What Every Dog Owner Should Know About Lyme Disease
Lyme disease, a tick-transmitted bacterial
infection, can lead to recurrent arthritic symptoms in dogs and humans.
Recent clinical studies indicate that Lyme disease in dogs may not be as
benign as once believed: bacterial infection appears to persist in many
dogs despite antibiotic therapy and even in individuals that are cured by
treatment, there is evidence of progressive joint deterioration.
Additionally, some breeds of dogs such as the Labrador retriever and
Golden retriever may be at additional risk to a fatal kidney disease (Lyme
nephritis) associated with Lyme infection. In light of these reports and
the estimate that 80% of dogs living in endemic regions of the United
States will become infected with Lyme disease, many clinicians are
recommending Lyme prevention in the form of vaccination. The following
article provides a detailed explanation of Lyme disease and explores the
benefits and risks of the current commercial vaccines available for
protecting dogs against Lyme disease.
The Lyme Organism. Borrelia burgdorferi is a bacterial
spirochete that is responsible for causing Lyme disease. Unlike its
distant relative, Leptospira spp. which cause canine leptospirosis,
B. burgdorferi cannot live in water and soil but are dependent
entirely on arthropod (insect) and vertebrate (mammals, reptiles) hosts to
carry out their life cycle. Differences in strains of Borrelia spp.
have been identified throughout the world and probably explain the
different clinical syndromes associated with infection in the United
States compared to other countries.
The Lyme Vector. For active Lyme infection to occur in dog or man, B.
burgdorferi requires an intermediate host; that is, the disease cannot
be directly transmitted from one host to another through contact with
infected body secretions such as blood, saliva, urine, etc. The primary
intermediate hosts for this spirochete are deer ticks belonging to the
genus Ixodes. Though other biting insects may be intermediate hosts for B.
burgdorferi, they were found to have an insignificant role in the
spread of Lyme disease.
Shortly after mating, the female tick will feed for 5-7
days on a host. In the spring, she will lay about 2000 eggs. Even if the
female is infected with B. burgdorferi, the larvae that hatch from
these eggs will not carry enough of the spirochetes to cause a threat of
infection. It is only when the larvae begin to feed on a host, usually the
white-footed mouse Peromyscus leucopus in the northeastern and
midwestern US, that they will ingest enough bacteria to become a vector
for Lyme disease. Interestingly, these infected mice do not develop
disease and, therefore, act as a perfect reservoir for B. burgdorferi..
[As an indication of the importance of the role that white-footed mice
have in the epidemiology of Lyme disease: in the mid-southern US where
incidence of Lyme disease is low, Ixodes spp found in that region (I.
scapularis) feed on lizards in which B. burgdorferi infection
is not maintained.]
The infected larvae molt into nymphs the following
spring and will also feed on the white-footed mice or others animals or
humans. At this point, an infected nymph may transmit B. burgdorferi
to the host, however, studies indicate that nymphs are less effective at
transmitting the bacteria than are adults. Uninfected nymphs are also
capable of becoming infected at this point if they feed upon an already
infected host. As a result, when nymphs molt again in the fall and become
adults, it is estimated that at least 50% of the tick population in areas
endemic for Lyme disease will carry B. burgdorferi. These adult
ticks are the primary vectors for disease transmission.
Disease Transmission. Lyme disease is transmitted by tick bite. B.
burgdorferi live in the midgut of ticks but will migrate to the
salivary glands once the tick attaches to a host and begins to feed.
Danger of infection with B. burgdorferi occurs when the tick
becomes engorged, usually after 24 hours of feeding, thereby increasing
the chances of bacteria-contaminated blood passing from tick to host. If
an infected tick is removed prior to 24 hours of attachment, chances of
the host acquiring Lyme disease are virtually non-existent.
Several clinical studies exploring the transmission of
Lyme disease indicate the necessity for the intermediate tick host. For
example, inoculation of healthy dogs with contaminated blood or urine from
infected dogs failed to produce clinical Lyme disease in the healthy dogs
at a later time. These dogs did go on to develop a positive titer to Lyme
disease, however, when blood from these dogs was examined, it was found
that the bacteria were not viable. Furthermore, using experimental tick
attachment models, clinicians found that pregnant bitches that became
infected with B. burgdorferi did not transmit the bacteria to their
fetuses. These studies support the need for the tick vector for Lyme
Disease Prevalence. It is estimated that although greater than 80%
of dogs in high risk areas of the US will be exposed to infected ticks,
only about 5% of these dogs will actually go on to manifest clinical Lyme
disease. High risk areas of the US include all coastal states from Maine
to North Carolina as well as New Hampshire and Pennsylvania. Other states
considered to be mildly at risk for Lyme disease include Wisconsin,
Minnesota, Michigan, Illinois, Missouri, Iowa, California and Oregon. The
remaining states are considered to have a very minimal risk for Lyme
Symptoms. Clinical studies exploring onset of Lyme disease
following infection with B. burgdorferi suggest that symptoms
appear usually 2-5 months after tick-induced infection. Primary symptoms
include lameness and joint pain. These symptoms may be sudden and severe.
