I have been
talking with some of the pet owners here at the company about
their concerns for their pets. These topics will be discussed in a
series of articles on this web site. These articles are in no way
meant to replace the advice of your veterinarian. They are meant
to supply knowledge because knowledge is empowering. -- Dr. Lisa
Your Pet and Lyme Disease
Lyme disease (borreliosis) is an infectious, tick-borne disease
caused by Borrelia burgdorferi, a type of bacteria called a
spirochete because of its corkscrew shape. Lyme disease was first
recognized in 1975 when an unusual outbreak of rheumatoid
arthritis occurring in children was reported in Lyme, Connecticut.
In 1982, the bacteria Borrelia burgdorferi was determined
to be the cause of that outbreak. This disease was first
recognized in dogs in 1984.
As you can see from the map below, only a relatively small portion
of the United States is endemic for the disease. This map was
obtained from the Centers for Disease Control and Prevention
website, which has a large amount of valuable information on this
topic.
B. burgdorferi requires a tick as a carrier and those are
the Ixodes ticks. This bacterium also requires a population of
wildlife to be the intermediate hosts. B. burgdorferi lives
in mice, deer, and other small mammals where they replicate
without causing these animals to become sick. When a new tick
feeds on infected wildlife, the tick picks up the bacteria that
are then transmitted to another animal the next time the tick
feeds.
For a tick to transmit the bacteria, it must be attached to the
host for at least 48 hours. If a tick dies or is removed within
this 48-hour period, transmission of the bacteria will not occur.
Even if a tick is a carrier of B. burgdorferi and it
attaches to the dog for more than 48 hours, the dog may not
contract the disease. Some studies indicate that bitches that
become infected while pregnant can transmit infection to their
fetuses.
Clinical Signs
Clinical illness usually occurs two to five months after initial
exposure, and the likelihood and the severity of the disease seem
to vary with the animal's age and immune status. Cats can develop
Lyme disease, but it occurs rarely in them, even in endemic areas.
Other domestic animals such as horses have contracted Lyme
disease, but it does not appear to be a significant problem.
The first stage of human Lyme disease, a skin rash called erythema
chronica migrans, is rarely seen in dogs. Dogs show several
different forms of the disease, but by far the most common
symptoms are a fever of between 103 and 105 degrees, shifting leg
lameness, swelling in one or more joints, lethargy, and loss of
appetite. Dogs show sudden lameness and sometimes signs of severe
pain. Joints are often swollen, hot, and painful on manipulation.
Lameness may recur after a period of several weeks' recovery.
Arthritis to the affected joints may be a result of incomplete
treatment or no treatment.
A few dogs have developed severe progressive renal disease as a
result of Lyme disease. This severe kidney failure is
nonresponsive to treatment and death is often the outcome but
fortunately, this form appears to be rare.
Diagnosis
The standard blood test (ELISA) detects antibodies made by the dog
in response to infection with B. burgdorferi. This means
that the test is not very specific. Dogs that are exposed to the
organism but fight the infection off on their own will show a
positive test as well as vaccinated dogs. However, the test can be
used along with several other criteria to gain a positive
diagnosis. Suspected animals should have a history of tick
exposure, compatible clinical signs, and have a rapid response to
antibiotic therapy along with the positive ELISA testing in order
to make a more positive diagnosis.
The western blot is a technique that determines antibodies against
multiple antigens of B. burgdorferi. This test can
distinguish between dogs that have been or are infected and dogs
that have been vaccinated against Lyme disease. It can also detect
the dog that has been both infected and vaccinated. The ELISA test
is a quantitative determination of all the antibodies produced
against many antigenic components of B. burgdorferi. The
western blot determines the unique pattern of antibodies produced
against antigens of a tick-induced infection, which is different
from the pattern produced following vaccination. This test is more
expensive than the standard ELISA test.
Treatment
Treatment for Lyme disease is fairly straightforward and consists
of using either a tetracycline or penicillin-based antibiotic.
