Canine Von Willebrand's Disease
Von Willebrand's disease (VvWD) is an inherited bleeding disorder. It is a complex and difficult disorder to deal with, because genetics, diagnostic abnormalities, pathogenic mechanisms, and sometimes conflicting clinical signs are all involved. The commonality between all vWD is a reduction in the amount or function of von Willebrand factor (vWF), which is manifested through abnormal platelet function and prolonged bleeding time. The vWF factor is a blood protein which binds platelets to blood vessels when they are injured. Absence or deficiency of the factor can, therefore, lead to uncontrolled bleeding episodes. In dogs, the most common clinical signs are spontaneous bleeding from the gums or nose, blood in the urine or gastrointestinal tract, or excessive bleeding at the time of surgery. Clinical signs also include epistaxis, prolonged estrus or postpartum bleeding, hematuria, melena, excessive bleeding after toe-nail cutting and sometimes hemorrhaging into body cavities and organs.
Diagnosis can be performed by measurement of plasma concentrations of vWF. TESTING SHOULD BE DONE AT AN EARLY AGE SINCE THE DISORDER OFTEN DIMINISHES WITH AGE, CAUSING FALSE-NEGATIVE TEST RESULTS IN OLDER ANIMALS. Additional screening tests such as bleeding times or platelet agglutination assays can also be performed. Precautions should be taken before surgery, so it is important to let your veterinarian know of bleeding problems in the past.
Different breeds exhibit different variations of the disease, and some individual animals appear to "acquire" vWD. While the bulk of the information available is based upon purebred dogs, the disease is not unknown in mixed breeds. The total number of breeds affected by vWF exceeds 50. The disease also appears in cats, pigs, horses, and humans.
Human variants of vWD are broken into three main types which can be used to describe canine vWD. Type I vWD is characterized by a low concentration of normally structured protein. In screening studies done at Cornell over a period of years (1982-1992), percentages of dogs of some breeds tested as carrying the disease, and with concentrations of vWF less than 50% of standard (considered to be at risk) were the following breeds: Corgi, Poodle (std. and min), Scottie, Golden Retriever, Doberman, Sheltie, Akita, Cairn.
Other breeds with a known prevalence of vWD in excess of 15% include Basset Hound, Dachshund (mini & std), German Wirehaired Pointer, German Shepherd, Keeshond, Manchester Terrier (std & toy), Miniature Schnauzer, and Rottweiler.
Type II vWD is characterized by a low concentration of abnormal vWF. Breeds in which severe type II has been diagnosed include American Cocker Spaniel, German Shorthaired Pointer, and German Wirehaired Pointer.
Type III vWD is essentially the complete absence of vWF. Severe type III vWD has been diagnosed in Australian Cattle Dog, Chesapeake Bay Retriever, Fox Terrier, German Shepherd, Scottie, and Shetland Sheepdog.
In vWD dogs, bleeding can be spontaneous, usually from the mucosa of the mouth, nose, or gastrointestinal tract. Injury that is accompanied by bleeding may continue unabated until a transfusion is administered. Whether or not bleeding from small wounds will stop without treatment is not predictable.
Living with one of these affected animals can get quite interesting. Because this disease can be eradicated before breeding (by having your dog tested) it can be eradicated. Unfortunately, experience and hearsay indicate that the AKC is not active in the enforcement of these preventive measures. Apparently the breeders, at least some of them are not either. Testing prior to breeding is a must.
For those who wish additional information, an excellent source concerning the disease is Ettinger's Textbook of Veterinary Internal Medicine.
Sources: Ettinger's Textbook of VIM; Sue Tornquist, DVM, Veterinary Clinical Pathologist, Dept. of Vet. Micro Pathology, Washington State Univ; Gary Mason, Research Manager, Interleaf, Inc. Waltham, MA.