Changes

Also Known As: '''''Enzootic Bovine Leucosis''''' — '''''Bovine Leukosis''''' — '''''EBL''''' — '''''BLV''''' — '''''Bovine Leukemia''''' — '''''Lymphosarcoma''''' — '''''Sporadic Bovine Leukosis''''' — '''''Bovine Malignant Lymphoma'''''  

Also Known As: '''''Enzootic Bovine Leucosis — Bovine Leukosis — EBL — BLV — Bovine Leukemia — Lymphosarcoma — [[Sporadic Bovine Leukosis]] — Bovine Malignant Lymphoma'''''  

==Introduction==

==Introduction==

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.

=Distribution=

==Distribution==

BLV is globally distributed, but prevalence widely varies.

BLV is globally distributed, but prevalence widely varies.

While 89% dairy operations in the USA showed seropositive results and 43.5% of all USA dairy cattle were seropositive <ref> USDA/APHIS/Veterinary Services, 1997. High prevalence of BLV in US dairy herds. Fort Collins, CO, USA: USDA: APHIS:VS Centers For Epidemiology and Animal Health.</ref>, seroprevalence in the EU rarely exceeds 0.5-1.5%. <ref>Lorenz, R. J., Straub, O. C. (1987) The epidemiology of enzootic bovine leukosis. In: Burny A, Mammerick, M, eds. Enzootic bovine leukosis and bovine leukemia virus. Boston, USA: Martinus Nijhoff Publishing, 51-68</ref>

While 89% dairy operations in the USA showed seropositive results and 43.5% of all USA dairy cattle were seropositive <ref> USDA/APHIS/Veterinary Services, (1997). High prevalence of BLV in US dairy herds. Fort Collins, CO, USA: USDA: APHIS:VS Centers For Epidemiology and Animal Health.</ref>, seroprevalence in the EU rarely exceeds 0.5-1.5%. <ref>Lorenz, R. J., Straub, O. C. (1987) The epidemiology of enzootic bovine leukosis. In: Burny A, Mammerick, M, eds. Enzootic bovine leukosis and bovine leukemia virus. Boston, USA: Martinus Nijhoff Publishing, 51-68</ref>

==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 colostrum/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

Gastrointestinal – Anorexia, hepatomegaly, dysphagia, constipation or diarrhoea, abomasal tympany, hypomotility

Gastrointestinal – anorexia, hepatomegaly, dysphagia, constipation or diarrhoea, abomasal tympany, hypomotility

Retrobulbar tumours sometimes cause blindness and other ocular signs.

Retrobulbar tumours sometimes cause blindness and other ocular signs.

Persistent lymphocytosis is defined by an increase in total lymphocyte count by 3 times the normal standard deviation above normal, persisting for at least three months with no clinical signs of neoplastic lesions. This is thought to represent 1/3 of all BLV infected cattle.

Persistent lymphocytosis is defined by an increase in total lymphocyte count by 3 times the normal standard deviation above normal, persisting for at least three months with no clinical signs of neoplastic lesions. This is thought to represent 1/3 of all BLV infected cattle.

=Diagnosis=

==Diagnosis==

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 - 4 weeks 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 testing|ELISA]] are also available. Antibodies may not be present for up to 12 weeks following onset of infection.

PCR can also be performed on peripheral blood lymphocytes.

PCR can also be performed on peripheral blood lymphocytes.

Multiple, firm white tumours may be present in any organ on post-mortem examination. In young animals, the common sites are the kidneys, thymus, liver, spleen, and lymph nodes. In adults, the heart, abomasum, and spinal cord are often involved.

Multiple, firm white tumours may be present in any organ on post-mortem examination. In young animals, the common sites are the kidneys, thymus, liver, spleen, and lymph nodes. In adults, the heart, abomasum, and spinal cord are often involved.

=Treatment=

==Treatment==

None Available

None Available

=Control=

==Control==

Testing and culling using the AGID test and PCR for young calves is effective, but not economically viable in high prevalence herds.

Testing and culling using the AGID test and PCR for young calves is effective, but not economically viable in high prevalence herds. In these circumstances, prevention of transmission between animals by direct contact with blood is the key focus. Some countries and states have mandatory management and monitoring practices in place which must be obeyed.

In these circumstances, prevention of transmission between animals by direct contact with blood is the key focus. Some countries and states have mandatory management and monitoring practices in place which must be obeyed.

Feeding young calves milk from seronegative dams can prevent further transmission ov BLV, although in high prevalence herds, frozen colostrums from infected dams has been used in order to provide passive immunity to the virus, while reducing lymphocyte infectivity. Note that these calves will then have a positive AGID result and therefore may be refused for export.

Feeding young calves milk from seronegative dams can prevent further transmission of BLV, although in high prevalence herds, frozen colostrum from infected dams has been used in order to provide passive immunity to the virus, while reducing lymphocyte infectivity. Note that these calves will then have a positive AGID result and therefore may be refused for export.

No vaccine is currently available for BVL/EBL.

No vaccine is currently available for BVL/EBL.

[[Category:Retroviridae]]

[[Category:Retroviridae]]

[[Category: To Do - CABI review]]

[[Category:Lymphoreticular and Haematopoietic Diseases - Cattle]]

[[Category: CABI Expert Review]]