Final Report of the. BWP Consulting Inc.

Transcription

1 Final Report of the Regional District of the North Okanagan West Nile Virus Risk Reduction Program, 2011 Report prepared December, 2011 By Burke Phippen, R..P.Bio Cheryl Phippen, RN,, BSc BWP Consulting Inc.

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3 TABLE OF CONTENTS Table of Contents... ii List of Tables... iii List of Figures... iii Executive Summary Introduction History of West Nile Virus in North America West Nile Virus Life Cycle Surveillance in British Columbia Overview of Grant Funding and Completed Activities Public Education Advocating Personal Protection Reducing Mosquito Larval Development Sites Understanding The Disease and Its Effects on Humans Adult Mosquito Surveillance Method of Adult Surveillance Results of Adult Mosquito Surveillance Crystal Sands Resort, near Mara Lake Community of Kingfisher South end of Mabel Lake (2945 Lumby-Mabel Lake Road) Twin Lake Road near Enderby Summary of Significant Mosquito Species Found in the RDNO Summary of West Nile Virus Vector Competency for BC Mosquito Species Biology of Major Mosquito Species Collected in the RDNO in Anopheles Species Anopheles earlei Anopheles freeborni Anopheles punctipennis Aedes and Ochlerotatus Species Aedes cinereus Aedes vexans Ochlerotatus canadensis Ochlerotatus communis Ochlerotatus dorsalis Ochlerotatus excrucians Ochlerotatus fitchii Ochlerotatus hendersoni Ochlerotatus increpitus Ochlerotatus sierrensis Ochlerotatus spencerii (both variants) Ochlerotatus sticticus Coquillettidia Species Coquillettidia perturbans Culex species Culex pipiens BWP Consulting Inc. Page ii

4 Culex tarsalis Culex territans Culiseta Species Culiseta incidens Culiseta inornata Culiseta morsitans Prevention of West Nile Virus Through Mosquito Abatement Larval Habitat Mapping and Larval Mosquito Surveillance Larviciding Summary Recommendations References Appendix A: Summary of Potential Larval Development Sites Identified From Appendix B: Summary of all Monitoring and Larviciding Activities in the RDNO, All treatments were made with Aquabac 200G LIST OF TABLES Table 1. Numbers of adult mosquitoes captured in a CDC black-light trap set at Crystal Sands Resort near Mara Lake, Table 2. Numbers of adult mosquitoes captured in a CDC black-light trap set at 1166 N. Mabel Lake Road in the Community of Kingfisher, Table 3. Numbers of adult mosquitoes captured in a CDC black-light trap set near the south end of Mabel Lake, Table 4. Numbers of adult mosquitoes captured in a CDC black-light trap set at 206 Twin Lakes Road in the Tween Lake area, Table 5. Mosquito species in British Columbia identified as potential human West Nile Virus Vectors (Belton, 2007) Table 6. Summary of Larval Development Site Locations and Larvicide Usage in the RDNO in LIST OF FIGURES Figure 1. Base 14.3 C degree-day map for the Southern Interior of BC, 2010 (from BCCDC, 2010)... 5 Figure 2. BWP Consulting Inc. banners for public education displays Figure 3. CDC mosquito black-light trap with dry ice canister BWP Consulting Inc. Page iii

5 EXECUTIVE SUMMARY Public education, mosquito surveillance, and vector larval mapping and larval control were conducted in the Regional District of the North Okanagan (RDNO) with grant funding from the Union of British Columbia Municipalities. BWP Consulting Inc. has been contracted to conduct all West Nile virus (WNV) activities under this grant funding. This is the final report for the West Nile Virus Risk Reduction Program in Public education was offered as a West Nile Virus information booth that was set up at the Interior Provincial Exhibition in Armstrong (August 31 st to September 4 th ). The display included banners, samples of live and preserved mosquito larvae, and a number of informational brochures. In addition, open houses were hosted in the communities of Coldstream, Enderby, Kingfisher and Lumby. A PowerPoint presentation was given, and residents were given the opportunity to ask questions. Finally, the RDNO pooled some of their funding with funding from the Regional District of Central Okanagan and Regional District of Okanagan-Similkameen and purchased radio, television and CastaNet advertising with WNV prevention messaging. Four adult mosquito trapping sites were selected by BWP Consulting Inc within in the RDNO. CDC black-light traps were initially set at these locations during the week of June 17 th. Samples were collected once per week for eight or nine weeks from each trap. A total of 3,314 mosquitoes representing 22 different mosquito species were captured in these four traps. The flood-water species, Aedes vexans and Ochlerotatus sticticus, were the commonest species captured in the traps and these species are causing a significant nuisance in some areas of the Regional District, especially Mara Lake and Mabel Lake. The two primary vectors of WNV, Culex pipiens and Culex tarsalis, were found in varying numbers in the trapping locations. Culex tarsalis appeared in highest numbers in the trap located near Mara Lake and Culex pipiens appeared in significant numbers at the Mara Lake and Tween Lake sites. A total of 2, kg of Aquabac 200G (PCP 26863) (Bacillus thuringiensis var israelensis) was applied by helicopter, hand, or backpack blower to ha of standing water containing mosquito larvae. Larvae of Culex and Culiseta mosquitoes were targeted during all larviciding treatments. BWP Consulting Inc. Page 1

