Infectious canine hepatitis – symptoms and treatment

Overview

The disease is also called hepatitis contagiosa canis, or HCC, and infectious hepatitis. Infection occurs worldwide. Widespread vaccination has made the disease uncommon today.

Hepatitis generally means liver inflammation; in infectious canine hepatitis, the cause is specifically adenovirus rather than any other cause of liver damage.

Severity ranges from mild fever to serious systemic infection and sudden death. Some dogs carry and spread virus without looking ill. This virus does not infect people.

Around 10–30% of affected dogs die. Mortality is highest in very young dogs. However, most dogs recover. Some may still be left with organ damage.

A surviving dog is believed to retain immunity to the same virus for life.

Causes

Adenovirus enters through the mouth or nose

The cause is canine adenovirus type 1, or CAV-1. It is a non-enveloped DNA virus. The closely related CAV-2 instead contributes to infectious canine respiratory disease.

Dogs usually become infected when urine, faeces or saliva from an affected animal enters the mouth or nose. Objects, contaminated surfaces or human hands may also transmit infection. Shared water and food bowls can spread virus.

An affected dog's eye and nasal secretions also contain virus, so contact with these fluids can transmit infection.

Blood vessel damage explains many signs

The virus first multiplies in the tonsils and nearby lymph nodes. It then enters the bloodstream and spreads around the body. A major target is the cell layer lining blood vessels.

In the liver, the virus can cause liver cell death. Vascular damage and reduced liver production of clotting factors together predispose to bleeding. The kidneys, spleen and lungs can also become infected.

Risk factors

Young dogs have the greatest risk of severe disease, with the poorest outlook in puppies. Unvaccinated dogs lack vaccine-derived protection. The speed and strength of an individual's immune response influence the consequences of infection.

Maternal antibodies may interfere with a puppy's own vaccine response until around 9–12 weeks of age. In an older dog, infection may be so mild that signs go unnoticed. Symptom-free shedders and a contaminated outdoor environment also maintain infection risk.

Virus can circulate in wild canids such as foxes and wolves. Few cases in pet dogs therefore do not mean the virus has disappeared from the environment.

An older dog's mild infection may also resolve without specific medical treatment.

Typical symptoms

The usual incubation period is around 4–9 days from infection to symptoms.

However, signs can begin within 2–5 days of exposure. At its longest, incubation may be around 14 days.

The first sign is often fever above 40°C. Fever lasts around 1–6 days and may rise in two phases.

Fever persisting beyond 1 day is usually associated with development of clear acute illness.

• Your dog becomes tired and appetite declines clearly.

• Thirst may increase despite poor appetite.

• Vomiting and diarrhoea may occur, sometimes containing blood.

• The abdomen may be painful and movement reluctant.

• The eyes become inflamed or watery discharge comes from the eyes and nostrils.

• Swelling may develop beneath the skin of the head, neck or body.

• Mucous membranes may be pale or show small haemorrhages.

The tonsils may enlarge. Jaundice is not a common acute finding even when the liver is damaged.

A mild infection may also cause coughing that is difficult to distinguish from ordinary kennel cough.

Complications and consequences

Neurological signs are generally rare.

Severe disease may involve DIC, a whole-body clotting disorder. Bleeding may occur around baby teeth and beneath the skin. Brain damage can cause seizures, paralysis or loss of vision.

Chronic glomerulonephritis, inflammation of the kidney's filtering structures, may remain after recovery. Liver inflammation may also continue after the acute phase. Concurrent parvovirus or distemper infection worsens the outlook.

Secondary infection of the kidney pelvis may also develop. Neurological signs can result from hepatic encephalopathy too, brain dysfunction associated with liver failure.

Around 25% of recovered dogs develop clouding of both corneas. It often appears 7–10 days after acute signs disappear. This corneal clouding, called blue eye, results from an antibody-complex reaction. Ordinary, uncomplicated clouding often resolves on its own.

Immune-related eye and kidney changes can also follow an infection that caused no visible acute illness.

Infection in a pregnant bitch can cause stillborn puppies or deaths soon after birth. The dam herself may have no symptoms.

Diagnosis at the vet

Blood tests show organ damage and clotting disturbances

Sudden illness and bleeding raise suspicion, but signs may resemble distemper, for example. Supportive care starts before final test results if necessary.

A very rapid course can resemble poisoning, so infectious disease is considered as an alternative too.

White blood cell counts may remain low throughout the fever. Clotting tests may show prolonged clotting time. Platelet counts can decrease. Increased ALT and AST enzymes indicate liver injury. Urine often contains more protein than usual.

Examination may identify a heart rate unusually fast for the degree of fever.

The severity of white blood cell reduction may reflect disease severity. Prolonged clotting time also relates to severity, helping the overall assessment.

