Canine Ehrlichiosis
March, 1997
Several months ago, my article dealt with Lyme Disease, a
bacterial infection spread by ticks. Another bacterial infection,
Ehrlichiosis, has some similarities to Lyme Disease. It is
tickborne, can cause chronic debilitating disease and can be
contracted by both dogs and humans. Unlike Lyme Disease, it is
carried by only one species of tick, the Brown Dog Tick. In the
U.S., it is found in the West, the Southwest and the Southeast.
There is an interesting progression of signs in dogs infected
with the bacteria Ehrlichia canis. After an acute phase of
disease, the signs resolve on their own, and then the chronic
phase starts with similar or different signs than those seen
during the acute phase.
The acute phase starts 1-3 weeks after infection occurs and may
last 2-4 weeks. Signs are usually nonspecific and include
lethargy, fever and poor appetite. During the subclinical phase,
signs have resolved but some abnormalities can still be detected
on bloodwork.
This chase usually lasts 1-2 months, but can be longer. The
chronic phase be characterized by mild signs, if the immune
system responds appropriately, but more often, this phase
involves severe illness. Many of the clinical signs seen during
the chronic phase are due to decreased bone marrow production of
blood cells.
This can include red blood cells (leading to anemia), white blood
cells (leading to susceptibility to infection) and platelets
(leading to bleeding tendencies). Other possible signs include
enlarged lymph nodes. eye abnormalities, neurologic signs and
arthritis.
Rarely, the organism can be found on a routine blood smear, so
diagnosis is usually dependent on finding antibodies against the
causative agent. Treatment involves supportive care and
antibiotics. The animal may require intravenous fluids, blood
transfusions or short-term cortisone administration.
The antibiotic of choice is tetracycline or its derivatives and
is given for a minimum of 2-3 weeks. Antibiotics are frequently
very effective if given during the acute phase, but sometimes not
effective at all during the chronic phase. Therefore, the
prognosis is mostly dependent on how early in the course of
disease treatment is begun.
Prevention can be accomplished by avoiding exposure to ticks
likely to be carrying the disease. At the present time there is
no vaccination against canine Ehrlichiosis. As previously
mentioned, people are also susceptible to infection with
Ehrlichia canis. However, tick bites are required for
transmission: the disease cannot be spread directly from dogs to
humans.