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7 1.0 INTRODUCTION 1.1. HISTORY OF WEST NILE VIRUS IN NORTH AMERICA West Nile Virus (WNV) is a new and emerging disease in North America. It was first detected in New York City in the summer of 1999, after the deaths of countless American Crows (Corvus brachyrhynchos). That summer, 62 human cases of WNV were identified in New York, resulting in seven human deaths (CDC, 2007). At that time, it was unknown if the outbreak would be an isolated event, and there were questions surrounding the ability of the virus to survive North America s winters. The following spring, these questions were answered as the virus reappeared and rapidly started its migration across the continent. For the next two years, viral activity was confined primarily to the east coast of the U.S. and Canada, but in 2002 it advanced quickly across the continent and in 2003 there were large outbreaks in the Canadian prairies. In 2004 and 2005, activity increased in California and Oregon. In August of 2009, the first human, non-travel-related, cases of WNV were found in the Okanagan, signaling the arrival of the disease in BC. By October of 2009, two locally-acquired human cases were reported in BC, as well as two horses and ten mosquito pools. In 2010, one person in the central Okanagan tested positive for WNV, and five birds from the central Okanagan tested positive for the virus. There was one equine case of WNV confirmed in the Central Okanagan in The apparent reduction in activity this year may be due to the fact that average temperatures were well below normal for much of the summer, resulting in fewer degree-days and therefore reduced numbers of generations of vector mosquitoes, and reduced incubation time for the virus (see Section 1.2). Across Canada it was a relatively quiet year, with 80 human cases (all in Ontario and Quebec) reported by mid-october, including two deaths. In the US, 555 human cases had been reported to the CDC by late-october 2011, including 34 deaths (CDC, 2011) WEST NILE VIRUS LIFE CYCLE WNV is primarily a disease affecting birds, especially those of the Corvid Family (crows, ravens, jays, and magpies). It is transmitted from host to host through the bite of particular species of mosquitoes. While a number of mosquito species are considered BWP Consulting Inc. Page 3

8 potential vectors (see Section 4.0 ) it is widely accepted that the two primary species of concern in Western Canada are Culex tarsalis and Culex pipiens. These species play different roles in the transmission of the virus, but both can be considered equally important. When a bird is bitten by an infected mosquito, the mosquito injects the virus into the bird. The immune systems of some bird species are able to fight the virus and do not allow the virus to significantly replicate. Members of the Corvid family, however, are especially susceptible to the virus; inside of these birds, the virus replicates rapidly and is soon present in high concentrations in the blood. When other mosquitoes bite the infected bird, they contract the virus and become infected themselves; approximately 9-12 days later, the newly infected mosquitoes are able to transmit the virus when they next bite. In British Columbia, as in most of western Canada and the United States, the species of mosquito known as Culex pipiens is responsible for amplifying the virus in the bird population. This species of mosquito feeds almost exclusively on birds, and will take numerous blood meals in a summer, so it has a number of opportunities to bite and thus an increased probability of biting an infected bird and subsequently transmitting the virus to a new host. Each time a female feeds, she then develops a brood of eggs and lays it on stagnant water. With each successive generation, the number of individual mosquitoes grows exponentially, simultaneously increasing the chance of a Culex pipiens feeding on an infected bird and communicating the virus. Populations of this insect peak in mid- to late- August, as do the number of cases of WNV in both birds and humans. Culex pipiens are common in urban settings and will readily breed in common waterholding containers such as bird-baths, old tires, eaves troughs, wheelbarrows, etc. This species can also breed in exceptionally large numbers in urban catch basins. Once the virus has increased, or amplified, in the bird populations, the risk of spillover into other hosts increases. A second species of mosquito, Culex tarsalis, is most often implicated in this bridging of the virus from bird populations to mammals. This species of mosquito also has multiple generations each summer and takes numerous blood meals Some recent Canadian studies suggest that the number of generations that can be produced in a summer is related to the number of degree-days above 14.3 C. The BWP Consulting Inc. Page 4

9 Regional District of the North Okanagan West Nile Virus Program, 2011 BC Center for Disease Control has produced a degree-day map of BC and has found that many areas of the Okanagan, Thompson-Nicola and Fraser valleys including the RDNO fall in an annual degree-day range of degree-days (Figure 1) ). This translates into a potential for 5-7 generations (or more) of Culex tarsalis per summer. In the early summer, Culex tarsalis plays a significant role alongside Culex pipiens in the amplification of the virus, and later in the summer becomes a significant vector of WNV to humans. What is different about this species is its willingnesss to take blood meals from bird hosts as well as mammal hosts, especially later in the summer. Therefore, if an individual of this species takes a meal from an infected bird, it may during a subsequent feeding transmit the virus to a human, horse, or other non-aviann host. In humans, the virus rarely causess serious illness; however, in approximately 20% of infections, humans can experience flu-likon of the brain and/or spinal cord (a condition called meningioencephalitis), whichh can occasionally resultt in symptoms. In less than 1% of human cases, WNV can cause inflammatio death. Figure 1. Base 14.3 C degree-day map for the Southern Interior of BC, 2010 (from BCCDC, 2010) BWP Consulting Inc. Page 5

