1. Eau Claire County Health Department
Adult Mosquito Surveillance for West Nile Virus
Jen Nimmo & Pang Xiong Yang
The West Nile Virus (WNV) originated in the remote areas of Africa, Eastern Europe,
West Asia, and the Middle East. The virus was first isolated in a Uganda woman in 1937.

2. From there the WNV disease spread throughout much of the world. In 1999, it first
appeared in North America, more specifically, New York City. Since then the virus has
been found in 47 states. The first human cases of WNV in Wisconsin appeared in 2002
(14). In 2014, it was reported that Wisconsin had 26 avian WNV cases, 2 horse WNV
cases, and 6 confirmed human WNV cases including 1 human death (14). Eau Claire was
the location of one of the reported positive avian cases. Currently for 2015, Wisconsin
has reported to have 8 WNV avian cases, one of which had been identified in Eau Claire
County. There are many different species of mosquitoes in Eau Claire County. However,
this study concentrates on the species of mosquitoes that carry the WNV: specifically
Aedes vexans, Culex Pipiens/restuans, and Coquillettidia perturbans.
MOSQUITO SPECIES
Aedes vexans is found in every state in the United States including Alaska and Hawaii
(1). During the spring A. vexans larvae hatch from overwintering eggs and start
appearing when temperatures reach 70o F (1). Thus, not making this species of
mosquitoes evident until June. A. vexans is commonly found in grassy pools that border
wooded areas; some may be found in partially shaded woodland pools, pooled water in
open fields, and roadside ditches. The distribution of this species depends upon the
rainfall patterns to restore the breeding habitat. Any transient water can support A.
vexans, however, non-shaded rain pools produce the largest quantity of this species.
Coquillettidia perturbans is found in the United States and eastern Canada. They are
always found associated with the roots and stems of vegetation surrounding bogs, ponds
and lakes that allow for swamp-like habitat to exist for the growth of cattails (6). The C.
perturbans is commonly known as the cattail mosquito. Typically found in areas of low
elevation and high vegetation during warm summers and high humidity. This species lay
their eggs in a marsh or swamp habitat that does not have a current (6).
Anophelines are found worldwide in a variety of habitats and is the primary vector for
malaria (this study does not include the surveillance for malaria) (3). The Anopheles
species prefers to feed on animals such as cattle and occasionally feed on humans (2).
They lay individual eggs on the water surface or on moist soil immediately adjacent to
fluctuating bodies of water.
Culex mosquitoes predominantly transmit West Nile Virus. The adult Culex mosquitoes
do not fly far from where they develop as larvae. Their eggs are laid on the surface of
standing water in areas of no plant life; such places include tin cans, garden pots, used
tires, children's pools. All of which are ideal receptacles for breeding (5). The adult
Culex is not like other mosquitoes that die with the first hard frost in the autumn; the
Culex can survive over the winter in protected places such as sewers, crawlspaces and
basements (10).
INTRODUCTION

3. The increase of the West Nile Virus (WNV) within the United States is becoming more
prevalent. Local Health Departments have started surveillance programs to determine the
quantities of vectors (mosquitoes) that can potentially carry the WNV with in given areas,
such as cities or counties. As positive WNV cases increase it is hypothesized that there
will be a high quantity of WNV carrier mosquito species within a given area. Thus,
creating a potential for an increase number of WNV cases in that given area. The
Objective of this research is to determine the quantities of mosquitoes that potential are
WNV carriers within the Eau Claire, WI area.
METHODS
Gravid traps are commonly used by mosquito control agencies nationwide to monitor
populations of mosquitoes carrying the WNV, especially the C. Pipiens. Placements of
these traps are limited due to the need to prevent tampering from the public (8). The traps
were placed in various places throughout Eau Claire County dependent on vegetation and
public traffic (See attachment for site details in Appendix A). The CDC found that
placement of traps above ground was a more effective method to collect mosquitoes than
that of placing traps below grounds (8). Therefore, the traps were hung approximately six
foot in the air, typically off of a tree branch, with the net hanging approximately a foot
and a half from the ground. Findings show that although mosquitoes are attracted to “skin
emanation,” when CO2 is added as a factor, it attracts many more mosquitoes than “skin
emanation” alone (8 & 11). There was approximately 3-5 pounds of dry ice placed in
canisters for the production of Carbon dioxide to attract the mosquitoes, along with a
light to provide a secondary attractant. The ice lasted approximately 25-30 hours
depending on the canister. The first two times of collection the traps were placed for 24
hours. After those collections it was determined that a collection time of 48 hours was
ideal. After the collection period, the nets were collected and sealed to contain the
mosquitoes. At which time the mosquitoes were frozen for preservation. Once the
mosquitoes were preserved, the mosquito species were identified using visual
identification with the use of a microscope and hand separation. During the duration of
the collection, the weather was also collected to analyze against mosquito quantities.
Some traps were not kept in the same areas for collection due to vegetation and quantity
of mosquitoes collected. For the areas that supplied high quantities of mosquitoes the
traps were set repeatedly in those areas. Towards the end of the summer collection traps
had malfunctioned and had to be replaced. Thus, resulting in the number of traps for
collection decreasing from four to two. The two locations that supplied the highest
quantities of mosquitoes continued to have traps set.
RESULTS
Throughout the summer of 2015, there was a total of six sites where traps were set and
then collected for further analysis. The amount of species collected at different sites vary
depending on vegetation, human trafficking, and the water sources. Within majority of
these sites, there was an abundance of Aedes and C. Perturbans collected throughout the
summer. Some sites yielded multiple mosquito species, while others yielded little to

