CLINICAL REVIEWS

West Nile virus infectionROY GUHAROY, SHELLEY A. GILROY, JOHN A. NOVIASKY, AND JONATHAN FERENCE

W ithin the past five years,West Nile virus (WNV), amosquito-borne flavivirus

and human neuropathogen com-monly found in West Asia, Africa,and the Middle East, has emerged asan important human, avian, andequine disease in the United States.'"Most people infected with WNV re-main asymptomatic, and about 20%develop mild flu-like symptoms.About 1 (<1%) in 150 develop acuteneurologic disease, which can lead tocoma, stupor, paralysis, and death.''"'

Clinical caseA 55-year-old African-American

man from upstate New York was ad-mitted in August 2002 with a chiefcomplaint of fever and confusion.According to the patient's wife, hehad been healthy until one day be-fore admission when he complainedof flu-like symptoms, including nau-sea, vomiting, and diarrhea. The pa-tient believed these symptoms werefrom eating contaminated venisonsausage. His medical history wassignificant for hypertension and hedenied the use of tobacco, alcohol,and illicit drugs. Other pertinent his-tory includes no recent travel out of

Purpose. The epidemiology, virology, andtransmission of West Nile virus (WNV) arereviewed, and the clinical features, diagno-sis, and treatment of WNV infection areexamined.Summary. WNV infection is caused by aflavivirus transmitted from birds to humansthrough the bite of culicine mosquitoes.WNV was discovered in the blood of a fe-brile woman from Uganda's West Nile prov-ince in 1937. The first case of domesticallyacquired WNV infeaion was reported in theUnited States in 1999 in New York. Sincethen, WNV infection has spread rapidlyacross the United States, with 9306 con-firmed cases and 210 deaths reported from45 States in 2003. It is still not clear howWNV was introduced into North America.WNV is a small, single-stranded RNA virusand a member of the Japanese encephalitisvirus antigenic complex. While most hu-mans infected with WNV are asymptomat-ic, some may develop an influenza-like

the area and previous employment ina factory. The patient was also anavid hunter. Physical examinationrevealed a well-developed, well-nourished individual who was con-fiised and agitated. While most of thepatient's physical examination find-ings were normal, his neck was rigid.

illness. Disease surveillance remains thecornerstone for the early recognition andcontrol of WNV. We describe one case ofWNV infection with an update on the dis-ease. Strategies for the prevention and con-trol of this infection are reviewed.Conclusion. There is no established treat-ment for WNV infection. Currently, preven-tion and control are the only measures thathelp decrease the morbidity and mortalityassociated with WNV infection. As the num-ber of cases escalates and the geographicdistribution of WNV infection widens, theepidemic will continue to pose a majorchallenge to clinicians in the coming years.There is an urgent need for more researchon the pathogenesis and treatment of WNVinfection.

Index terms: Diagnosis; Epidemiology;Mortality; West Nile feverAm J Health-Syst Pharm. 2004; 61:123541

Vital signs included a temperature of39.9 "C, blood pressure of 120/70mm Hg, a respiration rate of 22breaths per minute, and tachycardia.On neurologic examination the pa-tient showed signs of hyperreflexia ofthe upper and lower extremities andno evidence of focal signs of motor

ROY GUHAROY, PHARM.D.. F C P , F C C P , F A S H P , is Director of Phar-

macy Services, Department of Pharmacy, and A.ssociate Chief, Sec-tion of Clinical Pharmacology, Department of Medicine; andSHI;I,I.I:Y A. Gll.ROY, M.D., is Clinical Associate Professor of Medi-cine, Division of Infectious Disease, State University of New York(SUNY) Upstate Medical University, Syracuse. |OHN A. NOVIASKY,PllARM.D., is Clinical Coordinator, St. Flizabeth Medical Center.Utica, NY. lONATHAN FF.RENCi-., PHARM.D., is Pharmacy PracticeResident in Family Medicine. University of Pittsburgh Medical Cen-ter, Pittsburgh. PA.

