Canine ehrlichiosis
is a disease of dogs and wild canids (e.g.;wolves) and
is found worldwide. Canine ehrlichiosis is also known
by other manes such as ‘tracker dog disease, ‘tropical
canine pancytopenia,’ ‘canine hemorrhagic
fever,’ and ‘canine typhus. ‘It affected
a large number of military dogs in the war in Vietnam.
What causes ehrlichiosis?
Enrlichiosis in dogs is most commonly caused by Enrlichia
canis, E.chaffeensis, E.ewingii, and possibly E. ruminantium.
There are multiple strains of Ehrlichia, affecting different
species of animals. Some also affect people. Some organisms
that were formerly classified as Ehrlichia have now
been reclassified as Anaplasma. The Ehrlichia organisims
are what we call rickettsia, which on the evolutionary
scale are between bacteria and viruses.
How is Ehrlichia transmitted?
Ehrlichia are transmitted by ticks including the Brown
Dog Tick, Rhipicephalus sanguineus and the Lone Star
Tick Amblyomma americanum. The immature form of the
tick feeds on an animal infected with Ehrlichia. When
these immature ticks or a mature form of the tick feeds
on another animal, the Ehrlichia is passed on to that
animal, The Ehrlichia can remain alive in the developing
tick for up to 5 months. This means a tick could become
infected in the fall, and infect a dog the following
spring. Because the disease is transmitted by these
ticks, it can occur wherever Brown Dog and Lone Star
Ticks are found. Almost every state in the United Stated
has reported a case of ehrlichiosis.
What are the symptoms of ehrlichiosis?
Ehrlichiosis can have three phases. Signs of the acute
phase of the disease usually develop 1-3 weeks after
the bite of the infected tick. The acute phase of the
disease generally lasts 2-4 weeks. The Ehrlichia enter
white blood cells and reproduce inside of them. In addition
to the blood, these cells are found in the lymph nodes,
spleen, liver, and bone marrow. Platelets, the small
cell fragments that help blood to clot, are often destroyed,
as well. As a result of the infection, the lymph nodes,
liver, and spleen are often enlarged. Anemia, fever,
depression, lethargy, loss of appetite, shortness of
breath, joint pain and stiffness, and bruises are often
seen. Many dogs will be able to fight off the infection.
If not, they enter the subclinical phase.
In the subclinical phase the animal may appear normal
or show only slight anemia. During this phase the Ehrllichia
live inside the spleen. This phase can last for months
or years. Ultimately, the dog either eliminates the
Ehrlichia from the body or the infection may progress
to the chronic phase.
The chronic phase can be either mild or severe. Weight
loss, anemia, neurological signs, bleeding, inflammation
of the eye, edema (fluid accumulation) in the hind legs,
and fever may be seen. Blood tests show that one or
all of the different blood cell types are decreased.
One cell type, the lymphocyte may increase and be abnormal
in appearance. This can sometimes be confused with certain
types of leukemia. If a dog becomes chronically infected,
the disease can keep coming back, especially during
periods of stress. In some cases, arthritis or a Kinney
disease called ‘glomerluonephritis’ may
develop.
A decrease in the number of platelets (platelets help
the blood clot) in the blood is the most common laboratory
finding in all phases of the disease. Changes in the
protein levels in the blood are common. The most common
protein, albumin, is decreased and other types of protein
called ‘globulins’ are increased. Since
one tick could be infected with and transmit more than
one disease (e.g.;haemobartonellosis or babesiosis),
It is not all that uncommon to see a dog infected with
more than one of these diseases at a time, which generally
causes more severe symptoms.
How is ehrllichiosis diagnosed?
The diagnosis is based on the typical clinical signs
and results of special blood tests.
Two blood tests that detect the dog’s antibodies
(proteins produced to fight off the infection) to Ehrlichia
are available. One is called the indirect immunofluorescent
antibody (IFA) test, and the other is known as an ELISA
test. A veterinarian cannot rely solely on these tests
to make a diagnosis. The antibodies may not be detected
in the early phase of the disease, since it takes some
time for the body to make them. Also, if a dog is extremely
ill, he may not be able to produce enough antibodies
to be accurately detected. A positive test demonstrates
that the dog has been exposed to Ehrlichia, but not
that he necessarily is currently infected. In the acute
stage of the disease, the antibody level will rise significantly.
Often two tests will be done 2 weeks apart and the results
compared. Dogs with an active infection will show a
significant rise in the amount antibody present.
The antibodies can last for one or more years after
the infection, but they do not make the dog immune to
enrlichiosis – the dog could get reinfected.
A newer diagnostic test called the PCR tests for the
presence of the organism itself, not antibodies to it.
Unfortunately, it does not distinguish between live
an dead organisms.
For this reason, it is generally recommended to perform
the PCR along with one of the antibody tests to make
a diagnosis.
Sometimes, the organism can be seen inside cells on
a blood smear. To find them, a small drop of blood is
spread over a microscope slide, stained and examined
under the microscope. The organism can only be found
in the bloodstream for a few days during the acute phase
of the disease. So this method of diagnosis could miss
some cases of the disease.
How is ehrlichiosis treated?
The antibiotics, tetracycline or doxycycline are used.
Treatment is usually for 3-4 weeks, even though the
dog’s symptoms generally improve after several
days of therapy. Some dogs will need blood transfusions
or intravenous fluids depending on the severity of the
disease. Generally, the prognosis during the acute phase
is good, if the animal is properly treated. Dogs who
go on to the chronic phase have a poorer prognosis.
German Shepherds and Doberman Pinschers tend to have
a more severe chronic form of the disease. The drug,
imidocarb dipropionate, is sometimes used in conjunction
with the antibiotics. It is given as an injection, but
may not be available in all areas. Some of the damage
caused by Ehrlichia may be due to the dog’s own
immune response to the organism. For this reason, if
immune-mediated arthritis or decrease in platelets occurs,
corticosteroids (e.g., prednisolone) may be given.
How can I prevent ehrlichiosis in my pet?
Tick control is the main way to prevent ehrlichiosis.
Products which repel and kill ticks such as those containing
permethrins are excellent choices. Tick collars containing
the active ingredient amitraz (Preventic collars) are
also used, sometimes in conjunction with permethrin
products in those areas with high tick infestations.
If a large number of cases of ehrilichiosis are diagnosed
in an area, some veterinarians recommend placing dogs
on low doses of tetracycline or doxycycline during the
tick season.
There is no vaccine for ehrllichiosis.
Can people get ehrlichiosis?
Yes, The common symptoms in people include fever,
chills, headache, and muscle aches. Other less common
symptoms include nausea, loss of appetite, weight loss,
abdominal pain, cough, diarrhea and change in mental
status.
People do NOT get infected directly from a dog, but
through a tick bite. Also, the Ehrlichia species most
often implicated in human infections is E.Chaffeensis.
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