Canine Viral Hepatitis, Infectious Canine Hepatitis

Canine viral hepatitis, also called infectious canine hepatitis (ICH), is an infectious disease caused by canine adenovirus -1 (CAV-1). It was recognized as a specific viral disease of dogs in 1947. The virus is a medium sized DNA virus. The disease can result in severe disease in dogs, with the mortality rate of 25% in puppies. Bears, coyotes, wolves, mink, ferrets, striped skunks and raccoons are susceptible. Foxes infected with CAV-1 develop inflammation of the brain (encephalitis). Unvaccinated dogs can contract infection from wild species. The virus of canine hepatits does not infect humans.

The syndrome that gave the disease its name, infectious canine hepatitis, involves the massive destruction of liver cells (hepatocytes), resulting in death.

As with other adenoviruses, CAV-1 resists environmental inactivation with chemicals such as chloroform, ether, acid and formalin. The virus survives for days at room temperature and remains viable for months at temperatures below freezing. CAV-1 is inactivated after 5 minutes at 500°C to 600°C. Chemical disinfection is effective with iodine, phenol and sodium hydroxide.

Vaccination has greatly reduced the incidence of the disease and it is now rare in many countries. However, the infection is not eradicated and outbreaks occur. Most infections with ICH are mild, but occasionally the virus causes acute fatal disease that clinically resembles canine distemper and other canine virus infections.

Route of Infection

Infectious canine hepatitis is highly contagious. Natural infection with CAV-1 probably occurs via the oral route.⁴ The time from the moment of exposure to the virus until signs and symptoms of the disease appear (incubation period) is from 4 to 7 days. Virus multiplication occurs first in the tonsils leading to tonsillitis and inflammation of one or more lymph nodes. The virus then reaches the blood via the the main duct of the lymphatic system (thoracic duct). It is present in the bloodstream between 4 to 8 days after infection and spreads to other tissues and body secretions, including saliva, urine and feces. The virus persists in the kidneys and may be shed in the urine for up to 6 months after recovery.⁹

Signs

Early signs are fever, depression and lethargy and a respiratory disease. Later signs include reluctance to move, abdominal tenderness, pale mucous membranes, vomiting, diarrhea and loss of appetite. Inflammation of the throat and lymph nodes of the neck are common. In severe cases, bleeding around teeth may occur. Bleeding times may be prolonged. The liver becomes enlarged and may be palpated. Although central nervous system involvement is uncommon, dogs affected severely may convulse.¹⁰ There is also a form of the disease in which the animals are found dead without clinical signs after an illness of only a few hours. Some of these cases are associated with midbrain bleeding.

The cause of death in ICH is uncertain although the liver is the primary site of viral injury. Some dogs die suddenly. Death in these dogs may be as the result of damage to the brain, lungs, and other vital organs.

During the recovery period and 8-12 days after vaccination, corneal edema ("blue eye") is occasionally observed which disappears after a few days without consequence. The edema is due to the virus-antibody complexes deposited in the small blood vessels, interfering with the normal fluid exchange within the cornea. ¹⁰

Upon recovery, dogs eat well but regain weight slowly.

Prevention

Vaccination against ICH has proved very successful in significantly reducing the incidence of the disease throughout the world. Vaccination is carried out with a live modified vaccine, which can produce life-long immunity. Most vaccines contain weakened, less vigorous viruses (CAV-1 or CAV-2). Recommended vaccination schedules usually begin at about 6 weeks of age and may continue up to 4 months of age. Most dogs are exposed to the disease either in the form of the vaccine as young dogs, or in the form of the disease-causing virus as adults, and therefore most adult dogs will have serum antibodies. Most bitches will transfer antibodies against ICH in their colostrum to their pups shortly after parturition, giving them early protection from the disease. Annual vaccination has been recommended but is probably not essential due to the persisting immunity produced by the vaccine.

References:

1. An acute virus disease with liver lesions in dogs (hepatitis contagiosa canis): a pathologico-anatomical and etiological investigation. S. Rubarth. In: Acta. Pathol. Microbiol. Scand. Suppl. 69: 1-207, 1947.
2. Cross-protective immunity to canine adenovirus type-2 by canine adenovirus type-1 vaccination. Emery, J.B., House, J.A. and Brown, W.R. In: Am. J. Vet. Res. 39: 1778-1783, 1978.
3. Infectious canine hepatitis and canine acidophil cell hepatitis. Greene, C.E. (1999).
4. Canine viral diseases. In: Ettinger, S.J. (ED.): Textbook of Veterinary Internal Medicine. W.B. Saunders Co. Philadelphia. pp. 303-305, 1989.
5. Persistence of virus in urine as a factor in spread of infectious canine hepatitis. Poppensiek, G.G. and Baker, J.A. Proc. Soc. Exp. Biol. Med. 77: 279-281, 1951.
6. Carmichael, L.E.: The pathogenesis of ocular lesions of infectious canine hepatitis. II. Experimental ocular hypersensitivity produced by the virus. Vet. Pathol. 2: 344-359, 1965.
7. The liver and biliary system. In: Jubb, K.V.F., Kennedy, P.C. and Palmer, N. (Eds.): Pathology of Domestic Animals. Vol. 2. Academic Press, Inc. San Diego. pp. 364-366, 2000
8. Canine viral diseases. Hoskins, J.D. In: Ettinger, S.J. and Feldman, E.C. (Eds.): Textbook of Veterinary Internal Medicine. W.B. Saunders Co. Philadelphia. pp. 418-419, 2000.
9. Infectious diseases of wild mammals. Elizabeth S. Williams, Ian K. Barker
10. Veterinary virology. Frederick A. Murphy, E. Paul J. Gibbs (1999)