Virus and antibodies are investigated separately

PCR looks for viral genetic material, for example in a throat sample. During the first 10–14 days, virus may be found in all body fluids. Distinguishing CAV-1 from CAV-2 requires a test that differentiates the types.

A swab can also be taken from the eye's conjunctiva. Failed virus culture may result from the virus not remaining viable during sample transport.

Antibody testing may compare blood samples collected 2–3 weeks apart. Vaccination and previous infection can both explain blood antibodies. Results are therefore interpreted alongside vaccination history and other findings.

A negative urine PCR does not show that a recovered dog has definitely stopped being infectious. This is because urinary shedding is intermittent. A post-mortem examination of a suddenly deceased puppy can confirm diagnosis.

Liver histopathology may show characteristic viral inclusions within cell nuclei. At post-mortem, the gallbladder wall is also often swollen and thickened.

Treatment

Supportive care corrects dehydration and organ disturbances

There is no specific treatment that eliminates the disease; care gives the immune system time to respond. Supportive treatment for severe illness requires hospitalisation.

The vet treats the dog according to its signs and organ damage. Maintaining adequate fluid balance is fundamental. Intravenous fluids also correct electrolyte balance. Glucose is added to fluid therapy if needed.

Adequate nutrition forms part of supportive care. Severe bleeding or a clotting disorder may require plasma or whole-blood transfusion. Antibiotics may be used to prevent or treat secondary bacterial infections.

However, antibiotics do not act against adenovirus itself and do not replace other supportive care.

Liver enzymes may peak only around day 14 after infection and then decline slowly. Appetite may return before the dog regains lost weight.

Eye treatment and recovery monitoring

Temporary corneal clouding does not usually need specific treatment. Painful spasm of muscles inside the eye may be eased with veterinary-prescribed atropine eye ointment. A dog with cloudy eyes is protected from bright light. Oral or injected corticosteroids are unsuitable for treating this disease-associated clouding.

The outlook is reassessed throughout treatment because severity can change.

Prevention

Vaccination is the main way to prevent infectious canine hepatitis. An attenuated CAV-2 vaccine can provide cross-protection against CAV-1. Some commonly used combination vaccines include hepatitis protection alongside distemper and parvovirus protection.

Immunity from the hepatitis component of a combination vaccine usually lasts several years.

A dog being vaccinated should be healthy. Live-virus vaccination is not recommended for pregnant or immunocompromised dogs. Some dog-event organisers require hepatitis vaccination to be current too.

Read more about planning protection through your dog's vaccinations.

Infected dogs are isolated. Strict hygiene is maintained in the premises to prevent new infections. Surfaces are cleaned thoroughly before suitable disinfection. Virus may survive outdoors for weeks or months. Ordinary frost does not remove infection risk.

Virus can also survive for several weeks at around 30°C. A garden or other difficult-to-clean area may not be fully disinfected to a safe state.

Important for dog owners

A dog may spread virus in urine for another 6–9 months and sometimes longer.

Call the practice before arrival and mention the suspected infection so other dogs can be protected. Bring vaccination records and a description of possible dog contacts. At home, record fever, drinking, appetite, vomiting, stool colour and eye changes. Agree separately on post-discharge isolation, exercise areas and handling shared equipment. Mention other household dogs and any pregnant bitch. Arrange ongoing liver, kidney and eye monitoring even if your dog already looks healthy.

Frequently asked questions

Can a vaccinated dog develop infectious canine hepatitis?

An appropriately vaccinated dog has very good protection against the disease. However, maternal antibodies can interfere with a puppy's own vaccine response. Vaccine protection also declines over time. Records and product-specific development of protection are therefore considered in the vaccination plan.

Does a bluish eye always mean permanent blindness?

No: the disease-associated corneal clouding usually resolves on its own. However, inflammation inside the eye may accompany it, so veterinary examination is needed. An eye sign may be the dog's only visible indication of infection. Protect a dog with cloudy eyes from bright light during recovery.

Can a dog without symptoms still infect others?

Yes: some infected dogs do not become visibly ill. Virus may be shed in urine for 6–9 months or longer. One negative urine result does not show that the dog has stopped spreading infection.

Can infectious canine hepatitis spread to people?

CAV-1 is not a zoonotic infection transmitted to people. However, human hands and shared objects can carry virus to another dog. Careful hygiene and isolation of affected dogs are therefore needed even when the owner remains healthy.

Why does the hepatitis vaccine use a different adenovirus?

CAV-1 and CAV-2 are sufficiently similar in antibody terms for CAV-2 vaccination to protect against hepatitis too. CAV-2 vaccine causes corneal clouding or inflammation inside the eye much less often than the old CAV-1 vaccine. Its vaccine virus is not shed in urine either.