Mosquito surveillance in Ontario: 2002 Infection in mosquitoes West Nile virus 2003 Planning Workshop, Toronto, November 7, 2002 Robbin Lindsay, Health Canada

West Nile Virus Transmission Cycle Avian reservoirs VIRUS - Dead - end hosts Mosquito vectors Culex species mainly Spill-over via bridging vectors VIRUS Enzootic amplification

Mosquitoes “Infected” with WN virus – USA Aedes vexans-1 Culex pipiens-8 Cx. spp or mixed Aedes 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 2001 Aedes 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 cont’d Ochlerotatus 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 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 sites Moderate number of traps set at permanent sites Operated on a weekly basis Collected mosquitoes shipped to Brock Sub-samples of mosquitoes identified to species and pertinent information reported to health units Program 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 sites CDC light traps set at sites in vicinity of dead bird collection(s)/sightings Traps operated weekly & for as long as feasible Collected mosquitoes shipped to Brock University for identify,sorting, and most mosquito pools shipped to Winnipeg for eventual testing Positive results to OMHLTC then affected health units Turn-around times for mosquito testing depended on demand Priority 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 Species Culex pipiens Cx. restuans Mixed Culex spp. Ae. vexans Ae. vexans-cantator An. punctipennis Cq. perturbans Oc. triseriatus Oc. trivittatus Culex salinarius Total No. mosquitoes 2,910 2,847 9,107 10,726 1,767 1,417 6,753 1,086 1, ,300 No. + ve pools 44 (602) 31 (579) 96 (1353) 14 (1131) 2 (334) 2 (533) 5 (564) 3 (315) 3 (235) 18 (136) 218 (5,782) MIR* NC 5.7 *Minimum infection ratio calculated as (No. of +ve pools/No. of mosquitoes tested) X 1000

Health Units with WN virus infected mosquitoes Health Unit Toronto Peel Halton Windsor Oxford Chatham Niagara York Waterloo Middlesex Hamilton Durham No. + ve pools 62 (28.4) 40 (18.3) 24 (11.0) 18 (8.2) 11 (5.0) 10 (4.6) 8 (3.7) 7 (3.2) 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* Yes No Yes No Yes No *Infected potential bridging species detected

Health Units with WN virus infected mosquitoes (continued) Health Unit Peterborough Simcoe Brant Perth East. Ontario Hald. Norfolk Hasting P. Ed. No. + ve pools 2 (0.9) 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* Yes No *Infected potential bridging species detected

Permanent vs “hot spot” trapping sites Variables Total mosquitoes tested Total species Dominant spp. No. of pools tested No. of +ve pools No. of HU with +ves Timing of +ves No. of bridge spp. No. of BS +ve Overall MIR % BS +ve Permanent sites 22, Same as total 3, /7-1/10 (late July) ( ) “Hot spot” sites* 11, Same but more Cs 1, /6-12/9 (late Aug.) ( ) *Traps placed in vicinity of clusters of dead bird collections or sightings

Seasonality of infection in mosquitoes Probable date of onset: human cases

Seasonality of infection in mosquitoes Probable date of onset: human cases Proportion of pools of enzootic vectors +ve

6 Bridge -1 Enzootic –0 # of HU -1

6 Bridge -0 Enzootic –2 # of HU -1

8 Bridge -0 Enzootic –1 # of HU -1

12 Bridge -0 Enzootic –1 # of HU -2

19 Bridge -0 Enzootic –1 # of HU -2

26 Bridge -1 Enzootic –8 # of HU -7

26 Bridge -4 Enzootic –39 # of HU -11

26 Bridge -1 Enzootic –11 # of HU -12

29 Bridge -6 Enzootic –9 # of HU -13

30 Bridge -12 Enzootic –17 # of HU -13

33 Bridge -12 Enzootic –21 # of HU –14