Address correspondence to Dr. Ciuharoy at the Department of

Pharmacy, Room 119, University Hospital, SUNY Upstate Medi-cal University, 750 East Adams Street, Syracuse, NY 13210(guharoyr@upstate.edu).

The authors acknowledge the assistance of Amy Wagner, DanDIppel, and Diana Vitullo in the preparation of this manuscript. Theassistance of I.yle R. Petersen, M.D., lames ]. Sejvar. M.D,, and KayeBender, Ph.D., is also acknowledged.

Copyright © 2004, American Society of Health-System Pharma-cists, Inc. All rights reserved. 1079-2082/04/0602-t235$06.00.

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CI.I!VICAI> RKVIKWS West NUe virus

weakness. Both Babinski's sign andcomputed tomography of the brainwere negative. Chest radiograph wasalso read as negative. Laboratorytests revealed a serum peripheral leu-kocyte count of 12 X lO-/\iL, with84% neutrophils and 16% lympho-cytes. His serum creatinine phospho-kinase level was 336 units/L. Cere-brospinal fluid (CSF) analysisreveaied 62 white blood cells/^L, 51red blood cells/fiL, with 67% neutro-phils, 18% lymphocyte.s, 12% mono-cytes, a glucose concentration of 72mg/dL {serum glucose was 90 mg/dL), and protein levels of 51 mg/dL.Gram's stain, India ink capsule stain,and cryptococcal antigen capture as-say of the CSF were negative.

Based on these findings, the pa-tient's working diagnosis was herpesencephalitis, and i.v. acyclovir 800mg was administered every 8 hours.The patient also received i.v. ampicilJ-in 2 g every 4 hours and i.v. ceftriax-one 2 g every 12 hours with the intentof discontinuation on the return ofnegative bacterial cultures. After fivedays, the patient's fever resolved, andhis mental status improved. The acy-clovir was discontinued when theherpes polymerase chain reaction(PCR) was negative. Although initialWNV serology test results were nega-tive. CSF WNV PCR and CSF immu-noglobuiin M (IgM) ELISA resultswere positive. Repeat WNV immu-noglobulin G and IgM serology testswere positive two weeks later. Mag-netic resonance imaging revealed aleft basal ganglion lesion. The patientimproved after three weeks but com-plained of persistent lower extremityweakness and was discharged to arehabilitation facility. After twomonths, all of his symptoms resolved,and he was able to return to work.

EpidemiologyWNV was first discovered in the

blood of a febrile woman fromUganda's West Nile province in1937. Outbreaks in humans mainlyassociated with mild febrile illness

were reported infrequently in Israeland Africa until the early 1990s."However, outbreaks involving hun-dreds of people resulting in severeneurologic disease were reported inRomania, Russia, and Israel in thelate 1990s.'-" Although a large out-break of \VNV has yet to occur in theUnited States, the frequency and ter-ritory occupied by this disease havebeen increasing since 1999.'^ It is un-clear if changes in the severity andfrequency of WNV infection arc dueto changes in host factors, such asage, background immunity, or pre-disposing chronic conditions, or toincreasing virus virulence.'"

The first domestically acquiredhuman cases of West Nile encephali-tis were reported in Queens, NewYork, in the summer of 1999 and re-sulted in 59 clinical cases and 7deaths; the median age of these pa-tients was 71 years.'' Since then, thedisease has quickly spread tothe Midwest, along the Eastern sea-board, and into the Deep South. In

2002, there were 4156 laboratory-confirmed human cases, including2942 meningoencephalitis cases and284 deaths (9% fatality rate).'*-'From 1999 through October 22,2003, WNV infection had been re-ported in 45 states (Figure 1).'' As ofOctober 22, 2003, 7386 human casesand 155 WNV-associated deathswere reported in 2003." Fifty-threepercent of the infected patients weremen, and the median age was 47years. In addition, 10,453 dead birdswith WNV infection were reportedfrom 42 states in 2003." It is interest-ing to note that the first case of WestNile encephalitis was reported inNew York in the early 1950s whenthe virus was unsuccessfully used asan experimental treatment for ad-vanced cancer.-' WNV is also spread-ing rapidly throughout Canada.-'' Itwas first discovered in 2001 in birdsand mosquitoes in Ontario. Subse-quent cases were reported in NovaScotia, Quebec, Manitoba, Ontario,and Saskatchewan in 2002, with cases

of infection reported in Quebec andOntario in 2002. The peak trans-mission time for WNV ranges frommid-July to early December, mostcommonly in late August and earlySeptember."'