4. none. Site A resulted with a total of 810 mosquitoes. In the month of June, site A yielded
18 Aedes, 2 Anopheles, 523 c. perturbans, and zero culex. During the month of July and
August, site A yielded 8 Aedes, 10 Anopheles, 249 c. perturbans, and zero Culex. Site B
on the other hand resulted in 160 mosquitoes. In June, site B yielded a total of 40 Aedes,
zero Anopheles, 49 C. perturbans, and zero Culex. Through July and August, there was a
15 Aedes, 1 Anopheles, 55 C. perturbans. Site C resulted in 54 mosquitoes, in the month
of June there was 45 Aedes, zero Anopheles, 9 C. perturbans, and zer Culex. Site D
resulted in a total of zero mosquitoes found, this could have resulted from placement of
the traps, or site location. Site E resulted in 225 mosquitoes. In June there was 30 Aedes,
1 Anopheles, 64 C. perturbans, and zero Culex. In July and August there was 74 Ades, 4
Anopheles, 52 C. perturbans, and zero Culex. Site F resulted in a total of 133 mosquitoes.
In June, there was 20 Aedes, zero Anopheles, 25 C. perturbans, and zero Culex. Within
July and August, there are 19 Aedes, 1 Anopheles, 68 C. perturbans, and zero Culex.
During the month of June, there was a total of 826 mosquito species collected. While in
July, there was a total of 496 different species of Mosquitoes. On the other hand, August
had a total of 60 different species of mosquitoes collected. Overall, it is found that June
and July had the most abundant species of mosquitoes depending on many factors that
could have played an important role on the collection of mosquitoes.
The Culex species was never found in any locations during any months, there could have
been many factors that played in this result. Either the Culex species don’t reside here in
Eau Claire, or the attractant that was used doesn’t attract their species. Results from all
sites could also vary depending on the amount of rainfalls within these months,
equipment failures, placement of traps, and etc.
(Please see results in Appendix D)
DISCUSSION
The relations between mosquito species, vegetation and water sources are directly
associated, as seen with locations A, B, E and F. These locations included dense
vegetation that allowed for habitat and nutrients for mosquito survival, along with
constant water availability. Water sources near make the habitat more desirable for
breeding purposes. Location A, Braun’s Bay - Carson Park, includes the water habitats
from Braun’s Bay; also including an abundance of cattails creating the ideal habit for C.
perturbans. The cattails provide a breeding ground and protection for the mosquito's eggs
and larvae. Location B - Putnum Trail, includes a small creek and swamp
habitat. Location E - Hickory Hills Golf Course, includes 2 ponds and the grounds
sprinkler system. And location F - Residents of Balsam road, included an irrigated crop
field twenty feet from trap location. These four locations provide ideal growing and
breeding grounds for Aedes vexans, Culex Pipiens/restuans, and Coquillettidia
perturbans (species under surveillance). These locations are ideal for the production and
sustenance for mosquito survival. The areas that did not produce large collections of
mosquitoes were relocated to other areas that included dense vegetation and a water

