Veterinary Technician Advice: What is
Lyme Disease?
By Kami R. Guy, CVT
Lyme disease is an infection that can occur in both animals and humans and is
spread by ticks. It has been recognized in Europe for almost 100 years but was
not found in the United States until 1975 when Dr. Allen Steer of Lyme,
Connecticut discovered it following a mysterious outbreak of juvenile rheumatoid
arthritis. The infection is caused by a spirochete; a corkscrew shaped
bacterium, Borelia burgdorfei. It got the name when Willy Burgdorfer isolated
the spirochetes and found that it belonged to the genus Borrelia that comes from
the mid-guts of Ixodes ticks. It has been found that 85% of the cases occur in
the northeastern and mid-Atlantic areas of New York, Pennsylvania, New Hampshire
and all the coastal states from Maine to North Carolina. While 10% come from the
Midwestern areas of Wisconsin, Minnesota, Michigan, Illinois, Missouri and Iowa,
only 4% come from California and Oregon. That leaves 2/3 of the United States at
minimal risk of contracting Lyme Disease. The three types of ticks that most
commonly spread this disease are the Deer (bear) Tick, the Western Black-legged
Tick and the related Black-legged Tick. These ticks require three different
hosts and four different developmental stages to complete their two year life
cycle.
In the spring, the female lays about 2000 eggs and in the summer
the larvae emerge. They do not carry sufficient bacteria to induce infection and
most commonly feed on the white-footed mouse. The larvae become infected with
the Lyme Disease bacterium by feeding on a previously infected mouse. After the
larvae feed they drop off of the mouse and enter a resting stage for the winter.
The following spring the larvae molt into nymphs and begin feeding on many
animals such as the white-footed mouse, white tailed deer, dogs and humans. Only
25% of nymphs are infected with the disease and it is these ticks that will
infect the new host in their four-day feeding. If they are not already infected
with the disease they are able to get the disease from infected animals during
this four-day nymph feeding time. In the fall of this year the nymphs will molt
into adults. On the average, 50% of all adult ticks are infected with Lyme
Disease and are the main sources of transmission to dogs. While the adult ticks
are feeding on the host they will mate. The female will feed for 5-7 days and
then fall off to rest for the winter before laying her eggs the following
spring.
There are many signs of illness from this disease. The clinical
illness usually occurs within 2-5 months after exposure and the severity of the
disease is likely to vary with the dog’s age and immune status. Most dogs will
show symptoms of sudden lameness and severe pain with one or more joints
involved. Many times the infected joint will be swollen, hot and painful on
manipulation. Other signs that may occur are fever between 103-105 (normal is
101-102.5), swollen lymph nodes, anorexia, lethargy, myocarditis (a cardiac
disease), glomerulonephritis (a kidney disease) and in rare cases, neurologic
disease can occur. Since this disease can mimic many other diseases the best
diagnosis is response to antibiotic treatment.
There are three forms of
diagnosis of this disease. As mentioned in the last paragraph, antibiotic
treatment is the most used form of diagnosis. Another form of diagnosis is the
ELISA (Enzyme-linked Immunosorbant Assay) test that is performed by
collaborators in a diagnostic laboratory of a College of Veterinary Medicine.
This test is most useful in dogs that have not been vaccinated since these tests
cannot distinguish the dog’s antibody response from a vaccine or tick exposure.
The last test that can be performed is the Western Blot Technique. This
technique can distinguish between a dog that has been vaccinated and one that
has been exposed to or infected with this disease. This test can also detect a
dog that has been both vaccinated and infected. There are four criteria that
help in the diagnosis of Lyme Disease:
1. History of exposure to
ticks in endemic areas
2. Typical Clinical signs
3. A positive
antibody test
4. A quick response to antibiotics
It is very
unlikely for a dog to have Lyme disease if only one or two of the criteria are
met. At least three criteria have to be meet to confirm diagnosis.
There
is very little that can be done for this disease. The main form of treatment is
antibiotic therapy. The most common antibiotics are Tetracyclines such as
Doxycycline and Penicillin types such as Amoxicillin and Ceftriaxone. Since this
disease has a tendency to persist in dogs, antibiotics should be continued for
three to four weeks although the effects can be seen in two to three days. The
prognosis of this disease is good and in most cases the dog will fully recover.
In rare cases the dog may have a recurrence of the disease either by relapse of
initial infection or by reinfestation by an infected tick. Again, the dog will
respond to antibiotics and should have full recovery.
There are two
forms of prevention of Lyme Disease. The most important is tick prevention.
Using insecticides made for dogs that are applied once a month to repel ticks is
the best method. Flea and tick collars are not effective except the new Amitraz
collar. Using a spot on tick repellent monthly and an Amitraz tick collar will
provide the best protection in highly endemic areas along with keeping your pet
and yourself away from grassy areas with lots of shrubs and brush. The second
form of prevention is vaccination. Since no vaccination is 100% effective, tick
prevention is also necessary along with the vaccination. Treating the yard where
the dog stays is another form of prevention that will help keep ticks off the
area where the dog spends most of its time.
Ticks carry more than just
Lyme disease and preventing them from attacking your pet, will help to eliminate
all of these diseases. In the coming articles I will be writing about these
diseases.
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