role of corvids in the epidemiology west nile virus in california...erythrothorax 15 715 0...
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Role of Corvids in the epidemiology of West Nile virus in California*
William K. ReisenCenter for Vectorborne Diseases
Department of Pathology, Microbiology and ImmunologySchool of Veterinary MedicineUniversity of California, Davis
Email: [email protected] *2006 JME: in press
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Those that did the work….
Center for Vectorborne Diseases:C Barker, B Eldridge, B Park: spatial analysis, data managementH Lothrop, S Wheeler, M Kennsington, M Palmer, P Miller: field ecology Coachella ValleyJ Wilson: field ecology Los AngelesV Martinez, B Carroll, S Hallam, D Jurich, K Newlen: field ecology and vector competence, Kern CountyV Armijos, C Nielsen: field ecology Sacramento & Yolo CountiesY Fang, M Shafii, S Garcia, N Kahl, S Astari, B Cahoon-Young, A Brault: laboratory diagnostics
California Animal Health and Food Safety:L Woods: dead bird necropsies
Coachella Valley MVCD: B Lothrop, D Gomsi, A GutierrezGreater Los Angeles VCD: M Madon, J Hazelrigg, S Kluh, P OConnor, J Spoehl, S TabatabaeepourKern MVCD: R Takahashi, R QuiringSacramento-Yolo MVCD: S Wright, D Brown, G Yoshimura, D Eldin Elnaiem, K Kelly California Department of Health Services
C Glaser, C Jean: human surveillanceB Sun: veterinary surveillanceC Cossen, L Baylis: sentinel chicken serologyV Kramer, S Husted, A Hom, R Carney, L Marcus: dead bird surveillance, data reporting
Scripps Institute of Oceanography, University of California, San DiegoD Cayan, M Dettinger, M Tyree: Climate analysis
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Those that paid for the work….
National Institutes of Allergy and Infectious Diseases, NIHCenters for Disease Control and PreventionOffice of Global Programs NOAACoachella Valley, Greater LA, Kern and Sac-
Yolo MVCDsUniversity-Wide Mosquito Research Program
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Content – California focused
Background:Distribution of WNV in California, 2004
Natural experiment based on corvid distributions: 2004 epidemic in southern California
Distribution of CorvidsHost competenceMosquito infection ratesCase count and incidence of infection
Spatial analysis of dead birdsAmerican crowsWestern scrub jaysDead crows delineate foraging radius in LA
Culex infection ratesHuman case distributions
Importance of ‘herd immunity’ in peridomestic passerinesEmerging concepts of WNV epidemiology
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Distribution of WNV in California, December 2004
Widespread enzootic activity in SE California
Epidemic transmission in Los Angeles
Invasion and amplification in Kern County
Invasion of Sacramento
Dead birds
Mosquitoes
Chickens
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Natural experiment: three areas in southern California with different densities of corvids
Few AMCRsmoderate WESJs
Few corvids, except ravens
High AMCRs, moderate WESJs
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Distribution of effective hosts in California based on CBC data, 2003
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Distribution of effective WNV hosts in California based on BBC data [http://www.mbr-pwrc.usgs.gov/]
American crowWestern scrub jay
House finchHouse sparrow
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Viremia profiles [log10 PFU/mL] for two Corvid and two
peridomestic passerine species to West Nile virus infection
0
2
4
6
8
10
12
1 2 3 4 5 6 7 8
Days post infection
Vire
mia
AMCR* [8]W ESJ [5]HOFI [16]HOSP [6]
* Data from Komar et al. 2003 EID 9: 311
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Vector competence of Culex vectors in southern California, 2005
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
6-7 5-6 4-5 3-4 2-3
log10 PFU/mL
Perc
ent i
nfec
ted
tarsalisquinquefasciatusstigmatosoma
Data summarizes 2 experiments in each of 3 study areas, n = 20 – 30 females/exp
Most susceptible to infection
Least susceptible to infection
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Infection rates for Culex species tested from southern California, May – Sep 2004
Culex speciesPools tested
Total mosquitoes
testedWNV
positives
Infection Rate per
1,000Lower
LimitUpper
Limit
quinquefasciatus 132 3,132 4 1.29 0.42 3.08tarsalis 424 15,137 63 4.56 3.54 5.79erythrothorax 15 715 0
quinquefasciatus 406 15,325 86 6.42 5.17 7.89tarsalis 410 16,893 85 5.72 4.60 7.04
erythrothorax 263 12575 3 0.24 0.06 0.65quinquefasciatus 1029 38,420 270 8.09 7.18 9.09tarsalis 135 4,411 18 4.34 2.68 6.70stigmatosoma 37 613 6 10.22 4.32 20.89
Coachella Valley
Kern County
Los Angeles
MLE Calculated from Biggerstaff: http://www.cdc.gov/ncidod/dvbid/westnile/software.htm
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Incidence of WNV cases [CNS + fever] among human populations, California 2004
Data from: http://westnile.ca.gov/2004_maps.htm
Population size Incidence perArea (in 1000s)a WNV casesb 100,000 California 33,871 819 2.42 Coachella Valley 336 7 2.08 Los Angeles County 9,519 327 3.44 Kern County 662 60 9.06 a Based on 2,000 census figures b through 15 Dec 04, West Nile fever and Neurological Disease as well as infections detected by blood banks included.
