The Movement of West Nile Virus in North America UC Berkeley October 1, 2003 Lyle R. Petersen, M.D., M.P.H.. Division of Vector-Borne Infectious Diseases Fort Collins, Colorado Photo of Cx. quinquefasciatus courtesy of Dr. Stephen Higgs, UTMB/Galveston

Order of Topics What is it? What is different now? How did it get here? How it is spreading? How big is the problem? What will happen next? How do we prevent it?

West Nile Virus: Background RNA virus Family Flaviviridae, Genus Flavivirus Member Japanese encephalitis serocomplex Closely related to SLE virus Isolation in 1937, West Nile district of Uganda

West Nile Virus: Approximate Geographic Range Before 1999

West Nile Virus Before and After Mid-1990s Before Mild self-limited febrile illness Central nervous system involvement rare Periodic outbreaks After Outbreaks associated with severe CNS illness Some outbreaks associated with avian mortality First recognition in North America (New York City) in 1999

West Nile Outbreaks Israel 1941, , 1957, 1980, 2000 France 1962, 2000 South Africa 1974 Romania 1996 Italy 1998 Russia 1999 United States

Arrival in North America

Madagascar Uganda 1937 Central African Republic 2 Egypt 1951 France 1962 South Africa 1974 NE United States Israel 98/99/2000 India Kunjin Romania 1996 Italy 1998 Volgograd LINEAGEClade Eg 101 U.S./Israel Europe/Russia India Kunjin Phylogenetic Tree of West Nile Viruses Israel 2000

An exotic arbovirus in NYC was surprising and unexpected: Should it have been?

International Animal Importations Into New York August 1998 – July 1999 N = 2,873,144 none 1 – Animals

Top Ten Countries of Origin Passengers arriving into NY Airports July 1998 – June 1999 N = 4,850,090

West Nile Virus Transmission Cycle Mosquito vector Incidental infections Bird reservoir hosts Incidental infections West Nile Virus West Nile Virus

Incidental hosts Humans Horses Other mammals Other mosquito vectors * Culex salinarius Cx.nigripalpus Ochlerotatus sollicitans Oc. taeniorhynchus Aedes vexans Ae albopictus * With possible epidemic potential ? ? Amplifying hosts Passerine birds Enzootic/epizootic (amplifying) vectors Culex pipiens Cx. restuans Cx. quinquefasciatus Cx. tarsalis West Nile Virus Amplification Cycle

West Nile Virus Ecology in North America, as of Fall mosquito species 170 native and captive avian species Mortality varies greatly by species Very high viremias in some species Bird-to-bird transmission documented Virus in feces and oral swabs Oral infection possible 18 other species (e.g., cats, dogs, squirrels, chipmunks, harbor seal, alligator, bats, reindeer)

WNV Surveillance Dead birds (especially crows) Human surveillance Mosquitoes Horse surveillance Live captive sentinels (e.g. chickens) Live wild birds Zoo animals

Reported to ArboNET as of 09/03/2003 Year# States# CountiesDate Range AUG – 15 NOV **1456 FEB – 17 NOV **3598 APR – 26 DEC **2,5313 JAN – 19 DEC ,9541 JAN –29-SEP States and Counties Reporting WNV Activity, United States, * ** Plus D.C.

Reported WNV Disease Cases in Humans, United States, * * Reported as of 09/30/2003 Year# Cases# States# CountiesOnset Date Range AUG – 24 SEP JUL – 27 SEP JUL – 7 DEC 20024,15639**74019 MAY – 19 DEC 20035, MAR – 26 SEP ** Plus D.C.

Clinical Epidemiology Incubation period 2-14 days May be longer in immunosuppressed Approximately 20% mild febrile illness <1% severe neurological disease Meningitis, encephalitis, AFP Advanced age primary risk factor for encephalitis AFP patients may be younger Immunosuppressive drugs and hematological malignancies risk factors Approximate 10% mortality Long-term morbidity common

~80% Asymptomatic ~20% “West Nile Fever” <1% CNS disease WNV Human Infection “Iceberg” in fatalities ~ 3300 severe disease ~400,000 asymptomatic ~100,000 mild illness

Human WNV Illnesses (n=4156), by Month of Symptom Onset, st Case May 19 Last Case Dec 19

Human WNV Meningoencephalitis Incidence, by Age Group, United States, 2002 * States with human cases

Fatality Rate among Persons with WNV Meningoencephalitis, by Age Group, United States, 2002

Human WNV Disease Cases, by Age Group and Clinical Category, United States, 2003* * Reported as of 09/03/2003

Novel Modes of West Nile Virus Transmission, 2002 Transplanted organs One donor to four recipients Transfused blood 23 confirmed cases in 2002, many more likely WNV screening began in July Breast milk One case, infant asymptomatic Transplacental transmission One case, severe outcome to infant Percutaneous, occupational exposure

St. Louis Encephalitis Related Japanese encephalitis serocomplex flavivirus Endemic in the Americas Similar maintenance vectors Birds are main hosts Causes human epidemics Is SLE a model for the future behavior of WNV?

Reported and Estimated Number of St. Louis Encephalitis Cases, U.S., Sept 12, 2003

Reported Number of West Nile Meningoencephalitis Cases, U.S., Sep 30, 2003

DC SLE 1975 DC WNME 2002* >=10 1 – – 0.9 Incidence per 10 6 Reported Incidence in Humans: SLE 1975 vs. WNME 2002 * Reported as of 11/01/2002

West Nile Virus Future in the United States Worrisome for several reasons Prolonged transmission season Wide geographic range Many potential amplifying avian hosts High viremias in birds Many potential mosquito vectors Many potential human-biting mosquito species Persistent infections in areas over 5 years Urban / suburban / rural transmission

JOIN THE “SWAT TEAM” AGAINST WEST NILE VIRUS

Prevention Repellants DEET (up to 50% concentration); 10% in children Permethrin on clothing and fabrics Reduce mosquito breeding sites Long sleeves and pants Stay indoors when mosquitoes are biting (dawn and dusk) Bug zappers, sonic devices, CO 2 devices (mosquito magnet): no proven efficacy

Habitat elimination Larviciding Adulticiding