5. source to increase the collection data; such as location C and D. (Please see further
location descriptions in Appendix B)
The next important factors in the collection process include the carbon dioxide created by
the dry ice and the addition of the light. Both these items attract the mosquitoes to the
traps. The carbon dioxide mimics the respiration of a human resulting in the attraction of
mosquitoes for a potential blood meal. Followed by the light to attract them just above
the fan to blow the mosquito(s) down into the net for collection. When one of these items
was not provided the mosquito count was lower than the expected. As seen in the
collection on June 25th; location B and E traps both had lights out resulting in lower
quantities collected compared to the weeks before. Without the light the collection is
relying on the possibilities of the mosquitoes coming close enough to the fan to be drawn
down into the net.
In addition a major issue with this experiment was equipment failure; there was difficulty
with the continuing circuit from the power source (batteries) to keep the fan and light
functional. With the continuing failure of both the light and fan it decreased the number
of mosquitoes collected. The lack of the light decreased the mosquito attraction to the
trap and then when the fan was not in operation there was no force to keep the
mosquitoes in the trap. The majority of July collection was not conducted due to the
traps malfunctions and ordering of new traps.
The data that was collected this year included a wider range of dates than the previous
surveillance year. There were a few periods of time of no collection due to trap
malfunction. However, if data was collected during those times it would have provided a
better comparison of species numbers compared to the previous year. From the data that
was collected a bell shape distribution is noted; starting with the beginning of the season
(June) having low counts of mosquitoes collected. To the end of June and beginning of
July numbers peak, following into lower quantities in August. When comparing the data
from 2014 to this year there has been an increase in mosquitoes collected this year than
the previous year; one count reaching 440 identified C. perturbans. It is noted that there
is an increase in the number of mosquitoes collected at each run compared to the year
before. The surveillance from the previous year noted that C. perturbans had the highest
number collected, then Aedes vexans, Anopheles, and Culex. It was reflected to be the
same order this year, however, there were no Culex species collected. With the data that
is collected a direct comparison of quantities can differ since the locations are not exactly
placed in the same location. However, the type of ground cover was mimicked from the
previous year for this study to better collection results.
Looking back at the data that has been collected along with recalling the weather patterns
prior to the days that the traps were set, it appears that weather has an effect on quantities
collected. It is recalled that the collection days in July it had rained prior to setting the
traps and then temperatures had increased to about 75 degrees (weather conditions
recorded in appendix C). Creating ideal conditions for mosquitoes to reproduce and
hatch. Further weather data needs to be collected to determine a correlation between prior
weather conditions and quantities collected.

6. FUTURE WORK
The future of this research is very promising; moving forward there are areas of
improvement that can be made to enhance the research. Most importantly is to continue
annual sampling to track the mosquito species from year to year, allowing for changing
trends to be identified and studied. Thus, allowing for additional research to be
conducted if alarming trends are reported. Collection consistency, not only year to year,
but throughout the summer will enhance the research. The consistency will allow for
different patterns to be reported and analyzed. In addition, this will help analyze when
the greatest quantities of mosquitoes are collected in comparison to the time during
the summer months; potentially assisting in determining the times of high risk for the
public.
In addition, an increased number in traps would improve the data collection, including
increasing the number of trap locations. This would allow for a better understanding of
species in public areas throughout Eau Claire County. With four traps, collection was
only obtained through the central and southern parts of Eau Claire. Then following the
trap malfunctions trap locations dropped to two sites. Ideally the research would benefit
from at least five collection sites including: north, east, south, west and central public
locations of Eau Claire County. These areas should include moderate to dense vegetation,
trees/woods included, and a water source that would allow for reproduction and life cycle
of the mosquito. These locations could simply include a pond, lake or river with
vegetation.
This study would also benefit from tracking the weather before the traps are set to find
the relationship between weather and the quantities of mosquitoes collected. The present
study only recorded weather on the days that the traps were set. The relation
between rain, heat and quantities of mosquitoes would be an excellent addition to the
research. If a pattern is recognized between these items it could allow for a greater
quantity of mosquitoes to be collected and identified. This could lead into an increase in
public awareness at when high quantities of mosquitoes would be expected to be present.
Lastly, the research would benefit from the use of the PCR to analyze the
mosquitoes as West Nile Virus carriers. The use of this machine would elevate the
research to its maximum potential. For this summer's research, only species that are
potential WNV carriers could be determined through species identification. With the use
of the PCR it could determine which specific mosquito and location produced the WNV
carrier(s), allowing the Health Department to identify areas of high risk to inform the
public.
ACKNOWLEDGEMENTS
Shane Sanderson, Eau Claire Environmental Public Health Department
Laura Suppes, Environmental Public Health assistant professor
Office of Research and sponsored programs

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