10 1.3. SURVEILLANCE IN BRITISH COLUMBIA The British Columbia Centre for Disease Control (BCCDC) and health authorities have been anticipating cases of WNV in British Columbia since the summer of In that year, the province began collecting and testing corvids (crows, jays, ravens, and magpies) for the presence of WNV. They also began using CDC light traps and gravid traps to attract and collect mosquitoes which were then ground up and tested for the presence of the virus. In the last nine years, 6,618 corvids have been collected and tested, and 1,823,746 mosquitoes were trapped. All of the Culex female mosquitoes were separated and tested as well as many batches of females from other genera (BCCDC, 2010). In late August 2009, the first human case of locally-acquired (non-travel-related) WNV was discovered, along with a number of mosquito pools also found to contain the virus. In 2010, no mosquito pools tested positive for the virus, but there were five positive birds and one confirmed human case of WNV in BC. In 2011, in an effort to stay ahead of the virus, a number of traps were deployed by the Interior Health Authority in the North Okanagan in the municipalities of Armstrong, Spallumcheen, Enderby, and Coldstream and in the Regional District near Mara Lake. However, none of the mosquitoes collected in these traps tested positive for the virus in In 2011, no humans, mosquito pools, or birds tested positive for the virus anywhere in the province, but there was one equine case reported in the Central Okanagan OVERVIEW OF GRANT FUNDING AND COMPLETED ACTIVITIES This spring, the Ministry of Healthy Living and Sport offered grant funding to Municipalities and Regional Districts. Local governments were asked to review their risk assessments (prepared in 2010) and submit a budget for WNV Mitigation in RDNO applied for and received $74, and BWP Consulting Inc. was contracted to provide mosquito control, WNV education and adult mosquito surveillance for the Regional District. This is the final report of all activities completed under this contract in 2011, including a list of recommendations for future and further work (at the conclusion of this report). BWP Consulting Inc. Page 6

11 2.0 PUBLIC EDUCATION One of the most effective means of educating people is to meet them face to face. Public booths and presentations offer the opportunity for our staff to engage residents in discussion regarding questions and concerns that residents may have about WNV. Our educational material focuses on personal protection from West Nile virus and reduction of mosquito larval habitat around the home. Our company has a WNV information booth that includes banners with information on mosquitoes and WNV (Figure 1). Included with this booth are a number of WNV brochures and handouts as well as a display of live mosquito larvae. The display was set up at the Interior Provincial Exhibition in Armstrong (August 31 st to September 4 th ). In addition, an open house was hosted in each of the communities of Coldstream, Enderby, Kingfisher and Lumby. The open house dates were advertised in local newspapers and Cheryl Phippen, BSc, attended the events and gave a PowerPoint presentation which outlined the mosquito control program and risk of WNV. Finally, a portion of the funding was pooled with funding from the Regional District of Central Okanagan and the Regional District of Okanagan-Similkameen to purchase radio and television advertising that spanned the Okanagan Valley as well as CastaNet internet advertising. BWP Consulting Inc. Page 7

12 Regional District of the North Okanagan West Nile Virus Program, 2011 Figure 2. BWP Consulting Inc. banners for public education displays ADVOCATING PERSONAL PROTECTION An important part of WNV prevention includes educating the public on how to avoid being bitten by mosquitoes. Culex mosquitoess usually bite at dawn and at dusk, and so special precautions should be taken at these times to avoid being bitten. Individuals should wear long-sleeved, tight-knitted shirts and long pants during these prime biting times; also, active movement such as jogging or cycling rather than standing, sitting, or walking will reduce one s chancee of being bitten. Peoplee should ensure that the screens on their windows and doors are in good repair as Culex species will find the tiniest holes through which they can enter dwellings. When people are active outside during periods of high mosquito activity, repellents containing DEET should be applied to skin and clothing according to the label. BWP Consulting Inc. Page 8

13 2.2. REDUCING MOSQUITO LARVAL DEVELOPMENT SITES Since Culex and Culiseta mosquitoes will both readily breed in water-holding containers, homeowners are encouraged to reduce standing water around their homes. Water-holding items such as plastic containers, wheelbarrows, rain barrels and swimming pool covers should be emptied or turned upside-down. Eaves troughs should be cleared of debris to ensure that they are draining properly. Bird baths and children s wading pools should be dumped and filled with fresh water twice per week. Pumps should be used in ornamental ponds to circulate water (thus drowning larvae). Attempts should be made to educate the public and to enable people to identify mosquito larvae. Individuals should be encouraged to recognize the larvae and to remove the larvae from whatever container or pond which the larvae may occupy (many people mistake mosquito larvae for worms, tadpoles, or minnows) UNDERSTANDING THE DISEASE AND ITS EFFECTS ON HUMANS There are a number of misconceptions about WNV and its effects on humans. Extensive media coverage has served to induce undue levels of fear in a significant portion of the public. It is important for the public to be properly informed about the actual risks associated with WNV. While many people think of the extreme cases of human illness such as paralysis or death when they hear the words West Nile virus, the reality is that the majority of people who contract the disease an estimated eighty percent do not develop any symptoms, and unless tested, would probably never know that they had ever contracted the virus. Of the remaining twenty percent, most will develop West Nile Fever, which is characterized by flu-like symptoms; typically, about 1.0% of people infected with WNV develop serious infections of the central nervous system which could lead to long-term health effects or even death. 3.0 ADULT MOSQUITO SURVEILLANCE Adult mosquito trapping was initiated on June 17 th and ended August 26 th, with between eight and nine samples collected at each of the four sampling locations. The purpose of mosquito trapping is to determine the mosquito species composition and abundance. Since only a few mosquito species are capable of transmitting WNV, it is important to know which species are present in a given area, and to know the size of their populations to determine a level of risk for that area. BWP Consulting Inc. Page 9

14 CDC mosquito black-light trap with dry ice canister. Regional District of the North Okanagan West Nile Virus Program, METHOD OF ADULT SURVEILLANCE Adult mosquitoes were captured with the use of four CDCC black-light mosquito traps (Figure 3). The CDC traps were originally designed to be powered by 6V batteries whichh operate the traps for hours. However, inn order to reduce the amount of time required to maintain the traps, they have been adapted to use 110V power sources by wiring them to 6V adaptors. This allows the traps to be plugged in to available power sources. The CDCC traps are equipped with timers that activate the traps from dawn to dusk (when mosquitoes are most active). At dusk, a fluorescent black-light and a small fan are switched on. Mosquitoes are attracted to the light and, when they come near the fan, they are sucked into a collecting jar. In addition, when the technician visits the traps each week, she places dry ice in a small cooler hanging next to the trap. The dry ice sublimates into CO 2 which is a powerful mosquito attractant. Trap contents are collected once per week. There were four mosquito traps, with one located in each of the following areas: (1) near Mara Lake; (2) in the Community of Kingfisher; (3) at the south end of Mabel Lake; and (4) near Tween Lakes. Figure 3. BWP Consulting Inc. Page 10

