Infectious Canine Hepatitis
Introduction: Infectious canine hepatitis (ICH) is a worldwide, contagious disease of dogs with signs that vary from a slight fever and congestion of the mucous membranes to severe depression, low white blood cell count, and prolonged bleeding time.
It also occurs in foxes, wolves, coyotes, and bears.
Other carnivores may become infected without developing clinical illness.
The Cause: ICH is caused by canine adenovirus 1 (CAV-1), which is antigenically related only to CAV-2 (one of the causes of infectious canine tracheobronchitis). CAV-1 is resistant to lipid solvents and survives outside the host for weeks or months, but household bleach is an effective disinfectant.
Ingestion of urine, feces, or saliva of infected dogs is the main route of infection.
Recovered dogs shed virus in their urine for more than 6 months.
Initial infection occurs in the tonsils, followed by multiplication of the virus and and infection of the liver, kidneys, spleen, and lungs.
Chronic kidney lesions and corneal clouding ("blue eye") result from immune-complex reactions to the virus.
Clinical Findings
Signs vary from a slight fever to death.
The mortality rate is highest in very young dogs.
The incubation period is 4-9 days.
The first sign is a fever of >104° F (40° C), which lasts 1-6 days. If the fever is of short duration, leukopenia (low white blood cell count) may be the only other sign, but if it persists for more than a day, acute illness develops. Tachycardia out of proportion to the fever may occur. On the day after the initial temperature rise, leukopenia develops and persists throughout the febrile period. The degree of leukopenia varies and seems to be correlated with the severity of illness.
Exam findings are lethargy, lack of appetite, thirst, inflammation of the eyes (conjunctivitis), eye and nose drainage, and often GI signs such as vomiting.
Intense hyperemia or little hemorrhages of the oral mucosa, as well as enlarged tonsils, may be seen. There may be subcutaneous edema of the head, neck, and trunk.
Clotting time is directly correlated with the severity of illness. It may be difficult to control hemorrhage, which is manifest by bleeding around deciduous teeth and by spontaneous hematomas, because of underlying disseminated intravascular coagulation.
Respiratory signs usually are not seen in dogs with ICH; however, CAV-1 has been recovered from dogs with signs of infectious tracheobronchitis and from dogs with respiratory signs induced by exposure to the nebulated isolate.
Although CNS involvement is unusual, the severely infected dog may have a terminal convulsion, and brain-stem hemorrhages are common.
Foxes more consistently have CNS signs and intermittent convulsions during the course of illness, and terminal paralysis may involve one or more limbs or the entire body.
On recovery, dogs eat well but regain weight slowly. Seven to 10 days after the acute signs disappear, about 25% of recovered dogs develop bilateral corneal opacity, (blue eye) which usually disappears spontaneously.
In mild cases of ICH, transient corneal opacity may be the only sign of disease.
Chronic hepatitis may develop in dogs having low levels of passive antibody when exposed. Simultaneous infection with CAV-1 and distemper virus is sometimes seen.
Lesions seen on pathology or necropsy: Endothelial damage results in "paint brush" hemorrhages on the gastric serosa, lymph nodes, thymus, pancreas, and subcutaneous tissues. Hepatic cell necrosis produces a variegated color change in the liver, which may be normal in size or swollen. The gallbladder wall may be edematous and thickened; edema of the thymus may be found. Grayish white foci may be seen in the kidney cortex.
Treatment:
Blood transfusions may be necessary in severely ill dogs. In addition, 5% dextrose in isotonic saline should be given, preferably IV. In dogs with prolonged clotting time, SC administration of fluids may be dangerous.
A broad-spectrum antibiotic should be given. Because tetracyclines may cause discoloration of the teeth during tooth development, they should not be used in puppies before their permanent teeth erupt.
Atropine ophthalmic ointment may alleviate the painful ciliary spasm that is sometimes associated with corneal edema if present. Also, the dog should be protected against bright light if corneal clouding occurs.
Systemic corticosteroids are generally contraindicated for treatment of corneal opacity associated with ICH.
Prevention: Vaccination using the CAV-2 attenuated live virus strains, which provide cross protection against CAV-1, are recommended for puppies starting at 6-7 weeks old. Boosters are recommended at 10-11 weeks old.
However, maternal antibodies may intefer with successful immunization, so it's important to give another booster after 12 weeks old.
Annual revaccination is recommended by most vets but there is a consensus forming that this may not be necessary in mature dogs.
Note; the CAV-2 or hepatitis vaccine is part of the combination vaccine (also known variously as the 5 way or 7 way vaccine) containing vaccines for multiple strains of distemper, flu, and parvo virus.
