Virus Rhinitis and Primary Ciliary Dyskinesia

Bron: www.irishwolfhounds.org

The symptoms of these two disorders are the same, but it is almost certain that in Irish wolfhounds there are two separate disorders.

The symptoms are rhinitis (nasal discharge, usually greenish in colour and thick), a cough, wheezing breathing (the common name of virus rhinitis is snuffles). The lungs fill up with fluid and there are episodes of pneumonia. On antibiotics the lungs clear but it comes back when off them.

Some puppies are born with a nasal discharge. These are usually severely affected and survive only a few weeks. Others do not develop symptoms until later, sometimes months or even years later. The continual bouts of pneumonia cause damage to the lungs similar to - but not as severe as - that caused by cystic fibrosis. There is marked variation in the worst and least affected animals.

In the 1960s a breeder who had a problem with several litters instigated veterinary research into the disorder. It was decided that the condition was due to a viral infection (although the virus has not been isolated) but that there was an immune component, because it could not be given to healthy puppies even by injecting material from affected puppies. It was thus decided that a puppy was born with an immune deficiency and picked up the causative virus from its mother during birth. In the 1970s another researcher was looking into the condition in various breeds of dog, using the same basis for research, that of it being a viral infection of animals which were immune compromised.

It needs to be borne in mind that this is not a virus infection per se; it is an immunodeficiency disorder and the deficiency in the immune system allows the virus (if that is what the organism is) to take over and produce the symptoms that are recognised as virus rhinitis. This is different from an acute infection such as distemper but very similar in its cause to demodectic mange, in which the mite is present in all dogs but only causes a problem when there is immunodeficiency. (see page on the immune system for more details)

Primary ciliary dyskinesia (PCD) is quite a recent discovery and occurs in humans, dogs, cats, pigs, rats and mice. It is a genetic factor (usually autosomal recessive, occasionally autosomal dominant) and is due to the cilia (the hairlike structures on the mucus membranes lining areas such as the nose and lungs) being deformed structurally and in the way they are anchored. The cilia move together in a wave-like fashion to move fluids through the system and protect the respiratory system from inhaled pathogens. In PCD they are incorrectly formed, cannot move in unison, and so fluids collect, as do pathogens.

In diagnosis, apart from finding deformed cilia, the heart in about fifty per cent of cases is seen on x-ray (dorsal-ventral or ventral-dorsal, not lateral) to be over to the right instead of the left. In some cases the other internal organs may also be transposed. In males the sperm are affected, because the tail of the sperm is formed from cilia. This means that affected males are sub- or infertile, with a large proportion of the sperm immotile. The reproductive organs in bitches are likely to be very immature.

In a few cases in both humans and dogs, the cilia are structurally normal but their function is abnormal. This means that the cilia either do not move together in the normal wave motion that carries fluids through the respiratory system, or the beat frequency is abnormal.

There may be evidence on x-ray of bronchitis, bronchiectasis, and bronchopneumonia. Cases of PCD have been misdiagnosed as instances of canine distemper viral infection because of the characteristic symptoms of purulent nasal discharge, bronchiectiasis and bronchopneumonia.

Other organs can also be affected by PCD. These include the ears (giving rise to otitis media), kidneys (renal fibrosis), the brain (hydrocephalus), and the bones (abnormal sternum, vertebrae, and ribs).

Microorganisms that have been isolated from animals with PCD include Streptococcus, Staphylococcus, Pseudomonas and Mycoplasma species.

PCD has been diagnosed in Irish wolfhounds in Australia, the USA, and some European countries. One wolfhound in England, apparently suffering from virus rhinitis, has been tested and does not have PCD, so presumably he does have virus rhinitis. As others are tested we will gain some idea of whether we do have PCD in this country. The problem is (as was found in the '60s research) the condition is not widespread so it can be difficult finding enough animals to test. It has always appeared, then disappeared for a few years, then returned. All wolfhounds go back to just two littersisters, and there was only one stud dog used during the Second World War in Britain, so what appears elsewhere is likely to also be in this country.