West Nile Virus Weekly Surveillance Report

Transcription

1 West Nile Virus Weekly Surveillance Report Surveillance Week 31 (July 28 August 3, 2013) Provincial Trends 1 For week 31, there was one confirmed human case of West Nile Virus (WNV) in TOR, 19 WNV positive mosquito pools, and no horse cases reported in Ontario (Figure 1). Information from the Office of the Chief Veterinarian for Ontario has confirmed a WNV positive animal in HAL. To date, there has been one probable and one confirmed human case and 41 positive mosquito pools reported for 2013 (Tables 1 3). Aedes vexans, Coquillettidia perturbans and Culex pipiens/restuans comprised the majority of mosquitoes captured in Ontario (Table 4). Aedes and Coquillettidia are not a major vector of WNV in Ontario but are considered a biting nuisance. The majority of health units are capturing relatively high numbers of Cx. pipiens/restuans (Table 5). For week 31, WNV positive mosquito activity is lower than the activity experienced for week 31 in 2012 (Table 6). Degree day analysis shows that the majority of northern Ontario is still cool, with most of southern Ontario over 100 accumulated degree days (ADD), and areas of southwestern Ontario over 200 ADD (Figure 2). 1 Note: Mosquito data is downloaded from health unit data, via The Mosquito Database, every Monday by noon. Health unit data that is not reported by then is not included in the report. Human cases are from Ontario Ministry of Health and Long Term Care s integrated Public Health Information System (iphis) database, extracted by Public Health Ontario. Health unit site codes are available on the Definitions document. 1

2 Other Arboviruses and Mosquito Species of Interest There have been no reports of mosquitoes or horses testing positive for eastern equine encephalitis virus (EEEV). Cq. perturbans is not considered a competent vector species in the transmission of WNV due to the presence of a substantial salivary gland barrier (Sardelis et al. 2001) 2. Vector Borne Disease Activity in Other Jurisdictions WNV Canada (As of July 27, 2013): o Manitoba, Quebec, and Saskatchewan each have three positive mosquito pools 3. WNV United States (As of August 6, 2013): o Human: 99 human cases of WNV have been reported, with 38 states and the District of Columbia reporting WNV activity (e.g., birds, positive mosquito pools, humans) 4. o Mosquito: 2,840 positive pools have been found in 34 states and the District of Columbia 5. At this time, EEEV has not been reported in mosquito or horse populations in Ontario 6. In the US, there have been reports of EEEV positive mosquito pools, birds, sentinels (chickens) and horses. There have been two human cases of EEEV reported in Florida and one in Georgia 5. Additional Information Definitions: ons.pdf Accumulated Degree Days: 2 Sardelis M.R., M.J. Turell, D.J. Dohm and M.L. O Guinn Vector competence in selected North American Culex and Coquillettidia mosquitoes for West Nile Virus. Emerging Infectious Diseases, 7(6): Public Health Agency of Canada s WNV National Surveillance Report aspc.gc.ca/wnv vwn/ 4 US Centers for Disease Control and Prevention 5 US Centers for Disease Control and Prevention: 6 Ontario Ministry of Agriculture and Food: 2

3 TABLE 1. NUMBER OF POSITIVE MOSQUITO POOLS AND REPORTED CONFIRMED AND PROBABLE HUMAN CASES OF WEST NILE VIRUS, YEAR TO DATE AND YEARLY: ONTARIO, Year to Date Total* Yearly Total** Year # of Positive Pools # of Positive Humans # of Positive Pools # of Positive Humans TBD TBD Data sources: Human West Nile Virus cases: Ontario Ministry of Health and Long Term Care, integrated Public Health Information System (iphis) database, extracted by [2013/08/06]. Notes for data related to human cases: *Year to date total: counts of reported confirmed and probable cases of WNV illness with an episode date in iphis between January 1 and August 6 of each year. **Yearly total: counts of reported confirmed and probable cases of WNV illness with an episode date in iphis between January 1 and December 31 of each year. The Yearly total cells for 2013 are To Be Determined (TBD) because data for the full year are unavailable. The data only represent cases reported to public health units and recorded in iphis. Counts are subject to varying degrees of underreporting depending on the disease. iphis is a dynamic disease reporting system which allows ongoing updates to data previously entered. As a result, data extracted from iphis represent a snap shot at the time of extraction and may differ from previous or subsequent reports. Cases are reported based on "episode date. The Episode Date is an estimate of the onset date of disease for a case. In order to determine this date, the following hierarchy is in place in iphis: Onset Date > Specimen Collection Date > Lab Test Date > Reported Date. 3

