Canine parvovirus type 2 (CPV-2)

• In the Parvoviridae family
• Non-enveloped virus
  • Can survive for months in the environment
  • Resistant to many disinfectants
  • Sodium hypochlorite (bleach) is one of the effective disinfectants
• Icosahedral capsid
• Targets rapidly-dividing cells (cells in the S-phase)
  • Intestinal crypt cells
  • Bone marrow precursor cells
  • Cardiac myocytes in puppies <8 weeks old

Risk factors

• 6 weeks to 6 months old
• Some breeds appear to be higher-risk for severe disease
  • Rottweilers, Doberman Pinschers, GSDs
  • Exact cause isn’t fully known
• Overcrowded / high-risk environments (shelters, rescue centres, kennels, dog parks)
• Unhygienic conditions
• High density of unvaccinated animals
• Stressful environments

Wild canids (coyotes, wolves, foxes) as well as domestic cats, mustelids and racoons can also become infected

• There are rare reports of captive big cats being infected (likely through contact with infected dogs)

Pathogenesis

1. Virus is ingested via contaminated faeces, food, water or fomites
   • Faeco-oral transmission
   • Incubation period ~2-7 days
2. Initially replication occurs in the tonsils and lymphoid tissues of the oropharynx
3. Virus spreads in the bloodstream to bone marrow, lymphoid tissues, intestinal crypt cells and cardiac myocytes (in young puppies)
4. Destruction of intestinal crypt cells causes villus atrophy
   • Atrophy leads to malabsorption, diarrhoea, vomiting and dehydration
5. Reduced mucosal barrier integrity increases the risk of bacterial translocation from the gut lumen into the blood
   • Can lead to sepsis, endotoxaemia and SIRS
6. Bone marrow infection destroys haematopoeitic precursor cells
   • Results in leukopenia and an impaired immune response
7. Infection of cardiac myocytes leads to myocarditis and a reduced cardiac efficiency
   • Can result in arrhythmia, heart failure and sudden death
   • Now rare due to widespread vaccination and transfer of protective maternal antibodies
8. Infected animals can start shedding the virus before clinical signs appear and continue for 10-14 days after recovery

General signs

• Profuse, watery diarrhoea
  • Can be haemorrhagic
• Vomiting
• Severe dehydration
• Abdominal pain
• Pyrexia
• Anorexia
• Lethargy / depression

If bacterial translocation occurs and sepsis develops, signs may include tachycardia, weak pulses, injected / dark red mucous membranes and hypo OR hyperthermia

Cardiomyocyte infection can cause arrhythmias, weak pulses or even sudden death in young puppies

Parvovirus should be assumed until proven otherwise in all suspicious cases

All possible cases MUST be isolated with barrier nursing only

Clinical presentation

• Unvaccinated puppies around 6 weeks-6 months old
• Acute vomiting and diarrhoea
• Exposure to high-density or unhygienic conditions

Laboratory tests

• Faecal antigen ELISA
  • Detects CPV-2 antigens in faeces
  • Can be done in-house
  • Useful as a screening test as false positives are unlikely
  • A negative result doesn’t exclude parvovirus definitively
• PCR
  • Detects viral DNA in blood or faeces
  • Highly sensitive
  • Used as a confirmation test most often in cases with negative ELISAs but high index of suspicion

Imaging with radiographs or ultrasound can show distended bowel loops or fluid-filled intestines which can be supportive but are not specific for parvovirus

• Useful for ruling out differentials (obstruction, intussusception)

The hallmark finding on haematology is leukopenia due to bone marrow suppression

Biochemistry may also show hypoproteinaemia, hypoalbuminaemia and electrolyte derangements (hypokalaemia, hyponatraemia, hypochloraemia) due to vomiting and diarrhoea

There is no specific antiviral therapy for parvovirus, therefore treatment focuses on supportive care

Fluid therapy

• Essential for correcting dehydration, hypovolaemia, acid-base disturbances and electrolyte imbalances
• Severely hypovolaemic patients may need intraosseal (IO) fluids
• Hypoglycaemia and hypoalbuminaemia are common in parvo dogs so dextrose and colloids may be used
• Consider packed red blood cells (pRBCs) in severely anaemic patients

Medication

• Antiemetics (maropitant, ondansetron) to reduce vomiting
• Opioids (buprenorphine) for analgesia
  • NSAIDs are contraindicated due to risk of GI ulceration and renal injury in dehydrated patients
• Broad-spectrum antibiotics (amoxicillin-clavulanate) to prevent or treat bacterial translocation / sepsis
  • Fluoroquinolones should only be used in very severe or non-responsive cases due to the risk of cartilage defects in young animals

Once vomiting is controlled, early enteral nutrition is recommended

• Has been proven to support intestinal mucosal healing, reduce bacterial translocation and speed-up recovery

Small, frequent meals of easily-digestible food is ideal

Vaccination

• Parvovirus is a core vaccine for dogs
• Schedule
  1. 1st dose: 6-8 weeks old
  2. 2nd dose: 10-12 weeks old
  3. 3rd dose: 14-16 weeks old
  4. Booster at 1 year
• After the initial protocol, a booster is given every 3 years
• Maternally-derived antibodies are protective for the first 10-16 weeks of life, at which point they start to wane
  • Window of susceptibility before vaccine-induced immunity has fully developed

Other strategies

• Avoid unhygienic or overcrowded areas
• Disinfect with bleach / sodium hypochlorite
• Isolate any suspected patients
• Use strict barrier nursing

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