mosquito surveillance in ontario: 2002 infection in mosquitoes west nile virus 2003 planning...
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Mosquito surveillance in Ontario: 2002Infection in mosquitoes
West Nile virus 2003 Planning Workshop,Toronto, November 7, 2002
Robbin Lindsay, Health Canada
West Nile Virus Transmission Cycle
Avian reservoirs
VIRUS VIRUS
Dead - - end hosts
Mosquito vectors Culex species mainly
Spill-overvia bridging vectors
VIRUS
Enzootic amplification
Mosquitoes “Infected” with WN virus – USA1999-2001
1999
Aedes vexans-1
Culex pipiens-8
Cx. spp or mixed-8
2000Aedes albopictus
Ae. vexans-17
An. punctipennis
Culex pipiens-146
Cx. restuans-12
Cx. salinarius-50
Cx. spp or mixed-254
Cu. melanura-3
Ochlerotatus atropalpus
Oc. canadensis
Oc. cantator
Oc. japonicus-9
Oc. triseriatus-9
Oc. trivittatus-8
Ps. ferox
2001Aedes albopictus-5
Ae. cinereus
Ae. vexans-4
An. barberi
An. crucians-bradleyi
An. quadrimaculatus-5
An. punctipennis
An. atropos
Cq. perturbans-5
Culex pipiens-349
Cx. nigripalpus-5
Cx. quinquefasciatus-13
Cx. restuans-76
Cx. salinarius-70
Cx. spp or mixed-302
Cu. melanura-26
2001 cont’dOchlerotatus altanticus
Oc. canadensis-5
Oc. cantator
Oc. japonicus-8
Oc. sollicitans-6
Oc. taeniorhynchus-4
Oc. triseriatus-13
Oc. trivittatus-3
Orthopodomyia signifera-2
Ps. columbiae
Uranotaenia sapphirina
Deinocerites cancer-2
Not yet or only recently documented in Canada
In 2002, ten new mosquito species found “infected”
List of WN virus vectors from 1999-2002 now at 37 species
Mosquito surveillance in 2002
Why sample mosquitoes?
1) Provides data central to decision-making regarding need for control
2) Gain a better understanding of epidemiology of West Nile virus
Objectives in 2002
Conduct mosquito surveillance in health units in southern Ontario to:
• Determine species composition, relative abundance and local distribution of mosquito populations
• Obtain specimens for testing for infection with WNV (bridging and enzootic vectors)
• Establish inventory of mosquito collection equipment, train personnel (field and laboratory: mosquito identification and testing)
Mosquito surveillance in 2002
Two types of trap sites
Permanent trap sitesModerate number of traps set at permanent sitesOperated on a weekly basisCollected mosquitoes shipped to BrockSub-samples of mosquitoes identified to species and pertinent information reported to health unitsProgram from mid-June? to mid-October
Prior to WN virus activity and season-long
Mosquito surveillance in 2002
Once WN virus activity confirmed
“Hot spot” trapping sitesCDC light traps set at sites in vicinity of dead bird collection(s)/sightingsTraps operated weekly & for as long as feasibleCollected mosquitoes shipped to Brock University for identify,sorting, and most mosquito pools shipped to Winnipeg for eventual testingPositive results to OMHLTC then affected health unitsTurn-around times for mosquito testing depended on demandPriority setting (e.g., mosquito species, etc.) was instituted
Results of mosquito testing: 2002
Mosquitoes tested to-date
29 Health units collected 44,949 mosquitoes from 35 species grouped into 6,978 pools
11 species accounted for 96% of specimens tested
Enzootic vectors: Culex pipiens, Cx. restuans or mixed Culex groups: 32.6% of total
Other species: Aedes vexans (mixed Oc. cantator): 27.8%; Coquillettidia perturbans: 15.0%; Ochlerotatus excrucians: 6.1%; Anopheles punctipennis: 3.2%; Oc. canadensis: 3.1%; Oc. triseriatus: 2.4%; Oc. trivittatus: 2.3%; An. quadrimaculatus: 2.1%; Culex salinarius: 1.4%
Mosquitoes testing positive for WN virus: 2002
SpeciesCulex pipiensCx. restuans
Mixed Culex spp.Ae. vexans
Ae. vexans-cantator An. punctipennisCq. perturbansOc. triseriatusOc. trivittatus
Culex salinariusTotal
No. mosquitoes2,9102,8479,107
10,7261,7671,4176,7531,0861,033654
38,300
No. + ve pools44 (602)31 (579)
96 (1353)14 (1131)
2 (334)2 (533)5 (564)3 (315)3 (235)
18 (136)218 (5,782)
MIR*15.110.910.51.31.11.40.72.82.9NC5.7
*Minimum infection ratio calculated as (No. of +ve pools/No. of mosquitoes tested) X 1000
Health Units with WN virus infected mosquitoes
Health UnitToronto
PeelHalton
WindsorOxford ChathamNiagara
YorkWaterloo
MiddlesexHamiltonDurham
No. + ve pools62 (28.4)40 (18.3)24 (11.0)18 (8.2)11 (5.0)10 (4.6)8 (3.7)8 (3.7)7 (3.2)7 (3.2)6 (2.7)6 (2.7)
Pools (% +)607 (10.2)1005 (4.0)539 (4.4)412 (4.4)400 (2.7)221 (4.5)312 (2.6)269 (3.0)608 (1.1)559 (1.2)295 (2.0)182 (3.3)
IPBS*YesYesYesYesYesYesYesNo YesNoYesNo
*Infected potential bridging species detected
Health Units with WN virus infected mosquitoes(continued)
Health UnitPeterborough
SimcoeBrantPerth
East. Ontario Hald. NorfolkHasting P. Ed.
No. + ve pools2 (0.9)2 (0.9)2 (0.9)2 (0.9)1 (0.5) 1 (0.5) 1 (0.5)
Pools (% +)46 (4.3)
127 (1.6)149 (1.3)288 (0.7)198 (0.5)61 (1.6)
201 (0.5)
IPBS*YesYesNoNoNoNoNo
*Infected potential bridging species detected
Permanent vs “hot spot” trapping sites
VariablesTotal mosquitoes tested
Total speciesDominant spp.
No. of pools testedNo. of +ve pools
No. of HU with +vesTiming of +ves
No. of bridge spp.No. of BS +veOverall MIR
% BS +ve
Permanent sites22,362
26Same as total
3,7685113
10/7-1/10 (late July)45
1.30.1 (0.3-0.6)
“Hot spot” sites*11,071
22Same but more Cs
1,5454914
20/6-12/9 (late Aug.)46
3.90.4 (1.0-2.2)
*Traps placed in vicinity of clusters of dead bird collections or sightings
0
10
20
30
40
50
16-Jun 30-Jun 14-Jul 28-Jul 11-Aug 25-Aug 8-Sep 22-Sep
Date collected
Num
ber
of +
ve
pool
s
Enzootic Bridging
Seasonality of infection in mosquitoes
Probable date of onset: human cases
0
10
20
30
40
50
16-Jun 30-Jun 14-Jul 28-Jul 11-Aug 25-Aug 8-Sep 22-Sep
Date collected
Num
ber
of +
ve
pool
s
Enzootic Bridging % enzootic
Seasonality of infection in mosquitoes
Probable date of onset: human cases
Proportion of pools of enzootic vectors +ve