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Mosquito Control and West Nile Virus Information Sessions - July 25-29, 2011 - 145Kb PDF
West Nile virus (WNv) is a disease spread by mosquitoes. Mosquitoes
become infected with WNv by biting infected birds. WNv first appeared
in New York City in 1999 and has since spread throughout the United
States and into Canada. In 2001, Canada had its first case of WNv in
Ontario and since then it been reported in Nova Scotia, New
Brunswick, Quebec, Manitoba, Saskatchewan, and Alberta. As of the
spring of 2007, there have been no reports of WNv activity in British
Columbia. The British Columbia Center for Disease Control and Health Canada websites have regularly update information on WNv
and it presence in Canada.
There are four stages to the mosquito life cycle: egg, larva, pupa,
and adult (Figure 1). Eggs are laid on the surface of standing or still
water. Larvae hatch from the eggs (1) and develop in standing water
(2). Larvae go through four growth stages called instars. They feed on
organic matter by filtering the water and they must come to the
surface of the water to breath. At the end of the fourth instar, the
larvae transform into a pupae (3) which must also come to the water’s
surface to breathe but do not feed. The adult mosquitoes emerge from
the pupae (4), rest on the water’s surface to dry their wings and then
they fly away in search of a mate or a blood meal (5). Female
mosquitoes require a blood meal (6) in order to mature a new batch of
eggs, and they will bite before laying each batch. Male mosquitoes do
not bite; instead they feed on flower pollens.
Figure 1. Mosquito Life Cycle - Provided by the Florida Medical
Entomology Lab.
Figure 2. A 300ml Dipper loaded with mosquito larvae! It does not
take much water to product thousands of larvae.
Mosquitoes are called WNv vectors, which means that they are
responsible for transmitting the virus. Mosquitoes suck in the virus
when they bite an infected bird and then when the mosquito bites
another bird or a mammal (including humans), they pass on the virus.
Mammals, including humans, are considered “dead-end hosts”
meaning that they are unable to pass the virus on to other mammals
or back to mosquitoes (Figure 3).
Figure 3. West Nile Virus Cycle
Not all mosquito species are vectors of WNv. In the Interior Health
Authority there are approximately 30 species of mosquitoes, and only
two species are considered to be significant vectors of WNv. The
scientific names of these two mosquitoes are Culex tarsalis and Culex
pipiens.
In the Okanagan, these species have been found in very high numbers
in many locations.
Since the spring of 2004 the Ministry of Health Services has offered
grant funding for all municipalities, First Nations bands and Regional
Districts in the province. Regional Districts throughout the Okanagan
have been applying for and receiving this grant. The funding has been
used for mosquito surveillance, mosquito larval control, larval habitat
mapping and public education.
Adult mosquito surveillance is used to monitor mosquito abundance
and determine which species of mosquitoes are present in an area.
Mosquitoes are trapped using a mosquito light trap baited with dry ice
(Figure 6). Mosquitoes are attracted to the light and the CO2 from the
dry ice and they are sucked into a collecting container.
The Regional Districts and the Interior Health Authority have
participated in adult mosquito trapping throughout the Okanagan. All
mosquitoes trapped by the Interior Health Authority are shipped to the
British Columbia Centre for Disease Control where they are ground up
and tested for the presence of West Nile virus. Tens of thousands of
mosquitoes have been tested from the Okanagan and non have tested
positive for virus.
Figure 6. Mosquito Light Trap
Known mosquito larval development sites are monitored throughout
the summer in the Okanagan, and when mosquito larvae are present,
the Regional Districts consider the use of larvicides. The larvicide
product(s) that are being used are called Vectobac and/or Aquabac
whichever is more readily available at the time. These essentially
identical products contain the active ingredient Bacillus thuringiensis
israelensis (Bti)(Figure 7). Bti is a bacterium which occurs naturally in
soils and aquatic environments and although kills mosquito larvae, it is
safe for other insects, mammals, fish and amphibians. Bti is certified
for organic gardening.
Catch basins in urban areas of the Okanagan often contain larvae of
Culex pipiens. The larvicide VectoLex with the active ingredient
Bacillus sphaericus is used to control larvae in catch basins. This
product contains live bacteria that reproduce in the gut of mosquito
larvae and kill them. This product will kill larvae for up to 30 days and
is safe for all other organisms.
Figure 7. Aquabac- Bacillus thuringiensis israelensis formulated on
corn-cob
What attracts mosquitoes?
Mosquitoes are attracted by body odour, perspiration, heat, light, and
carbon dioxide.
Why do mosquitoes bite?
Only female mosquitoes bite and they use the blood to obtain protein
for egg development.