Virology

The WNV is a small, single-stranded RNA virus of the familyFlaviviridae and genus Flavivirus anda member of the Japanese encephali-tis virus antigenic complex.'"'^ Thecomplex includes Alfuy, Cacipacore,Japanese encephalitis, Koulango,Kunjin, Murray Valley encephalitis,St. Louis encephalitis, Rocio, Strat-forde, Usutu, Yaounde, and WNV.The flaviviruses measure 40-60nm in diameter, are symmetrical inshape, and have posilive-sensesingle-stranded RNA. As with othermembers of the Japanese encephali-tis virus antigenic complex, WNVpossesses E-glycoprotein as the viralhema^utinin and mediator of virus-host cell binding.""'-'' E-glycoproteinelicits most of virus-neutralizing an-tibodies. The flavivirus virion has anicosahedral core composed of multi-ple copies of a capsid protein, whichencloses positive-sense single-stranded RNA. A host-cell-derivedenvelope encloses the capsid. Thisclose antigenic relationship betweenthe flaviviruses accounts for the sero-logic cross-reactions observed in thelaboratory.'"

Although two genetic lineages ofWNV have been identified, all NorthAmerican strains are closely relatedto phylogenetic lineage I WNV."Lineage II WNV remains in enzooticfoci in Airica, where large outbreaksof encephalitis have not been report-ed.̂ " It has been suggested that lin-eage II WNV may be less virulent inhumans-'; however, a mouse modelhas demonstrated that WNV fromboth lineages is neuroinvasive.-'* Al-though WNV has caused infectionsworldwide, mortality from WNV in-fection has occurred only in theUnited States and Israel.

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CI.INICAK REVIi:WS West NUe vims •

Figure 1 . Status with reported West Nile virus activity in the United States, 1999-2003. Available from www.cdc.gov/ncidod/dvbid/westnile/surv8icontroi03Maps99_01,htm,www.cdc.gov/ncidod/dvbid/westnile/surv&controi03Maps02.htm, and www.cdc.gov/ncidod/dvbid/westnile/surv&control03Maps.htm.

West Nile Virus rn the United States, 1999-2001 West Nile Virus in the United States, 2002

D.C.MOIDCM)

tit A Patiern indicates human cases

2 0 0 0 - 2 0 0 T •Vepmont repofledWNV inlectlon

2001 In 2000, bul notIn 2001

Verlfled avian, animal, and mosquito infections during 2002

indicates human case(s)

West Nile Virus Disease2003 Human Cases, by clinical syndrome

as of March 31, 2004, 3 a.m. MST*

D IndlcBiflB human disease case(s)

I ! Avian, animal, or moBqiilto Infections.

Ecology and transmissionII is still not dear how WNV was

introduced into North America. Pos-sible mechanisms include importa-tion or migration of infected birds ormosquitoes and international travelof infected persons.

WNV is maintained in a enzooticcycle involving several species ofmosquitoes and birds before infect-ing humans (Figure 2). Hence, themost common route of WNV trans-mission to humans is through thebite of an infected mosquito.'•*•"'Mosquitoes become infected v/ithWNV when they feed on a bird car-

rying the virus in its blood. Birds inthe Corvidae family (e.g., crows, bluejays) are particularly susceptible vec-tors because of their high viremia.-^While it is unclear which mosquitospecies is primarily responsible forWNV transmission to humans,Ciilex pipiens, Ctilex restuans, andCulex quinquefasciatus appear to bethe virus's most important vectors.WNV transmission occurs betweenbirds and maintenance-vectormosquitoes until the early fall.Twenty-seven mammalian specieshave been shown to be susceptibleto WNV infection and disease, in-

cluding humans and horses."'"Within 10-14 days of becoming in-fected, a mosquito can transmit thevirus in its saliva to another bird oranimal. During the bird-mosquito-bird cycle, viral amplification oc-curs, increasing the likelihood ofWNV infection when an individualis bitten.̂ "*'̂ "

