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HAEMOPHILIA B (Factor IX deficiency)


1. Brief description
Haemophilia B is a rare blood disorder in which the blood is unable to clot properly, leading to excessive bleeding. Coagulation is the process of clot formation, when blood transforms from a free flowing liquid into a thickened gel like state, or clot. This process is critically important to seal open wounds, allowing them to stop bleeding and heal. Haemophilia B is caused by a hereditary deficiency of the blood clotting protein, factor IX, one of the substances responsible for blood clotting, causing prolonged bleeding from sites of injury, trauma and surgery or through gum disease which causes bleeding. Under these circumstances, affected animals show abnormally prolonged bleeding, because clot formation is ineffective.  
The clinical signs of haemophilia B include episodes of lameness, swelling and bruising under the skin that resolve with no treatment, weakness, lack of appetite, fever and depression. Affected dogs may show small spots of bleeding under the skin (only readily apparent in areas that are hairless and unpigmented) or inside the tissues of the mouth. Internal bleeding may occur within organs or body cavities, resulting in bloody vomit or stools, rectal or vaginal bleeding, nose bleeds, breathing difficulties, abnormal heart rhythm, swollen distended abdomen and/or excessive thirst. Bleeding inside the eyes and into the brain can occur, and this can lead to blindness or neurological signs (signs of abnormal brain function). Regular episodes of bleeding may cause regenerative anaemia, due to loss of blood, and this may cause weakness, lethargy, irregular heartbeats and shortness of breath.
Rhodesian ridgebacks have a severe form of haemophilia B, often with factor IX deficiency of <5% and more pronounced clinical signs. Extremely affected dogs (factor activity <1%) usually die at birth or shortly thereafter. Severely affected dogs (<5% activity) bleed spontaneously and are at risk of death due to severe bleeding or anaemia.

2. Intensity of welfare impact
Severely affected animals (those with factor IX activity less than 1%) may die at birth due to excessive umbilical bleeding or they may die shortly after due to body cavity haemorrhage.  
For animals not so severely affected, the clinical signs may be less obvious, but they may suffer intermittently from anaemia, weakness, periodic lameness or fever. Affected dogs may also lose bodyweight as a result of inappetance. If bleeding occurs into confined body cavities, such as within the eyeball, the skull or joints, this can cause severe pain due to the increased pressure within the cavity. Severe bleeding following trauma or surgery and severe anaemia can also be life threatening.
Owners of affected dogs can reduce the risk of trauma and injury in their dog– by avoiding situations where they may injure themselves eg in rough play with other dogs or exercise in potentially harmful environments - and by maintaining good dental hygiene to avoid excessive bleeding of the gums (eg with gingivitis). There is no curative treatment for the condition. Antifibrinolytic agents can be given by a veterinarian to stem bleeding, eg after surgical procedures. If anaemia is severe, transfusions of fresh whole blood transfusions may be required.

3. Duration of welfare impact
Affected dogs are born with defects in haemostasis (blood clotting) and the clinical signs of haemophilia usually appear before 6 months of age. At this time, bleeding and bruising or haematomas at the site of injections may be noticed following routine procedures, such as vaccination, castration, or spaying. Severe cases of haemophilia B are lethal due to severe bleeding (external or internal) or anaemia. For cases which are less severe, animals may still experience clinical signs – such as bruising, nosebleeds or blood-tinged vomit, urine or faeces, weakness, lameness – intermittently throughout their lives.

4. Number of animals affected
Haemophilia is rare in dogs, although the exact prevalence is unknown. Haemophilia B is reported to be inherited in Rhodesian ridgebacks. Male dogs are more commonly affected than female dogs, since the genetic defect is on a sex-linked chromosome.

5. Diagnosis
Blood can be tested for platelet count, and activated clotting time; dogs with haemophilia B have a slower clotting time and a deficiency of factor IX protein activity.

6. Genetics
A mutation in the gene that codes for the expression of Factor IX protein is responsible for haemophilia B in Rhodesian ridgebacks. Haemophilia B is a sex-linked recessive disorder, as the mutation is found on the sex chromosome X; males have one X and one Y. If a male, inherits an X chromosome carrying the mutated gene then it will be affected by the haemophilia B disorder. For females to be affected they have to be homozygous for the condition, that is both X chromosomes have to carry the mutated gene; but this is less common. Heterozygous females, which carry one copy of the genetic mutation, are therefore unaffected carriers for the disorder. Mating of a female carrier with a homozygous affected male will result in half of male offspring being affected and the other half of male offspring being clear. Half of female offspring will be affected and the other half will be carriers (unaffected but able to pass on the condition to their offspring).

7. How do you know if an animal is a carrier or likely to become affected?
Haemophilia B can be detected using a genetic test, with DNA from blood or saliva samples. Dogs with haemophilia B can be diagnosed using measures of blood clotting, where abnormal clotting times and a deficiency of factor IX are found.

8. Methods and prospects for elimination of the problem
Although the condition is considered to be rare, breeding from affected dogs should be avoided since it will result in both affected dogs and carriers (females only). Prospective breeders should seek testing for haemophilia B in dogs showing clinical signs, via a veterinarian, before choosing to breed the dog.







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