Just as in humans, hepatitis in dogs can result from a variety of causes, many of which are either unknown or only suspected. The term hepatitis is a generic term used to describe an inflammatory disease of the liver, which can be either acute or chronic (i.e., lasting more than six months), without specifying the cause.
The liver is the chemical laboratory of the body in dogs, as it is in all species. Its proper functioning is essential for several important processes, such as: carbohydrate, lipid, and protein metabolism; fat digestion; detoxification of the body from waste metabolites, drugs, and toxins; storage of vitamins, glycogen, fat, iron, and other trace metals; synthesis of blood and coagulation proteins; and immunoregulation. Any disease affecting the liver, including hepatitis, can negatively impact these vital functions. However, the liver has a remarkable functional reserve and regenerative capacity. This means that hepatic cells in a resting state, or even new hepatic cells, can replace the function of damaged or dead cells. As a result, relatively specific signs of hepatic disease and dysfunction typically appear late in the disease progression, after the liver’s functional reserves have been exhausted.
Signs of Hepatitis in Dogs
Early clinical signs of hepatic inflammation (both acute and chronic) are usually nonspecific and can mimic symptoms observed in other organ systems. These signs are typically related to the gastrointestinal system (diarrhea, anorexia, and vomiting) and renal system (increased urination, leading to increased thirst), and can result in severe dehydration. As mentioned, specific signs of hepatic dysfunction typically appear late in the disease progression. These signs include: icterus (yellow discoloration of the mucous membranes associated with the accumulation of bilirubin), hypoglycemia (caused by glycogen depletion or failure of glucose synthesis), bleeding tendencies (associated with a failure in the synthesis of coagulation proteins), abdominal enlargement (due to liver enlargement, hepatomegaly, or ascites, the accumulation of fluid in the abdominal cavity), and hepatic encephalopathy (a neurological condition resulting from the liver’s inability to detoxify neurotoxins produced in the intestinal tract).
Acute hepatitis in dogs is often referred to as idiopathic, meaning the cause is usually unknown. However, like in many other species, viruses may be the cause, while bacterial infections almost never cause acute hepatitis in dogs. In acute hepatitis, the liver’s functional reserve is almost always preserved, and recovery typically occurs spontaneously in about three weeks without specific treatment. Supportive treatment, such as antiemetic therapy for severe vomiting or fluid therapy for dehydration, may be indicated.
The most serious concern with acute hepatitis in dogs is that it can progress into chronic hepatitis, which, if untreated in the early stages, can lead to liver fibrosis and cirrhosis. Therefore, whenever acute hepatitis is diagnosed, it is crucial for the veterinarian to perform a follow-up liver biopsy 4-5 weeks later to determine whether the acute form is evolving into the chronic form. Early treatment of chronic hepatitis can help prevent further liver damage.
Chronic hepatitis in dogs, also known as inflammatory canine hepatic disease, refers to a syndrome where hepatic cell death (hepatocellular necrosis) occurs, associated with a chronic inflammatory process that typically progresses to liver fibrosis (replacement of hepatic tissue with fibrous tissue) and cirrhosis (progressive derangement of liver architecture and function). Chronic hepatitis in dogs may be caused by various factors, including drugs (e.g., acetaminophen), mushroom toxins (e.g., phalloidine), metals (e.g., copper), and infectious agents (e.g., leptospirosis). However, in many cases, a specific cause cannot be identified, and the condition is referred to as chronic idiopathic hepatitis, with an immune-mediated mechanism suspected, at least in part, to be involved in the disease’s development. Certain breeds are predisposed to chronic hepatitis and liver fibrosis or cirrhosis. Breeds reported to have an increased frequency of chronic hepatitis include Doberman Pinschers (especially middle-aged, female individuals), Bedlington Terriers, West Highland White Terriers, and Dalmatians, which are particularly prone to copper-associated hepatitis.
An important mechanism involved in chronic hepatitis, regardless of its cause, is oxidative damage. This damage results from the release of oxygen free radicals from inflammatory and immune cells during the inflammatory process. Oxygen free radicals are toxic to cells, as they damage the membranes surrounding living cells, their nuclei, and other organelles, ultimately leading to cell death. This explains why antioxidants are crucial in preventing and treating chronic liver inflammation.
Treating Chronic Hepatitis
Treatment of chronic hepatitis in dogs depends partly on the underlying cause, if known. The first-choice treatment for chronic idiopathic hepatitis (where an autoimmune mechanism is suspected) is steroid therapy, typically with prednisolone. Corticosteroids have anti-inflammatory and antifibrotic effects, helping to combat inflammation and prevent hepatic fibrosis. However, glucocorticoids also have several unwanted side effects and are contraindicated when an infectious cause is identified, as these drugs suppress the immune response, which can help fight the infection, especially in the early stages of chronic hepatitis. A safer alternative to glucocorticoids is UDCA (ursodeoxycholic acid), a natural bile acid produced in the liver and secreted with bile into the small intestine to aid fat digestion. UDCA has been shown to have a positive effect on liver function through several mechanisms: it prevents hepatic cells from undergoing apoptosis, enhances bile flow, promotes the excretion of toxins accumulated in the liver, modulates the immune system by reducing the immune response, and increases the production of glutathione (GSH) and metallothionein, which play an essential role in preventing oxidative damage.
In cases of chronic hepatitis caused by copper accumulation in the liver, chelation therapy is necessary. Copper chelators, such as D-penicillamine, bind free copper and promote its excretion in the urine through the kidneys. As mentioned earlier, antioxidant therapy plays a vital role in treating most forms of chronic hepatitis by preventing liver oxidative damage. The primary antioxidants used in liver disease treatment include vitamin C, vitamin E, silymarin (the active ingredient from the fruit of milk thistle), and S-adenosyl-L-methionine (SAMe). Additionally, UDCA itself has antioxidant properties.
Dietary management is also crucial in treating chronic hepatitis. For instance, a low-sodium diet can help control ascites, while a low-copper diet is recommended for copper-associated hepatitis. A diet with reduced aromatic amino acids and supplemented with lactulose and soluble fiber may aid in managing hepatic encephalopathy. Commercial diets specifically formulated to support liver function are available and provide the proper energy content, reduce aromatic amino acids, and contain low levels of copper and sodium, as well as sufficient soluble fiber.
To sum up, there is no universal therapy for chronic hepatitis in dogs. Treatment must be tailored to the underlying cause of the liver inflammation and adjusted according to each individual patient’s needs. The key to successful treatment is early intervention, which can prevent total liver dysfunction and its life-threatening consequences.
