Canine parvoviral enteritis

What it is

Canine parvovirus type 2 (CPV-2, with the variants 2a, 2b and 2c) is a small, non-enveloped DNA virus that replicates only in rapidly dividing cells. After oronasal infection it replicates in the lymphoid tissue of the oropharynx, spreads by viraemia and infects the crypt epithelium of the small intestine, the bone marrow and lymphoid tissues. Loss of the crypts prevents renewal of the villi, which collapse: the result is malabsorption, fluid and protein loss, and breakdown of the mucosal barrier, so that intestinal bacteria and endotoxins enter the blood while neutrophils are depleted. The virus is shed in large amounts in faeces and survives in the environment for months, resisting many common disinfectants.

Who it affects

Mainly unvaccinated or incompletely vaccinated puppies between about 6 weeks and 6 months of age, when maternal antibodies wane. Rottweilers, Dobermanns, American pit bull terriers and German shepherds have been reported to be at higher risk. Infection of neonates or in utero, now rare, caused myocarditis.

Anatomy involved

• Small intestine: the jejunum and ileum are most affected, with segmental, thickened, haemorrhagic walls and serosal congestion; histologically, crypt necrosis and villous blunting and fusion. Intussusception can complicate it.
• Bone marrow and lymphoid tissue: destruction of precursors and lymphocytes, with leucopenia and lymphoid depletion of Peyer's patches, lymph nodes and thymus.

Clinical signs

Sudden lethargy, anorexia and fever, followed by profuse vomiting and diarrhoea, often haemorrhagic and foul-smelling. Rapid dehydration, abdominal pain, hypoglycaemia and, in severe cases, septic shock with collapse and death.

Diagnosis

• Faecal antigen ELISA (point-of-care test): rapid and specific; it may be falsely negative early in the disease or once shedding has dropped, and briefly positive after vaccination with modified live vaccine.
• Faecal PCR: more sensitive.
• Blood count: leucopenia (neutropenia and lymphopenia) supports the diagnosis and has prognostic value.
• Biochemistry: hypoglycaemia, hypoalbuminaemia, hypokalaemia.

Treatment

There is no specific antiviral therapy; treatment is supportive and intensive: intravenous fluids with potassium and glucose, antiemetics (maropitant, ondansetron), early enteral nutrition, analgesia, and parenteral broad-spectrum antibiotics to cover bacterial translocation and sepsis. Colloids or plasma are given for hypoalbuminaemia. With hospital treatment most puppies survive; without it, mortality is high. Infected dogs must be isolated and the environment disinfected with products that inactivate parvovirus, such as diluted sodium hypochlorite or potassium peroxymonosulfate. Vaccination (a core vaccine) is the main prevention, with the puppy series completed at 16 weeks or later.