Infected dogs also often exhibit depression, lethargy and loss of
appetite. Fever may or may not be present, however, one or more affected
joints are often swollen, hot and painful upon examination. In some cases,
there may be lymph node enlargement. Rarely, infected dogs will develop
complete heart block, renal failure, or neurological symptoms such as
seizures, aggression or other behavioral changes. The rash typically
appearing in the first stages of Lyme disease in humans is usually absent
Diagnosis. Standard blood studies are not very helpful in the
diagnosis of Lyme disease. Patient blood values are usually within normal
ranges despite symptoms of infection. Analysis of joint fluid, however,
often shows an increase in white blood cell count and changes in
hematologic components indicative of infection and inflammation. Despite
this, many canine disorders can present with similar symptoms. For this
reason, clinicians propose 4 criteria for establishing a diagnosis of Lyme
disease: 1) history of tick exposure; 2)typical clinical symptoms; 3) a
positive serology and 4) a response to antibiotic treatment.
In regard to serological tests, dogs exposed to B.
burgdorferi begin to make antibodies within 4 to 6 weeks. The antibody
titer will increase to high levels and then remain constant for about 18
months. Usually, by the time symptoms of Lyme disease manifest, antibody
titers should be sufficient to rule out the possibility of false-negative
tests. Though the enzyme linked immunosorbent assay (ELISA) and indirect
fluorescence antibody (IFA) test are sometimes used for the diagnosis of
Lyme disease, these methods are unable to distinguish antibodies made in
response to infection from antibodies made in response to vaccination
against Lyme disease. Therefore, false-positive results are a common
limitation to serological testing with ELISA and IFA. However, another
method called Western blotting is capable of distinguishing between these
types of antibodies and, therefore, can determine if a dog is infected
with B. burgdorferi even in the presence of a vaccine-induced
antibody titer to B. burgdorferi.
Treatment. Antibiotic treatment is the current treatment of choice
for Lyme disease. Doxycycline (tetracycline) for adult dogs or amoxicillin
for young, growing dogs produce complete remission of clinical symptoms in
dogs within 24-48 hours of initiation of treatment. Drug administration
should be continued, however, for one month because of the slow
reproduction cycle of the bacteria and its tendency to persist in dogs.
Non-steroidal anti-inflammatory drugs are useful for alleviating arthritic
symptoms associated with Lyme disease. However, many clinicians prefer not
to use these drugs because they mask symptoms which may indicate possible
progression of disease despite treatment with antibiotics. Clinical
evidence suggests that corticosteroid (ex. prednisone) treatment is
contraindicated for use in dogs with Lyme infection. In regard to this
latter finding, studies have shown that the immunosuppression caused by
these drugs may reactivate infection in dogs in which bacterial infection
has not been totally eradicated.
Prognosis. In most cases, clinical symptoms of Lyme disease in the
canine respond well to treatment with antibiotic therapy. Even without
treatment, many dogs recover from symptoms spontaneously. Additionally,
many dogs who are serologically positive for Lyme disease may never
manifest clinical symptoms of disease. In cases where symptomatic dogs
treated for Lyme disease develop recurrent symptoms at a later time in
their lives, repeating the antibiotic treatment was found to be effective
at controlling disease.
Despite this, however, it is believed that antibiotic
therapy may not completely cure dogs of Lyme disease. In fact,
histological studies of tissues from asymptomatic and antibiotic-treated
dogs suggests that even in the absence of clinical symptoms, mild
arthritic changes continue to occur in affected joints that may limit
mobility later in life. Furthermore, although clinical studies suggest
that dogs are rarely at risk to the chronic arthritis and severe central
nervous system syndromes that pose risks to humans who contract Lyme
disease, some breeds of dogs such as the Labrador retriever and the Golden
retriever are at risk to contracting a fatal kidney disease ( Lyme
nephritis) caused by B. burgdorferi that is not treatable with
Prevention. Prevention of Lyme disease in the dog may occur at two
levels: prevention of tick bites and inoculation against B.burgdorferi
with a commercial vaccine. Prevention of tick bites includes the daily
grooming of dogs to remove ticks and use of repellents or insecticides in
the form of collars, dips, sprays or creams. A discussion of vaccination
for the prevention of Lyme disease follows here.
Lyme Vaccines: Benefit or Risk?
