west nile

West Nile Virus

Center for Food Security and Public Health Iowa State University 2004

OverviewOverview

• Organism• History• Epidemiology• Transmission• Disease in Humans• Disease in Animals• Prevention and Control

The Organism


The AgentThe Agent

• Flaviviridae−Flavivirus

Single stranded RNA

• Related to SLE, JE, Murray Valley, Kunjin

• Infects humans, birds, mosquitoes, horses and other mammals

History


HistoryHistory

• 1937: West Nile District, Uganda• 1950

−Egypt Ecology studied Disease varies

− Israel 1951-54 1957

Meningoencephalitis in elderly


HistoryHistory

• 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

Epidemiology


United States - 1999United 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


1999 NYC area - WNV activity 1999 NYC area - WNV activity

MosquitoesMosquitoes

BirdsBirds

HumansHumans


1999 – NYC WNV Cases1999 – NYC WNV Cases


Possible Modes of Introduction of West Nile Virus into the U.S.

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


Spread of WNV in the U.S.: 1999-2002

Spread of WNV in the U.S.: 1999-2002


WNV Monthly Onset: 1999-2001WNV Monthly Onset: 1999-2001


Age distribution of WNV cases: 1999-2001

Age distribution of WNV cases: 1999-2001


WNV in the U.S., HumansWNV in the U.S., Humans

Year Cases Deaths

1999 62 7

2000 21 2

2001 66 9

2002 4156 284

2003 9862 264


WNV in the U.S.: 2003WNV in the U.S.: 2003


WNV in U.S.: as of July 6, 2004

WNV in U.S.: as of July 6, 2004


WNV Positive Animals, 2003WNV Positive Animals, 2003

• U.S. Cases−4,554 equine −30 dogs−17 squirrels−1 cat−32 unidentified animal

species


WNV Equine Cases: 2003WNV Equine Cases: 2003


WNV Equine Cases: 2004WNV Equine Cases: 2004


2002 WNV World Distribution2002 WNV World Distribution

Transmission


Incidental hosts

Vectors

Humans, horses, and other animalsAmplifying hosts

Birds

Culex sp., Aedes sp., Ochlerotatus sp.


Ecology & TransmissionEcology & Transmission

• Primary vector is Culex sp.− 43 species

• Isolated uncommonly from ticks− Asia, Russia− Role in transmission

not clear


Culex pipiensCulex pipiens


Culex restuansCulex restuans


Culex salinariusCulex salinarius


Aedes vexansAedes vexans


Ecology & TransmissionEcology & Transmission

• Infected mosquitoes overwinter

• Transovarial transmission

• Birds− Contact

transmission− Migratory transport


Human TransmissionHuman Transmission

• Laboratory acquired−Laceration during necropsy on blue jay−Needle stick

• Blood transfusions−23 cases in 2002− Implemented screening in 2003

737 presumptive West Nile viremic donors 2 transfusion associated cases


Human TransmissionHuman 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

Disease in Humans


Human DiseaseHuman 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



• Less than 1% (1:150) infected−Develop severe illness

With neurological component

−Encephalitis (meningoencephalitis) Fever, confusion, disorientation, seizures,

ataxia, tremors, neck stiffness, ± coma

−Muscle weakness to flaccid paralysis of extremities



• Severe illness−Case-fatality rate: 3-15%−Highest among elderly

Those over 50 yrs at greatest risk

• Overall death rate: 0.1%−1:1,000 infections


Diagnosis in HumansDiagnosis 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


Diagnosis in HumansDiagnosis in Humans

• Plaque reduction neutralization test− To differentiate 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


Treatment in HumansTreatment in Humans

• No specific therapy• Supportive care• Ribavirin?• Interferon alpha-2b? • Vaccine in Phase 1 of clinical trial

Animals and West Nile Virus


WNV in AnimalsWNV 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 (*)


Clinical Signs in WildlifeClinical 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


Clinical Signs in Large AnimalsClinical 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


Clinical Signs in Small AnimalsClinical 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


Clinical Signs in Small AnimalsClinical 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


Clinical Signs in HorsesClinical Signs in Horses

• Paralysis of lips, facial muscles, or tongue

• Head tilt, difficulty swallowing

• Altered mentation • Sound sensitive • Blindness • Troubling righting• Drowsiness

• Flu-like, anorexia, depression

• Muscle and skin twitching

• Hyperesthesia• Propulsive walking• Weakness, ataxia,

recumbency• Seizures


Diagnosis and Treatment in Horses

Diagnosis and Treatment in Horses

• Diagnosis−Serology

Seropositive & unvaccinated = WNV infection

• Immunity−Many months or longer

• Perform necropsies with proper precautions

• Supportive treatment


WNV Vaccine for HorsesWNV Vaccine for Horses

• Fully licensed vaccine−November 2002−Killed product−2 doses

3-6 weeks apart−Annual booster−Restricted use

to veterinarians only

http://www.goodnewsforpets.com/whats_new/images/WestNile_lg.jpg

Prevention and Control


Mosquito ManagementMosquito Management

• Surveillance• Source reduction• Personal protection• Biological control • Larvicide• Adulticide


SurveillanceSurveillance

• Dead bird testing• Sentinel chicken flocks• Mosquito collection

−Test for pathogens−Account for species

• Larval and adult mosquitoes−Map habitats−Record keeping

• Determining nuisance vs. vectors


Source ReductionSource Reduction

• Eliminating larval habitats−Tires, bird baths, containers, rain

gutters, unused swimming pools


Source ReductionSource Reduction

• Making habitats unsuitable for larval development

• Public education• Marsh water

management−Drain, fish access,

gated


Personal ProtectionPersonal 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


Biological ControlBiological 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


LarvicidesLarvicides

• 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


LarvicidesLarvicidesProductName

Product(Larvae, Pupae, Adult)

Temephos Abate (L)

Methoprene Altosid (L)Oils BVA, Golden Bear (L, P)Monomolecular film Agnique (L, P)

Bacillus thuringiensis israelensis (BTI)

Aquabac, Bactimos, LarvX, Teknar, Dunks (L)

Bacillus sphaericus VectoLex (L)

Pyrethrins Pyrenone, Pyronyl (A, L)


AdulticidesAdulticides

• 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


AdulticidesAdulticidesChemical

NameProduct

Malathion Fyfanon, Atrapa, Prentox

Naled Dibrom, Trumpet

Fenthion Batex

Permethrin Permanone, AquaResilin, Biomist, Mosquito Beater

Resmethrin Scourge

Sumithrin Anvil


BiosafetyBiosafety

• 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


AcknowledgmentsAcknowledgments

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.


AcknowledgmentsAcknowledgments

Author:

Co-authors:

Reviewer:

Radford Davis, DVM, MPH

Ann Peters, DVM, MPHStacy Holzbauer, DVM

Jean Gladon, BS

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