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West Nile Virus Primer

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West Nile Virus Primer Powered By Docstoc
					West Nile Virus
               Overview
•   Organism
•   History
•   Epidemiology
•   Transmission
•   Disease in Humans
•   Disease in Animals
•   Prevention and Control

                             Center for Food Security and Public Health
                                     Iowa State University 2004
The Organism
                   The Agent
•   Flaviviridae
    − Flavivirus
         Single stranded RNA
•   Related to SLE, JE,
    Murray Valley, Kunjin
•   Infects humans, birds,
    mosquitoes, horses
    and other mammals

                                Center for Food Security and Public Health
                                        Iowa State University 2004
History
                       History
•   1937: West Nile District, Uganda
•   1950
    − Egypt
         Ecology studied
         Disease varies
    − Israel
         1951-54
         1957
            Meningoencephalitis in elderly


                                             Center for Food Security and Public Health
                                                     Iowa State University 2004
                           History
• 1962, 2000: France
• 1973-74: South Africa
• 1996: Romania
    −   First outbreak in
        industrialized urban area
• 1998: Italy
• 1999
    − Russia
    − United States, New York
            First occurrence in the western hemisphere


                                                 Center for Food Security and Public Health
                                                         Iowa State University 2004
Epidemiology
           United States - 1999
•   New York City
    − 62 cases
    − 7 deaths
    − Zoo birds, crows,
      horses
•   St. Louis Encephalitis
    virus first suspected
•   Similar to virus strain
    found in Israel
                              Center for Food Security and Public Health
                                      Iowa State University 2004
 1999 NYC area - WNV activity

Mosquitoes
  Birds
Humans




                       Center for Food Security and Public Health
                               Iowa State University 2004
1999 – NYC WNV Cases




                Center for Food Security and Public Health
                        Iowa State University 2004
    Possible Modes of Introduction
    of West Nile Virus into the U.S.
• Infected human host
• Human-transported vertebrate host
    − Legal
    − Illegal
•   Human-transported vector(s)
•   Storm-transported vertebrate host (bird)
•   Intentional introduction


                                Center for Food Security and Public Health
                                        Iowa State University 2004
Spread of WNV in the U.S.:
        1999-2002




                    Center for Food Security and Public Health
                            Iowa State University 2004
WNV Monthly Onset: 1999-2001




                    Center for Food Security and Public Health
                            Iowa State University 2004
Age distribution of WNV cases:
          1999-2001




                      Center for Food Security and Public Health
                              Iowa State University 2004
WNV in the U.S., Humans
 Year    Cases   Deaths

 1999     62            7

 2000     21            2

 2001     66            9

 2002    4156       284

 2003    9862       264

                  Center for Food Security and Public Health
                          Iowa State University 2004
WNV in the U.S.: 2003




                 Center for Food Security and Public Health
                         Iowa State University 2004
  WNV in U.S.:
as of July 6, 2004




                 Center for Food Security and Public Health
                         Iowa State University 2004
    WNV Positive Animals, 2003
•   U.S. Cases
    − 4,554 equine
    − 30 dogs
    − 17 squirrels
    − 1 cat
    − 32 unidentified
      animal species



                        Center for Food Security and Public Health
                                Iowa State University 2004
WNV Equine Cases: 2003




                 Center for Food Security and Public Health
                         Iowa State University 2004
WNV Equine Cases: 2004




                 Center for Food Security and Public Health
                         Iowa State University 2004
2002 WNV World Distribution




                    Center for Food Security and Public Health
                            Iowa State University 2004
Transmission
                        Incidental hosts
                         Humans, horses,
Amplifying hosts         and other animals
       Birds




     Vectors
Culex sp., Aedes sp.,
  Ochlerotatus sp.         Center for Food Security and Public Health
                                   Iowa State University 2004
        Ecology & Transmission
•   Primary vector is
    Culex sp.
    −   43 species
•   Isolated
    uncommonly from
    ticks
    − Asia, Russia
    − Role in transmission
      not clear


                             Center for Food Security and Public Health
                                     Iowa State University 2004
Culex pipiens




                Center for Food Security and Public Health
                        Iowa State University 2004
Culex restuans




             Center for Food Security and Public Health
                     Iowa State University 2004
Culex salinarius




               Center for Food Security and Public Health
                       Iowa State University 2004
Aedes vexans




               Center for Food Security and Public Health
                       Iowa State University 2004
        Ecology & Transmission
• Infected
  mosquitoes
  overwinter
• Transovarial
  transmission
• Birds
    − Contact
      transmission
    − Migratory transport



                            Center for Food Security and Public Health
                                    Iowa State University 2004
           Human Transmission
•   Laboratory acquired
    − Laceration during necropsy on blue jay
    − Needle stick
•   Blood transfusions
    − 23cases in 2002
    − Implemented screening in 2003
         737 presumptive West Nile viremic donors
         2 transfusion associated cases


