West Nile Virus

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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

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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

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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)

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West Nile virus Approximate geographic range as
of 1998
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WNV Basic Transmission Cycle
Most important cycle is from mosquito to bird to
mosquito
Incidental infections unlikely amplifying hosts
Amplifying hosts
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2000
1999
2001
2002
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2003
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2003
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WNND County Level Incidence per Million, United
States, 2003
Incidence per million
.01-9.99
10-99.99
gt100
WNND West Nile Neuroinvasive Disease
Reported as of 4/9/2004
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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)

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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

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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

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West Nile VirusClinical Disease
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WNV Human Infection Iceberg
10 fatal (lt0.1 of total infections)
For every case of illness involving the brain or
spinal cord, 150 total infections
lt1 CNS disease
Very crude estimates
20 West Nile Fever
80 Asymptomatic
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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

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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

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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

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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

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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

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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

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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 gt50
  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.

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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.

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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).

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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/reso
  urces/fact_sheet_clinician.htm

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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.

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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

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WNVLong-term problems When will I get
better?

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

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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

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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-a
• WNV-specific immune globulin (IVIG)
• Results are only preliminary now
• Basic problemdrug has to be given very early,
  almost before the person is very sick

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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!

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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 bodys reaction
  to the virus, to determine if the virus was
  present in the body recently or in the more
  distant past.

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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.

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WNV Prevention

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

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WNVPersonal 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)

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• 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

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