15 3.2. RESULTS OF ADULT MOSQUITO SURVEILLANCE The following is a discussion of the results from the adult mosquito trapping at each trapping location in the RDNO over the course of the summer. Results are summarized in tables following each description Crystal Sands Resort, near Mara Lake A CDC black-light trap was set at the Crystal Sands Resort near Mara Lake on Jun 17 th, 2011, and operated until August 26 th, 2011, with nine sets of samples collected during that period. A total of 1,683 mosquitoes were captured, down from the 2,795 captured in 2010, the 4,908 mosquitoes captured in 2009, the 5,491 mosquitoes captured in 2008, and the 10,930 mosquitoes captured in As in previous years, Aedes vexans, a significant pest mosquito, was the predominant species captured, comprising 58% of the total trap count. Aedes vexans can be ferocious biters, but are rarely implicated in WNV transmission. The two key WNV vector in Western Canada, Culex tarsalis and Culex pipiens, were present. Culex pipiens was found in relatively low numbers (17 specimens), while Culex tarsalis was found in abundance (350 specimens). Numbers of Culex tarsalis were up considerably from 2010, when only 28 individuals were caught, but similar in number to the years prior that, when 235 individuals were captured in 2009, 931 specimens were captured in 2008, and 251 specimens were caught in BWP Consulting Inc. Page 11

16 Table 1. Numbers of adult mosquitoes captured in a CDC black-light trap set at Crystal Sands Resort near Mara Lake, Date (2011) Species Jun Jun Jul Jul Jul Aug Aug Aug Aug Total Aedes vexans Anopheles earlei Anopheles freeborni Anopheles punctipennis Coquillettidia perturbans Culex pipiens Culex tarsalis Culex territans 1 1 Culiseta incidens Culiseta inornata Culiseta morsitans Ochlerotatus communis 3 3 Ochlerotatus dorsalis 1 1 Ochlerotatus increpitus Ochlerotatus spencerii var spencerii 1 1 Ochlerotatus sticticus Mosquito unidentifiable* Ochlerotatus male unidentified** Total Number Captured ,683 No of males (out of total above) *Specimen too damaged to identify **Ochlerotatus males can be difficult to identify BWP Consulting Inc. Page 12

17 Community of Kingfisher A CDC black-light trap was set at 1166 N. Mabel Lake Road in the community of Kingfisher on June 17 th (Table 2). Over the eight weeks of sampling, 401 specimens from nine species were captured, down considerably from the 2,219 specimens captured in 2010, the 865 specimens captured in 2009, the 2,840 specimens caught in 2008 and the 1,299 specimens caught in The primary species captured were Ochlerotatus sticticus and Aedes vexans (together accounting for 89% of the mosquitoes captured). These species are singlegeneration nuisance mosquitoes and are not considered to be a significant vector of WNV. There were low numbers of the primary WNV vector species, Culex tarsalis, captured at this site Table 2. Numbers of adult mosquitoes captured in a CDC black-light trap set at 1166 N. Mabel Lake Road in the Community of Kingfisher, Date (2011) Species Jun Jun Jul Jul Jul Aug Aug Aug Total Aedes cinereus 1 1 Aedes vexans Anopheles punctipennis Coquillettidia perturbans Culex tarsalis Culiseta inornata Ochlerotatus fitchii 1 1 Ochlerotatus increpitus 2 2 Ochlerotatus sticticus Mosquito unidentifiable* Ochlerotatus male unidentified** Total Number Captured No of males (out of total above) *Specimen too damaged to identify **Ochlerotatus males can be difficult to identify No mosquitoes seen BWP Consulting Inc. Page 13

18 South end of Mabel Lake (2945 Lumby-Mabel Lake Road) A CDC black-light trap was set at 2945 Lumby-Mabel Lake Road near the south end of Mabel Lake on June 17 th (Table 3). Over the course of the summer, 500 specimens from sixteen species were captured, down slightly from the 653 mosquitoes from fifteen species captured in 2010 and down considerably from the 3,282 mosquitoes captured in 2009, the 2,393 specimens caught in 2008 and the 45,000 mosquitoes captured in As in the past, the majority of the specimens collected were Aedes vexans and Ochlerotatus sticticus (together making up 81% of the total catch). Both of these insects are ferocious biters and severe nuisance mosquitoes, and, although they are considered low risk for transmitting WNV, they both show up on Peter Belton s list of potential WNV vectors. These two species will develop together in the same larval development habitat following a large flooding event, such as we see annually with the spring freshet of the Shuswap River. Culex tarsalis, the most significant WNV vector in Western Canada, was found in moderate numbers (29 specimens), and the other significant vector, Culex pipiens, was not found. BWP Consulting Inc. Page 14

