Chicken Anaemia Virus Disease

Also known as: Chicken Anaemia — Blue Wing Disease — BWD — Anemia Dermatitis Syndrome — Chicken/Avian Infectious Anaemia — Hemorrhagic Aplastic Anemia Syndrome — Infectious Chicken Anaemia — CAV — Chicken Infectious Anaemia Virus — CIAV — Chicken Anaemia Agent — CAA

Scientific Classification
Kingdom	Virus
Family	Circoviridae
Genus	Circovirus
Species	Chicken anaemia virus

Introduction

Chicken anaemia virus disease is commonly referred to as chicken anaemia, chicken infectious anaemia and blue wing disease. It is caused by the chicken anaemia virus (CAV), which is a non-enveloped icosahedral single stranded DNA (ssDNA) virus. CAV is 23-25 nm diameter and is part of the Circoviridae, composing of a small circular genome of negative sense. The virus is difficult to eradicate as it is very hardy and resistant to high temperatures, acidic pH (pH3), chloroform and commercial disinfectants. CAV can be destroyed with hypochlorite and iodophor and formalin can reduce its infectivity. It is also morphologically and antigenically different to other circoviruses such as Porcine circovirus (PCV) and Psittacine beak and feather disease virus (PBFDV).

CAV produces three types of proteins: VP1 (52kDA), VP2 (24 kDA) and VP3 (14 kDA). Structural protein VP1 is the intracellular form of the capsid protein and VP2 is found in small amounts in the purified virus. Vaccines need to contain both of these to be antigenic. VP3 is involved in apoptosis which involves the programmed and controlled death of a cell. This process does not involve the lysis of the cell and therefore limits damage to surrounding cells and tissues. It also initiates pathogenicity and apoptosis of infected stem cells in the bone marrow (BM), resulting in damage to the BM. As a result, the virus inhibits the production of red blood cells (RBC), white blood cells (WBC) and platelets. Lymphoid tissues are also affected. Due to its apoptotic properties VP3 has the potential to be an anti-cancer agent. It is not considered a zoonosis.

CAV is difficult to grow but can be grown in chickens, embryonated eggs and in cell culture. The most commonly used cell line is MDCC-MSB1 (a Marek’s disease transformed chicken lymphocyte cell line). Virus production in this way may lead to the potential for Marek’s disease virus contamination of vaccines.

Signalment

The disease affects chickens but can also affect quail. Poultry that have previously been exposed to CAV and have CAV antibodies develop immunity. Disease is more severe in chicks.

Clinical Signs

Clinical signs consist of pale comb, wattle, eyelids, legs and carcass, anorexia, weakness, stunting, unthriftiness, weight loss, cyanosis, petechiation and ecchymoses, lethargy and sudden death. Neurological signs include, dullness, depression and paresis.

Epidemiology

The disease is mainly spread by vertical transmission, which is of particular importance to intensive breeding populations. The age of the bird has a marked effect on the development of clinical signs.Chicks hatching from infected layers of naive flocks (vertical transmission) show clinical signs after 10-14 days of age over a period of 3 to 6 weeks. After which the breeder layers develop sufficient CAV antibodies to stop the transmission of the virus to the egg. Mortality peaks during the third week of life around 5 to 10% but can be as high as 60%. Older chicks (>14 days old) that become infected via faecal-oral route (horizontal transmission) do not exhibit clinical signs but the growth and health of the birds may be affected. Fomites may assist the transmission of the virus.

Distribution

Worldwide distribution including commercial poultry and in specific pathogen free (SPF) flocks.

Diagnosis

Diagnosis can be made on the above clinical signs and decreases in haematocrit from normal ranges (32-37.5%) to below 27% and increases in the amount of immature blood cells.

Virus isolation can confirm diagnosis of disease but growth of CAV in cell cultures can be difficult. Levels of infection can be estimated by the detection of raising antibody titres and many diagnostic tests have been developed that include immunoperoxidase staining, ELISA, PCR and indirect immunofluorescence.

Post mortem finding include severe atrophy of the lymphoid organs. The thymus, bursa of Fabricius, and to a lesser extent the spleen are all affected by a depletion of lymphocytes and sequential hyperplasia of reticular cells. Common finding include haemorrhages throughout the skeletal muscle and subcutaneous tissue and pale watery bone marrow. Severe aplasia of the bone marrow occurs and haematopoietic cells are replaced with adipose tissue, giving the bone marrow its watery texture and characteristic change in colour from red to yellow.

Treatment

There is no specific treatment for infected birds with this virus and culling is likely to be the most appropriate option for commercial flocks.

Control

Vertical spread of the disease can be controlled by the vaccination of breeding hens with both live attenuated and wild vaccines that reduces the vertical transmission rate. Wild type vaccines are cheaper but can increase horizontal transmission rates and hidden reduction in production of older birds.

At a farm level rigorous cleaning with hypochlorite, iodoform or formalin is recommended and biosecurity is important to try to eradicate on farm infections.

Chicken Anaemia Virus Disease Learning Resources
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References

Schat, K.A. and van Santen, V.L. (2008) Chicken Infectious Anaemia. 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 211-235

Todd, D. and McNulty, M.S. (2007) Circoviridae. In: Poultry Diseases, 6th Edition (eds. Pattison, M., McMullin, P., Bradbury, J., Alexander, D.) Saunders, Elsevier, pp 398-405

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 18 June 2011.