4 TABLE 2. TOTAL NUMBER OF WNV POSITIVE MOSQUITO POOLS BY HEALTH UNIT. 7 MOH Region HU CDC Week Total DUR HKP PEE Central East PTC SMD TOR YRK Central East Total BRN HAL HAM Central West HDN NIA WAT WDG Central West Total EOH HPE Eastern KFL LGL OTT REN Eastern Total ALG NPS North East PQP SUD TSK North East Total North West NWR THB North West Total CHK ELG HUR South West LAM MSL OXF PDH WEC South West Total Ontario Total Blank entries indicate no pools were tested or reported. 4

5 TABLE 3. AVERAGE INFECTION RATE AND VECTOR INDEX OF CX. PIPIENS/RESTUANS BY HEALTH UNIT, WEEK 31, MOH Region Central East Central West Eastern North East North West South West Number of Sites Pools Tested Number Tested Positive Pools Average infection rate (/1000 mosq) Average vector index HU DUR HKP PEE PTC SMD TOR YRK BRN HAL HAM HDN NIA WAT WDG EOH HPE KFL LGL OTT REN NPS PQP SUD TSK NWR THB CHK ELG HUR LAM MSL OXF PDH WEC

6 TABLE 4. AVERAGE NUMBER OF MOSQUITOES PER SPECIES PER TRAP PER NIGHT BY HEALTH UNIT IN WEEK 31, MOH Region Central East Central West Eastern North East North West South West Number of Sites Cx. pipiens/restuans Ae. vexans/cantator Cq. perturbans Anopheles species Cs. melanura Culiseta species Culex species Oc. japonicus Oc. triseriatus/hendersoni HU DUR HKP PEE PTC SMD TOR YRK BRN HAL HAM HDN NIA WAT WDG EOH HPE KFL LGL OTT REN NPS PQP SUD TSK NWR THB CHK ELG HUR LAM MSL OXF PDH WEC Oc. trivittatus Oc. stimulans/excrucians Oc. broad banded Oc. canadensis Oc. black legged Oc. sollicitans Ae. cinereus Other species Background colour definitions: value < <= value < <= value < <= value 6

7 TABLE 5. AVERAGE NUMBER OF CX. PIPIENS/RESTUANS PER TRAP PER NIGHT BY WEEK AND BY HEALTH UNIT. MOH Region Central East Central West Eastern North East North West South West Total Avg. for CDC Week Weeks HU DUR HKP PEE PTC SMD TOR YRK BRN HAL HAM HDN NIA WAT WDG EOH HPE KFL LGL OTT REN ALG NPS PQP SUD TSK NWR THB CHK ELG HUR LAM MSL OXF PDH WEC Background colour definitions: value < <= value < <= value < <= value 7

8 TABLE 6. COMPARISON OF NUMBER OF POSITIVE MOSQUITO POOLS AND POSITIVE VECTOR SPECIES IN WEEK 31 TO PREVIOUS YEARS IN WEEK 31 Year # of Positive Pools # of HUs Positive Vector Species Ae. vexans vexans, Ae. vexans/cantator, An. punctipennis, Cq. perturbans, Culex species,cx. pipiens/restuans, Cx. salinarius Cx. pipiens/restuans Culex species, Cx. pipiens/restuans Cq. perturbans,cx. pipiens/restuans, Oc. sollicitans Ae. vexans vexans, Cq. perturbans, Cx. pipiens/restuans, Oc. trivittatus Cx. pipiens/restuans Cx. pipiens/restuans N/A Cx. pipiens/restuans Ae. vexans vexans, An. quadrimaculatus, Cx. pipiens/restuans, Oc. japonicus, Oc. triseriatus Cx. pipiens/restuans Cx. pipiens/restuans 8

9 FIGURE 1. LOCATION OF POSITIVE MOSQUITO POOLS IN WEEK 31,

10 FIGURE 2. ACCUMULATED DEGREE DAY MAP FOR ONTARIO (UP TO WEEK 31, 2013). 10