Bovine leukemia virus: Difference between revisions
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'''Bovine leukemia virus''' ('''BLV''') is a bovine virus closely related to [[HTLV|HTLV-I]], a [[human tumour virus]]. |
'''Bovine leukemia virus''' ('''BLV''') is a bovine virus closely related to [[HTLV|HTLV-I]], a [[human tumour virus]]. |
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BLV is a [[retrovirus]] which integrates a DNA intermediate as a [[provirus]] into the DNA of B-lymphocytes of blood and milk. It contains an [[oncogene]] coding for a protein called Tax. Nevertheless in its natural host the [[cattle]] leukemia is rare. Because the oncogenic properties of the virus were discovered early, a search for evidence of pathogenicity humans started soon after discovery. Mostly farm workers drinking raw milk were tested for disease, especially for leukemia. But neither leukemia nor other signs of infection could be detected. So many in many states it was not tried to get rid of this infection**. Testing strategies have recently changed since the virus was first detected in Cows; "Only very recently have currently available and highly sensitive assays such as Western blot and ELISA been employed in testing human sera. Buehring et al (2003) detected antibodies against BLV p24 capsid antigen in 74% of human sera tested using Western blot, while none of the samples that had given the most intense reaction was positive when tested with one of the earlier techniques." |
BLV is a [[retrovirus]] which integrates a DNA intermediate as a [[provirus]] into the DNA of B-lymphocytes of blood and milk. It contains an [[oncogene]] coding for a protein called Tax. Nevertheless in its natural host the [[cattle]] leukemia is rare. Because the oncogenic properties of the virus were discovered early, a search for evidence of pathogenicity humans started soon after discovery. Mostly farm workers drinking raw milk were tested for disease, especially for leukemia. But neither leukemia nor other signs of infection could be detected. So many in many states it was not tried to get rid of this infection**. Testing strategies have recently changed since the virus was first detected in Cows; "Only very recently have currently available and highly sensitive assays such as Western blot and ELISA been employed in testing human sera. Buehring et al (2003) detected antibodies against BLV p24 capsid antigen in 74% of human sera tested using Western blot, while none of the samples that had given the most intense reaction was positive when tested with one of the earlier techniques."<ref>{{cite journal |author=Buehring GC, Philpott SM, Choi KY |title=Humans have antibodies reactive with Bovine leukemia virus |journal=AIDS Res. Hum. Retroviruses |volume=19 |issue=12 |pages=1105–13 |year=2003 |month=December |pmid=14709247 |doi=10.1089/088922203771881202 }}</ref><ref name=Johnson05>{{cite journal |author=Johnson ES |title=Assessing the role of transmissible agents in human disease by studying meat workers |journal=Cellscience Reviews |volume=2 |issue=1 |pages= |year=2005 |issn=1742-8130 |url=http://web.archive.org/web/20061018094713/http://www.cellscience.com/Reviews5/Transmissible_Agents_Meat.html}}</ref> |
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High prevalence of virus was found from testing by USDA. "As part of the 2007 dairy study, bulk tank milk was collected from 534 operations with 30 or more dairy cows and tested with an Enzyme Linked-Immunosorbent Assay (ELISA) for the presence of antibodies against BLV. Results showed that 83.9 percent of U.S. dairy operations were positive for BLV (table 1)." |
High prevalence of virus was found from testing by USDA. "As part of the 2007 dairy study, bulk tank milk was collected from 534 operations with 30 or more dairy cows and tested with an Enzyme Linked-Immunosorbent Assay (ELISA) for the presence of antibodies against BLV. Results showed that 83.9 percent of U.S. dairy operations were positive for BLV (table 1)."<ref name=NAHMS07>{{cite web |title=Bovine Leukosis Virus on U.S. Dairy Operations, 2007 |work=NAHMS Dairy 2007 |publisher=U.S. Department of Agriculture |url=http://www.aphis.usda.gov/animal_health/nahms/dairy/downloads/dairy07/Dairy07_is_BLV.pdf |format=PDF}}</ref> |
