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

6Bridge -1

Enzootic –0

# of HU -1

6Bridge -0

Enzootic –2

# of HU -1

8Bridge -0

Enzootic –1

# of HU -1

12Bridge -0

Enzootic –1

# of HU -2

19Bridge -0

Enzootic –1

# of HU -2

26Bridge -1

Enzootic –8

# of HU -7

26Bridge -4

Enzootic –39

# of HU -11

26Bridge -1

Enzootic –11

# of HU -12

29Bridge -6

Enzootic –9

# of HU -13

30Bridge -12

Enzootic –17

# of HU -13

33Bridge -12

Enzootic –21

# of HU –14