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An
Overview of West Nile Virus
The West
Nile Virus (WNV), a member of the flavivirus family, was first isolated
during 1937 in the West Nile Region of Uganda. Despite having since
caused encephalitis outbreaks in Africa, Eastern Europe, Western Asia,
and the Middle East, WNV did not invade North America until its 1999
appearance in New York State. Infection with the virus can trigger a
range of symptoms in humans, from none at all to mild, flu-like sensations
to encephalitis, a potentially fatal inflammation of the brain.
WNV is
a cause for concern partly because it has public health implications
but largely because there is a great deal we do not yet know about it.
We are not certain how the virus made its way to the United States.
Speculation ranges from the illegal exotic bird trade to an errant mosquito
catching a plane ride across the Atlantic. We don’t know why some
people are more severely affected than others, though experts think
it has to do with age and immune system efficacy. Precisely which animals
are susceptible to the virus remains a bit of a mystery – the
list of species with documented infections changes often.
The West
Nile Virus is of concern to everyone – whether they own pets or
not. But pet owners must take additional measures in order to limit
the level of exposure for their pets. WNV is rapidly spreading to all
corners of North America; 32 states and several Canadian provinces have
already reported virus activity in 2003, compared to the mere 20 from
last year. The following information is intended to provide you with
an up-to-date overview of WNV, its dangers, and preventative measures
you can take to minimize exposure for both you and your dog. It is important
to remember however that specific information regarding veterinary insect
repellents and the like should always be gained from your veterinarian.
How does infection occur?
WNV is
harbored by mosquitoes of many kinds – at least 20 species are
known to be carriers. A mosquito contracts the virus upon biting an
infected animal, most often a bird. The infected mosquito then transmits
the virus to new animals when it finds and bites a suitable host. It
should be remembered that relatively few mosquitoes carry the virus
and that even if an animal is bitten by an infected mosquito it will
not necessarily become infected.
It is
also possible for WNV to be transmitted via blood transfusions and organ
transplants, but this has only occurred in a very few cases and should
not be viewed as a serious threat. It is not believed that WNV can be
transmitted through casual touching or kissing. Further, there is no
evidence that an infected dog, cat or other animal can pass the virus
directly to humans, so this should not be of concern to owners of infected
pets.
What are the symptoms
of WNV?
In humans
there is an incubation
period of 3 to 14 days between initial infection and onset
of symptoms. The incubation period in dogs is much longer and may last
up to several months.
Approximately
80% of infected humans – and likely just as many or more dogs
– never suffer any visible symptoms of WNV. Of those people that
do develop symptoms, the great majority suffer only mild effects. Mild
cases present like the common flu, with fever, headache, nausea, vomiting,
and sometimes swollen lymph nodes and a rash on the chest, stomach and
back. Vague symptoms usually endure for only a few days and are not
fatal.
More severe
human cases, which strike a mere 1 in 150 infected but may well prove
fatal, are indicated by high fever, headache, neck stiffness, stupor,
disorientation, coma, tremors, convulsions, muscle weakness, vision
loss, numbness, and paralysis. These more sever symptoms, if they do
not prove fatal, may last several weeks, and neurological damage is
often permanent.
Dogs seem
to be more resistant to the virus than humans and rarely fall ill, but
certain symptoms have been observed consistently across cases. Signs
of a WNV infection in your dog may include poor coordination, depression,
decreased appetite, difficulty walking, tremors, abnormal head posture,
circling, and convulsions. Such symptoms may be indicative of a number
of disorders, but all are serious and any dog exhibiting neurological
abnormalities should be promptly examined by a veterinarian.
Diagnosis
of WNV is finalized using laboratory tests which must be administered
by a medical professional or veterinarian.
What are the treatment options for animals with WNV?
Treatment
is almost purely supportive and symptom-specific. At this point nearly
every dog infected with WNV is expected to recover fully.
Is there a vaccine available for WNV?
Unfortunately,
no. There is a vaccine on the market for use on horses, but none exists
at this time for humans or small animals.
How else can I help prevent the disease?
Given
that much about WNV remains a mystery, our best defense is currently
prevention. A number of steps may be taken to reduce risk for both you
and your pets.
Limiting
exposure to mosquitoes is perhaps the most obvious but also the most
effective method of prevention. Mosquitoes tend to be at their most
active early in the morning and near dusk. Keeping yourself and your
pet indoors as much as possible during these hours will expose you to
fewer insects.
It is
important to ensure that all window and door screens are in good repair.
This will minimize the number of mosquitoes that can enter your home.
When you
do venture outdoors, insect repellents can minimize the number of times
an individual is bitten. For humans, repellents containing DEET are
the most effective. Because DEET can be harmful if ingested, it is no
approved or appropriate for use on animals – while grooming they
could easily ingest the spray or residue. There are however a number
of products approved for use on dogs. Some of them are marketed as equine
products, but they are safe for canine companions as well.
- Flysect
Super 7 by Equicare
- Petguard
gel by Virbac
- VIP
Fly Repellent Ointment by VPL
- Flea
and Tick Mist by Davis
- Adams
Flea and Tick Mist by VPL
- Happy
Jack Flea-Tick Spray by Happy Jack
- Ultrashield
by Absorbine
These
products are available at local pet and feed stores or through your
veterinarian.
 Additional
resources on the web: Centers
for Disease Control
In-depth West Nile site contains question and answer sections, data
on current case count, prevention techniques, and more.
VetCentric
Summarizes what is known about West Nile, how to protect domestic
animals (including dogs and horses) and links to webpages with other
information.
VeterinaryPartner.com
Discusses West Nile in a Question & Answer format focused on
dogs and cats. |
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