Adenovirus 1 in Dogs

Adenoviruses are a large group of structurally similar viruses containing a single molecule of unenclosed DNA. Adenovirus 1 causes infectious hepatitis in dogs, a serious liver disease which can be fatal in about 10-30% of cases. The virus is spread via feces and contaminated fluids from infected dogs, and may be present in a recovered dog for at least six months. It is more common and more severe among young dogs who have not yet been vaccinated. Vaccines are effective at preventing the disease. Adenovirus 1 is rare among regularly vaccinated household dogs, but it remains a threat from wild populations of dogs and other related carnivores.

Most commonly, the first sign of the disease is a low fever (above 104) which may drop and rise again. If the fever persists, it will lead to leukopenia (a drop in white blood cells) and more severe symptoms. Infectious hepatitis can range from a mild, barely noticeable illness to a life-threatening condition. The following symptoms in your dog may indicate Adenovirus 1:

• Fever
• Congestion
• Depression or apathy
• Thick discharge from eyes and nose
• Milky or blue appearance to eyes
• Thirst
• Lack of appetite and weight loss
• Tender abdomen
• Vomiting
• Diarrhea
• Elevated heart rate
• Increased blood coagulation
• Bleeding in the mouth and gums
• Convulsions
• One or more paralyzed limbs

Types

Canine adenovirus belongs to the genus Mastadenovirus, which includes viruses that affect mammals rather than birds. Types of adenovirus also infect horses and other farm animals. There are two commonly recognized types of adenovirus which can cause disease in dogs:

• Adenovirus 1 - causes infectious liver disease.
• Adenovirus 2 - causes respiratory infection (Infectious Tracheobronchitis) and is commonly also used in vaccines against both diseases.

Adenovirus 1 is a contagious disease which is spread from dog to dog. Dogs may catch the virus from another dog who is sick with the disease or one who has recently recovered. Some dogs may carry and spread the virus without manifesting symptoms. The virus is more commonly present where there are large populations of dogs congregated in one place, such as a kennel or an animal rescue center.

Common methods of transmission include:

• Eating infected feces.
• Saliva or mucus transported through the air (a cough or sneeze from an infected dog)
• Contact with contaminated urine.
• Staying in a kennel where there are other infected dogs.
• Spending time in a dog park or crowded dog walking area.

The virus will survive on its own for several months, so contaminated surfaces remain dangerous for quite some time. The most effective method for preventing infection from contaminated surfaces is cleaning with a bleach solution. Dogs who are too young to receive vaccinations are the most susceptible to the disease.

Making an appointment with your vet as soon as you notice symptoms of fever in your dog can result in the earliest possible diagnosis and the highest level of treatment. The veterinarian will suspect adenovirus 1 based on the symptoms although occasionally it can be confused with canine distemper or parvovirus both of which create similar symptoms. Blood and urine tests will further indicate the presence of infectious hepatitis. If your dog has not yet received vaccinations and spends considerable time among large groups of other dogs, this will increase the likelihood of the illness being related to adenovirus 1.

It’s not known what causes more acute cases of infectious hepatitis. The degree of antibody already present in the dog may be a factor, as well as combined infection with other diseases such as canine distemper or parvovirus. In general, a more severe drop in white blood cell counts at the beginning of the disease will indicate more pronounced symptoms and a higher chance of fatal liver failure, but this is something that will need to be diagnosed and evaluated by your veterinarian.

There is no cure for adenovirus 1, but treatment can decrease the severity of the symptoms. Antibiotics are given to eliminate the development of bacterial infection which can result from a weakened immune system. An IV is administered to balance fluids and electrolyte levels, and sometimes blood transfusions will be needed in extreme cases. Severely ill dogs will be kept for treatment and monitoring until their system has returned to normal. Maintaining fluids and healthy blood levels can increase your dog’s chance of survival, but recovery will also depend on the severity of the attack.

Once a dog has recovered from adenovirus 1, he will be immune for life. Lesions and tissue damage are sometimes visible on the interior organs of dogs who have survived severe forms of the disease, but these do not usually present a problem. Lesions are also often present on the cornea both during and after the disease, which results in a clouded or blue appearance to the eyes (sometimes called hepatitis blue eye.) This condition will make your dog’s eyes more sensitive, so bright, direct lights should be avoided. Occasionally, dogs suffer from short, sharp eye pain due to the corneal lesions. If your dog exhibits this condition, the pain can be treated with medication.

Some dogs who have been vaccinated with weakened strains of adenovirus 1 can develop the same clouded, blue-eyed appearance from corneal lesions, and the same resulting problems with bright light and pain. This is one of the reasons adenovirus 2 is used in most vaccines in the US. Both the MLV (modified live) and killed versions can create immunity to the two forms of the virus without negative side-effects.

In order to prevent adenovirus 1, young dogs should begin vaccination at around 6-8 weeks of age. Before this time, an antibody from the mother will prevent the vaccine from being effective. Three doses will be given at one-month intervals. When adult dogs are vaccinated, they receive 1 or 2 doses depending on whether the MLV or killed vaccine is used. The vaccine is often combined with the canine distemper and parvovirus vaccines. Yearly booster shots have been traditional; however recent studies show that dogs remain immune for at least 4 years after receiving the shot, and your veterinarian may recommend a longer interval.