19 Table 3. Numbers of adult mosquitoes captured in a CDC black-light trap set near the south end of Mabel Lake, Date (2011) Species Jun Jun Jul Jul Jul Aug Aug Aug Total Aedes cinereus 2 2 Aedes vexans Anopheles earlei 2 2 Anopheles freeborni 1 1 Anopheles punctipennis 3 3 Culex tarsalis Culiseta incidens 1 1 Culiseta inornata Ochlerotatus canadensis 2 2 Ochlerotatus excrucians 2 2 Ochlerotatus fitchii Ochlerotatus hendersoni 1 1 Ochlerotatus increpitus Ochlerotatus spencerii var spencerii Ochlerotatus sticticus Mosquito unidentifiable* Ochlerotatus male unidentified** Total Number Captured No of males (out of total above) *Specimen too damaged to identify **Ochlerotatus males can be difficult to identify No mosquitoes seen Twin Lake Road near Enderby A CDC black-light trap was set at 206 Twin Lakes Road near Tween Lakes on June 17 th (Table 4). The trap count for the nine sampling weeks was 730 specimens from 17 species, up somewhat from the 370 specimens from 14 species captured in 2010 but down from the 1,341 specimens captured in 2009 and the 1,587 specimens caught in 2008 and up slightly from the 695 mosquitoes captured in Unlike previous years, when the majority of the mosquitoes captured at this site were Coquillettidia perturbans, this year the primary species was the nuisance mosquito Aedes vexans (38% of mosquitoes captured). There were still high numbers of Coquillettidia perturbans (175 specimens, or 24% of the catch). The key WNV vector species Culex tarsalis and Culex pipiens were present in moderate numbers (67 specimens and 50 specimens, respectively). BWP Consulting Inc. Page 15

20 Table 4. Numbers of adult mosquitoes captured in a CDC black-light trap set at 206 Twin Lakes Road in the Tween Lake area, Date (2011) Species Jun Jun Jul Jul Jul Aug Aug Aug Aug Total Aedes cinereus 1 1 Aedes vexans Anopheles earlei 1 1 Anopheles freeborni Anopheles punctipennis Coquillettidia perturbans Culex pipiens Culex tarsalis Culex territans 1 1 Culiseta inornata Culiseta morsitans 1 1 Ochlerotatus canadensis 1 1 Ochlerotatus excrucians Ochlerotatus increpitus Ochlerotatus sierrensis Ochlerotatus spencerii var spencerii 1 1 Ochlerotatus sticticus Mosquito unidentifiable* 4 4 Total Number Captured No of males (out of total above) **Ochlerotatus males can be difficult to identify 4.0 SUMMARY OF SIGNIFICANT MOSQUITO SPECIES FOUND IN THE RDNO A total of 3,314 adult mosquitoes representing 22 species from all six of BC s genera were captured in four light traps in the RDNO (Table 1 to Table 4). This is down from the 6,037 mosquitoes representing 20 species captured in 2010, the 10,396 adult mosquitoes representing 20 species captured in 2009, the 12,311 mosquitoes captured in 2008 and the 58,074 mosquitoes caught in This is quite remarkable given the extent of the flooding seen in 2011, and is likely due in part to comprehensive larviciding, especially in the Mabel area where a helicopter was used to cover a large area of habitat. The majority of the mosquitoes captured were of the flood-water type (Aedes and Ochlerotatus genera), and the most common species were Aedes vexans and Ochlerotatus sticticus. In most cases, these mosquitoes are not considered a major problem in terms of WNV, but they can pose serious problems as persistent and ferocious nuisance mosquitoes. BWP Consulting Inc. Page 16

21 Both of the most important species for transmitting WNV, Culex tarsalis and Culex pipiens, were found in the RDNO. The site with the highest number of Culex tarsalis mosquitoes (Mara Lake, with 350 specimens), had considerably more of this species than in 2010 when only 28 specimens were captured, but had similar numbers to those captured in 2008 or 2009, when 931 individuals and 235 individuals, respectively, were captured. Other species that may have the ability to be WNV vectors, although to a much lesser degree, have also been present in light traps, including: Aedes cinereus, Aedes vexans, Anopheles punctipennis, Anopheles earlei, Culiseta incidens, Ochlerotatus canadensis, Ochlerotatus dorsalis, Ochlerotatus sierrensis, Culiseta inornata, and Coquillettidia perturbans (Belton, 2007). Culex pipiens and Culex tarsalis tend to show up in increasing numbers in late July and August. These mosquitoes have multiple generations in a summer and, by August populations are generally at their peaks. The population of floodwater mosquitoes (Aedes and Ochlerotatus) tend to peak between mid-june and mid-july, and their numbers decrease as the summer progresses because their eggs are laid in the soil and hatch when they become wet with the spring snow-melt and freshets. The following Section (Section 5.0 ) contains an overview of potential WNV vector mosquitoes as predicted by Peter Belton, PhD, Mosquito Expert from Simon Fraser University. Section 6.0 contains short summaries of the biology of most of the genera and mosquito species captured in the RDNO this summer. 5.0 SUMMARY OF WEST NILE VIRUS VECTOR COMPETENCY FOR BC MOSQUITO SPECIES Although it is widely accepted that Culex pipiens and Culex tarsalis are the two primary vectors of WNV in western Canada, Peter Belton, a retired professor from Simon Fraser University and an expert in the field of mosquito biology, has assembled a list of potential WNV vectors that are present in British Columbia, and has assigned them vector competency ratings (Table 5). It is important to understand the factors that must be met for a mosquito to be considered a good WNV vector. First, the mosquito must be willing to bite birds. In a natural setting, WNV can only be contracted from birds, as other hosts contain BWP Consulting Inc. Page 17

