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I recently attended lectures given by Ed
Breitschwerdt, DVM, Dipl. ACVIM from North Carolina State College of
Veterinary Medicine that I found stimulating and interesting. The
Vector Borne Diseases Diagnostic Laboratory at NCSU offers the most
comprehensive veterinary panel for vector (tick and other insect)
borne diseases. At some point I would love to go into a great deal
more detail on his seminars, but for now I will restrict myself to a
few important points he raised, as well as some others I gleaned
from a lecture on the Epidemiology of Tick Borne Disease East of the
Rockies by Michael Dryden, DVM, MS, PhD. I had to miss the companion
lecture on TBD West of the Rockies.
Lyme and many other vector borne diseases (Anaplasma,
Babesia, Bartonella, Ehrlichia and Leishmania spp.) as
well as other microorganisms (Chlamydi, Mycoplasma spp. and
retroviruses) can set up long-term or even permanent house-keeping
in the body, and while treatment may control symptoms they will not
eradicate the disease. Transmission of more than one disease by a
single vector is not uncommon. These diseases can result in chronic,
insidious disease – glomerulonephritis (glomerular kidney
disease), polyarthritis) or acute decompensation – immune-mediated
hemolytic anemia (AIHA), immune-mediated thrombocytopenia (IMTP).
While these can occur in dogs of any age, breed or sex, infection in
older animals will likely be more severe and atypical of
expectations for a particular disease. The interactions between the
various organisms in a multiple disease infection can also
contribute to the range of symptoms.
A word about AIHA and IMTP would be appropriate
as they are of particular interest to Beardie owners. While we have
been led to believe that these diseases are always genetic in
origin, this is not necessarily the case when they are induced by
vector borne diseases. There is some evidence that some dogs may be
more susceptible to developing these manifestations of the diseases,
and genetics can play a role, but other factors are involved. Dr.
Breitschwerdt pointed out that the presence of AIHA, IMTP and
glomerulonephritis may obscure diagnosis of the underlying vector
borne disease. Once immunosuppressive treatment has been begun for
suspected AIHA, ITP or SLE (systemic lupus erythematosus – which
can manifest as glomerulonephritis and polyarthritis) low or
non-existent titers for tick borne disease may sky rocket. It is
always advisable to retest for tick borne diseases after starting
treatment, lest the underlying cause be missed.
The reason these diseases make us and our dogs
sick is that we are non-reservoir hosts. Parasitic diseases will not
survive if they kill their host species, and so have evolved in
conjunction with reservoir hosts – insects, mammals etc – in
which they do not cause disease. Only when they end up in the wrong
place is disease created. It has recently been shown that Ehrlichia
and Anaplasma species can inhibit white cell apoptosis
(natural cell death) and so prolong the life span of the cells they
inhabit. Chronic infection can not only complicate diagnosis of
these illnesses, it can also influence and complicate other
illnesses that a patient experiences over time – whether they are
degenerative, immune-mediated, allergic or neoplastic. As the
incidence of these illnesses increases with age, so will the
severity of bizarre presentations from vector borne and other
persistent infections. These organisms could also influence the
body’s response to normal bacteria that colonize the skin,
gastrointestinal system or urinary tract.
It has been demonstrated that many animals are
co-infected with Lyme disease and Anaplasma phagocytophilum.
Dogs with both organisms are far more likely to become severely ill
than those infected with only one of the two. The same is true of
other co-infections. Toxicity, nutrition and genetics as well as the
burden of multi-organism infection are all factors in determining
whether or not a dog will develop immunity to the disease organisms
or become sick. Antibody titers cannot determine whether a dog
becomes sick or not, they only tell us that the dog has been exposed
to the disease.
Many people believe that ticks jump onto passing
dogs from trees and tall bushes, but most ticks are found on plants
under 18” in height. There they wait upside down for a carbon
dioxide secreting organism to pass and drop off onto it. Most ticks
will therefore be found on the front end of the dog, which is the
part they are most likely to encounter. People have reported ticks
persisting well into the winter this year, and they can be expected
to be active if there is no snow cover whenever temperatures rise
over 35 oF. Further disturbing news is that the Lone Star Tick,
which as its name implies used to be primarily resident in Texas is
now found in virtually all states east of Texas up to and throughout
New England. The distribution of other tick species is also
expanding. Different ticks serve as hosts for different diseases,
and we need to improve our ability to identify the different tick
species in our area. We also need to expand our testing for tick
borne diseases to include diseases which in the past were ignored.
Lyme disease goes hand in hand with the deer
population. When settlers pretty much eradicated the white tailed
deer, they also saw virtually no ticks. The white tailed deer
population is soaring so is that of the tick. Other factors are at
play though. Ticks acquire the spirochetes of Lyme disease from
blood meals taken as larvae and nymphs from small mammals, most
often the white footed mouse. In Florida, instead of mice most
larvae and nymphs get that blood meal from lizards that do not host
the spirochetes. So despite the burgeoning populations of deer and
ticks in Florida the incidence of Lyme is only about 20% of that in
states with similar deer densities where mice are the preferred
snack. Another interesting fact is that humans are primarily
infected by ticks in the nymphal stage, much smaller than the adult,
which is also pretty small, and explaining why so few people know
they were bitten by the tick. Dogs, OTOH, are almost always infected
by the adult tick. How long it takes for the tick to infect the dog
is unclear, but it is probably less than 40 hours, much faster than
we used to believe.
Dr. Breitschwerdt likes to quote Voltaire:
“Doctors put drugs of which they know little, into our bodies of
which they know less, to treat disease of which they know nothing at
all.” We have made a little progress since the 18 th century, but
we still have a long way to go.
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PON Digest would like to extend a grateful thank
you to Dr. Aronson for allowing the use of her articles.
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