Signalment:  

Adult, spayed, female ChihuahuaThis dog developed vomiting, diarrhea and anorexia one day following routine vaccinations and was treated symptomatically with fluids and antibiotics. However, the patient continued to deteriorate with evidence of a progressively worsening liver disorder and was euthanized eight days following the vaccinations.

Gross Description:  

The submitting veterinarian did a necropsy on the patient but did not report abnormal findings. Fixed specimens of spleen, kidney and liver were received from the referring veterinarian for histopathology.

Histopathologic Description:

The section of liver is characterized by marked centrilobular and midzonal hepatic necrosis (Fig. 1-1) with sparing of hepatocytes located adjacent to portal triads. Canalicular plugging with bile is frequently observed between surviving hepatocytes (Fig. 1-2). In the necrotic tissue, ghost-like remnants of necrotic hepatocytes and the accompanying sinusoids can generally be visualized (coagulative necrosis). Inflammatory cell activity is minimal in all areas.

Morphologic Diagnosis:  

Marked acute hepatic necrosis with periportal sparing and periportal intrahepatic cholestasis, Chihuahua, canine.

Condition:  

Vaccine-induced hepatotoxicity

Contributor Comment:  

Upon further investigation, the referring veterinarian discovered that the patient had inadvertently been vaccinated by injection with an intranasal trivalent Bordetella bronchisepticacanine parainfluenza-canine adenovirus-2 vaccine product due to an error in vaccine preparation by a newly hired technician. The product package insert warns that subcutaneous or intramuscular administration of the intranasal product may result in icterus or death from liver failure, but we were unable to find any information in the scientific literature to explain the mechanism of hepatic injury or which component in the vaccine might be responsible for the injury. There is one published report of acute hepatic necrosis associated with subcutaneous administration of an intransasal canine Bordetella-canine parainfluenza vaccine, but the authors did not speculate as to pathogenesis. The patient survived and hepatocellular disease was still present two months later based on hepatic biopsy and serum bile acid concentrations.⁵ Equine serum hepatitis, sometimes known as Theilers disease, occurs subsequent to vaccination with biologics that contain equine serum and has a similar pattern of marked hepatic necrosis with periportal sparing. However, after nearly one hundred years since equine serum hepatitis was first reported, the pathogenesis of the disorder remains elusive.² Ordinarily, massive hepatic necrosis in dogs suggests a toxic etiology. Although many drugs, toxins and chemicals have been shown to cause hepatic injury in dogs², it is difficult to find a comprehensive list of substances in which the toxicosis in dogs is predominately manifested by acute, severe hepatic necrosis. In our laboratory, ingestion of xylitol, cycad palm, poisonous mushrooms (particularly Amanita sp.), or water containing blue-green algae are our first considerations as causes of marked hepatic necrosis when there has been no known exposure to drugs or chemicals.

JPC Diagnosis:  

Liver: Hepatocellular necrosis, acute, submassive to massive, diffuse, with hemorrhage and canalicular cholestasis, Chihuahua (Canis familiaris), canine.

Conference Comment:  

Massive hepatic necrosis is defined as necrosis of entire acini. In the sections examined at the conference, there are acini that are entirely necrotic as well as acini that are largely necrotic with a rim of surviving hepatocytes around the portal areas. Massive necrosis leads to collapse of the remaining stroma, impaired regeneration and postnecrotic scarring. It is usually, but not always, caused by toxins. Hepatosis dietetica is a nutritionally induced form of massive hepatic necrosis.⁴

Hepatotoxic agents can be divided into two broad categories based on their predicted activity. Predictable hepatotoxins are those that produce a generally consistent activity in the majority of the animals that are exposed. The extent of injury produced in an individual animal by a predictable hepatotoxin may differ depending on various factors including age, sex, diet, and endocrine function. Idiosyncratic drug reactions are caused by those agents that produce an effect in a small minority of the animals exposed, such as carprofen occasionally causing acute hepatic necrosis in Labrador retrievers and diazepam causing acute fatal hepatic injury in some, but not all, cats.²

