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Slide 1 :
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WNV Vertebrate Ecology and Biology-Birds Nicholas Komar, ScD Arbovirus Diseases Branch, DVBID, CDC Fort Collins, CO |
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Slide 2 :
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Experimental infection of WNV in 25 species of birds Komar et al., 2003, EID 9(3): 311-323; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm Other studies: Senne et al. 2000 Swayne et al. 2000 Langevin et al. 2001 Swayne et al. 2001 McLean et al. 2002 |
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Slide 3 :
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Very Competent Species Mean Reservoir Days Peak Competence Species (n) Infectious* Viremia Index, ci
Blue Jay (4) 4.0 11.0 2.6 Common Grackle (6) 3.0 9.4 2.0 House Finch (2) 5.5 8.5 1.8 American Crow (8) 3.2 10.1 1.6 House Sparrow (6) 3.0 8.9 1.6
*Infectious viremia = log 5 or greater per ml serum |
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Mean Reservoir Days Peak Comp. Species (n) Infectious* Viremia Index, ci
Ring-billed Gull (2) 4.5 7.4 1.3 Black-billed Magpie (3) 3.0 8.7 1.1 American Robin (2) 3.0 8.5 1.1 Red-winged Blackbird (3) 3.0 8.1 1.0 Killdeer (2) 3.0 8.1 0.9 Great Horned Owl (1) 4.0 7.6 0.9 American Kestrel (2) 3.0 8.4 0.9 Fish Crow (8) 2.8 6.8 0.7 * Infectious viremia = log 5 or greater per ml serum Moderately Competent Species |
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Mean Reservoir Days Peak Comp. Species (n) Infectious* Viremia Index, ci Mallard (2) 3.0 6.7 0.5 European Starling (6) 2.0 6.0 0.2 Mourning Dove (3) 1.7 5.3 0.2 Northern Flicker (1) 1.0 5.4 0.1 Canada Goose (3) 0.3 4.7 0.03 * Infectious viremia = log 5 or greater per ml serum Weakly competent species |
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Mean Reservoir Days Peak Comp. Species (n) Infectious* Viremia Index, ci American Coot (1) 0 4.6 0 Rock Dove (6) 0 4.3 0 Chicken (11) 0 3.4 0 Northern Bobwhite (3) 0 2.8 0 Ring-necked Pheasant (3) 0 2.5 0 Budgerigar (3) 0 2.5 0 Monk Parakeet (3) 0 2.4 0 Japanese Quail (3) 0 2.2 0 * Infectious viremia = log 5 or greater per ml serum Non-competent species |
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Summary of Competence Studies Passerines are most competent
jays, crows, sparrows, finches, blackbirds, etc.
Not all passerines are equally competent
Not all birds are competent
pigeons, chickens incompetent
Competence does NOT imply Reservoir Status |
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Reservoir Host Criteria Competent
Naturally Exposed
Abundant |
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Natural Exposure: Seroprevalence Studies High seroprevalence (typically >30%) in resident birds after epizootic transmission
Low seroprevalence (typically <1%) in enzootic foci, in non-resident birds, early in transmission season |
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WNV Seroprevalence in Birds Queens, September 1999 Species POS/Total % POS
Domestic Goose 6/ 7 86
Turkey 2/ 3 67
Chicken 89/141 63
House Sparrow 12/ 20 60
Pigeon 13/ 49 27
Canada Goose 2/ 7 29
Mallard 1/ 16 6
Ref: Komar et al. 2001. Emerg. Inf. Dis. 7(4): 621-625. |
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Relative Abundance of Birds, Queens Relative Relative Infection no. of Species Abundance Rate Infections
House Sparrow 6000 0.60 4186
Pigeon 1000 0.27 314
Mallard 60 0.06 4
Canada Goose 60 0.29 20
Chicken 3 0.63 2
Domestic Goose 1 0.86 1
Ref: Komar et al. 2001. Emerg. Inf. Dis. 7(4): 621-625. |
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Reservoir Potential of Birds, Queens A x B = C
Relative no. Competence Reservoir Species infections Index Inoculation Index
House Sparrow 4186 1.6 11,000
Pigeon 314 0 0
Mallard 4 0.5 3
Canada Goose 20 0.03 1
Chicken 2 0 0