Several tetracyclines, such as doxycycline, and penicillin-like
antibiotics, including amoxicillin and ceftriaxone, are very
effective. Because B. burgdorferi has the tendency to
persist in dogs, antibiotics should be given for three or four
weeks, even though a beneficial effect can be seen after a few
days of treatment. The long duration of therapy is also warranted
because this organism multiplies very slowly. It can take 12 hours
or more to double in number as opposed to minutes like most other
bacteria. However, some preliminary studies show that some animals
may not even clear the organism after 30 days and will relapse
once the antibiotic is discontinued. In these cases, the animal
may have to be on the antibiotic for much longer. It appears that
some animals may never completely rid themselves of B.
burgdorferi despite aggressive treatment. These animals may
suffer from increased degenerative changes in the joints leading
to premature arthritis.
Prevention
There are two approaches to preventing infection in dogs. One is
to control the tick population by using tick repellents and/or
grooming daily. The other is vaccination. Attempts to reduce the
deer tick population by radically reducing the deer population
have been only somewhat successful because other wildlife can
replace the deer as hosts. Selective chemical control of ticks in
areas appears to be more promising, although only small areas can
be covered.
Tick control is probably the most important thing an owner can do
to prevent Lyme disease in their pet. Ticks carry many other
diseases besides Lyme disease. By preventing ticks from attaching
to your pet, you will be preventing more than just Lyme disease.
Avoiding areas of high tick infestation during periods when ticks
are active is one of the best ways to avoid contact.
Using insecticides on the dog that repel ticks is another method.
With the introduction of once-a-month topical insecticides, tick
control has gotten easier and more effective. Please read the
labels carefully because some products are not meant for cats.
Studies have shown that amitraz collars are very effective at
preventing transmission of B. burgdorferi. Amitraz is an
organophosphate that is very effective at repelling and killing
ticks but has little effect on fleas. Despite the claims made by
many products to be effective against ticks, do not be fooled.
Ticks are very tough and hard to kill.
There are several whole-cell, killed vaccines on the market that
are licensed for use in the dog, but total protection through
vaccination is difficult. One reason is that a strain of Borrelia
bacteria can mutate into a different strain. Unfortunately,
antibodies made in response to one strain will not always be able
to kill a different strain. In addition, if an animal is
previously infected with the disease, the vaccine will not offer
any protection. These facts coupled with the relatively long
incubation period (up to 5 months) contribute to the failure of
some of these vaccines in preventing disease.
If you would like more information, you can search the web site
for the Centers for Disease Control and Prevention. If you are
concerned about your pet's protection, contact your veterinarian.
They can help you tailor a prevention program to suit your pet
specifically.
References:
Elfassy OJ, Goodman FW, Levy SA, Carter LL. "Efficacy of an
amitraz-impregnated collar in preventing transmission of Borrelia
burgdorferi by adult Ixodes scapularis to dogs." Journal
of the American Veterinary Medical Association 2001 Jul
15;219(2):185-9.
Grauer GF, Burgess EC, Cooley AJ, Hagee JH. "Renal lesions
associated with Borrelia burgdorferi infection in a
dog." Journal of the American Veterinary Medical Association
1988 Jul 15;193(2):237-9.
Gustafson JM, Burgess EC, Wachal MD, Steinberg H.
"Intrauterine transmission of Borrelia burgdorferi in
dogs." American Journal of Veterinary Research 1993
June;54(6):882-90.
Levy SA. "Veterinarians still faced with difficulty in
diagnosing Lyme disease." DVM Magazine.
Magnarelli LA, Anderson JF, Schreier AB, Ficke CM. "Clinical
and serologic studies of canine borreliosis." Journal of the
American Veterinary Medical Association 1987 Nov 1;191(9):1089-94.
Sheets JT, Rossi, CA, Kearney BJ, Moore GE. "Evaluation of a
commercial enzyme-linked immunosorbent assay for detection of Borrelia
burgdorferi exposure in dogs." Journal of the American
Veterinary Medical Association 2000 May 1;216(9):1418-22.
Straubinger RK, Straubinger AF, Summers BA, Jacobson RH, Erb HN.
"Clinical manifestations, pathogenesis, and effect of
antibiotic treatment on Lyme borreliosis in dogs." Wein Klin
Wochenschr 1998 Dec 23;110(24):874-81.
Straubinger RK, Summers BA, Chang YF, Appel MJ. "Persistence
of Borrelia burgdorferi in experimentally infected dogs
after antibiotic treatment." Journal of Clinical Microbiology
1997 Jan;35(1):111-6.