22 insufficient amounts of the virus to be infectious. Next, the mosquito must have the correct receptors in its gut to accept the virus and transfer it into the mosquito s circulatory system. Later, the mosquito must be able to transfer the virus from its circulatory system into its salivary glands so it can inject the virus during its next blood meal. This brings us to the next point: a mosquito must be willing to take more than one blood meal in its life, and must be a long-lived species, since it can take up to two weeks for the virus to be transported to a mosquito s salivary glands and render that mosquito infectious. Another factor is the temporal distribution of a species: WNV tends to be at its worst in July and August, so the vector must be present in high numbers during this time of the year. Finally, in order to be a human vector, the mosquito must not only be willing to bite birds, but it must also be willing to bite humans. With all of these factors considered, Culex tarsalis should be identified as the most significant concern as a human vector in British Columbia and Culex pipiens as the most significant vector within bird populations. However, Peter Belton has included 21 British Columbian species in his list, based on a United States Centre for Disease Control list of species that has tested positive for the virus (indicated by a P in the Table 5) and a system of ranking discussed in Turell et al. (2005). Peter Belton has assigned mosquitoes a relative competency ranking of + to ++++ (Table 5). Species not included in the study by Turell et al, (2005), but still given consideration by Peter Belton based on their ability to transmit other viruses, are ranked with a question mark. BWP Consulting Inc. Page 18

23 Table 5. Mosquito species in British Columbia identified as potential human West Nile Virus Vectors (Belton, 2007). Potential Vectors in BC Positive (P) Competence (+) Feeding preference, biology Culex tarsalis P ++++ Birds, mammals 3 Ochlerotatus togoi ++++? Birds, mammals 4 Culex pipiens P +++ Mostly birds 3 Coquillettidia perturbans P + Birds, mammals 2 Culiseta inornata P +++ Birds, mammals 3 Culiseta morsitans P ++? Mostly birds 5 Ochlerotatus dorsalis P +++ Mammals, occasionally birds 1 Ochlerotatus melanimon P +++ Mammals, occasionally birds 1 Ochlerotatus canadensis P ++ General feeder 1 Ochlerotatus sierrensis + Mammals 4 Ochlerotatus sticticus P +? Mammals 1 Aedes vexans P ++ Mostly mammals 1 Aedes cinereus P +? Birds? mammals 1 Anopheles punctipennis P +? Mammals, birds? 3 Anopheles earlei P +? Mammals, birds? 3 Ochlerotatus hendersoni +++? Birds? mammals 1 Culiseta incidens ++? Mostly mammals 3 Ochlerotatus fitchii P 0? Mostly mammals 1 Ochlerotatus provocans P 0? Mostly mammals? 1 Culex territans P 0? Mostly amphibia 3 Culiseta impatiens P 0? Mostly mammals 5 1 Eggs overwinter, one or two generations/year 2 Larvae overwinter, one generation/year 3 Females overwinter, several generations/year 4 Eggs and larvae overwinter, several generations/year 5 Females overwinter, one generation/year 6.0 BIOLOGY OF MAJOR MOSQUITO SPECIES COLLECTED IN THE RDNO IN ANOPHELES SPECIES Anopheles species of mosquitoes are quite different in appearance than other mosquitoes, with narrow wings and long slender bodies. When standing, their hind legs are well elevated from their bodies, distinguishing them from other mosquito species. Because of these anatomical differences, they have been placed in their own subfamily. Females overwinter as adults and hide in culverts, bridges, inside eaves, and in the roofs of sheds (Belton, 1983). In urban areas, they hibernate in burrows, caves, hollow trees, and other sheltered places (Belton, 1983). They prefer fresh, clean water, and they lay eggs singly among vegetation at the edges of water bodies. Anopheles species have been implicated in the transmission of malaria, and were no doubt involved in malarial BWP Consulting Inc. Page 19

24 outbreaks in Canada in the 19 th century. Three species of Anopheles were captured in the RDNO in Anopheles earlei Female Anopheles earlei overwinter in buildings, caves, and mammal burrows, as well as in hollow logs and in tree trunks (Wood et al. 1979). When they overwinter, they are not blood-fed and have not laid eggs, but feed soon after leaving hibernation (Wood et al. 1979). In the southern part of the province, they are capable of two generations per year, weather permitting. The species is widely distributed throughout BC, and the females are vicious biters, able to attack in weather so cold that other mosquitoes are not capable of flying (Belton, 1983). Because of their ferocity, they can be localized pests when present in significant numbers. Belton (2007) gives this species a vector competency rating of + (Table 5) Anopheles freeborni Anopheles freeborni females overwinter in various sites including talus slopes, abandoned mines and buildings, and root cellars. They tend to breed in pools and sloughs formed by creeks, large marshes and irrigated pastures in Washington (Wood et al. 1979). In California, rice fields are a significant breeding site (Wood et al. 1979). They are capable of rearing in slightly saline water (salinity as much as 5%). It is potentially an effective vector of malaria and has been found naturally infected with Western Equine Encephalitis, but is never found in high enough concentrations to be important for disease transmission. Belton (2007) does not include this species on his list of vector competency Anopheles punctipennis Anopheles punctipennis is the only anopheline found on Vancouver Island to date, and is fairly widespread throughout the province. Larvae are found in almost any kind of standing water (Belton, 1983), and there are generally two or three generations annually (Wood et al. 1979). Females bite humans freely after dark and are persistent in entering houses, but are not found in high enough concentrations to be a concern as a disease vector (Belton, 2983). Belton (2007) gives this species a vector competence rating of +. BWP Consulting Inc. Page 20