This section of the article addressing the pros and cons of
Lyme vaccination pertains to those dogs living in areas of the US
considered endemic for Lyme disease (New England, the
mid-Atlantic coastal states from North Carolina to New England and
including Pennsylvania, Wisconsin, Minnesota, Michigan, Illinois,
Missouri, Iowa, California and Oregon). Unless a dog living
outside of these states travels to an endemic area, then risk for
Lyme infection in said dog is only about 1%. As such, clinical
experts agree that dogs living outside of these areas should not
be vaccinated for Lyme disease because benefits of vaccination are
outweighed by risks associated with vaccine side-effects.
The Need for Lyme Prevention. Early arguments directed against
vaccinating for Lyme disease included the observation that although up to
80% of dogs in endemic regions become infected with B. burgdorferi,
only 5% of these dogs actually go on to manifest clinical symptoms of
disease. In light of this and the fact that clinical symptoms appear to
respond well to antibiotic treatment, Lyme disease in the canine has not
been viewed as a particularly life-threatening disease. Recent clinical
information suggests, however, that Lyme disease may not be as benign as
formerly believed. Examination of dogs experimentally infected with B.
burgdorferi and then treated with the usual course of antibiotics has
shown that despite reduction of joint lesions, bacterial infection was
still present. This finding probably explains recurrent cases of Lyme
disease observed in some dogs previously treated for infection. In another
clinical study, histological examination of joints from dogs
"cured" of Lyme disease showed progressive arthritis in joints
previously infected with the bacteria. Furthermore, in some rare cases, B.
burgdorferi infection transmitted by ticks leads to a fatal kidney
disease, Lyme nephritis, for which Labrador retrievers and Golden
retrievers appear to have a higher predisposition. Since vaccines that
inoculate against B. burgdorferi only protect against infection if
they are administered prior to infection, more clinicians are recommending
preventative vaccination as the best defense against Lyme disease.
Commercial Lyme Vaccines. There are currently two Lyme vaccines
available. The first vaccine has been around for nearly a decade and is a
killed, whole-cell bacterin. Though administration of this vaccine is
generally safe, observations supporting its efficacy to prevent infection
are not very strong since laboratory animals (hamsters) immunized with
this vaccine and later challenged with ticks infected with B.
burgdorferi went on to develop arthritis several weeks or months
A second vaccine which became available for dogs in
1996, consists of a recombinant outer surface protein A of B.
burgdorferi (OspA). This vaccine induces a immune response to one
specific protein on the surface of the bacterial organism. The same type
of vaccine has recently been approved by the Food and Drug Administration
for human immunization. Interestingly, the antibody induced by the OspA
vaccine in the host actually works by stopping the bacteria while it is
still in the tick. When a tick attaches to a vaccinated host and begins to
feed, blood from the host contains the antibody to the bacteria. The
antibody will bind to and block the bacteria in the mid-gut of the tick
before it can migrate to the salivary glands of the tick and be passed to
the host. As a result, the host does not become infected. Unfortunately,
however, the antibodies cannot cure infection if the dog has already been
exposed to B. burgdorferi.
Limitations to Safety and Efficacy. As with all vaccines, there are
several limitations that may influence safety and efficacy of the OspA
vaccine. In terms of safety, recent clinical studies exploring persistent
arthritis in humans infected with, but treated for Lyme disease has
identified a condition referred to as "molecular mimicry"
involving B. burgdorferi. It has been observed that a small
population of individuals have inherited a protein on their cells that is
immunologically identical to OspA found on the surface of B.
burgdorferi. When these people become infected with the Lyme disease
organism, their bodies make antibodies to this protein in order to
fight-off the infection. Once the infection is eradicated, however, these
antibodies will continue to attack their own cells which have this same
surface protein. Hence, symptoms of arthritis and inflammation will
persist despite the fact that the bacterial infection is cured. Therefore,
in a small population of individuals receiving the OspA vaccine, it is
anticipated that the vaccine may induce symptoms of arthritic disease in
the absence of infection. Though incidence of molecular mimicry has not
been examined for occurrence in dogs specifically vaccinated with the OspA
vaccine, some dogs develop Lyme symptoms even though they have antibodies
only for the Lyme bacterin (vaccine-induced). This finding may be
indicative of a vaccine-associated arthritic syndrome and suggests that
similar to humans, a small population of dogs may be at higher risk for
developing a reaction to vaccination with the OspA Lyme vaccine. This idea
is further supported by a recent clinical study in which laboratory
animals (hamsters) injected with recombinant OspA protein, the same
protein used to manufacture the OspA Lyme vaccine, and then later
challenged with B. burgdorferi developed severe destructive
arthritis. Furthermore, when animals were immunized with another form of
an OspA subunit vaccine, greater than half of them went on to develop this
severe form of arthritis after infection with B. burgdorferi. When
OspA was combined with aluminum hydroxide, a compound often added to
vaccines to increase immunogenicity, all the vaccinated animals developed
severe arthritis after being challenged with B. burgdorferi. These
findings suggest the potential that OspA vaccines, though protecting
against bacterial infection, may contribute to or even exacerbate an
immune-mediated arthritic syndrome associated with Lyme disease in some
individuals. In regard to this latter information, however, one must
recognize that this is an experimental model and that these findings have
not yet been explored in the dog.