Read: “For every one WNV-infectious Culex pipiens infected by a Canada goose, there were 3 infected by mallards and more than 11000 infected by house sparrows” |
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Birds affected by WNV – 162 spp. |
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Avian Mortality: Disease Impact Studies Surveillance data lack attack rates, mortality rates
Preliminary observations were made in 2002 of three marked crow populations: Stillwater, OK; Ithaca NY; Chicago, IL |
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Species n mortality rate controls
American Crow 20 100 8 Black-billed Magpie 5 100 1 Blue Jay 6 83 0 House Finch 3 67 3 Fish Crow 11 64 5 Ring-billed Gull 2 50 1 Common Grackle 10 40 2 House Sparrow 12 25 5
These birds infected by natural means (mosquito, oral, bird-bird) Experimental WNV Mortality -1 Komar et al., 2003, EID 9(3): 311-322; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm |
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Experimental WNV Mortality -2 Species n mortality rate controls
European Starling 6 0 2 Rock Dove 6 0 6 Chicken 18 0 24 Ring-necked Pheasant 3 0 0 Canada Goose 3 0 0 American Robin 3 0 3 Red-winged Blackbird 3 0 0 Mourning Dove 3 0 3 Budgerigar 3 0 3 Monk Parakeet 3 0 3 Japanese Quail 3 0 3 Northern Bobwhite 3 0 3 Komar et al., 2003, EID 9(3): 311-322; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm |
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Slide 17 :
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Alternative Transmission in Birds |
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Slide 18 :
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WNV Cage Mate Transmission Species No. of cages No. of transmissions
American Crow 4 4 Black-billed Magpie 3 2 Blue Jay 2 2 Ring-billed Gull 1 1 Chicken 18 1 Other species (n=13) 30 0 Komar et al., 2003, EID 9(3): 311-322; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm |
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Slide 19 :
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WNV Oral Transmission Species n dose no. viremic
Common Grackle 4 1000 pfu 4
House Finch 1 mosquito 1
House Sparrow 6 107 pfu 6
American Crow 6 sparrow 5
American Crow 3 107 pfu 3
Great Horned Owl 1 mice 1 Komar et al., 2003, EID 9(3): 311-322; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm |
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Cloacal shedding in crows Threshold of infectiousness ????? |
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Slide 21 :
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Persistence of WNV in Tissues Viral Days Species Tissue Load post-viremia Killdeer 1 Skin 110 pfu/0.5 cm3 9 Killdeer 2 Spleen 550 10 Killdeer 2 Skin 20,000 10 Mourning Dove Kidney 100 11 Budgerigar Heart 130 13 Blue Jay Eye 360 9 Common Grackle Skin 380 11 Common Grackle Eye 150 11 House Sparrow 1 Skin 370 8 House Sparrow 2 Spleen 120 10 House Sparrow 2 Lung 590 10 House Sparrow 3 Brain 300 8 Komar et al., 2003, EID 9(3): 311-322; www.cdc.gov/ncidod/eid/vol9no3/02-0628.htm |
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Birds as Dispersal Vehicles No hard evidence yet
Laboratory studies pending
Field studies unsuccessful to date
Significance of prolonged viral persistence in organs? |
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Slide 23 :
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Ecological Factors Affecting Transmission |
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Slide 24 :
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Pigeons seroconverted 270% more frequently in the canopy in New York City: 32 vs 12 in 2002 |
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Slide 25 :
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Acknowledgments |
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Slide 26 :
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West Nile Virus: Primary Passerine-Culex Transmission Cycle |
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