Von Willebrand's Disease In Dogs

There are many factors that affect how well blood clots. If a dog is missing any one of these crucial factors, a clotting disorder will develop. Dogs with clotting disorders will bleed more than a typical dog, and may have life-threatening bleeds during routine surgeries, like neutering. The most common clotting disorder in dogs is called von Willebrand's Disease, which is often detected by a common screening tests at the veterinarian's office (the so-called gum prick test). During surgery, the animal may bleed profusely, triggering suspicion of von Willebrand's Disease (vWD). Some breeds are more likely to have vWD and will be tested specifically for the problem by their breeder. What is von Willebrand's Disease? Animals who do not have a normal level of von Willebrand's Factor (vWF) will not form blood clots in a normal time frame. WF is crucial for normal platelet function, and the lack of vWF will prevent platelets from aggregating properly at a wound site.

Willebrand Factor is made by the epithelium lining the blood vessels. It acts as a "glue" to bind platelets to the site of the wound. When a dog doesn't have a normal level of vWF, the platelets cannot bind to the broken blood vessel walls, which causes prolonged bleeding. Fortunately, most dogs have a mild presentation of von Willebrand's. This means that the bleeding disorder will rarely cause problems, and your pet will likely have a full life. Some forms of von Willebrand's are more severe and these dogs require specialized care. Most dogs are screened for clotting disorders prior to surgery. A test known as the mucosal bleeding test is generally performed before spay and neuter operations. The vet will prick the gum of the dog and the time to clot formation is noted. Dogs with a prolonged clotting time may have one of several disorders, including von Willebrand's.

There are two specific tests for vWD: one is a genetic test, and the other measures activity of vW Factor in the blood. Veterinarians can order both tests. How do Dogs get von Willebrand's? Willebrand's Disease is a hereditary clotting disorder, where levels of von Willebrand's Factor are less than 60% of normal. There are three types of vWD in dogs: the first type tends to be mild, and the last two types are severe. Type I vWD: occurs in many breeds, and the dogs have a reduced level of von Willebrand's Factor. The severity of the bleeding increases as the level of vWF decreases. This type is inherited as an "incomplete dominant," meaning that puppies will inherit it from their affected parent, but the degree will vary depending on how much of the gene is expressed. Two pups from the same litter may have dramatically different levels of vWF.

This type is the most mild type, and most dogs live a full life. If both parents have the vWF gene, puppies who inherit both copies of the gene will be stillborn or die shortly after birth. Type II vWD: This type is extremely severe and causes profuse bleeds in affected dogs. This type of vWD is not caused by a low level of von Willebrand's Factor, but by an abnormally functioning factor. This type of vWD is seen in the pointer breeds. This is the rarest of the vWD types. Type III vWD: This type is also rare and extremely severe. These dogs do not have any von Willebrand's Factor at all. This type of von Willebrand's is autosomal recessive, so carriers of the disorder will not display any type of bleeding disorder at all. 25% of the puppies will inherit the bleeding disorder (getting both copies of the gene). Up to 10% of Scottish Terriers carry this gene, making the disorder a serious problem for breeders.

Many dog breeds are affected by Type I vWD, the mildest version of the disease. Type II vWD is extremely rare, and has been observed in the German Short-Haired Pointer. Type III vWD is also rare and has been reported in the Scottish Terrier, Shetlands, and (rarely) in Chesapeake Bay Retrievers. Aggressive play should be kept to a minimum. Visits to the dog park, for example, could be dangerous for a dog with von Willebrand's. If another animal bites or otherwise injures the dog, profuse bleeding could result. All dogs should undergo a clotting screening prior to surgery, and breeds with a known predisposition to the more severe forms of vWD should have genetic testing performed. Any dog with a known clotting disorder should receive prophylactic treatment before any surgery is considered. There is no cure for von Willebrand's, but appropriate steps may be taken to ensure the animal is kept as healthy as possible. Transfusions of vWF are possible for dogs with a more severe form of the disorder (or for dogs who have recently undergone trauma). For dogs with known vWD, an elective transfusion may be given prior to any surgery to ensure the dog does not bleed excessively during the procedure. Many dogs who have vWD also have a low thyroid hormone level. Dogs with von Willebrand's should have their thyroid level tested and treated, if low, to help improve blood clotting ability. Dog HealthWhat is Addison's Disease in Dogs? Oh, he looks great. Be careful with heavy exercise because of the von Willebrand's!