Wednesday, May 1, 2013

So you want to learn more about Canine Adenovirus? Great! We will begin with a comprehensive discussion on the virus itself, as well as some information about vaccines.

There are two Canine Adenoviruses (Types 1 and 2) that are very closely related.  They affect the same animals, but they cause different diseases.  CAV-1 produces a disease known as Infectious Canine Hepatitis, while Canine Adenovirus Type 2 causes respiratory signs, such as a cough.  More focus is generally given to CAV-1 due to the fact that it causes a more severe disease.

Canine Adenovirus Type 1 causes a systemic disease in all species of canines, as well as in bears.  The virus contains linear, double-stranded DNA, and is of the icosahedral shape.  It is a non-enveloped virus, and thus is resistant to disinfectants. The disease produced by CAV-1, Infectious Canine Hepatitis, was first described in foxes, but was found in dogs in the year 1930.  It is seen all over the world.  Among CAV-1’s target tissues are the liver and blood vessels.  Because of the involvement of the blood vessels, the virus causes severe inflammation all over the body, which can result in death.  CAV-1 can also cause secondary problems in the kidneys and eyes due to an overwhelming immune system response. 

The best method of control and prevention of CAV-1 is through vaccination.  The vaccine is considered a “core vaccine” for dogs, meaning it is recommended that all dogs be current on this immunization.  AAHA currently recommends that all puppies are immunized beginning at 6-8 weeks of age, and continuing every 3-4 weeks until about 16 weeks of age.  A booster vaccine should be given one year later, and then every three years after that.  The vaccine is often given in combination with other viral vaccines, such as Canine Distemper.   
The original vaccine caused undesirable side effects in dogs, so a new vaccine was developed.  This vaccine is based on CAV-2, but due to the similarities between the types, it protects extremely well against CAV-1.

Because of the immunization protocol that is in place today, diseases caused by Canine Adenovirus are not commonly seen in the United States, although they are seen in other countries without effective protocols.  It is important to know the basics of these diseases so that signs can be recognized in unvaccinated dogs.  Because the modified live CAV-1 vaccine had so many detrimental reactions in the past, dog owners may be hesitant to vaccinate their dog for CAV-1; however, it important to know that the new, much safer, CAV-2 vaccine effectively vaccinates for both Adenovirus types.  It is also important to know the vaccine guidelines so that this disease may be kept out of the dog population in the US.

We will now discuss how the virus will affect an unvaccinated animal

CAV-1 most often causes a natural infection in unvaccinated dogs, less than 1 year of age. The virus will enter the body through the oral and nasal  passages and implant within the tonsils. Here it will replicate, and within four to eight days, begin spreading throughout the body by entering into the bloodstream (a condition known as viremia). Once viremia has occurred, the virus can be shed through saliva, urine, and feces, all of which are infectious to other unvaccinated animals (Maclachlan 208).

CAV-1 primarily targets liver tissues and the inner lining of blood vessels (Greene 208). More specifically, this virus has adapted to live and replicate within the immune cells of the liver (Kupfer cells). This intracellular pathogen can then spread and damage the functional liver cells (hepatocytes) causing a severe hepatitis (inflammation of the liver) (Greene 208).

Some animals may mount a type III immune complex hypersensitivity reaction to the virus, in which immune complexes are formed that contain the virus and antibodies made against the virus (Maclachlan 208).T
hese complexes will circulate throughout the body and will occur 10-21 days after the recovery stage of the infection (Gelatt 492). Immune complexes most often affect the eye by clogging ocular capillaries and causing severe anterior uveitis (inflammation), which then leads to a secondary corneal edema. Clinical presentation of corneal edema is often referred to as "blue eye" because the eye appears cloudy and blue. Twenty percent of dogs recovering from a natural CAV-1 infection will present with bilateral corneal edema from anterior uveitis, but this reaction is usually transient and will clear within 2-3 weeks (Gelatt 492). If the damage is severe, permanent glaucoma and blindness may be a result (Gelatt 492).

