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| − | == Introduction ==
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| − | This virus is of the family [[Retroviridae]], which is a family of viruses that eventually all cause tumours. There are three subgroups of this virus to note. Groups A and B are found in 10% of layers and cause occasional B cell leukosis, J has been found in up to 40% of broilers causing up to 10% of deaths by myeloid tumors. All three subgroups are transferred vertically and horizontally. Vertical transmission is most important by infection of the egg white in infected breeders (who are long-term carriers), lateral transmission is poor but infection may occur by the faecal-oral route, especially in young birds. The causative viruses are rapidly inactivated at ambient temperature and on exposure to most disinfectants.
| + | ====Antigenicity==== |
| | + | 3 subgroups of note: |
| | + | *A and B are found in 10% of layers, causing occasional B cell leukosis |
| | + | *J has been found in up to 40% of broilers causing up to 10% of deaths by myeloid tumors |
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| − | The disease is complex and has various manifestations such as lymphoid leukosis, myeloblastosis (see Sero-type J), erythroblastosis, osteopetrosis, myxosarcomas, fibrosarcomas and other tumours. It affects chickens worldwide with susceptibility varying considerably among different strains and types of stock, with layers being more susceptible to lymphoid leukosis.
| + | ====Epidemiology==== |
| | + | *All three subgroups are transferred vertically and horizontally |
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| − | Morbidity is low but mortality is high in many cases of the disease.
| + | ====Control==== |
| − | | + | *Selective breeding has now controlled the virus: |
| − | == Clinical Signs == | + | **Hens whose eggs testing positive for antigen in albumin are removed from the flock |
| − | | + | [[Category:Avian_Type_C_retrovirus]][[Category:Avian]][[Category:Poultry]] |
| − | Signs include depression, emaciation, weight loss and enlargement of the abdomen, liver or bursa. However, many birds are asymptomatic.
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| − | == Diagnosis == | |
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| − | History, signalment and clinical signs are indicative of the disease, but differentials such as [[Mareks Disease|Marek's disease]] and coligranuloma need to be excluded.
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| − | Necropsy can be carried out and lesions seen will include focal grey to white tumours, initially in the bursa, then liver, spleen, kidney etc. The liver may be very large. Microscopic examination will reveal lymphoplastic cells.
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| − | == Control ==
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| − | Selective breeding has now controlled the virus type J and may lead to eradication of this group. This has been done by identifying hens whose eggs testing positive for antigen in albumin and removing them from the flock. | |
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| − | Control measures include general good hygiene, management systems such as an 'all in/ all out' production system and removal of the litter after every batch. It is also important to control [[:Category:Arthropods|arthropods]] especially [[:Category:Mites|mites]].
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| − | == References ==
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| − | Bridger, J and Russell, P (2007) '''Virology Study Guide''', ''Royal Veterinary College''
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| − | Merck & Co (2008) '''The Merck Veterinary Manual''' (Eighth Edition), ''Merial''
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| − | Jordan, F, Pattison, M, Alexander, D, Faragher, T, (1999) '''Poultry Diesease''' (Fifth edition), ''W.B. Saunders''
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| − | Randell, C.J, (1985) '''Disease of the Domestic Fowl and Turkey''', ''Wolfe Medical Publication Ltd''
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| − | Saif, Y.M, (2008) '''Disease of Poultry''' (Twelfth edition), ''Blackwell Publishing ''
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| − | {{review}}
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| − | {{OpenPages}}
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| − | [[Category:Avian_Viruses]] [[Category:Retroviridae]][[Category:Expert_Review - Viruses]] | |