                                       Center for Food Security and Public Health
                                               Iowa State University 2004
         Human Transmission
•   Organ transplantation
    −4  documented cases from 1 organ donor
    − Organ donor received blood from
      viremic blood donor
•   Transplacental transmission
    − WNV   27th week gestation
•   Breast feeding
    − Mother received contaminated blood
    − Infant WNV positive
                                  Center for Food Security and Public Health
                                          Iowa State University 2004
Disease in Humans
               Human Disease
•   Incubation: 3-14 days
    − 80% asymptomatic or mild flu-like illness
    − 20% develop sudden fever, weakness,
      headache, myalgia, nausea, vomiting
•   Symptoms last 3-6 days
•   Fine maculopapular rash
         More frequent in children
•   Recent epidemics: menigoencephalitis

                                      Center for Food Security and Public Health
                                              Iowa State University 2004
               Human Disease
•   Less than 1% (1:150) infected
    − Develop    severe illness
         With neurological component
    − Encephalitis    (meningoencephalitis)
         Fever, confusion, disorientation, seizures,
          ataxia, tremors, neck stiffness, ± coma
    − Muscleweakness to flaccid paralysis of
     extremities


                                          Center for Food Security and Public Health
                                                  Iowa State University 2004
               Human Disease
•   Severe illness
                  rate: 3-15%
    − Case-fatality
    − Highest among elderly
         Those over 50 yrs at greatest risk
•   Overall death rate: 0.1%
    − 1:1,000    infections




                                         Center for Food Security and Public Health
                                                 Iowa State University 2004
          Diagnosis in Humans
•   Antibody detection
    − Serum or CSF
    − IgM capture ELISA (MAC-ELISA)
         Within 8 days
    − Fourfold   or greater rise in titer
         Acute/convalescent – 3 weeks apart
         Strong evidence of infection
    − IgM in CSF strongly suggests
      CNS infection
    − Cross reaction to other viruses
                                       Center for Food Security and Public Health
                                               Iowa State University 2004
           Diagnosis in Humans
•   Plaque reduction neutralization test
    − Todifferentiate cross-reaction
    − CDC test for state’s initial case
    − Negative tests
       Collected within 14 days of illness
       Reconfirm

•   Duration of immunity
    − Unknown
    − IgM may last 6 months or more in blood
    − Up to 16 months in CSF
                                              Center for Food Security and Public Health
                                                      Iowa State University 2004
        Treatment in Humans
•   No specific therapy
•   Supportive care
•   Ribavirin?
•   Interferon alpha-2b?
•   Vaccine in Phase 1 of clinical trial




                                 Center for Food Security and Public Health
                                         Iowa State University 2004
Animals and West
Nile Virus
            WNV in Animals
Horses (*)      Black Bear               Bats
Goats (*)       Wolf (*)                 Llama (*)
Sheep (*)       Alpaca (*)               Cattle (*)
Dog (*)         Mountain Goat            Seal (*)
Rabbit          Alligator (*)            Cat (*)
Chipmunk        Gray Squirrels (*)       Deer
Skunk
Crocodile (*)


                                     Center for Food Security and Public Health
                                             Iowa State University 2004
      Clinical Signs in Wildlife
•   Birds
    − Commonly     found dead (Corvids esp.)
•   Bats, chipmunks, skunks, and
    domestic rabbits
    − Majority   do not develop clinical signs
•   Gray Squirrels
    − Lethargy, biting paws,
     vocalization, ataxia, circling,
     encephalitis, myocarditis
                                       Center for Food Security and Public Health
                                               Iowa State University 2004
Clinical Signs in Large Animals
•   Bovine
    − Ataxia   progressing to paresis
•   Alpaca, Sheep, Goats
    − Fever,  horizontal nystagmus,
      torticollis, ataxia, recumbency
    − Vocalization
    − The alpaca had mild to moderate,
      diffuse, non-suppurative
      meningoencephalitis

                                        Center for Food Security and Public Health
                                                Iowa State University 2004
Clinical Signs in Small Animals
•   Dogs and Cats
    •   Rarely exhibit clinical illness
         •   Fever, depression
         •   Muscle weakness, spasms
         •   Seizures, paralysis, myocarditis
•   Wolf- 1 case
    −3       months old, zoo animal, CNS signs
•   Suspect WNV in animals exhibiting
    neurological and cardiac symptoms
                                            Center for Food Security and Public Health
                                                    Iowa State University 2004
Clinical Signs in Small Animals
•   Dogs and cats experimentally infected
    − Mosquito    bite: dogs
         All dogs showed viremia, no clinical signs
    − Mosquito    bite: cats
       All cats showed viremia
       All but one showed mild clinical signs
    − Infected   prey: cats
         All cats developed viremia
         None showed clinical signs
•   Conclusion: readily infected, but not
    amplifying hosts
                                          Center for Food Security and Public Health
                                                  Iowa State University 2004
       Clinical Signs in Horses
•   Paralysis of lips,      •   Flu-like, anorexia,
    facial muscles, or          depression
    tongue                  •   Muscle and skin
•   Head tilt, difficulty       twitching
    swallowing              •   Hyperesthesia
•   Altered mentation       •   Propulsive walking
•   Sound sensitive         •   Weakness, ataxia,
•   Blindness                   recumbency
•   Troubling righting      •   Seizures
•   Drowsiness
                                        Center for Food Security and Public Health
                                                Iowa State University 2004
     Diagnosis and Treatment
            in Horses
•   Diagnosis
    − Serology
         Seropositive & unvaccinated
          = WNV infection
•   Immunity
    − Many    months or longer
•   Perform necropsies with proper
    precautions
•   Supportive treatment
                                        Center for Food Security and Public Health
                                                Iowa State University 2004
      WNV Vaccine for Horses
•   Fully licensed vaccine
    − November   2002
    − Killed product
    − 2 doses
         3-6 weeks apart
    − Annual  booster
    − Restricted use
      to veterinarians only
                              Center for Food Security and Public Health
                                      Iowa State University 2004
Prevention and
Control
       Mosquito Management
•   Surveillance
•   Source reduction
•   Personal protection
•   Biological control
•   Larvicide
•   Adulticide