25 6.2. AEDES AND OCHLEROTATUS SPECIES Until recently, all of the floodwater species (i.e. laying their eggs on moist soil rather than on the water s surface) of mosquitoes in BC were classified as Aedes, but a number of species have now been reclassified into the genus Ochlerotatus. However, the life cycle and the physiology of Aedes and Ochlerotatus species are similar. Aёdes is the Greek word for disagreeable (Belton, 1983), and is an accurate reflection of these species in terms of both numbers and ferocity. Aedes and Ochlerotatus species lay their eggs at the edges of water bodies and rely on warm temperature and/or low oxygen levels in flood-water to induce their eggs to hatch. Most of the floodwater species peak in late June (following snowmelt and then river flooding) and die in late summer and the populations over-winter as eggs. Mosquitoes that are viewed as nuisance species (i.e. present in high numbers and biting ferociously) are generally from this group, as large areas of habitat often become active at once with rising floodwaters and therefore huge batches of mosquitoes hatch at the same time. This is due primarily to the fact that eggs laid by most species remain viable for a number of years, and therefore egg concentrations in the soil can become very dense. Adults are generally short-lived (two to six weeks), and generally seek shade during hot summer days as they are prone to desiccation. Most species have only one generation each year, although some species are capable of two or more generations when conditions are suitable. Twelve species of Aedes and Ochlerotatus mosquitoes were trapped in the RDNO in Aedes cinereus Aedes cinereus is present throughout British Columbia and is capable of completing up to three generations per year (Belton, 1983; Wood et al., 1979). Larvae have been found in rain pools, swamps, and flood water (Belton, 1983). This species is not known to fly any great distance, and is generally considered a minor pest although isolated populations may be aggressive and persistent biters, even during the heat of the day (Belton, 1983). This species is given a vector competency rating of + : low in Belton s (2007) list of potential WNV vectors. This species was found in relatively low numbers in all of the trapping locations. BWP Consulting Inc. Page 21

26 Aedes vexans This mosquito species is considered the worst mosquito pest in Canada (Wood et al., 1979). Aedes vexans appear in extremely large numbers in almost any habitat where there are permanent, semi-permanent, or transient pools that have been flooded from snowmelt or rain. In the heat of summer, these mosquitoes can mature from the egg to adult in as short as five days, existing as larvae for as little as three days (Wood et al., 1979). Eggs of Aedes vexans can remain viable in the soil for many years, and because not all individuals hatch when submerged, multiple cycles of flooding and drying are needed for all eggs to hatch (Wood et al., 1979). Adult Aedes vexans are notorious fliers, capable of flying as far as 20 to 50 km, or of riding low jet streams for hundreds of kilometers (Belton, 1983). Specimens of Aedes vexans have been found carrying the western equine encephalitis (WEE) virus in Alberta, Saskatchewan, and the north western United States (Belton, 1983). Belton (2007) has included Aedes vexans as a potential WNV vector with a vector competency rating of ++ since individuals of this species have tested positive for the virus in some areas of the United States (Table 5). However, even though some specimens have tested positive, it is not clear if this species is actually capable of transmitting WNV since it rarely takes a second blood meal. This species was found in all of the light trapping locations, and was the dominant species in the RDNO, representing 48% of all mosquitoes captured (1,577 of the 3,314 mosquitoes captured) Ochlerotatus canadensis Ochlerotatus canadensis eggs usually hatch in temporary woodland pools as early as the beginning of April, although some eggs seem to have a delayed hatching mechanism as they have been observed hatching throughout the summer as late as August (Woods et al., 1979). Belton (1983) reports that this species in usually not considered a pest in BC due to its low numbers. However, it can be a persistent biter in the forest and tends to bite on the lower legs. This species is rated ++ as a WNV vector (Belton, 2007) since individuals of this species have tested positive for the virus in other areas of North America. BWP Consulting Inc. Page 22

27 Ochlerotatus communis This species is one of the most abundant and widely distributed species, occurring throughout the forested part of Canada as well as the northern US and northern Eurasia (Wood et al. 1979). Larvae generally rear in shaded pools (Belton, 1983), and in the Ottawa area, develop in large numbers in deciduous forest pools with a high tannic acid content (Wood et al. 1979). Eggs generally hatch in early spring, and female adults bite fiercely throughout the day. Although it is a fierce biter, it is not considered a major pest in BC due to relatively low numbers (Belton, 1983) except in northern areas. It is not included on the list of potential vectors (Belton, 2007) Ochlerotatus dorsalis This species thrives on the interior plateau, breeding in saline swamps and pools as well as fresh water (especially irrigation seepages) (Belton, 1983). It is capable of traveling many kilometers, and females of this species are vicious biters both during the day and at night (Belton, 1983). When conditions are favourable, Ochlerotatus dorsalis may have two or more summer generations, resulting in a very large population (Wood et al. 1979). Belton (2007) gives Ochlerotatus dorsalis a vector competence rating of +++, primarily because Western Equine Encephalitis and West Nile Virus have occasionally been isolated in adult females Ochlerotatus excrucians Ochlerotatus excrucians can be found throughout Canada south of the arctic tundra (Woods et al., 1979). Larvae of this species can be found in almost any ground pool, but seem to prefer the edges of larger semi-permanent marshes. Adults are large in size and will survive well into late summer. When present, females are fierce biters, but rarely occur in large numbers in British Columbia (Belton, 1983). This species does not appear on Belton s list of Potential WNV Vectors (Table 5) Ochlerotatus fitchii Ochlerotatus fitchii occur nearly everywhere in Canada south of the tree-line, (Woods et al.,1979). Larvae of this species are often collected in the same locations as the larvae of Ochlerotatus excrucians or early in the spring in snowmelt pools with Ochlerotatus increpitus (Belton, 1983; Woods et al., 1979). It is described as an aggressive pest mosquito of the southern interior and can be a nuisance at elevations as BWP Consulting Inc. Page 23