 The severity of the infection depends on the length of time the animal has been infected, as well as how effectively the animals immune system responds to the virus. In severe peractue cases, there will be so much vascular damage that the animal will develop Disseminated Intravascular Coagulopathy (DIC) which is an acutely life threatening disorder (DIC, Cornell). Animals will deteriorate quickly, and die a few hours after clinical signs. In acute cases, the animals immune system will mount an attack against the virus and they will show signs of systemic disease, as well as liver, vascular, and kidney disease (Greene 208).

Clinical signs of peractue CAV-1 infection include:
  • Fever
  • CNS signs
  • DIC-overt hemorrhage/bleeding
Clinical Signs of Acute CAV-1 infection include:
  • Fever
  • Tonsilar Enlargement
  • Vomiting
  • Anorexia
  • Abdominal Pain
  • Diarrhea (with or without hemorrhage)
  • Enlarged Liver (hepatomegaly)
  • Hemorrhage 

Clinical Signs for an animal experiencing Type III hypersensitivity to CAV-1 infection includes:
  • Corneal edema and anterior uveitis --> clouding of the cornea most commonly referred to as Blue Eye, 4-6 days after infection. 

You have seen the clinical signs and you are suspicious that your dog has canine adenovirus, so what do you do? 

Despite your suspicions, the only one that can diagnose your dog is your veterinarian, but there are some diagnostics that you should be prepared to talk to your veterinarian about.  There are three different ways to diagnose canine adenovirus beyond recognition of clinical signs and patient history. 

The first method is to isolate the virus from any secretions or excretions from the animal, think along the lines of urine and saliva.  This is generally a good option, but virus isolation can take time.  Second,   the antibodies against the virus can be observed in the blood via serology. The blood is easy to collect, but in order to get the best results blood needs to be collected twice, once every 14 days.  Finally, the viral antigen, or a protein specific to the virus, can be recognized in a sample of tissues via immunofluorescence.  Any of these three options would be considered definitive; it is up to you and your veterinarian to determine the most appropriate option given time and your budget. 

Unfortunately once your veterinarian has diagnosed your dog with canine adenovirus, the best you can do is give them time.   Your veterinarian will be able to provide supportive care, including a plan for monitoring the blood glucose (or blood sugar), and the blood levels of ammonia which can have negative effects on brain function if they rise too high.  The veterinarian will also address any metabolic acid/base disturbances that would disrupt normal bodily functions by administering fluids.  Finally your veterinarian might recommend antibiotic therapy to prevent the normal bacteria contained in your dog’s stomach from abnormally moving throughout the body and causing problems. 

Fortunately, with time and supportive care canine adenovirus can be medically managed, and depending on the severity of the viral infection, your dog can expect to feel better within several months.  Canine adenovirus poses no health threat to you or your family, but will be shed in your dog’s excretions for the duration of the infection.  A responsible owner should be fastidious about cleaning up after their dog and should avoid communal dog areas where the possibility to spread the virus further will be heightened. 
A good vaccination program and an annual checkup with a veterinarian familiar with the clinical signs associated with canine adenovirus will go a long way towards ensuring a long and happy life for you and your dog. 


"Disseminated Intravascular Coagulation." DIC. Cornell Veterinary Medicine, n.d. Web. 29 
       Apr. 2013.
Gelatt, Kirk N., and Kirk N. Gelatt. "Ocular Manifestations of Viral Disease." Essentials of 
       Veterinary Ophthalmology. Ames, IA: Wiley-Blackwell, 2008. 492. Print.
Greene, Craig E. Infectious Diseases of the Dog and Cat. Third ed. St. Louis, MO: 
       Saunders/Elsevier, 2006. Print.
Maclachlan, Nigel James., and Frank Fenner. "Adenoviridae." Fenner's Veterinary Virology: 
       Ed. by N. James Maclachlan... London: Elsevier Academic, 2011. 208. Print.

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