# Presentation: 228502

## West Nile Virus

**Emily Zielinski-Gutierrez, DrPH**
**Lisa Lundgren, RN, MSN, FNP-C**
**Division of Vector Borne Infectious Diseases (DVBID)**
**National Center for Infectious Diseases**
**Centers for Disease Control and Prevention**
**Fort Collins, Colorado**

## West Nile Virus (WNV) before 1996

**First discovered in 1937 in the West Nile district of Uganda**
**Mild feverish illness**
**Severe illness, like meningitis or encephalitis, was rare**
**Wide distribution in Asia, Eastern Europe, Africa **

**Notes:**
Important things to realize here are that, prior to 1996, WNV was mainly associated with a mild, nonspecific febrile illness.  Ex.  South Africa 1975—25,000 cases of infection—only one documented case of Encephaltitis or CNS involvement.

## WNV is an Arthropod-Borne virus

**Transmitted by mosquitoes**
**Can infect people and other animals**
**Similar to some other viruses**** ****(a Flavivirus, in the Japanese Encephalitis Antigenic Complex – e.g. similar family         to Yellow Fever, St. Louis encephalitis virus)**

## West Nile virus: Approximate geographic range as of 1998

**West Nile virus: *****Approximate***** geographic range as of 1998**

## 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.

## 1999

**1999**

**2000**

**2001**

**2002**

## 2003

**2003**

## 2003

## WNND County Level Incidence per Million, United States, 2003*

**WNND County Level Incidence per Million, United States, 2003***

**Incidence per million**

- 	.01-9.99

- 	10-99.99

- 	>=100

**WNND: West Nile Neuroinvasive Disease                 *Reported as of 4/9/2004 **

## Transmission

**The MOST IMPORTANT route of infection is bite of infectious mosquito**
** ****2002 revealed novel modes of transmission**
**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 being screened for WNV (nucleic acid amplification testing rather than antibody screening)**
**Testing being conducted under IND**
**Minipool vs. individual testing**
**Presumptive viremic donors important for surveillance**
**Will be updated in MMWRs/website**
**Risk through transfusion very, very low**

## Mosquito Vectors

***Mosquito Vectors***

**Important vectors vary by geography, e.g.**
***Culex tarsalis***** ****(western states)**
***Culex pipiens****** *****(Midwest, and elsewhere)**
***Culex quinquefasciatus****** *****(south)**
**Different behaviors – some fly very long distances**
**Feeding habits, infection rates, breeding areas all important**

**Nearly 50 species of mosquitoes capable (at least in the lab) of transmitting WNV**

*Culex tarsalis *feeding

## West Nile Virus—Clinical Disease

| Prior to 1996:
 | Since 1996: |
| --- | --- |
| * Mild illness with fever | *  More severe illness, more of the sick dying |
| * Young adults in Africa, Middle East | * Older adults, people who have immune system problems |
| * Outbreaks infrequent | *  More frequent outbreaks |
| * Rare involvement of the brain, spinal cord or nerves | * Increased reporting of meningitis and encephalitis |

## WNV Human Infection “Iceberg” 

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

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

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

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

**WNV Human Infection “Iceberg” **

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

_***Very***_** crude estimates**

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

## WNV Fever

**Most people who get sick from WNV infection have WNV fever**
**Time from exposure (usually by mosquito bite): 3-14 days**
**Fever, chills, headache, fatigue**
**Can be severe**
**Nausea, vomiting (can be severe)**
**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

**Similar to other meningitis from viruses**
**Fever, headache, meningismus (neck stiffness, light bothering eyes)**
**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**
**People who are older (over 50) and/or who have chronic medical problems are usually the ones to have WNV encephalitis**

## WNV Encephalitis 

**There are a number of other problems that people with WNV encephalitis may suffer:**
**Tremor**
**Myoclonus **
**Quick, uncontrolled muscle jerking**
**Problems with balance**
**Dizziness**

## WNV-Associated Flaccid Paralysis

**Seen more frequently over the last 2 years**
**Unclear how often it is happening:**
**May be present in almost 15% of people with severe illness**
**Affects relatively young people who are often healthy otherwise**
**May not have fever or headache before paralysis**

## WNV-Associated “Poliomyelitis-like illness”

**Most cases of WNV-associated weakness that is persistent**
**Clinical hallmarks:**
**Onset early in infection**
**Weakness can often be in only one limb**
**Absence of numbness; pain sometimes present**

