Strike Before the Snake Does - Dale M. Wallis, DVM - Red Rock Biologics
Rattlesnake bite is a veterinary emergency
that results in serious injury or even death to
thousands of dogs each year. Rattlesnake
venom is a complex mixture of toxins that
spreads through a dog’s body following the
bite. Red Rock Biologics have developed
a vaccine that is quite effective in the prevention
and/or minimization of complications
involving snakebites (envenomations)
by the Western Diamondback (Crotalus
atrox), and some of its subspecies. Red Rock
Rattlesnake Vaccines defend your dog by
creating an immunity that works right away
to help neutralize the toxins. That’s rattlesnake
protection that will put you and your
dog at ease.
The Western Diamondback, which can exceed
seven feet in length, is the largest of
twenty plus species and sub-species of
Southwestern desert rattlers. Although it is
mostly commonly expected in the desert, the
Western Diamondback can be found in
many areas where hunters venture with their
hounds. It occupies diverse habitats, anywhere
from sea level to 7000 feet, and ranging
from desert flats to rocky hillsides, grassy
plains, forested areas, river bottoms and
coastal prairies. Its range spans much of Arkansas,
most of Texas and Oklahoma, the
southern parts of New Mexico and Arizona,
the southern tip of California, and the northern
parts of Mexico’s Chihuahua and
Sonora.
A boldly-patterned snake, The Western
Diamondback’s basic color ranges from
brown to gray - even pinkish, depending on
the shade of its habitat. Along the back are
dark, diamond-shaped blotches outlined by
lighter-colored scales. Two dark stripes distinguish
the head, one on each side of its
face, which run diagonally, (much like a
mask) from its eyes back to its jaws. The tail
is encircled with several alternating black
and white bands, like the pattern of a
raccoon’s tail. The patterns are most distinctive
when the snake is young, and are
more faded, blurred and camouflaged as
the snake ages.
Like its relatives, a clan of some 100 species
of poisonous snakes generally called
“pitvipers” – the Western Diamondback
comes equipped with a spade-shaped
head, a ferocious fang and venom system,
elliptical pupils and heat-sensing facial
pits. It has reserve fangs to replace
those which might break off into a victim.
The venom causes extensive tissue damage,
bleeding and swelling.
Rattlesnake venoms are complex mixtures
of protein toxins. Each is unique to a given
species of rattlesnake. Yet fortunately,
many venom components found in a
given snake’s venom are antigenically related
to components found in many other
types of venom. This means that immunity
to one venom (multiple components) will
often cross-react, or neutralize some or all
of the components in a different venom.
This fact was used in the development of
antivenom about seventy-five years ago,
and is the reason that the Crotalus atrox
toxoid vaccine generates immunity to
much more than just the Western Diamondback
venom.
The Red Rock Rattlesnake Vaccine has
been licensed by U.S.D.A for use in healthy
dogs as an aid in the prevention of morbidity
and mortality due to envenomation
by Crotalus atrox. The initial sequence is two
doses spaced one month apart, beginning
about two months before anticipated exposure
to rattlesnakes. Peak immunity is
reached four to six weeks after the second
dose, and declines over time. By six months
about half the vaccinated dogs have declined to levels
where a booster dose isappropriate if snake exposure is likely.
Single dose boosters should be given at
six to twelve month intervals, depending
upon the level of rattlesnake exposure:
for dogs exposed to snakes longer than
six months of the year, a sex month
booster interval is appropriate. For many
hunting dogs, where exposure is only
three to four months (while hunting) of the
year, a single booster one month prior to
exposure is sufficient.
What does this vaccination mean to you?
This vaccine is a novel approach to the
problem of rattlesnake bite especially in
our higher risk hunting dogs. Rather than
repeatedly vaccinating a donor animal
(horse, sheep etc.) to generate high-titer
antivenom that is used in treating a
snakebite after it happens, vaccine is not
a treatment for snakebite, but prophylaxis
(prevention) against venom injury.
Because of this, the vaccine is only useful
if given long enough before expected
snake exposure to allow time for antibodies
to be produced in the dog.