28 high as 1500m (Belton, 1983). Although individuals of this species have been found infected with WNV, they are unlikely to transmit the illness Ochlerotatus hendersoni Ochlerotatus hendersoni is uncommon in the province and larvae develop in water-filled rot holes in trees (Belton, 1983). Little is known concerning the biology of this species. Belton (2007) gives this species a potential WNV vector rating of Ochlerotatus increpitus Ochlerotatus increpitus is fairly widespread and numerous throughout BC, with larvae found in flood waters, irrigation seepage, ditches, and rain or snowmelt pools (Belton, 1983; Wood et al. 1979). While female Ochlerotatus increpitus are an important pest in Nevada and Utah, they are generally not common enough in Canada to be considered a significant pest (Wood et al. 1979). However, in those localized areas of BC where large numbers are found, the females are eager biters and can be a serious pest of cattle (Belton, 1983). Belton (2007) does not include this species on his list of potential WNV vectors Ochlerotatus sierrensis Ochlerotatus sierrensis larvae develop in tree-holes. Larvae have also been found in tires and hollow stumps in the province (Woods et al., 1979). As this species rarely occurs in high numbers, it is not considered a significant pest in British Columbia. Peter Belton (2007) includes this species on his list of potential vectors, with a rating of Ochlerotatus spencerii (both variants) Ochlerotatus spencerii larvae can be found very early in the spring, and then throughout the summer. They can be found in snow and rain pools, irrigation seepage, and floodwater sites (Belton, 1983). In the interior of BC, they have been found in the same pools as Aedes vexans and Ochlerotatus dorsalis. When this mosquito is present in high numbers, it can be an aggressive and persistent biter, even during the heat of the day. There are two variants of this species in BC, idahoensis and spencerii. The difference between these two variants lies in the markings present on their tergites (the main body segments). BWP Consulting Inc. Page 24

29 Ochlerotatus sticticus Ochlerotatus sticticus is primarily a floodwater mosquito and is therefore usually associated with the floodplains of large rivers and widespread excessive precipitation (Wood et al., 1979). With each peak of a river, a fresh hatch of Ochlerotatus sticticus can appear (Belton, 1983). This species is almost always associated with Aedes vexans (Wood et al., 1979). Eggs of Ochlerotatus sticticus can remain viable for about five years, so there may be years when this species may not appear at all as it waits for a significant flood (Belton, 1983). Like Aedes vexans, Ochlerotatus sticticus are ferocious biters and readily enter houses day and night (Belton, 1983). This species is not considered to be a strong West Nile Virus vector in British Columbia, with a vector competence rating of + (Belton, 2007). This species was relatively abundant at the Mabel Lake, Mara Lake and Kingfisher sites COQUILLETTIDIA SPECIES Coquillettidia perturbans The genus Coquillettidia has replaced the genus Mansonia in most of the recent literature, although Mansonia is still used by some authors. Only one species from this genus, Coquillettidia perturbans, is found in Canada. They are often called cattail mosquitoes, as the siphon of the larvae and trumpets of the pupae are modified to attach themselves to the outside of a cattail and burrow through the side, leaving the body of the larvae protruding (Belton, 1983). This exposure to the air inside the cattail fulfils their oxygen requirements, enabling them to remain buried in the mud at the bottom of the swamp (Wood et al. 1979). The marshes where they are found must remain permanently wet, because although there is only one generation per year, larvae are present year-round and are killed by drought, especially in the winter (Wood et al. 1979). Females are strong fliers and feed on both birds and mammals, and will occasionally feed more than once before laying eggs (Wood et al. 1979). For this reason, Belton (2007) has given them a vector competency rating of +. This species was captured in high numbers at the Tween Lakes site this summer. BWP Consulting Inc. Page 25

30 6.4. CULEX SPECIES Culex is the Latin word for mosquitoes and was used to describe all mosquito species prior to 1818, at which time the genera Anopheles and Aedes were named (Belton, 1983). There are only three species of Culex in BC (Culex tarsalis, Culex pipiens, and Culex territans). Culex females lay their eggs in rafts on the surface of almost any water, and all species found in BC overwinter as fertilized females. As well, all Culex species in BC can produce several generations a year, providing that the summer is warm enough. These mosquitoes are generally not considered a nuisance as they are usually found in lower concentrations and are not particularly aggressive biters of humans (they tend to prefer either birds or amphibians). Because they have multiple broods in their lifetime, they have the potential to transmit viruses such as WNV and other encephalitis such as Western Equine Encephalitis. This is because they must take a blood meal before laying each batch of eggs, and after feeding on an infected host, the female has the potential to transmit the virus to her next host. All three of British Columbia s Culex species were identified in the RDNO this summer Culex pipiens The common names for Culex pipiens are rain-barrel mosquito and Northern House Mosquito. These mosquitoes are common in both urban and sub-urban settings, and since they rarely fly more than 2-3 km from their larval development sites, when they are found, it can be assumed that they developed in a local larval development site (DeBess, 2003). These mosquitoes breed readily in highly organic water such as storm water catch basins, sewage treatment plants, ditches, birdbaths, rain gutters, plant pot drip trays, tires, and basically any water-holding containers that are commonly found in urban areas (DeBess, 2003). Females emerge in the spring in search of a blood meal; this species has a strong preference for the blood of birds. The blood is used by the female to help develop her eggs she lays approximately eggs on the surface of her chosen water habitat. Larvae emerge from the eggs in 1-2 days, after which the development of the larvae into adults is temperature dependent, but usually takes approximately 8-12 days in the summer (Savage & Miller, 1995). A single female may take multiple blood meals and lay multiple batches of eggs in a summer. BWP Consulting Inc. Page 26