Questions and Answers
August, 1998
Dear Dr. Silverio,
Would Erlichia or Lyme’s disease show up in a spinal tap or
by imaging an MRI? My Shep/Collie mix dies from some sort of
undiagnosed neurological disorder. He had an MRI and a spinal
tap, both having shown nothing. During a 6 month period he had
bizarre seizures (paddling, sniffing at invisible flies, etc.)
and at the 6th month, vestibular disease. That was when he went
in for testing, and died of aspiration pneumonia at the end.
The neurologist speculated he had either a tick-borne disease or
GME. My dog had never shown signs of any other illness during his
life. He was very active and seemingly healthy for a dog of 13,
except for the problems I just described.
Have you ever seen or heard of a case like this? I’ve spoken
with a few other vets but no one can help me. I am frightened my
new puppy may develop this disorder.
Thank you (I know you are very busy))
RKetley933@aol.com
Dear R. Ketley,
I’m sorry for the loss of your companion. It seems that you
miss him very much. Unfortunately, false-negative results occur
with possibly every diagnostic test available, including a spinal
tap and the very sesitive MRI. The likelihood of a tick-borne
disease depends on several factors, such as the prevalence of
these diseases in your area, any other signs your dog showed, and
the results of any other test performed.
Most of the potential causes of seizures can be ruled out from
the information you supplied. Epilepsy is very common but starts
earlier in life. Poisonings, such as lead, insecticides,
strychnine, antifreeze and snail bait would be more short-lived.
Infections such as canine distempter virus, Rabies, or the
coccidian parasite Toxoplasmosis (SPO Dec. ‘97) are not
likely to have a chronic course as you described.
Both of the infections you mentioned, Lyme disease (SPO Nov.
‘96 and July ‘97) and Ehrlichiosis (SPO March ‘97)
can last for months. These diseases, which are both carried by
ticks, would be strong possibilities if your dog had shown some
other signs. They can both cause general signs such as lethargy,
poor appetite and fever, and Lyme commonly causes lameness. If
none of these signs were seen, there was no know tick exposure
and these infections are rare in your area, I would be suspicious
of a space-occupying brain lesion, such as a brain tumor or the
inflammatory disease GME (granulomatous
meningoencephalomyelitis).
The cause of GME is unknown, but it is associated with excessive
inflammation in the central nervous system (the brain and spinal
cord). It can sometimes be controlled with corticosteroids (SPO
March ‘98), but it always progresses. GME sounds more likely
in this case because it can hide from detection by MRI more
easily that a brain tumor and it can hit multiple sites in the
central nervous system. Apparently your dog had at least 1
seizure focus in the brain and then vestibular signs (equilibrium
and balance problems caused by an alteration in the vestibular
apparatus) and finally aspiration pneumonia. I’m assuming
aspiration occured due to a disturbance in the nerves that
control the swallowing reflex. It sounds as if several areas of
the central nervous system were affected over time, and that best
fits a diagnosis of GME. This is a disease which you could not
have prevented or cured, and it has never shown signs of being
contagious, so you don’t have to worry about your new puppy
getting this life-threatening disease.
Dear Dr. Silverio,
As a point of information, I read an article in a rival magazine
(June 1996). It pertains to a study of the development of a
vaccine to immunize dogs against brown dog tick disease. The
potential of this vaccine would kill the tick before it could
transmit any disease.
This study, by Omar O. Barriga, DVM PhD - and his team of
investigators, is proposing to develop an antigen (any substance
that causes the body to become immune) that prevents ticks from
feeding and reproducing, thus possibly preventing the release of
disease pathogens from the tick into the bloodstream of dogs. It
states that traditional methods of tick control (shampoos, dips,
and tick collars) which use chemicals to destroy ticks are
becoming less effective because of the resistance being developed
to these chemicals. This is a one year Morris Animal Foundation,
sponsored study made possible by the Bernice Barbour Foundation,
Inc.
Has anything been concluded from this study? Has such a vaccine
been developed?
Harry Marini
Tri-County of Mass. Beagle Club
Dear Harry,
A past article in SPO Magazine (Nov. ‘96) mentioned the
conventional methods of tick control, which involve modifying
their habitat and treating with chemicals to kill ticks on human
and animal hosts. Recent research is directed at finding a
vaccine against ticks. At first, this seems like an unusual
concept. All of our routine vaccines protect against viral or
bacterial disease. These microscopic organisms have the potential
to get into the bloodstream, where they can be recognized as
foreign intruders by the immune system, which then produces
antibodies to attack them. Vaccines are produced by killing or
modifying these disease-causing microbes so they no longer can
create disease, but can still be recognized by the immune system.
When injected into a person or animal, they stimulate the
production of antibodies against that specific organism, so that
an effective attack can be mounted if a true infection occurs.
Because ticks are not microscopic organisms capable of entering
the bloodstream, antibody protection is not part of our natural
protection against ticks. However, researchers have been able to
identify specific proteins vital to the makeup of the tick
intestinal tract. When these proteins are used as a vaccine,
antibodies are produced against them. When an unsuspecting tick
feeds on a vaccinated host, his gut fills with the blood
containing the antibodies and the damage is done.
Australia has already licensed the only commerically available
anti-tick vaccine. The only problem is that it takes 6 days or
more of feeding for the tick to die, where ticks carrying
diseases such as feeding for the tick to die, where ticks
carrying diseases such as Lyme, Ehrlichiosis or Rocky-Mountain
Spotted Fever usually spread these organisms within 2 or 3 days.
The vaccine is therefore effective against the minor annoyance or
skin itchiness that ticks can cause, but not against the more
serious problem of transmission of harmful and life-threatening
diseases. Ticks apparently already have a well-developed defense
system of binding proteins that attach to potentially harmful
antibodies and transport them out of the gut to the salivary
gland and the feeding site, where they do no damage.
Research fosucing on the use of tick salivary gland components in
anti-tick vaccines has been unsuccessful. If we can develop a
vaccine against the binding proteins and combine it with the
existing vaccine, we may be able to kill ticks before they can
transmit disease.