Big Liver and Spleen Disease

Introduction

This condition was first seen in Australia in 1980. It is now known to be caused by an Avian Hepevirus. Related viruses have been reported to cause a hepatitis/splenomegaly syndrome in the USA, sub-clinical infection in pigs and Type E Hepatitis in man. The pig origin virus can cause disease in man, but avian hepeviruses are believed not to be zoonotic. The lesions are associated with deposition of antigen/antibody complexes in tissues. Only chickens are known to be naturally affected, most commonly broiler parents in lay. Natural infections have only been demonstrated in chickens over 24 weeks of age though it is possible that vertical transmission and/or infection in rear occurs with a subsequent period of latency. Transmission is usually by the faecal/oral route. Faecal contamination of drinking water is likely to be an efficient means of spread of this infection. Embryos inoculated intravenously become persistently antigen positive.

Signs

• Chronic under production or egg drops of up to 20%.
• Mortality of up to 1% per week for 3-4 weeks.
• Anaemia.
• Premature moulting.

Post-mortem lesions

• Enlarged spleen (over 1gm/kg bodyweight, often with pale foci).
• Liver usually enlarged, sometimes with subcapsular haemorrhage.
  
  Affected birds may also have:
  
• Lung congestion
• Ovarian regression
• Yolk peritonitis
• Pale foci and haemorrhages in pancreas.

Diagnosis

Typical signs and lesions. Must be confirmed by laboratory tests. Serological tests (agar gel immunodiffusion) may be used to detect either the specific antigen (which is likely to be positive first) or the antibody response to it. Elisa tests have been developed experimentally. A RT-PCR test may be used to detect viral RNA in tissues. Viral particles may be demonstrated in bile. Histopathology may also be used but the findings are not specific to this condition.

Treatment

No specific treatment known. It may be helpful to control other conditions which may be occurring at the same time. Drinking water which is well chlorinated should be helpful in reducing challenge by this route.

Prevention

Thorough cleaning and disinfection after depletion of an affected flock. Good biosecurity. All-in/all-out production.