Lyme Disease
November, 1996
Lyme Disease is a serious infectious illness threatening both
humans and dogs who spend their time in tick infected areas. It
is caused by Borrelia burgdosferi, a spiral-shaped bacteria known
as a spirochete. The disease was first found in the mid nineteen
seventies in Lyme, Connecticut. Now it is found throughout the
United States, but is most common along the East Coast, the West
Coast and upper Midwest. The organism has been isolated from at
least six different ticks, but the primary vector in the
transmission of Lyme Disease is the Deer Tick, carried by the
White Tailed Deer as well other mammals and even birds. The
larvae and nymph stages of the tick’s life-cycle acquire the
infection while feeding on small mammals and even, frequently the
white-footed mouse. The organism is then spread to humans and
dogs while nymphs, or adult ticks, are feeding on these hosts.
Ticks need to be attaches to their host for 48 - 72 hours for
effective transmission to occur. Therefore, early detection and
removal of ticks is an important preventive measure.
Lyme Disease was not reported in dogs until 1984. The most common
syndrome involves sudden onset of lameness, fever, lethargy and
poor appetite. One or more joints may be involved. Pain is
present on manipulation of infected joints, with or without
swelling. Occasionally lymph nodes are enlarged. Sometimes the
pain is more generalized and the dog is reluctant to move,
extremely depressed and has a high fever. Just as in humans with
Lyme Disease, the infection may become chronic, with recurring
bouts of lameness shifting from one joint to another. Less common
signs include kidney disease, heart disease (such as irregular
heart rhythms) or neurological signs (such as seizures or nerve
paralysis). The typical bulls-eye rash seen at the site of the
tick bite in humans may not be seen on the dog.
Diagnosis is difficult and is frequently based only on clinical
signs, a history of likely exposure to Lyme infected ticks and a
favorable response to antibiotics. It is difficult or impossible
to isolate Borrelia burgdosferi from infected individuals and
blood tests that measure antibodies are not reliable enough to
base a diagnosis on. The common screening test produces a number
of false positive results and a more specific test, the Western
inamunoblat test, can give false negative results, especially
early in the course of the disease, when it is most responsive to
antibiotics. Diagnosis is further complicated by the fact that
the incubation period is lengthy and variable, usually one to
five months.
The antibiotic most frequently used to treat Canine Lyme Disease
is amoxicillin. Other good choices include tetracycline,
doxycycline, cephalexin and chloramphemical. If caught early in
the disease ten to fourteen days of treatment can result in a
cure. When recurrent lameness is seen, one month of treatment at
a time is warranted, Pain relievers, such as aspirin or cortisone
are rarely needed, because response to antibiotics is usually
rapid.
Prevention of Lyme Disease is accomplished by decreasing tick
bites and by vaccinating dogs that are considered susceptible.
Insecticidal collars, sprays, shampoos and dips are available.
Many effective ones contain permathrin as the active ingredient.
One compound found in many human insecticidal products,
diethyltobiamide, or DEET, is a very effective tick repellent,
but can be toxic to dogs. Cutting thick brush or grass, limiting
exposure to high risk areas, and prompt removal of attached ticks
(less than 48 hours, as previously mentioned) are effective
methods of control. A safe and effective method of tick removal
is to wear gloves and grasp the attached tick with small forceps
or tweezers as close as possible to the skin. Moving the tick
back and forth while applying gentle traction can extract the
tick with its head intact. Leaving the head behind rarely causes
a serious reaction in the dog.
Two vaccines are currently licensed for use in protecting dogs
from Lyme Disease. They do not affect ticks at all, but are
designed, like all vaccinations, to stimulate the dog to produce
antibodies against the disease. Recent studies show vaccination
to be 80 - 85% effective in preventing clinical signs of Lyme
Disease with minimal side effects. The effectiveness is
significantly decreased if given after likely exposure to the
organism. I recommend vaccination of all puppies that will spend
any time in or near areas where Lyme Disease exists.
You can write to Mark Siverio, DVM
c/o SPO Magazine.