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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.

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west nile virus
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
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
wnv is an ar thropod bo rne virus
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)
slide5

WNV: Basic Transmission Cycle

Most important cycle is from mosquito to bird to mosquito

“Incidental” infections: unlikely amplifying hosts

Amplifying hosts

slide6

2000

1999

2001

2002

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
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
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
slide12

Mosquito Vectors

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

Culex tarsalis feeding

  • 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
slide14

WNV Human Infection “Iceberg”

For every case of illness

involving the brain or spinal

cord,

~150 total infections

~10% fatal

(<0.1% of total infections)

<1%

CNS

disease

Very crude estimates

~20%

“West Nile Fever”

~80%

Asymptomatic

wnv fever
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
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
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 encephalitis18
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
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
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
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
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
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).
diagnosis 4
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
  • 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
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
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-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
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
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
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
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
WNV Prevention
  • Treatment is symptomatic – therefore prevention of illness is crucial
  • Preventive measures
    • Personal
    • Household
    • Community / environmental
wnv personal protection
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)
slide35
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