In 2002, four novel routes ofWNV transmission to humans werereported: (1) blood transfusion, (2)organ transplantation, (3) transpla-cental transfer, and (4) breast-feeding.̂ -'̂ '''̂ ' '̂ In 2002. 23 people inthe United States were reported to

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^ RE\aEWN West Nile

Figure 2. West Nile virus transmission cycle. Reprinted from reference 30, with permission.

Bird reservoir hosts

Incidental infection Incidental infection

have acquired WNV infection afterreceiving blood components from 16WNV-infected blood donors.' Perthe recommendation of the Foodand Drug Administration, blood-collection agencies have since im-plemented WNV nucleic acid am-plification tests to screen all blooddonations in order to quarantine in-fectious blood components.^ Theimplementation of national blood-donor screening has significantlyreduced the risk of WNV transmis-sion by removing hundreds of unitsof potentially infectious blood do-nated by asymptomatic donors.WNV titers in infected blood com-ponents can be as low as 0.8 plaque-forming units/mL, which is lowerthan titers reported for other blood-borne viral pathogens, such as hu-man immunodeficiency virus andhepatitis C virus.' As of September16, 2003, 489 WNV-viremic blooddonors and two cases of confirmedtransfusion-associated events hadbeen reported, demonstrating thatthe risk of transmission has not been

eliminated by screening, possibly be-cause of low viremia or other un-known mechanisms.̂

Clinical featuresWhile most humans infected with

WNV are asymptomatic, some maydevelop an influenza-Iike illness,manifested by sudden onset of highfever with chills after an incubationperiod of 3-14 days, and symptomsusually last 3-6 days.^ ''̂ Patients mayalso have malaise, headache, arthral-gia, lymphadenopathy, backache, an-orexia, vomiting, myalgia, and retro-orbital eye pain made worse by eyemovement."'^

Of more concern is West Nile en-cephalitis which was first document-ed in 1957 in an Israeli nursinghome.'" While more recent out-breaks of West Nile encephalitis havebeen associated with morbidity andmortality, reports of severe neuro-logic disease caused by WNV remainuncommon.'*''"' WNV-related neu-rologic disease can manifest as men-ingitis, encephalitis, or acute flaccid

paralysis (Table i).^-'oi' More than90% of patients with neurologic dis-ease have fever accompanied by gas-trointestinal symptoms and head-ache.'" Meningoencephalitis hasbeen reported more frequently thanmeningitis alone in patients withWest Ni!e encephalitis.'''* WNV mayalso cause a flaccid paralysis of thelimbs and respiratory tract, as seen inmany patients during the 1999outbreak in New York City.'' Otberneurologic symptoms, such as trem-or, myoclonus, and parkinsonianfeatures (including rigidity, brady-kinesia, and postural instability)have been reported with WNV

Age is an important prognostic in-dicator, as younger patients are morelikely to develop West Nile feveralone. On the other hand, the risk ofdeveloping severe neurologic diseaseincreases dramatically in patientsover 50 years of age.

Diagnosis

Indirect immunofluore.scence as-says using murine monoclonal anti-bodies are sensitive for rapid testingof mosquito pools, avian tissues, andhuman specimens."-'"'" WNV infec-tion should always be considered inpatients with encephalitis and men-ingitis whose cause cannot be deter-mined. This is especially true in eld-erly patients with encephalitis whodevelop these illnesses in the latesummer or early fall. Detection ofIgM antibody to WNV in serum orCSF using ELISA is the most efficientdiagnostic method. As IgM does notcross the blood-brain barrier. IgMantibody to WNV detected in theCSF strongly suggests central ner-vous system involvement.̂ ''

In most patients, IgG antibodiescan be detected three weeks after in-fection. IgG titers increase betweendays 7 and 21 in patients with acuteinfection. Clinicians should be awarethat false-positive serologic resultscan occur in patients recently vacci-nated against yellow fever or Japa-