## Diagnosis of WNV Infection (1)

**Based on high index of clinical suspicion *****and***** obtaining specific laboratory tests**
**Consider WNV, or other arboviral diseases such as St. Louis encephalitis, (esp. in adults >50 years) w/ unexplained encephalitis or meningitis (esp. in summer or early fall). **
**The local presence of WNV enzootic (bird, mosquito, vet) activity or other human cases should further raise suspicion. **
**Recent travel history also important. **

## Diagnosis (2)

**Testing obtained through local or state health departments and increasingly through private labs**
**Public health laboratories usually perform an IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA).**
**W/ this test virus-specific IgM can be detected in **_**nearly all**_** CSF and serum specimens from WNV-infected patients at time of clinical presentation**
**Serum IgM antibody may persist for + 1 yr., so physicians must determine whether the antibody is result of a previous WNV infection and unrelated to the current clinical presentation. **

## Diagnosis (3)

**Most conclusive to identify person w/CNS infection is WNV-specific IgM in CSF using MAC-ELISA. Strongly suggests acute CNS infection.**
**If no CSF and using serum samples, paired acute and convalescent-phase samples should be acquired.**
**Acute at initial presentation, convalescent 7-14 days later.**
**If no convalescent sample, acute specimen should be tested w/ MAC-ELISA. If IgM neg, acute WNV infection unlikely. If IgM pos and clinically compatible may be recent WNV infection (see note about other flavivirus infections).**

**Notes:**
Note that some Fever patients had not mounted detectable IgM response yet at initial clinical presentation.

## Diagnosis (4)

**Ideally MAC-ELISA should be performed using WNV and SLE viruses**
**If WNV and SLE results similar – necessary to use PRNT to confirm. **
**Recent vaccination (e.g. yellow fever) or related flavivirus infection may (e.g. dengue) may result in positive WNV MAC-ELISA.  **
**See: ****http://www.cdc.gov/ncidod/dvbid/westnile/resources/fact_sheet_clinician.htm**

## Reporting

**Reporting procedures vary by state – refer to state coordinators/state websites**
**Neuroinvasive disease is nationally notifiable, fever is not. States differ in their reporting of these. **

## WNV: Illness Outcomes

**Current information limited**
**Fatality rates**
**10-20% with severe disease die**
**Fatalities primarily among elderly, immunosuppressed**
**Unknown why some people do not get sick and some get extremely sick**

## WNV—Long-term problems:         “When will I get better?”

**Fatigue**
**Headache**
**Difficulty with concentration or memory**
**However—most people eventually ****DO**** get better (based on limited observations to date)**
**May take many months**

## WNV-Long-term outcomes

**WNV Poliomyelitis-like illness**
**Outcomes vary**
**Some people from 2002 and 2003 have had dramatic, almost complete recovery; others have had continued weakness**
**We do not know why some people improve and some do not BUT**
**Those with less severe initial weakness tend to have a better prognosis**

## WNV--Treatment

**As is true for most viruses that cause human illness, there is no specific treatment for WNV**
**Studies of:**
**Antisense WNV-RNA **
**Interferon-****α**
**WNV-specific immune globulin (“IVIG”)**
**Results are only preliminary now**
**Basic problem—drug has to be given very early, almost before the person is very sick  **

## Q: Once someone gets infected with WNV, can they get sick with WNV again?

**A:  If someone was sick with WNV last summer, they are probably immune.  We think that this immunity lasts a long time (many years).  However, mosquitoes can carry other viruses that can make people sick, so they should still take care to avoid mosquito bites!**

## Q: When a person tests positive for WNV, does that mean that the virus is still in them?

**A:  By the time someone gets sick, the virus is long-gone.  The test measures the body’s reaction to the virus, to determine if the virus was present in the body recently or in the more distant past.****  **

## Q: What is the status of a human vaccine for WNV?

**A: Several agencies and companies are working on a vaccine for humans, and one is planned for testing next year. **

## WNV Prevention

**Treatment is symptomatic – therefore prevention of illness is crucial**
**Preventive measures**
**Personal**
**Household**
**Community / environmental**

## WNV—Personal Protection

**Use mosquito repellent**
**DEET (skin or clothing)**
**Up to 50% concentration**
**Permethrin (clothing)**
**Wear long sleeves, pants**
**Emphasize protection at times of high mosquito activity (dawn/dusk) or stay indoors**
**Protect your house and yard**
**Use/ fix screens**
**Air-conditioning**
**Empty water (breeding sites)**

## After getting sick, recovery can take a long time, but most people do improve
Avoiding getting bitten by mosquitoes is the only way to prevent WNV
There is no treatment, but people are working very hard to develop one

**Avoiding getting bitten by mosquitoes is the only way to prevent WNV**
**There is no treatment, but people are working very hard to develop one**

** **

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