Von Willebrand Disease, also called von Willebrand’s Disease (vWD) is a hereditary blood clotting disorder. This disorder occurs when a dog has in insufficient level of von Willebrand factor (also called factor VIII) – a plasma protein necessary for proper blood clotting.
Factor VIII (vWF) is produced by the cells lining blood vessels and by platelets. It is a protein complex, made up of many smaller proteins bound together. If there is a defect in any of the proteins that make up the complex, von Willebrand’s Disease is the result.
When a dog’s blood vessel tears, and the animal begins to bleed, platelets go to the area to clump together to staunch the bleeding and plug the hole. When that happens, additional blood clotting factors become activated, and this leads to the production of fibrin (what scars are made from). In the meantime, von Willebrand’s factor acts like glue to hold the platelets to each other and to the surface of the affected blood vessel. vWF also has a role in stabilising one of the proteins that form the fibrin.
A dog with vWD suffers from inappropriately prolonged bleeding when wounded.
There are three types: Type I, where all of the proteins are present but in very low amounts; Type II, where only the smaller proteins are present; and Type III, where the dog completely lacks all von Willebrand’s factor. Type I is the most common, and tends to cause mild to moderate symptoms. Types II and III cause severe symptoms.
Genetic mutation that affects the stability, synthesis, function, or release of vWF causes von Willebrand disease. The severity of the disease is dictated by the degree to which those mutations are expressed.
The only way to prevent von Willebrand disease is to prevent affected animals from breeding. Any dog at risk of carrying the mutation should be screened and removed from the breeding population, even if they show no clinical signs.
Sometimes it can take years for a dog affected by a mild to moderate case to be diagnosed. In those situations, it is a surgery or other trauma that reveals they have a clotting disorder. More severe forms are usually apparent by the time the dog is one year old. Symptoms may include bloody urine; gastrointestinal bleeding; recurrent episodes of spontaneous bleeding from the nose or gums; bloody or black stool; excessive bleeding during heats or whelping; anemia; or prolonged bleeding from loss of teeth, nail clipping, superficial wounds, or surgical incisions. This disorder can also cause lameness, since the minor injuries that can occur during play cause bleeding within the joint.
Dogs at Risk
Different breeds are prone to different types of vWD. Breeds prone to Type I are Shetland Sheepdog, German Shepherd Dog, Standard Poodle, and the Doberman Pinscher. Breeds prone to Type II are Wire-Haired and German Short-Haired Pointers. Type III is most commonly seen in Chesapeake Bay Retrievers, Scottish Terriers, and Shetland Sheepdogs. Von Willebrand disease can occur in any dog breed, and affects males and females equally.
Testing and Diagnosis
When a dog shows signs of a possible bleeding disorder, the vet will often perform a bleeding time assessment. This test determines the amount of time it takes for clots to form and the bleeding to stop when a small cut is made in the dog’s gum. Blood tests measure the levels of von Willebrand factor in the dog’s blood, and can give a tentative diagnosis. Recently developed genetic tests can definitively diagnose cases of vWD; these tests can even identify carrier dogs that may show no clinical signs of the disease.
Treatment and Prognosis
Dogs that bleed profusely during surgery may require blood transfusions to regain the appropriate amount of vWF, which will help them clot and heal after surgery. Dogs with more severe forms will require several transfusions. Bleeding can be externally controlled using sutures, bandaging, pressure wraps, and tissue glue. When it is known that a dog suffers from vWF, clotting factors and medicine that aids in clotting should be administered before surgery to help prevent bleeding complications.
Dogs diagnosed with this disorder should not be allowed to play roughly with their owners or other dogs. Soft food can help reduce injury to the gums, and hard treats or chew bones should be avoided. These dogs should be checked for hypothyroid conditions every year. Dogs that have a factor VIII mutation should never receive any drug that has anticoagulant or antiplatelet effects. These include sulfonamide antibiotics, plasma expanders, cytotoxic medications, non-steroidal anti-inflammatory drugs, heparin, and coumadin.
Prognosis for dogs with von Willebrand’s disease depends upon the severity. Dogs with mild to moderate forms have a good prognosis and may live fairly long lives with occasional transfusions administered as necessary. Dogs with severe forms have a guarded to poor prognosis if they experience trauma before being diagnosed. Dogs that are diagnosed early on have a much better chance of surviving. As long as the owner works to reduce the potential trauma to which the dog is exposed, and has the dog blood typed and cross-matched for emergency use, prognosis is good.