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CLINICAi> RKVIKWS West Nile viniM

Table 1.Neurologic Manifestations of West Nile Virus^

Diagnosis Criteria

West Nile meningitis

West Nile encephalitis

Acute flaccid paralysis

A. Clinical signs of meningeal inflammation,including nucha! rigidity, Kemig orBrudzinski sign, or photophobia orphonophobia

B. Additional evidence of acute infection,including one or more of the following:fever (>38 "C) or hypothermia (<35 °C);cerebrospinal fluid pleocytosis (>5leukocytes/mm^); peripheral leukocytecount >10,000/mm^- neuroimagingfindings consistent with acute meningealinflammation

A. Encephalopathy {altered level ofconsciousness, lethargy, or personalitychange lasting >24 hr)

B, Additional evidence of central nervoussystem inflammation, including two ormore of the following: fever (>38 ""C) orhypothermia (<35 "C); cerebrospinal fluidpleocytosis {>5 leukocytes/mm^);peripheral leukocyte count >10,000/mm , neuroimaging findings consistentwith acute inflammation (with or withoutinvolvement of the meninges) or acutedemyelination; presence of focalneurologic deficit; meningisimus (asdefined in A); electroencephalographyfindings consistent with encephalitis;new onset or exacerbation of previouslycontrolled seizures

A. Acute onset of limb weakness withmarked progression over 48 hr

B. At least two of the following: asymmetryto weakness; areflexia/hyporeflexia ofaffected limb(s); absence of pain,paresthesia, or numbness in affectediimb(s); cerebrospinal fluid pleocytosis(>5 leukocytes/mm^) and elevatedprotein levels (>45 mg/dL);electrodiagnostic studies consistent withan anterior horn cell process; spinal cordmagnetic resonance imagingdocumenting abnormal increased signalin the anterior gray matter

*Bepf inted from reference 10. with permission.

nese encepbalitis and those who re-cently had dengue or St. Louisencepbalitis because ot the close anti-genic relationships between tbe fla-viviruses"'; therefore, it is critical toobtain a travel and immunizationhistory for accurate interpretation ofserologic resuhs. The plaque reduc-tion neutralization test may helpdistinguish these false-positive re-sults.' Clinicians should also notethat virus isolation from serum orCSF is often unsuccessful because oflow viremia.' ' Viremia may last

longer in patients taking immuno-suppressive drugs or with advancedmalignancies.

Another consideration is that pa-tients in endemic areas may beasymptomatic but still have IgM an-tibodies for at least six months. Ifthese patients become ill from an un-related infection and are tested forWNV antibodies, the diagnosis maybe confusing.'" In these patients,acute infection may be confirmed byan increase in WNV-speciflc neutral-izing antibody titer in the serum.

Clinically, patients may have mildleukocytosis or mild leukopenia.""Mild hyponatremia can occur and ismore common in patients v̂ ath en-cephalitis, CSF findings include mildpleocytosis with lymphocytic predom-inance, mild to moderate protein ele-vation, and normal glucose levels.'*"-'Computed tomography usually showsno sign of acute disease.""

TreatmentCurrently, there is no established

treatment for WNV infection. Treat-ment consists only of supportive andsymptomatic care, including respira-tory support, intravenous fluids, andprevention of secondary infections.Human vaccines for WNV are beingdeveloped."'"'"'" The vaccines use theprotype flavivirus, yellow fever 17D,as a live vector and replace the genesencoding the premembrane and en-velope protein of yellow fever 17Dvaccine with the correspondinggenes of WNV. The resulting viruscontains the antigens responsible forprotection against WNV.""" High-dose ribavirin and interferon alfa-2bhave shown efficacy in vitro.^' Inter-feron alfa (a glycoprotein cytokine)has produced positive results in opentrials in patients with Japanese en-cephalitis and St. Louis encephali-tis.^'''^ However, a randomized,double-blind, placebo-controlled tri-al of patients with |apanese encepha-litis treated with interferon alfa {10million units/m' for seven days)demonstrated no benefits.'" High-dose ribavirin did not show any ben-efit during the WNV outbreak inIsrael in 2000.''* The use of cortico-steroids, antiseizure medications,and osmotic agents has yet to bestudied in the management of WestNile encephalitis. An intravenousimmunoglobulin preparation con-taining a high titer of anti-WNV an-tibodies has been successfully used inan immunosuppressed patient'^ anddemonstrated prophylactic and ther-apeutic efficacy in mice.'"^ Largerstudies are required to establish the

