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Rhinitis, PCD, and Chronic
Pneumonia: Are They Related?
Margret L. Casal, Dr. med. vet., Phd
A syndrome of rhinitis in Irish Wolfhounds was first described by
Wilkinson in 1969. The primary symptom is a watery nasal discharge that
progresses to a purulent or even blood-tinged discharge. The discharge
usually is present at birth and may be chronic or recur at short intervals.
Many dogs develop a chronic moist cough and typically die at a young age
due to pneumonia. Most often only a part of a litter is affected and the
rest, even when housed with affecteds, are healthy. This disease has apparently
been present in the Wolfhounds for decades and has not disappeared. For
years it was thought to be caused by a virus or by an immune deficiency
(an incomplete immune system that leads to frequent infections). No one
has ever been able to isolate a virus. More recently, we have been able
to perform studies that look at the immune system in great detail and have
not found any abnormalities, suggesting that there is a different cause
for rhinitis. We have performed studies examining the function of the cilia,
the fine hair that line the airways (nasal passages, trachea and larger
bronchi). The cilia are part of the mucociliary apparatus that is responsible
for transporting particles (viruses, bacteria, dust) out of the lungs,
similar to an escalator. We have been able to observe the cilia of normal
and affected Wolfhounds in action, we have performed electronmicroscopic
evaluation of the cilia from Wolfhounds with rhinitis, and we have done
mucociliary clearance studies. We have been able to show that the cilia
from affected Wolfhounds do not beat in a coordinated fashion and that
the cilia are not lined up in parallel on electronmicroscopy. The mucociliary
clearance studies demonstrated that the particles do not clear the lungs
at the expected speed, in fact, they often did not move at all. All of
these results are highly suggestive of primary ciliary dyskinesia (PCD).
There is a second fairly common syndrome in the Wolfhounds, which we call
chronic pneumonia. These dogs have pneumonias as early as 6 months
of age, but never showed any signs of rhinitis early in life (remember:
rhinitis is just a symptom and not a cause or diagnosis). Many of the affected
dogs will have chronic recurrent pneumonia, which as most owners/breeders
know is not readily apparent to the untrained "eye". Affected
Wolfhounds (as all Wolfhounds) are of a very stoic nature and the only
sign of illness may be the reluctance to lie down or loss of appetite.
In general, the affected dogs do not cough at first, but there are often
already severe changes present on lung radiographs (X-rayed). The dogs
need to be treated immediately and our recommendation is to give an initial
dose of Baytril and ampicillin IV and then switch to azythromycin orally.
Furthermore, coupage/steam inhalation (nebulization) should be performed
and possibly a mucolytic agent given. For complete details, see your veterinarian
or contact us at the University of Pennsylvania.
What makes this chronic pneumonia interesting? It is quite possible that
this is an incomplete form of PCD. We and others have established that
PCD is inherited as an autosomal recessive trait, meaning that it takes
two copies of the "bad" or PCD gene to cause the disease in the
offspring (one copy came from the mother and one from the father). Two
copies make the cilia virtually non-functional. On the other hand, if a
dog was to inherit only one PCD gene and a normal one from the other parent,
then it is possible that half of the cilia function normally and the other
half doesn't. As the dog grows older, the mucociliary system "wears
out" (gets overwhelmed) and the normal cilia cannot keep up. The result
is pneumonia. At this time this is just a theory and has yet to be proven.
So what are we doing to get to the bottom of all of these diseases (or
this complex of rhinitis/chronic pneumonia)? Cilia have the same basic
structure as do sperm tails. This turns out to be handy because it is easier
and less traumatic to obtain sperm tails than it is to obtain tracheal
biopsies (the seat of the cilia). The plan is to compare the proteins present
in sperm tails from healthy Wolfhounds compared to affected Hounds. Jennifer
Scheidt, now a veterinary student, had been working on examining the immune
system in PCD Wolfhounds as a technician. She has now just completed developing
a method to clearly separate sperm tails from the sperm heads. This was
a time consuming task, as the preparation has to be completely free of
heads, because this would contaminate the analysis. With this method in
hand, we will submit the various samples for protein comparison and anticipate
that a difference in proteins will become clear. The differences will be
analyzed and we should be able to deduct which gene is causing the disease.
As a last step (not always an easy one), we will sequence the gene to find
the mutation. Once we have the mutation, we will be able to offer a genetic
test.
Margret L. Casal, med. vet, PhD, All Rights
Reserved
Dr. Margret L Casal, med. vet, PhD
Section of Medical Genetics
VHUP Room 4015
3900 Delancey Street
Philadelphia, PA 19104-6010
Ph: 215-898-8894
FAX: 215-573-2162
Reprint requests should be directed to the author through the IW Study
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