There are two considerations when addressing
limitations of efficacy with the OspA vaccine. The first entails duration
of protective immunity. In light of the recent controversy surrounding
frequency of booster vaccinations, it is once again important to reiterate
that the current consensus regarding long-term duration of immunity to
viral antigens such as distemper, parvovirus, adenovirus, coronavirus,
etc. should not be generalized to bacterin vaccines. Bacterin vaccines
which provide immunity against Lyme disease, Leptospirosis and kennel
cough are of short-term duration with immunity wearing-off within 12
months of vaccination. Indeed, clinical studies with the OspA vaccine for
Lyme disease found complete and protective immunity up to 6 months
following inoculation but the importance of a yearly booster vaccine,
prior to the early spring and tick season, is necessary for continued
protection against Lyme infection. The second limitation to efficacy with
OspA is the potential for Lyme disease caused by infection with a
different strain of B. burgdorferi for which antibodies directed at
OspA will not recognize. Currently, this is not a concern in the US where
90% of the strains have the OspA, however, over the course of time it is
not unheard of for less common, resistant strains to become more
prevalent. This is currently an issue concerning Leptospirosis infection
and vaccination (see Canine
Leptospirosis: Current Issues on Infection and Vaccination).
Frequently Asked Questions Concerning Dogs and Lyme
If my dog becomes infected with Lyme disease, can I get Lyme disease
from my dog?
No. Although B. burgdorferi have been found
in the urine and saliva of infected dogs, the bacteria do not survive well
in these media and would not be viable to bring about clinical infection
in another host.
Can my dog contract Lyme disease if he/she is bred to an infected dog?
No. B. burgdorferi do not maintain viability
in semen or vaginal secretions and therefore would not bring about
clinical infection if transmitted during breeding.
Does owning a dog put me at higher risk for getting Lyme disease?
Not likely. If your dog picks up infected ticks
while out in the woods the risk that the dog may transport the infected
tick to you is considered very unlikely. Once on the dog's hair, the ticks
usually seek out the skin where they will embed. Since ticks are not
intermittent feeders, once attached, the tick will only become detached
once it completes its feeding or if it is removed.
What will happen if my dog already has Lyme disease, without any
symptoms, and I vaccinate him?
It is unknown what effects, if any, vaccinating an
infected, asymptomatic dog will have. Clinical studies suggest that the
vaccine will not assist in eliminating the present infection. Major health
problems have not been reported for administering vaccine to dogs that
already have the disease. To avoid potential complications, however,
serological testing may be performed prior to vaccinating. If the dog is
found to be sero-positive for Lyme, the dog can be treated with
antibiotics first, then vaccinated to prevent re-infection at a later
What other diseases may appear as Lyme disease?
Other diseases with symptoms that closely resemble
Lyme disease include but are not limited to: rheumatoid arthritis,
infectious or immune-mediated arthritis (e.g. systemic lupus erythmatosis),
osteopathies, degenerative joint diseases, Rocky mountain spotted fever,
ehrlichiosis, and bacterial endocarditis.
Should I keep my dog on antibiotics to prevent infection?
Dogs in endemic areas are exposed to ticks too
frequently to use prophylactic antibiotics on a regular basis. An
alternative is to check your dog daily for ticks. Since ticks must be
embedded for more than 24 hours to cause infection, removing ticks on a
daily basis will decrease risk of infection in your dog.
I live in an endemic area, should I vaccinate for Lyme disease?
When considering any vaccine, one must take into
consideration and weigh the benefits and risks of administering the
vaccine. It is estimated that at least 80% of dogs in endemic areas will
become infected with Lyme disease. As such, this constitutes a high risk
for dogs in these areas and reinforces the need for some form of
prevention to protect dogs from infection. Alternatives to vaccines (such
as daily grooming and removal of ticks with concomitant use of tick
insecticides and repellents) are viable approaches for protection against
Lyme infection, however, to be effective, they require firm commitment and
diligence by the dog owner. If a dog owner is not meticulous in carrying
out these alternatives, then the dog will remain in the high risk category
for Lyme infection. In such an instance, vaccinating healthy dogs against
Lyme disease becomes the next best form of protection. The ultimate
decision to use the Lyme vaccine, however, should be discussed at length
with your veterinarian. Some of the direct risks associated with Lyme
vaccine are discussed above, for more information on general risks of
vaccination please refer to Vaccines,
Infectious Diseases, and the Canine Immune System.