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CMNIOAl. RKVIKW'S >\'est Nile virtis

therapeutic role of immunoglobulinsin patients with WNV infection.'"

Prevention

Prevention can be divided intothree general categories: (1) prevent-ing mosquitoes infected with WNVfrom biting humans, (2) reducing thenumber of mosquitoes, and (3) pub-lic education.̂ ^"^ Of these, mosquitocontrol is the most effective means toprevent WNV transmission.

Insect repellent should be appliedto exposed skin and clothing beforegoing outdoors. The most effectiverepellents contain DEET (N,N-diethyl-m-toluamide). Products witha DEET concentration of >50% donot increase the length of protection,and products containing no morethan 10% DEET are appropriate forchildren 2-12 years of age. Repellentsshould not be placed on the hands ofchildren, and care should be taken toavoid the products' contact withtheir mouth and eyes.̂ ^ Protectiveclothing, such as long sleeves, longpants, and socks, should be wornwhenever possible when outdoors.Clothing should be sprayed with re-pellents since mosquitoes can bitethrough thin clothing. Stay indoorsbetween dusk and dawn, as that is thepeak time for mosquito bites.

Environmental measures includecreating barriers, such as properly in-stalled window and door screens, andminimizing mosquito-breed ing areas,by draining standing water. Watershould be routinely emptied fromflowerpots, clogged rain gutters,swimming pool covers, pet bowls,discarded tires, buckets, barrels,cans, and other items that collect wa-ter. Local health authorities shouldbe alerted to potential mosquito-breeding sites in areas, such asstorm sewers, ditches, and aban-doned properties with standingwater. Dead or dying birds andhorses that are suspected of beinginfected with WNV should also bereported. Each state and county re-ports this information to the Cen-

Since this manuscript was ac-cepted for publication, more re-cent data on the spread of WNVhave been released. In 2003,9,306 human infections and 210deaths were associated withWNV.*" In addition, 11,597 deadbirds tested positive for WNV in-fection. CDC has recently rec-ommended that pregnant wom-en with meningitis, acute flaccidparalysis, or unexplained fever inan area of WNV transmissionshould have serum (and CSF, ifclinically indicated) tested forthe presence of WNV IgM anti-body.''̂ This new recommenda-tion also suggests that pregnantwomen living in areas withWNV-infected mosquitoes applyinsect repellent to clothes andskin, wear clothing to protectagainst mosquito bites, andavoid the outdoors during peakmosquito-feeding times. Con-cern for WNV infection also ap-plies to infants born to motherswho were diagnosed or suspectedto have been infected with WNVduring pregnancy. Clinical andlaboratory evaluations should beconducted as indicated."*''

ters for Disease Control and Pre-vention (CDC)."

Public education about WNV andthe potential health and environ-mental impact of mosquito controlis essential. Surveillance of birddeaths, mosquito-breeding sites, andhuman cases of WNV is also criticalfor improving infection-controlstrategies.""' Additional informationabout WNV is available from CDC'sDivision of Vector-Borne InfectiousDiseases at www.cdc.gov/ncidod/dvbid/westnile/city_states.htm.

Conclusion

There is no established treatmentfor WNV infection. Currently, pre-

vention and control are the onlymeasures that help decrease the mor-bidity and mortiUity associated withWNV infection. As the number ofcases escalates and the geographicdistribution of WNV infection wid-ens, the epidemic will continue topose a major challenge to cliniciansin the coming years. There is an ur-gent need for more research on thepathogenesis and treatment of WNVinfection.

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