Parvovirus in Dogs

Parvovirus, also referred to as parvoviral enteritis and "parvo", has been present in Australia since the 1970's. The virus is highly contagious and persistent in the environment, and passes easily to susceptible dogs through oral or nasal constant with infected feces, vomit, objects or surfaces which have come into contact with the virus. Signs of infection will generally appear 7 to 10 days after exposure.

Animals most susceptible to the virus include unvaccinated or incompletely vaccinated puppies, adults which have lapsed in vaccination immunity and immunocompromised animals. There are three strains of canine parvovirus worldwide, 2a and 2b have been detected in Australia, as well as the 2c strain, which is yet to be detected here. Vaccination, using proven products at the correct interval, is protective against all three strains.

Signs of Infection

Clinical signs of parvovirus vary between each case, and include:

- Lethargy
- Inappetance
- Vomiting
- Weakness
- Dehydration
- Diarrhoea (sometimes containing blood)

If any of the above signs are noted in your pet, it is vital that you seek veterinary attention as soon as possible, as untreated, parvoviral enteritis can have up to a 95% fatality rate, where as with prompt and appropriate treatment, this rate reduces to 15 - 35% (Merck Veterinary Manual, 8th Ed).

How Parvovirus Affects the Body

Parvovirus attacks rapidly dividing cells in the body, particularly affecting the cells that make up bone marrow, the lining of the intestines, and in young dogs, the heart. The clinical signs of the disease reflect the organs which have become infected.

In the bone marrow, parvovirus results in the destruction of hematopoietic cells - the stem cells which produce white and red blood cells. Destruction of the white blood cells, which form part of the immune system, decreases the body's ability to destroy viral and bacterial invaders, leading to overwhelming infection and sepsis, which can then affect any of the major organ systems. Red blood cells are responsible for transporting oxygen from the lungs to the organs and tissues. Without sufficient red blood cells, anemia results and organs become starved of vital oxygen, and wastes build up within the cells, which can lead to organ failure.

Within the intestines, parvovirus infects the cells which line the inner surface of the intestines. Once within these cells, the virus hijacks the cell's inner workings, forcing the cell to reproduce millions of copies of the original virus. Once sufficient virus has been produced, the cell is forced to explode (lyse) allowing viruses to move on and attack adjoining cells. As the intestinal lining is destroyed, the seal it forms between the intestinal contents and the body is lost - allowing bacteria to move from the intestine into the body, resulting in overwhelming infection (sepsis), as well as the loss of valuable water and electrolytes (salts) , resulting in severe dehydration of the patient.

In young animals (less then 8 weeks), parvovirus can also attacked the cells which are forming the heart, resulting in weakness of the heart muscle and poor function, which then affects the heart's ability to pump blood efficiently around the heart. These patients often become gradually weaker, eventually succumbing to heart failure, although some of the cases present as sudden death. Some people refer to this scenario as "fading puppy syndrome".

As all of these conditions can rapidly lead to a fatal outcome in affected dogs, it is vitally important that parvovirus be diagnosed as quickly as possible, allowing appropriate, intensive treatment to commence.

Diagnosis

Diagnosis of parvoviral enteritis starts with a physical examination, where your pet's general well being, vital signs and physical state will be assessed. The veterinarian will also discuss any signs that you may have noted prior to the appointment, as well as the vaccination history - if you have records of precious vaccinations, such as vaccination certificates, it is advisable to bring these with you to the appointment. As parvovirus is highly contagious, refrain from allowing your pet to wander freely in the waiting area of the clinic.

Additional laboratory tests are used to confirm the presence of parvovirus and to assess the degree of dehydration and blood cell changes in your pet. An in-clinic ELISA test (also known as a SNAP test) can be performed on feces to confirm the presence of parvovirus particles, as most, but not all affected dogs, will excrete these. Radiographs (X-rays) and ultrasound images may be used to identify other causes of vomiting, such as intestinal obstructions.

Once parvovirus has been confirmed, your pet will likely be admitted into a contagious disease isolation unit to begin intensive treatment.

Treatment

Treating parvovirus requires intensive care aimed at correcting and avoiding dehydration, pain and nausea management, nutritional support and treatment for sepsis. Treatment costs will vary depending on the severity of the case and the length of stay required, but can range from $1500 to $5000+, and lengths of stay can be anything from 2-3 days to 2 weeks plus.

On admission, your pet will generally be placed on an intravenous drip to correct dehydration, and receive medication, generally by injection in animals which are vomiting, to treat the nausea, pain and cramping, as well antibiotics and nutrition. Blood tests may also be used to monitor your pet's recovery. Treatment is deemed successful when blood cell counts and chemistry have returned to normal, diarrhea has lessened or ceased and the patient is able to eat and drink normally.

While your pet is in hospital, contaminated surfaces at home should be disinfected with solutions appropriate for viruses and your surfaces. Unfortunately, contaminated soil may remain infective for a year or more, so any further dogs introduced to the area must be fully vaccinated.

Prevention

As the old adage goes, 'prevention is better then cure'... And far more affordable. Several excellent commercial vaccines have been developed to inoculate your pet against this deadly virus. These products, when administered by your veterinarian at the manufacturer's recommended appropriate interval, have an excellent success rate in preventing parvovirus in dogs. The injections usually commence at 6 to 8 weeks of age, with boosters given until 16 weeks or greater. Regular booster vaccination and / or titres (a blood test used to assess the levels of protective antibodies stimulated by vaccination) will then be carried out throughout your pet's life to ensure continued protection from this deadly disease.