|
Lyme disease as well as Anaplasma
phagocytophilum and Ehrlichia canis now occurs in all of the
contiguous 48 States and in many other places around the world.
With widespread testing we are picking up many dogs that test
positive but show no signs of disease. This leads to the
question of whether these dogs should be treated. In areas
where Lyme infection is high the question is how best to avoid
infection and whether or not it is helpful and/or safe to vaccinate
dogs against the disease.
Only about 5 to 10% of owner
presented dogs that test positive for Lyme disease show apparent
signs of the disease, although more than 60% have been reported to
in some studies where they have been more closely observed.
Signs tend to occur 2 to 5 months after infection and include
lameness, arthritis in one or more joints, enlarged lymph nodes,
lethargy and fever. The target lesions or any other skin
lesion is uncommon in dogs, and even less likely to be seen through
their hair. The signs will usually resolve within three days,
often spontaneously or in some cases with antibiotic therapy.
Other more serious conditions have also been noted in conjunction
with Lyme infection including kidney disease (Lyme nephritis), heart
disease (myocarditis) and neurologic disease, as well as hemolytic
anemia and thrombocytopenia – low platelets.
Lyme disease is diagnosed
serologically by looking for antibodies as very few bacteria are
needed to produce infection. The ELISA test is non specific
although very sensitive. It does not distinguish between
antibodies produced by infection and vaccination. There are
two tests that detect antibodies against the Lyme C6 protein.
Because this protein is expressed only when the animal is infected
naturally through a tick, vaccinated dogs will not test positive
unless they have also been infected. The in-house SNAP 3Dx
(also tests for heartworm and E. canis) and 4Dx (same as 3Dx, but
also tests for A. phagocytophilum) are used to screen dogs for
exposure to Lyme infection. Dogs that test positive have a
current active Lyme infection. The quantitative C6 Lyme test
will give you a titer that correlates to circulating anti-Lyme
immune complexes and this is used by some practitioners to decide
whether or not to treat the individual dog.
We used to believe that it took 48
hours for attached ticks to transmit Lyme disease to their hosts.
We now know that transfer can occur in as little as 18 hours, while
the tick and especially the nymph may still be too small to see.
Still, if you see a tick it should certainly be removed. Using
K9 Advantix, Frontline or other proven products is very effective at
preventing infection in dogs exposed to infected ticks.
I really can’t recommend
vaccination against Lyme disease. There are two types of
vaccine. Both work by binding the bacteria in the gut of the
tick while it’s dining on the host’s blood. Once bacteria
enter the dog the vaccine is no longer effective. Both
types of vaccine will need to be boostered at least every 12 months
and possibly more often. They do not protect against other
tick borne disease, and even against Lyme disease a high infestation
can easily overwhelm the protection they do offer. The big
question though is their safety. I have seen bleeding problems
in dogs post vaccination with these products. Often dogs show
signs of Lyme infection 4 to 8 weeks after vaccination, but test
negative fore the disease. Other complications include
rheumatoid arthritis and acute kidney failure. Lyme nephritis
is the result of immune complexes (antibody-antigen) accumulating in
the kidneys, and vaccination may contribute to the condition,
although this has not been proven as yet.
The common signs of Lyme disease
resolve quickly, often without antibiotic treatment and never even
develop in most infected dogs, but it is likely that in many dogs
even prolonged antibiotic treatment does not rid the body of
bacteria and they can re-emerge later, probably when the body’s
immune system is stressed and weakened. The more serious
effects of Lyme disease are also the most difficult to treat.
Certainly, any dog showing clinical signs of Lyme disease should be
treated, preferably with doxycycline, and I prefer to treat for 8
weeks. Some vets treat all dogs that test positive for Lyme
disease on the SNAP tests, while others require a certain titer to
be reached on the quantitative C6 test. Given that synovitis
(inflammation of the joint capsule) has been found in virtually all
dogs that test positive for Lyme - regardless of whether or not they
show clinical signs – at necropsy, while about 25% show more
serious signs of inflammation of the blood vessels and nerve
sheaths, I would err on the side of treating all positive dogs, and
hopefully avoiding more serious complications
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
A very grateful thank you to Linda
Aronson, DVM for the use of this article.
|
