Copper toxicosis may alternatively be referred to as Copper Storage Disease, Copper Storage Hepatitis, Copper Hepatoxicosis, Hepatic Copper Toxicosis or Copper-associated Hepatopathy in scientific publications, particularly where these are of non-UK origin
The BTHG wish to express their thanks to Roger Bannister (MRCVS) for his help in preparing these notes.
These notes should be read in conjunction with the accompanying notes from Dr Susan Haywood and with the Report on the CT Seminar
Copper is one of several essential elements that are necessary for survival but that need to be provided in the dogs diet only in very small amounts, i.e. as micro nutrients. It is thought that copper is involved in a wide range of biological processes in the body and 3 important roles have been identified:
It is a constituent (as a co-factor) of many enzyme systems.
It is closely linked with iron metabolism. A deficiency of copper impairs the absorption and transport of iron and causes a decrease in synthesis of the haemoglobin which is essential for transporting oxygen in the blood. This results in a form of anaemia which can occur even when the animals intake of iron is normal.
Copper is essential for the formation of collagen fibres and a deficiency can result in bone/joint disorders.
Under normal circumstances adequate copper is provided in the dog’s diet and there is no necessity to provide any form of supplement. Only sufficient copper to satisfy the dog’s physiological needs is retained in the liver and copper surplus to these requirements is converted by a series of enzymes into a form that can be incorporated into bile, which is manufactured in the liver. This bile is then stored in the gall bladder prior to being secreted into the small intestine and excreted in the faeces.
However, copper is highly toxic if levels within the body exceed the normal physiological need of the dog. Hence, if this regulatory mechanism should fail, for whatever reason, copper will accumulate in the liver and this will result in copper toxicosis.
This regulatory activity is genetically determined.
The cause of Copper Toxicosis
Copper toxicosis in Bedlington terriers is a progressive degenerative disease of the liver which results directly from the malfunction of the enzyme system responsible for processing the surplus copper in the liver cells. Any malfunction of this enzyme system leads to an accumulation of copper in the liver tissues. In other words, copper toxicosis results from the inability of the affected dog to mobilise and excrete dietary copper which is surplus to its requirements.
The copper content of liver tissue of a healthy dog varies within the range 20-70 µg per gm liver tissue `wet' weight which equates to 100-400 µg per gm liver tissue “dry” weight. In dogs affected with copper toxicosis the level of copper in the liver tissue is considerably higher than this and is often 1000-2500 µg per gm liver tissue “dry” weight. It may even exceed 10,000 µg. The critical level for the diagnosis of the “affected” status is generally accepted to be 1000 µg per gm liver tissue dry weight.
Copper toxicosis in Bedlington terriers was first reported in 1975 in the USA by Hardy, Stevens and Stowe and has since then it has been recognised in a number of other countries. It was established later (Johnson et al, 1980) that the form of the disease found in Bedlingtons terriers was apparently caused by the presence of an autosomal recessive gene in affected dogs - it is a genetic disorder and in order for the condition to develop in a dog/bitch a copy of this defective gene must have been passed to the affected animal by both parents, i.e. the affected dog must have two “copies” of the defective gene in its body cells.
The form of copper toxicosis which affects Bedlington terriers is often referred to as “copper storage disease” and is regarded as a “primary” copper disorder. In this context, the term “primary” is used to denote that the condition is direct consequence of the accumulation of copper in the liver tissues and is a direct result of the presence of the inherited “copper accumulation” genes, i.e. it is not the consequence of a malfunction caused by another factor such as damage to the gall bladder which would impair the removal of bile and therefore copper.
In 1986, Thornburg and his co-workers reported that this primary form of copper toxicosis has also been recognised in West Highland Terriers. Although there have been reports that copper toxicosis has been diagnosed in other breeds, there appears to be some confusion in the literature about whether or not these reported cases refer to secondary copper storage disorders, i.e. that the development of the copper toxicosis is a result of other factors which caused liver malfunction.
The Incidence of inherited Copper Toxicosis
In 1979, it was suggested (Twedt et al.) that the incidence of copper toxicosis in Bedlington terriers in the USA may be as high as 50% and another source suggested that 66+% of Bedlingtons may be affected. However, it was thought that the situation in the UK was somewhat better. An investigation into the status of 92 Bedlingtons carried out by Herrtage and his fellow workers, reported in 1987, recorded an incidence of 33.9% even though none of the dogs in the survey showed clinical signs of liver disease.
Please note that the figure of 33.9% “affected” dogs quoted above relates to a survey done on the results from dogs that had been liver biopsied and no indication was given about the number of dogs considered to be “normal”. Moreover, the figure relates to the situation as it was in the mid-1980s. Considerable care is needed when interpreting any data obtained from a limited sample of dogs and extrapolating the information to project the national situation. However, it was obvious that there was a serious problem.
An incidence level of 36% was also reported in the Netherlands.
To download Dr Susan Haywood's report on Copper Toxicosis in the Bedlington Terrier,
click the link below