                          Center for Food Security and Public Health
                                  Iowa State University 2004
              Surveillance
•   Dead bird testing
•   Sentinel chicken flocks
•   Mosquito collection
    − Testfor pathogens
    − Account for species
•   Larval and adult mosquitoes
    − Map habitats
    − Record keeping
•   Determining nuisance vs. vectors
                              Center for Food Security and Public Health
                                      Iowa State University 2004
           Source Reduction
•   Eliminating larval habitats
    − Tires,bird baths, containers, rain
      gutters, unused swimming pools




                                   Center for Food Security and Public Health
                                           Iowa State University 2004
           Source Reduction
•   Making habitats
    unsuitable for larval
    development
•   Public education
•   Marsh water
    management
    − Drain,   fish access,
      gated

                              Center for Food Security and Public Health
                                      Iowa State University 2004
            Personal Protection
•   Reduce time outdoors
    −   Especially evening hours
• Wear long pants and sleeves
• Use mosquito repellent
    −   35% DEET
• Do not use DEET on
  your animals
• Make sure all window screens are intact
• Use yellow “bug” light bulbs in outdoor
  light fixtures
                                   Center for Food Security and Public Health
                                           Iowa State University 2004
            Biological Control
•   Utilizes predators, both natural and
    introduced, to eat larvae and pupae
    − Mosquito fish
        Gambusia affinis, G. holbrooki most common
        Fundulus spp., Rivulus spp., killifish

•   Other agents have been used but are
    not readily available
    − Fungus,   protozoa, nematodes
•   Copepods

                                         Center for Food Security and Public Health
                                                 Iowa State University 2004
                  Larvicides
•   Use when source reduction and
    biological control not feasible
•   More effective and target-specific
•   Less controversial than adulticides
•   Applied to smaller geographic areas
    − Larvae   concentrate in specific locations




                                     Center for Food Security and Public Health
                                             Iowa State University 2004
               Larvicides
     Product                 Product
      Name            (Larvae, Pupae, Adult)
Temephos              Abate (L)
Methoprene            Altosid (L)
Oils                  BVA, Golden Bear (L, P)
Monomolecular film    Agnique (L, P)
Bacillus              Aquabac, Bactimos,
thuringiensis         LarvX, Teknar, Dunks (L)
israelensis (BTI)
Bacillus sphaericus   VectoLex (L)
Pyrethrins            Pyrenone, Pyronyl (A, L)
                                     Center for Food Security and Public Health
                                             Iowa State University 2004
                  Adulticides
•   When other control
    measures unsuccessful
•   Least efficient
•   Proper type and time of
    application helps efficacy
    − Ultra   Low Volume foggers
         1 ounce per acre
    − Small  droplets contact and
      kill adults
                                    Center for Food Security and Public Health
                                            Iowa State University 2004
           Adulticides
 Chemical             Product
  Name
Malathion     Fyfanon, Atrapa,
              Prentox
Naled         Dibrom, Trumpet
Fenthion      Batex
Permethrin    Permanone,
              AquaResilin, Biomist,
              Mosquito Beater
Resmethrin    Scourge
Sumithrin     Anvil
                                Center for Food Security and Public Health
                                        Iowa State University 2004
                  Biosafety
•   Mosquito avoidance precautions
    − Bug   spray, long sleeves, etc
•   Wear gloves or double plastic bags to
    collect dead birds
•   Wash hands after handling
•   Manipulate carcasses in biosafety
    cabinet when possible for necropsy


                                       Center for Food Security and Public Health
                                               Iowa State University 2004
Acknowledgments
Development of this
presentation was funded
by a grant from the
Centers for Disease Control
and Prevention to the
Center for Food Security
and Public Health at Iowa
State University.


                 Center for Food Security and Public Health
                         Iowa State University 2004
              Acknowledgments
Author:       Radford Davis, DVM, MPH


Co-authors:   Ann Peters, DVM, MPH
              Stacy Holzbauer, DVM


Reviewer:     Jean Gladon, BS




                                        Center for Food Security and Public Health
                                                Iowa State University 2004

				
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