The vaccine promotes the formation of
venom-neutralizing antibody in the vaccinated
dog so that the antibody is
present at the time of the bite. The intent
here is not to replace antivenom but to
buy extra time for an owner to reach a
veterinary clinic after a snakebite occurs,
and to minimize the overall risk of injury
to the bitten dog. Even if a snakebite occurred
in the veterinary clinic itself, it
would still require 20-30 minutes to prepare
and begin administration of
antivenom: during that time, the injected
venom might already be causing irreversible
tissue damage in an unvaccinated dog. This is why
rattlesnake bites often result in necrosis (dead tissue)
and sloughing, even when antivenom is promptly
administered.
In the vaccinated dog, the antibodies
from the vaccine are already present and begin
neutralizing venom immediately. In two
years of use in California, vaccinated dogs
have not experienced the tissue damage following
snakebite that is typically seen in nonvaccinates.
The vaccine has been safely administered to
dogs as small as two pounds, as large as 175
pounds as young as four months, as old as fifteen
years, and even to pregnant or lactating
dogs, with no ill effects. It may be given to dogs
that were previously bitten, and does not appear
to increase the risk of adverse events in
dogs that require antivenom. Since immunity
increases with each dose of vaccine and since
the vaccine has an excellent safety record,
dogs at particular risk may benefit from a three
dose initial sequence, followed by single dose
boosters as appropriate. Each owner should
discuss with their veterinarian the relative risk of
vaccination (minimal to nonexistent for most
dogs) vs. the relative risks of envenomation injury
under their particular rattlesnake exposure
circumstances to choose the best option for
vaccinating their dog(s).
The following must be taken in context; they are
anecdotal reports from veterinarians who are
trained to be observers, but we really never
know what the dog’s antibody level was at the
time of the bite, nor do we know how much
venom the snake deposited in the dog. If the
dog’s immunity is a good match for the
amount and type of venom he receives, additional
veterinary treatment (possibly including
antivenom) is warranted. It must be emphasized
that prompt veterinary evaluation and
care is essential to ensure the optimum possible
outcome in envenomations, even for vaccinated
dogs. The veterinarian is the person best
able to determine whether the dog’s immunity
alone is sufficient to deal with the venom
dose received. Delays in seeking veterinary
care even for vaccinated dogs have contributed
to a small number of fatal outcomes in
envenomations.
The best coverage of the vaccine-elicited immunity
is against Western Diamondback (Crotalus
atrox) venom, but good to excellent coverage
has been demonstrated against the
venoms of several subspecies of the western
rattlesnake (Crotalus viridis) as well. These are
the populations that predominate west of the
Mississippi River. Good coverage has been
demonstrated against the venom of the Timber
rattlesnake (Crotalus horridus).
Fair to good coverage has been demonstrated
against venoms of the Sistruris species
as well (Massassauga and Pygmy rattlesnakes).
There is a little protection against the
Eastern Diamondback (Crotalus
adamanteus). Interestingly, the vaccine-elicited
antibody has been shown protective
against the venom of the copperhead
(Agkistrodon contortrix) but not at all against
the cottonmouth (Agkistrodon piscivoris). Most
of these venoms contain components that act
against blood or blood vessels; vaccine-elicited
antibody blocks the effects of many of
those components.
There are a few enclaves of Crotalus rattlesnakes
(e.g. Crotalus scutulatus or Mojave
Green) that also have neurotoxins, these
venom components act by paralyzing the
muscles required for breathing, walking, etc.
At this time, we have no evidence that vaccine-
elicited antibody can neutralize neurotoxins,
but further research is ongoing.
Overall, bite reports in vaccinated dogs have
been very favorable. There is less swelling and
pain in vaccinates, and less tissue damage.
Dogs appear to recover faster (1-2 days) following
a bite, compared to the usual four to
six days. Bites in vaccinated dogs may result
in swelling at the bite location, but bruising
and hemorrhage are reduced compared to
what veterinary clinics are used to seeing.
Moreover, several clinics have reported that
swelling is already starting to decrease in vaccinated
dogs upon presentation at the clinic
(prior to any treatment being given), which
is unusual. Many reports indicate swelling is
decreased by over 75% within twenty-four
thirty-six hours following a snakebite in a vaccinated
dog. Even with antivenom, it usually
requires several days to see this kind of regression.
If you would like more information on the
availability of the Red Rock Rattlesnake Vaccine,
or other vaccines as they are developed,
visit our website at
http://www.redrockbiologics.com/ , or contact us
at:
Red Rock Biologics - P.O. Box 8630 - Woodland,
CA 95776 1-866-897-7625
(Edited by B. Saunders, April 2005)