Pneumonia and PCD Studies and Treatment Protocol

Treating Chronic Pneumonia/PCD

There are some dogs that require maintenance antibiotics all the time. These dogs may be kept on first generation cephalosporins or Clavamox for maintenance. Third generation cephalosporins, or azithromycin (Zithromax), are reserved for acute infections with clinical signs. Occasionally, resistance to some of these antibiotics develops, and it may be necessary to change to a combination of enrofloxicin (Baytril) and ampicillin. Doses should be determined by your veterinarian.

Dr Casal uses the following protocol in a university clinic setting:

Cephalexin: 22-30 mg/kg twice daily for dogs who have had chronic pneumonia until the next pneumonia occurs, then

Zithromax: 5-10 mg/kg. To prevent nausea from the Zithromax, the first dayʼs dosage is 5mg/kg, then increase the dose to 10mg/kg from the second day on. Continue the high dosage amount of Zithromax until 5 days after the last clinical signs have disappeared.

Chronic Pneumonia, Rhinitis, and PCD: Are They Related?

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 were 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 doesnʼt. 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 deduce 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.