Hepatotoxic agents can be classified into six different categories based on their cellular target.² 1. Production of toxic metabolites by the cytochrome p450 system is the most common form of hepatocellular injury. The enzymes of this system are located in the smooth endoplasmic reticulum and are found in the highest concentration of centrilobular hepatocytes. They function to metabolize lipid-soluble chemicals into water-soluble compounds for excretion. 
2. Drugs and cellular enzymes may combine together to form neoantigens. When transported to the cell surface and presented as antigens, these neoantigens may stimulate both cellular and humoral immune responses resulting in either direct cellular cytotoxicity or antibody-dependent cellular cytotoxicity. (halothane)
3. Some toxins may directly initiate apoptosis by stimulating proapoptotic pathways within hepatocytes. (hydrophobic bile acids)
4. Certain toxins may directly damage cellular membranes disabling calcium homeostasis and resulting in cell death. (carbon tetrachloride)
5. There are chemicals that will bind and disrupt the canalicular pumps that normally secrete bile into the canaliculi. This disruption results in cholestasis. (estrogen, erythromycin)
6. Direct damage to mitochondria decreases production of adenosine triphosphate as well as resulting in the release of cytochrome-c leading to apoptosis or necrosis. (antiviral nucleosides, intravenous tetracycline)


Certain toxic compounds may affect cells other than hepatocytes.² Damage to biliary epithelium may be caused by trimethoprim-sulfa or sporidesmin, while damage to Kupffer cells can be caused by endotoxin. Arsenicals damage endothelial cells of the liver, and vitamin A excess causes activation of hepatic stellate cells. 

Selected hepatotoxins extracted from Cullen²

Category	Members	Mechanism of action	Remarks
Blue-green algae	Anabaena, Aphanizomenon, Microcystis	Microcystin LR (cyclic heptapeptide)	More closely related to bacteria
Pyrrolizidine alkaloids	Senecio, Cynoglossum, Crotalaria, Heliotropium	Ingested alkaloids converted to pyrrolic esters by cytochrome p450 enzymes	Esters are alkylating agents that act on cytosolic and nuclear proteins. Megalocytes due to antimitotic effect.
Aflatoxin	Aspergillus flavus	Aflatoxin B1 (toxic intermediates produced by cytochrome p450 enzymes)	Toxin and carcinogen.  Sheep more resistant.
Sporidesmin	Pithomyces chartarum (fungus growing on dead rye grass)	Necrosis of the epithelium of large intrahepatic and extrahepatic biliary ducts	Results in cholestasis with failure to excrete phylloerythrin leading to photosensitization
Mushroom	Amanita sp.	Toxic cyclopeptides Palloidin (toxic heptapeptide)	Inhibition of RNA polymerase II function disrupting DNA and RNA transcription Disruption of intracellular actin filaments

Equine serum hepatitis is an idiopathic condition most closely associated with administration of equine-origin biologics.^1,3 It is generally reported 41-60 days following administration of a biologic product, and is characterized by acute hepatic centrilobular necrosis.¹

References:

1. Aleman M, Nieto JE, Carr EA, Carlson GP: Serum hepatitis associated with commercial plasma transfusion in horses. J Vet Intern Med 19:120-122, 2005
2. Cullen JM: Liver, biliary system, and exocrine pancreas. In: Pathologic Basis of Veterinary Disease, eds. McGavin MD, Zachary JF, 4th ed., pp. 440-447. Elsevier, St. Louis, MO, 2007
Divers TJ: Liver disease and liver failure in horses, in Proceedings. Am Assoc Equine Pract
3. Guglick MA, MacAllister CG, Ely RW, Edwards W: Hepatic disease associated with administration of tetanus antitoxin in eight horses. J Am Vet Med Assoc 11:1737-1740, 1995
4. Stalker MJ, Hayes MA: Liver and biliary system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp. 322-333. Elsevier Limited, St. Louis, MO, 2007
5. Toshach K, Jackson MW, Dubielzig RR: Hepatocellular necrosis associated with the subcutaneous injection of an intranasal Bordetella bronchiseptica-canine parainfluenza vaccine. J Am Anim Hosp Assoc 33:126-128, 1997

A virtual slide is not available for this case.

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(Fig 1-1) Liver

(Fig 1-2) Liver

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