How do people become infected with WNv?
People become infected with WNv when they are bit by an infected
mosquito.
What are the chances of getting infected with WNv?
The chances of getting WNv are very low. Approximately 80% of
people infected with WNv will not get sick at all; the remaining 20%
will experience flu-like symptoms (fatigue, fever, headache, body
aches) that last about a week or less. In very rare cases (less than
1%), infected people can develop encephalitis, inflammation of the
brain, or meningitis, inflammation of the lining of the brain, which can
result in death.
Does WNv only infect humans?
No. There have been cases of horses, birds, cats, chipmunks, domestic
rabbits, squirrels, and skunks being infected by WNv. These animals
cannot infect other animals or humans.
Can my pet get West Nile virus?
- West Nile virus can infect domestic dogs and cats however, these
infections very rarely develop into serious illness. These animals
usually fully recover without treatment and usually show no
symptoms whatsoever.
- Domestic birds such as parrots can be infected and may become
very ill or die from the virus.
- Horses are the most susceptible domestic animals to serious West
Nile virus illness and up to 40% of infected horses will die. There
is a vaccine available for horses.
- All domestic animals acquire the virus through the bite of a
mosquito and none are able to pass on the virus to other animals
or humans once they are infected. Please contact your local
veterinarian for more information about protecting domestic
animals from West Nile virus infection.
Why should I report a dead bird?
Members of the corvid family (crows, ravens, magpies, blue jays, and
Steller’s jays) are particularly sensitive to the virus causing high death
rates if infected and are therefore good indicator species of WNv
activity.
Who do I call if I find a dead bird?
Birds of the corvid family which include crows, ravens, magpies, blue
jays and Steller’s jays that are dead but not decayed should be
reported to the Interior Health Authority (IHA) at 1-866-300-0520.
Efforts will be made to collect the bird and send it for testing at the
provincial Animal Health Lab in Abbotsford, BC. If at all possible, place
the bird in a double bag and store in the freezer until a representative
from the IHA can collect the bird.
Can I get WNv directly from birds?
No. Precautions should be taken when handling dead birds due to the
fact that you don’t know the bird’s cause of death. Avoid bare-handed
contact; use gloves or double plastic bags when handling dead birds
and wash your hands after disposal.
How can I protect myself from WNv?
The best way to protect yourself from WNv is to minimize your
exposure to mosquitoes and to reduce mosquito larvae development
sites. The following are ways to accomplish this:
- reduce mosquito larvae development sites around your home by
draining standing water on a regular basis
- change the water frequently in bird baths, pet dishes and
children’s wading pools
- keep gutters clear so they will drain properly
- empty or turn over anything that holds standing water
such as buckets, wheel barrows, old tires, and toys
- drill holes in tire swings
- empty water out of plant saucers
- keep a fine mesh screen over rain water barrels so female
mosquitoes cannot land on the water and lay eggs
- aerate ornamental ponds or stock with fish
- repair holes in screens on windows and doors
- wear tightly woven clothing with long sleeves, and long pants.
Try to wear light-coloured clothing (Mosquitoes are attracted to
dark clothing because it absorbs heat)
- use insect repellent that contain DEET (important: read the
product label for proper use) or Oil of Lemon Eucalyptus
products such as OFF! Botanicals®
What product is being used to kill mosquito larvae in stagnant
water?
Aquabac 200G or Vectobac 200G. These are larvicides that contain
the bacterium Bacillus thuringiensis var israelensis which is certified
for organic gardening. The bacteria is attached to ground corn cob
and spread on the surface of standing water containing larvae.
Mosquito larvae eat the bacteria and it causes their death. Other
insects, amphibians, fish, birds and mammals are unharmed by this
naturally occurring bacteria.
Is Aquabac/Vectobac safe for the environment?
Aquabac and Vectobac are two of the least toxic insecticides used
today. Bacillus thuringiensis var israelensis, the active ingredient in
these products, is a naturally occurring bacterium found in soil and
aquatic environments.
How does Aquabac/Vectobac work?
Aquabac and Vectobac are applied to standing water that contains
larvae in their third and fourth instar. Once in the water, the Bacillus
thuringiensis var israelensis is eaten by the larva which causes death
within 4 to 24 hours.
For more information, refer to the British Columbia Center for Disease
Control website at www.bccdc.org, the Interior Health Authority
website at www.interiorhealth.ca or call the Interior Health West Nile
Virus information line at 1-866-300-0520
For enquiries to the RDNO West Nile Virus Program, please contact:
John Friesen, RPF
Bylaw Enforcement Officer
Phone: (250) 550-3749
Fax: (250) 550-3701
E-mail: john.friesen@rdno.ca
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