# Presentation: 378696

## West Nile VirusJuly 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

## 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

## WNV: Basic Transmission Cycle

- Most important cycle is from mosquito to bird to mosquito

- Amplifying hosts

- “Incidental” infections: unlikely amplifying hosts

**Notes:**
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.

## 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

## 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

## 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)

## 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

## Presumptively Viremic Blood Donors, 2004

## Presumptively Viremic Blood Donors, 2005

- As of July 5, 2005

## 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?

## 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

**Notes:**
Most infants seemingly health (point 1)

## WNV Human Infection “Iceberg” 

**~80****%**
**Asymptomatic**

**~****20%**
**“****West Nile Fever”**

**<1%**
**CNS**
**disease**

**~****10% of CNS ds are fatal**
**(<0.1% of total infections)**

**WNV Human Infection “Iceberg” **

**For every case of illness**
**involving the brain or spinal**
**cord,**
**~150 total infections**

**Notes:**
The crows remain an important part of the avian mortality surveillance

## 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

## 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

## WNV Encephalitis

- Severity ranges from mild confusion to coma and death
- Other symptoms
- Tremor
- Myoclonus
- Dizziness

## 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

## Risk for Severe Disease 

- Persons over 50 at higher risk
- Solid organ transplant recipients

## 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

## Reporting

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

## WNV Treatment

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

## 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

## WNND County Level Incidence per Million, United States, 2004

## 2004, WNV Activity

**(available : http://www.cdc.gov/ncidod/dvbid/westnile/surv&control04Maps.htm)**

## 2005 WNV Activity, as of 5 July 2005

## 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

## 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