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²[[Category: To Do - Steph]]
²[[Category: To Do - Steph]]
[[File:BLV.jpeg|thumb|200px|right|Conjunctival prolapse in cow with bovine viral leucosis (sourced from Wikimedia Commons)]]
[[File:BLV.jpeg|thumb|200px|right|Conjunctival prolapse in cow with bovine viral leucosis (sourced from Wikimedia Commons)]]
Also Known As — '''''Enzootic Bovine Leucosis''''' — '''''Bovine Leukosis''''' — '''''EBL''''' — '''''BLV''''' — '''''Bovine Leukemia''''' — '''''Lymphosarcoma''''' — '''''Sporadic Bovine Leukosis''''' — '''''Bovine Malignant Lymphoma'''''
=Introduction=
=Introduction=
Bovine leukaemia virus is a retrovirus causing two specific diseases: Bovine lymphosarcoma and Persistent lymphocytosis.
Bovine leukaemia virus is a '''retrovirus''' causing two specific diseases: '''Bovine lymphosarcoma''' and '''Persistent lymphocytosis'''.
Bovine lymphosarcoma is fatal while persistent lymphocytosis is not usually so.
Bovine lymphosarcoma is fatal while persistent lymphocytosis is not usually so.
Bovine leukosis is not transmissible to humans.
Bovine leukosis is not transmissible to humans.
This disease is notifiable to the World Organisation for Animal Health ([http://www.oie.int/ OIE])
This disease is '''notifiable''' to the World Organisation for Animal Health ([http://www.oie.int/ OIE])
=Signalment=
=Signalment=
Cattle are thought to be the only species naturally susceptible, and prevalence rates are higher in dairy breeds than beef.
Cattle are thought to be the only species naturally susceptible, and prevalence rates are higher in '''dairy breeds''' than beef.
The majority of infected animals are more than 2 years of age, with younger animals developing sporadic bovine leukosis which is thought to be unrelated – see below.
The majority of infected animals are more than 2 years of age, with younger animals developing sporadic bovine leukosis which is thought to be unrelated – see below.
Manifestation of the fatal neoplastic lymphosarcoma form of disease also appears better represented in dairy cattle.
Manifestation of the fatal neoplastic lymphosarcoma form of disease also appears better represented in dairy cattle.
Sporadic bovine leucosis is seen in young animals and causes thymic and cutaneous lymphosarcome. These animals are usually seronegative for EBL and so the pathogenesis is thought to be different to enzootic bovine leukosis.
'''Sporadic bovine leucosis''' is seen in young animals and causes thymic and cutaneous lymphosarcome. These animals are usually seronegative for EBL and so the pathogenesis is thought to be different to enzootic bovine leukosis.
=Distribution=
=Distribution=
===Transmission===
===Transmission===
Transmission of bovine leukaemia virus is mainly horizontal. Iatrogenic procedures are an important route as they facilitate transfer of contaminated blood between individuals, e.g. vaccinations, dehorning, rectal examinations and surgical procedures. Natural transmission by direct contact requires contact with infected blood, exudates or tissues which enter through broken skin.
Transmission of bovine leukaemia virus is mainly '''horizontal'''. '''Iatrogenic procedures''' are an important route as they facilitate transfer of '''contaminated blood''' between individuals, e.g. vaccinations, dehorning, rectal examinations and surgical procedures. Natural transmission by direct contact requires contact with infected blood, exudates or tissues which enter through broken skin.
Vertical transmission is most likely from colostrums/milk and is less important, although it does provide a method for control.
Vertical transmission is most likely from colostrum/milk and is less important, although it does provide a method for control.
===Lymphosarcoma===
===Lymphosarcoma===
The most common presentation is that of enlarged lymph nodes which may cause multiple palpable swellings in the pharynx, flanks and limbs.
The most common presentation is that of '''enlarged lymph nodes''' which may cause multiple palpable swellings in the pharynx, flanks and limbs.
This is often an early indicator of disease.
This is often an early indicator of disease.
5-20% cases are peracute and present as sudden death. This is thought to be due to sequelae such as adrenal gland involvement or rupture of abomasal ulcers etc.
5-20% cases are peracute and present as '''sudden death'''. This is thought to be due to sequelae such as adrenal gland involvement or rupture of abomasal ulcers etc.
Other signs are multisystemic and non-specific:
Other signs are '''multisystemic''' and non-specific:
Cardiovascular – Dysrhythmmias, jugular distension, tachycardia, murmurs
Cardiovascular – Dysrhythmmias, jugular distension, tachycardia, murmurs
Neurological signs and lameness also sometimes occur due to local tumour growth.
Neurological signs and lameness also sometimes occur due to local tumour growth.
Animals are usually afebrile.
Animals are usually '''afebrile'''.
Infected animals become permanent carriers.
Infected animals become permanent carriers.
Identification of enlarged lymph nodes without a raised rectal temperature may instigate suspicion.
Identification of enlarged lymph nodes without a raised rectal temperature may instigate suspicion.
Agar Gel Immuno Diffusion (AGID) is the official standard test approved by most governments. This test is usually accurate by 2-4weeks following infection. This test however cannot differentiate between infected cattle and those with passive immunity from colostrum.
'''Agar Gel Immuno Diffusion (AGID)''' is the official standard test approved by most governments. This test is usually accurate by 2-4weeks following infection. This test however cannot differentiate between infected cattle and those with passive immunity from colostrum.
Radioimmunoassay and serum or bulk milk ELISA are also available. Antibodies may not be present for up to 12 weeks following onset of infection.
Radioimmunoassay and serum or bulk milk ELISA are also available. Antibodies may not be present for up to 12 weeks following onset of infection.