Miscellaneous Liver Diseases

Geoffrey W. Smith

Rift Valley Fever

Rift Valley fever, also known as enzootic hepatitis, is an acute febrile arthropod-borne disease of sheep, goats, cattle, and humans present in most countries of sub-Saharan Africa.

With the current threat of bioterrorism, it could appear in other parts of the world.^1,2 Rift Valley fever is caused by a virus of the genus Phlebovirus. More than 20 species of mosquitoes have been implicated as possible vectors for the virus, including some North American mosquitoes that are competent laboratory vectors.² The disease causes abortion in pregnant females and a febrile condition with rapid death in lambs, kids, and calves. The mortality rate in young animals approaches 100% but it is much less (20% to 30%) in older animals.² Clinical signs may include fever, anorexia, weakness, salivation, diarrhea, and sometimes abdominal pain, and almost all pregnant animals will abort. The primary gross lesion is hepatomegaly and hemorrhage. Histologically, a focal hepatic necrosis is identified, and eosinophilic intranuclear inclusion bodies are present. Confirmation of the diagnosis is made in the laboratory by virus isolation or immune tests. If the disease is suspected, state and federal regulatory veterinarians should be contacted.

Telangiectasia

Hepatic telangiectasia, commonly known as “sawdust livers” in packing houses, is a focal degeneration in liver lobular circula­tion characterized by red-brown foci 1 to 5 mm in diameter. These lesions account for more than 10% of the bovine liver condemnations but do not result in any clinical signs.³ Micro­scopically, hepatocytes are distorted and sinusoids congested.⁴ Hypotheses proposed to explain the pathogenesis of the lesions include necrotizing hepatitis, ischemia induced by emboli or other vascular pathologies,⁵ dilation of Disse spaces, reduced density of the reticulin framework, vitamin E-selenium deficiency, alteration of the sinusoidal barrier, and immune- mediated disease.³ Some human pathogens have been isolated from these livers as well as normal livers, but livers are con­demned on the basis of aesthetics according to current U.S. Department of Agriculture (USDA) regulations.³

Ischemia, Hypoxia, and Congestion

Ischemia and hypoxia can lead to death of hepatocytes, but less severe insults cause fatty infiltration because lipoprotein synthesis depends on oxidative metabolism.

Fetal Liver Damage

The liver of the fetus may be damaged by infectious and toxic agents, but the result is usually abortion or birth of a weak neonate with signs related to other systems. The lesions in the liver may be diagnostic of the disease. Equine herpesvirus infection of the fetus causes hepatocyte necrosis, with acidophilic intranuclear inclusion bodies in more than 50% of the hepa­tocytes. Aborted fetuses of cattle with infectious bovine rhi­notracheitis may have some focal necrosis of the liver, but this is not enough to be diagnostic.