Avian Nephritis

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Also Known As: Baby Chick Nephropathy — BCN

Caused By: Avian Nephritis Virus (ANV)

Introduction

Avian nephritis is caused by an astrovirus and affects solely chickens.

Distribution

The virus is present in Japan, Europe, USA and New Zealand.

The principle method of disease transmission is via faeces. AN is also transmitted vertically to eggs and chicks from infected hens.

Signalment

The chicken is the only significant host for ANV. Turkeys appear to neither develop disease nor specific antibodies against ANV.

Most infections even in young chicks are mild or sub-clinical, but nephrosis and death can result in susceptible and immunosuppressed chicks.

Only chicks less than 2 weeks old usually exhibit clinical signs.

Clinical Signs

As the first cells to be infected are enterocytes, diarrhoea is a common first feature of AN. It may be accompanied by polyphagia, emaciation and sudden deaths particularly in young chickens.

Growth retardation can be severe and variable and may be accompanied by poor feather development.

Dermatological signs of disease include erythema of the skin, ruffling of the feathers and vent soiling along with oedema and hindlimb swellings.

Disease is more severe when combined with other immunosuppressive agents such as Infectious Bursal Disease and also with cold stress and poor nutrition.

In cases of baby chick nephropathy, incidence peaks at ~5 days of age, and mortality rates may rise to 6%. This condition is thought to occur at a low level in most broiler flocks and is exacerbated by many factors.

Diagnosis

Definitive diagnosis requires demonstration of the virus, usually in kidney tissues.

Smears of kidney tissue can be fixed onto slides and immunofluorescence or immunohistochemistry can be used to demonstrate viral antigens. Faeces and liver can also be used for viral detection. Viral presence can also be confirmed by immunofluorescence, neutralisation and RT-PCR.

Serological tests comprise of virus neutralisation, ELISA and indirect immunofluorescence, of which neutralisation is the most sensitive and can be used from one week after initial infection. Antibodies to ANV are however often an incidental finding.

On post-mortem, nephritis and widespread urate deposits are often present in young birds. Kidneys have a pale cortex and general pale yellowish discolouration. Gouty nodules and tubular casts have been observed in some cases. Granulocyte infiltration is often seen with tubule degeneration on histological analysis. Nuclei of affected tubular cells are often swollen or fragmented due to viral propagation. General signs of enteritis are often present grossly, microscopically and histologically but are non-specific.

In cases of Infectious Shunting Syndrome (ISS), lesions appear in the crypts of lieberkuhn featuring degenerate macrophages accumulating in the lamina propria and cystic crypts in the jejunum. Mineralisation and fibrosis may result in advanced chronic cases of ISS.

Treatment

There is no effective treatment for birds infected with AN.

Control

Maternal antibodies are usually protective so immunisation of breeding hens is potentially possible but no vaccine is available despite experimental success. This is due to the economic impact of AN being unclear, and knowledge of avian astroviruses insufficient, and therefore investment seeming unjustified.

An all-in-all-out policy, thorough emptying of sheds between batches and formaldehyde disinfection have all been demonstrated to reduce incidence of AN and ISS. Reducing exposure to cold weather, dehydration, transport, overcrowding and other diseases which may be immunosuppressive are also key to prevention of AN.

Avian Nephritis Learning Resources
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References

Gough, R.E. and McNulty, M.S. (2007) Astroviridae. In: Poultry Diseases, 6th Edition (eds. Pattison, M., McMullin, P., Bradbury, J., Alexander, D.) Saunders, Elsevier, pp 392-398

Imada, T. (2008) Avian Nephritis. In: Diseases of Poultry, 12th Edition (eds. Saif, Y.M., Fadly A.M., Glissen J.R., McDougald L.R., Nolan L.K., Swayne D.E.) Wiley-Blackwell, pp 409-413

Reynolds, D.L. and Schultz-Cherry S.L. (2008) Astrovirus Infections. In: Diseases of Poultry, 12th Edition (eds. Saif, Y.M., Fadly A.M., Glissen J.R., McDougald L.R., Nolan L.K., Swayne D.E.) Wiley-Blackwell, pp 351-355

This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project. The datasheet was accessed on 20/06/2011.