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Crows at large staging area, Whittier Narrows Wildlife
Area, Sep, 2004
Spatial distribution: Dispersion of corvids determines the patterns of risk
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Distribution of dead corvids [AMCR & WESJ] reported by the public that tested positive for WNV, 2004
SaTScan software version 5.1 (http://www.satscan.org)
Cluster Radius [km]1 18.42 26.83 154 15.85 22.66 9.8
Avg 18.1
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Human density per sq mi in relation to dead bird clusters in southern California, 2004
Dead bird clusters near humans:•Humans have to find and report dead birds•Corvids:
•Live near periurban areas•Forage in peridomestic areas
•Clusters - communally roosting AMCRs• WESJs are highly territorial and evenly distributed
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Mosquito trap locations, Greater LA VCD, and dead bird clusters, 2004
Cx. quing infection rate
02468
10
In OutIR
per
1,0
00
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Congruent clusters of human cases per zip code in relation to dead corvid clusters
Data:• Only 41% of human population lived within clusters• 75% cases lived within clusters• Incidence per 100,000
• in clusters = 5.9 • outside clusters = 1.3
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WNV seroprevalence in House finches and House sparrows and
the occurrence of human cases, Los Angeles County
0
10
20
30
40
50
60
70
80
90
100
Jan
Mar
May Ju
l
Sep Nov Jan
Mar
May Ju
l
Sep Nov Jan
Mar
May Ju
l
Human casesHOSPHOFI
2003 2004 2005
Because ca. 75% of HOFI die during acute infection, with a 40% seroprevalence rate, 85% of the population may have been infected
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Predictionsfor 2005
BBS survey of American crow distributionCalifornia
2005 Epicenter?
Epidemic will subside south of Tehachapi Mts because most crows have died or are now immuneEnzootic transmission will intensify in Central Valley, driven by American crows and Western scrub jaysPeak transmission will occur later in summer in Central Valley than in SOCALHuman involvement will be focal, periurban and associated with communal crow roosts that ‘drive’ virus into Cx. pipienspopualtionsEpidemic could worsen
BBS of WESJ
????
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188 human cases:•1 death•51 cases of neuroinvasive disease•121 cases of WNV fever• 15 asymptomatic cases
53.6 % infection rate in 110 sentinel chickens19,429 dead bird reports
47 infections in horses
Sacramento-Yolo Counties: The 2005 WNV Epicenter
Slide from Dia-Eldin A. Elnaiem, Sac-Yolo MVCD
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Sac-Yolo Counties Monthly dead birds
reports, 2005
August: 6098 birdsSeptember: 1084 birds
Jan-May: 1224 birdsJune: 1140 birds
July: 6283 birds
Slide from Dia-Eldin A. Elnaiem, Sac-Yolo MVCD
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Rural cycles Urban cycle
????
Bird/Mosquito Movement?
West Nile virus transmission cycles in California
OchlerotatusOchlerotatus
Culex tarsalisCulex tarsalis
CulexCulexpipienspipiensstigmatstigmat..??erythroerythro..Other
species
Dead end hosts
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Summary
Competence and distribution of mosquito vectors in relation to avian hosts determines the efficiency of local transmission Virulence of WNV for corvids and the resulting elevated viremia seem critical to efficiently infect moderately susceptible urban mosquitoes in the Culex pipiens complexDistribution patterns of Corvids seems to determine the distribution of human cases in urban landscapes