Liver Diseases of Horses (Hostnik)

Question 1

Equine:
What empties into the duodenum at the major duodenal papilla, located on a slightly raised mucosal ridge?

Answer 1

Both the bile duct and pancreatic duct

Question 2

Equine:
What opens at the minor duodenal papilla?

Answer 2

Accessory pancreatic duct

Question 3

Equine Definition:
Is a complex clinical syndrome characterized by the abnormal mental status that accompanies severe hepatic insufficiency

Answer 3

Hepatic Encephalopathy (HE)

Question 4

(T/F) Hepatic Encephalopathy generally is considered to be a potentially reversible metabolic encephalopathy

Answer 4

True

Question 5

Acute Disease:
- Is a hepatotropic Single-stranded DNA virus capable of causing hepatitis in infected horses
- Has been found in consecutive horses with Theiler’s disease that received tetanus antitoxin or other equine-origin blood products

Answer 5

Equine parvovirus

Question 6

Equine:
What was the first of the three new blood-borne viruses to be reported?

Answer 6

Nonprimate Hepacivirus
- is a flavivirus, uncommon in mules or donkeys

Question 7

List the nutrient metabolism of liver functions:

Answer 7

• Carbohydrates
• Fat
• Protein

Question 8

What are common clinical findings of liver disease in a horse?

Answer 8

• Depression
• Anorexia
• Colic
• Weight loss
• Icterus (important indicator)
• Pigmenturia
• Hepatic Encephalopathy (HE)

Question 9

• Caused by hyperbilirubinemia
• 10-15% of horses normally have slightly yellow sclera
  - related to fasting

Answer 9

Ictures (jaundice)

Question 10

• Phylloerythin (derived from chlorophyll) is normally metabolized and excreted by the equine liver
• In disease, increases in phylloerythrin in the blood react with UV light to cause damage and necrosis of unpigmented skin
  - the liver is not detoxifying that substance properly

Answer 10

Photosensitization

Question 11

• Augmented GABA activity in the brain (sleepy horses)
• Altered expression of benzodiazepine receptors
• Increased neurosteroids (not much is known)
• False neurotransmitter accumulation
• Inflammatory mediator expression
• Increased BBB permeability and cerebral hypertension
  These are other mechanisms/pathogenesis that may be involved with …

Answer 11

Hepatic Encephalopathy

Question 12

What are the main enzymes that we look for in lab testing in a clinical assessment of the liver in horses?

Answer 12

• Asparte aminotransferase (AST)
  - Not specific to the liver (come from muscle, RBCs)
• Sorbitol dehydrogenase (SDH)
  - Liver-specific in a horse
  - is the main one that we look at for hepatocellular leakage
  (both are hepatical leakage enzymes when the hepatocyte is damaged they leak out into the blood)

Question 13

Clinical Assessment of the liver in horses
List the two enzymes that are liver-specific:

Answer 13

• SDH
  
  • increases seen with ongoing injury
  • shorter half-life than AST (increase quicker, and decrease quicker)
• GGT

Question 14

Clinical Assessment of the liver in horses
What enzymes are biliary/cholestatic (hepatobiliary)?

Answer 14

• Gamma-glutamyl transferase (GGT)
• Alkaline phosphatase (ALP)
  - non-specific (also bone, intestinal, renal, mammary, placenta, leukocytes, corticosteroids)
  (are actually induced)

Question 15

Equine Functional Tests:
- Indirect (unconjugated)
- Direct (conjugated)
- In horses with Anorexia of any cause, we see an increase in UNconjugated ___________ due to a decrease in the proteins required to import UNconjugated __________ into the liver

Answer 15

bilirubin (increase)

Question 16

Equine Functional Tests:
- Per- and post-prandial measurement is not necessary since horses continuously secrete bile
- Horses DON’T have a gallbladder

Answer 16

Increase Bile Acids

Question 17

Equine Functional Tests Results: Liver Disease

Answer 17

• Increased Bilirubin
• Increased Bile Acids
• Increased Ammonia
• Decreased UREA (BUN)
• Decreased Glucose
• Coagulation testing (depends on what you are measuring)

Question 18

Bilirubin
- Hemolysis
- Fasting hyperbilirubinemia

Answer 18

Unconjugated (indirect)

Question 19

Bilirubin
- Cholestasis

Answer 19

Conjugated (direct)

Question 20

(T/F) Abdominal radiographs are useful to evaluate the liver in equids

Answer 20

False, Abdominal radiographs are NOT useful

Question 21

• Chronic megalocytic Hepatopathy
• Delayed onset, chronic, progressive liver failure due to ingestion of pyrrolizidine alkaloid-containing plants
• Metabolized by the liver after ingestion into toxic pyrrole derivatives
  - Alkylate nucleic acids and protein, preventing cellular replication and protein synthesis
  - Causes hepatocytes to enlarge -> megalocytes
  - When megalocytes die, it causes fibrosis

Answer 21

Pyrrolizidine Alkaloid Toxicity

Question 22

Equine:
What do you see in a liver biopsy of a horse with pyrrolizidine alkaloid toxicity?

Answer 22

• Megalocytosis
• Biliary hyperplasia
• Fibrosis

Question 23

NAVLE

• Clostridium piliforme
  
  • Motile, pleomorphic, Gram-Negative, spore-forming, obligate intracellular bacterium
• Acute necrotizing hepatitis in FOALS (3 weeks old - between 7 & 42 days)
• Foals ingest contaminated soil or feces from the dam (relatively common in the enviroment - cases are sporadic)
• Travels to the liver and heart via lymphatics and hematogenous spread

Answer 23

Tyzzer’s Disease

Question 24

What is the primary disease associated with Tyzzer’s Disease (highly fatal)?

Answer 24

Acute, multifocal hepatitis
(but also myocarditis and enteritis are seen)
-> will see grossly an enlarged, swollen lover with 1- to 5-mm white foci throughout (coagulative necrosis and inflammation)

Question 25

• Serum hepatitis, serum sickness, acute hepatic necrosis
• Now –> Viral hepatitis
• Acute or subacute hepatitis with liver necrosis in Adult Horses
• Association with the administration of equine-derived biological products (typically 4-10 weeks before the onset of hepatic failure)
  - Most common is Tetanus Antitoxin

Answer 25

Theiler’s Disease

Question 26

• Likely caused by Equine Parvovirus-Hepatitis (EqPV-H) – acute hepatic necrosis and subclinical hepatitis
• Equine Hepacivirus – mild, subclinical hepatitis

Answer 26

Theiler’s disease
- Treatment:
- Supportive care
- Prognosis is guarded with acute disease and hepatic failure