ANAL FURUNCULOSIS (Perianal Fistulas)
Description
Anal Furunculosis is a painful condition and is described as deep unsightly sinuses that track through the skin, sometimes with flat open areas of ulceration. They are usually confined to the area around the anus.CauseThe cause is unknown, but the disease is mainly found in German Shepherds or German Shepherd crosses, aged 3-8 years. Years ago, it was thought to be due to the fact that the GSD carries the tail low, thus harbouring infection, but it is now known to be an immune mediated disease with more than one hereditary factor. Research is ongoing to try and isolate the genes responsible for causing the disease, so in the future a DNA test may hopefully become available.
Signs
The skin lesions are irritable and painful, resulting in the dog licking and nibbling the affected area. There may be pain, straining and difficulty during defecation. The dog may be reluctant for the owner to lift the tail or inspect the area due to the discomfort.
Diagnosis
is confirmed by physical examination.The very early signs are licking the anal region and slight difficulty in defecation. At this stage, only a tiny hole may be visible on the outside. This is often the 'tip of the iceberg' and should not be ignored, as the outcome is normally more successful if the condition is treated early.
Treatment
If caught early, the condition can be quite successfully treated with immuno-suppressant drug therapy. Cyclosporin (Atopica) has been used with good results, although it is very expensive and not all German Shepherds respond to it. An alternative is Azathioprine combined with Medrone and/or Metronidazole, which is cheaper and effective. Tacrolimus ointment applied topically may be used in mild cases.
Surgical treatments include Radical Surgery where all the diseased tissue is removed and the wounds left open to heal, or Cryosurgery using freezing liquid nitrogen. Repeated surgery and cryosurgery can lead to fibrosis making defecation difficult or leading to incontinence.
Prognosis
The prognosis is guarded as recurrence is common and treatments often have to be repeated.
There is a DNA test available to detect the DRB*00101 allele, which is known to increase susceptibility to anal furunculosis.
Dogs may be clear of the risk allele and therefore be of no increased risk of developing the disease.
A carrier (Heterozygote) carries one copy of the risk allele and is therefore 5 times more likely to develop the disease and will transfer the defect to approx 50% of its offspring.
An Affected (Homozygote) carries 2 copies of the risk allele and is 5 times more likely to develop the disease at a young age and will transfer the defect to 100% of its offspring.
The following is taken from the Genoscoper website in Finland, where the test is available:
The cause of anal furunculosis is unknown but recent studies have revealed that it has a hereditary immunological background. It is an autoimmune disease, which can be activated by different bacterial or yeast inflammations and stress. The disease is very difficult for the dog and usually hard to treat. Over 80% of treated anal furunculosis occur among German Shepherds. This clearly indicates familial susceptibility among the breed.
Recent studies have revealed that susceptibility to anal furunculosis is associated with DRB*00101 allele. This form of immunegene was found mainly in dogs that suffer from anal furunculosis. Anal furunculosis is not monogenic recessive disease and it is likely that other unknown genes are involved. This means that even if a dog carries the risk allele it will not necessarily get the disease because there might be some other genetic or environmental factors that prevent the dog from having the disease. In addition some dogs that do not carry the risk allele have anal furunculosis so this also proves that there are several genetic factors behind the disease.
However the DRB*00101 allele increases the risk of getting anal furunculosis and its frequency in the population should be lowered. Dogs that carry the risk allele need careful consideration before using them for breeding purposes. Unfortunately, it is likely that there are more genes involved in anal furunculosis and absence of this allele does not guarantee a dog will not develop the disease.
