNV and Pregnancy Nine major birth defects were detected (12 percent of live births) Chance occurrences Phenotypic inconsistency (except microcephaly) Maternal WNV infection often followed expected timing of defect development Registry for pregnant women with WNV Most infants seemingly health (point 1) Most infants seemingly health (point 1)

12. The crows remain an important part of the avian mortality surveillanceThe crows remain an important part of the avian mortality surveillance

13. WNV Fever Most who get sick from WNV infection have WNV fever Time from mosquito bite to illness averages 3-5 days Fever, chills, headache, fatigue can be severe Nausea, vomiting Rash, usually not itchy, lasting a few days, mainly on chest, back, abdomen, and/or arms Usually better within a week, though persistent headache, fatigue common -- reports of weeks, even longer among otherwise healthy persons

14. WNV Meningitis Fever, headache, meningismus, photosensitivity White blood cells in the cerebrospinal fluid Headache may be quite severe Most people improve, though persistent headache, fatigue common

15. WNV Encephalitis Severity ranges from mild confusion to coma and death Other symptoms Tremor Myoclonus Dizziness

16. WNV-Associated Flaccid Paralysis Recognized more frequently in the last 2 years Affects relatively healthy young people May not have fever or headache before paralysis Clinical hallmarks: Onset early in infection Weakness can often be in only one limb Absence of numbness; pain sometimes present

17. Risk for Severe Disease Persons over 50 at higher risk Solid organ transplant recipients

18. Diagnosis of WNV Infection Suspect in meningitis, encephalitis, or flaccid paralysis from summer through fall, or December in the South Consider other arboviral diseases such as St. Louis encephalitis Local WNV enzootic activity or other human cases should raise suspicion Recent travel history also important State labs can help with diagnostic testing of serum or CSF for WNV IgM and/or IgG

19. Reporting Reporting procedures vary by state – Check with state coordinators/state websites All human WNV illness is reportable as of 2004

20. WNV Treatment No specific treatment for WNV disease 3 IRB-approved, randomized, double-blinded, placebo-controlled clinical trials available

21. WNV Outcomes Neuroinvasive disease 10-20% with severe disease die Fatalities primarily among elderly, immunosuppressed WNV flaccid paralysis Some people with almost complete recovery; others with continued weakness Those with less severe initial weakness tend to have a better prognosis

22. WNND County Level Incidence per Million, United States, 2004

23. 2004, WNV Activity

24. 2005 WNV Activity, as of 5 July 2005

25. Info Online West Nile Virus: Information and Guidance for Clinicians http://www.cdc.gov/ncidod/dvbid/westnile/clinicians/ http://www.cdc.gov/ncidod/dvbid/westnile/clinicalTrials.htm Diagnosis section http://www.cdc.gov/ncidod/dvbid/westnile/resources/fact_sheet_clinician.htm

26. Registry for Women Infected with WNV while Pregnant Interim Guidelines for the evaluation of infants born to women infected with WNV during pregnancy. See: http://www.cdc.gov/ncidod/dvbid/westnile/DuringPregnancy/WNV_duringPregnancy.htm