3
In those few cases where the
disease is present, symptoms
appear 3 to 14 days after being
bitten. Only about 20 percent of
those affected will have the typical
fever, headache, flu-like body
aches, and perhaps a rash and
swollen lymph glands. These mild
forms of the virus usually last just
a few days.
There is some evidence that the
virus can be transmitted through
breast milk, but there are no
reports of any infants infected in
this way showing serious
symptoms, and the benefits of
breast-feeding are felt to outweigh
any possible risks.
Overall, children less than one-
year-old are rarely infected by the
virus. There is no evidence that
WNV can be transmitted through
pregnancy or birth.
Of those adults who do have
symptoms, less than one percent
will become seriously ill. Those over
50 years of age, or with
compromised immune systems
from other causes, are the most
at risk for more serious cases of
the disease. These more severe
symptoms (including high fever,
stiff neck, disorientation, and
tremors) can last several weeks.
At this time it is assumed that
anyone infected with WNV will
acquire lifelong immunity.
There have been some reports
about possible transmission of
WNV through blood transfusions
or organ transplants. This is being
studied carefully, and physicians
and blood banks are now aware of
the issue and are being as careful
as possible.
It is important to remember
that donating blood poses no risk
to the donor, and that it is critical
that the nation’s blood supply be
kept at safe levels. Several
companies are working to develop
screening tests, vaccinations, and
treatments, but nothing is yet
available at the time of this
writing.
Often the first reaction of
communities faced with evidence
of WNV is to call for chemical
spraying of neighborhoods and
wetlands. This process can
change the natural environment,
actually making it more
hospitable to mosquitoes by
killing predators (such as fish,
other insects, and birds).
In addition, most insecticides
have been designed for agricultural
use, and have not been tested or
evaluated for repeated contact
with humans.
A further concern is the speed
at which insects reproduce, giving
them the ability to build up a
resistance to an insecticide far
more rapidly than larger
predators. Some of these, such as
bats, may actually die out in an
area before they can build up a
tolerance, while the newly-adapted
mosquitoes will keep on
multiplying.
There are two kinds of pesticides
used: adulticides, which target the
mature mosquitoes, and larvicides,
which are aimed at the eggs and
larvae. Adulticides are the less
efficient and potentially the more
dangerous of the two.
Some communities spray with
malathion, an organophosphate.
Organophosphates are known to
be nerve toxins, and as such need
to be used with extreme caution
since the results of long-term
human exposure are not yet known.
Other commonly-used
adulticides are based on
pyrethroids, which are derived from
the flowers of the pyrethrum
plants (such as
chrysanthemums) or a synthetic
equivalent.
Pyrethroids break down quickly,
especially in sunlight, and they
bind to the soil so they are less of
a threat to the environment.
However, they are highly toxic to
bees and aquatic life, so any
benefits are not without serious
drawbacks.
Any adulticide product will kill
all insects indiscriminately. Not
only does this lower the
population of beneficial insects,
but it also cuts down on the
food supply for both local and
migratory insect-eating bird
species.
Larvicides tend to be more
effective in controlling mosquito
populations than adulticides.
They can be applied selectively, in
more controlled conditions. They
include both natural bacteria and
chemicals. Some of the more
common ones are microbial Bti,
which kills the larvae when they
ingest it, and surface oils which
are spread on top of water to
suffocate eggs, larvae, and
pupae.
Although safer than
adulticides, larvicides can be
highly toxic to aquatic life,
including amphibians, insects,
and fish, and in high doses can
cause serious reactions in
humans.
Reducing the number of
mosquitoes is obviously the best
way to lower the chances of being
bitten, but there are many
precautions that people can take
which pose no danger to wildlife
or the environment. Basic home
maintenance is important,
including making sure that there
are screens on windows and
doors, and that these screens
are free from holes that would
allow the insects to enter.
In the yard, watch for any
containers that could retain
standing water, even in very small
amounts. These might include old
tires, flower pots, clogged
gutters, pool covers, even
children’s toys.