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Many potential routes of BLV transmission exist. Transmission through procedures that transmit blood between animals such as gouge dehorning, vaccination and ear tagging with instruments or needles that are not changed or disinfected between animals is a significant means of BLV spread. Rectal palpation with common sleeves poses a risk that is increased by inexperience and increased frequency of palpation. Transmission via colostrum, milk, and in utero exposure is generally considered to account for a relatively small proportion of infections. Embryo transfer and artificial insemination also account for a small number of new infections as long as common equipment and/or palpation sleeves are not used. While transmission has been documented via blood feeding insects, the significance of this risk is unclear. The bottom line appears to be that transmission relies primarily on the transfer of infected lymphocytes from one animal to the next and that BLV positive animals with [[lymphocytosis]] are more likely to provide a source for infection. |
Many potential routes of BLV transmission exist. Transmission through procedures that transmit blood between animals such as gouge dehorning, vaccination and ear tagging with instruments or needles that are not changed or disinfected between animals is a significant means of BLV spread. Rectal palpation with common sleeves poses a risk that is increased by inexperience and increased frequency of palpation. Transmission via colostrum, milk, and in utero exposure is generally considered to account for a relatively small proportion of infections. Embryo transfer and artificial insemination also account for a small number of new infections as long as common equipment and/or palpation sleeves are not used. While transmission has been documented via blood feeding insects, the significance of this risk is unclear. The bottom line appears to be that transmission relies primarily on the transfer of infected lymphocytes from one animal to the next and that BLV positive animals with [[lymphocytosis]] are more likely to provide a source for infection. |
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In general BLV causes only a benign [[Infectious mononucleosis|mononucleosis]]-like disease in [[cattle]]. Only some animals later develop a [[B-cell]] [[leukemia]] called [[enzootic bovine leukosis]]. Under natural conditions the disease is transmitted mainly by [[milk]] to the calf. Infected lymphocytes transmit the disease too. So for artificial infection infected cells are used or the more stable and even heat resistant DNA. Virus particles are difficult to detect and not used for transmission of infection. It is possible that a natural virus reservoir exists in the [[domestic buffalo|water buffalo]]. |
In general BLV causes only a benign [[Infectious mononucleosis|mononucleosis]]-like disease in [[cattle]]. Only some animals later develop a [[B-cell]] [[leukemia]] called [[enzootic bovine leukosis]]. Under natural conditions the disease is transmitted mainly by [[milk]] to the calf. Infected lymphocytes transmit the disease too. So for artificial infection infected cells are used or the more stable and even heat resistant DNA. Virus particles are difficult to detect and not used for transmission of infection. It is possible that a natural virus reservoir exists in the [[domestic buffalo|water buffalo]]. |
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In Europe attempts were made to eradicate the virus by culling infected animals. The first country considered to be free of infection was Denmark**. Soon the United Kingdom followed. Like the North American states, those of the Eastern block in Europe did not try to get rid of the virus. But the Eastern Europe states started to become leukosis free after the political changes at the end of the last century. A very disturbing quote from a USDA fact sheet, "The high individual animal prevalence of BLV reported in the Dairy 1996 study suggests that testing and culling seropositive animals may not be a cost effective method to control the disease. Instead, preventing disease transmission by implementing preventive practices would likely be more cost-effective." |
In Europe attempts were made to eradicate the virus by culling infected animals. The first country considered to be free of infection was Denmark**. Soon the United Kingdom followed. Like the North American states, those of the Eastern block in Europe did not try to get rid of the virus. But the Eastern Europe states started to become leukosis free after the political changes at the end of the last century. A very disturbing quote from a USDA fact sheet, "The high individual animal prevalence of BLV reported in the Dairy 1996 study suggests that testing and culling seropositive animals may not be a cost effective method to control the disease. Instead, preventing disease transmission by implementing preventive practices would likely be more cost-effective."<ref name=NAHMS07/> |
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Natural infection of animals other than cattle and [[Bovinae|buffalo]] are rare, although many animals are susceptible to artificial infection. After artificial infection of sheep most animals succumb to leukemia. Rabbits get a fatal [[AIDS]] like disease similar to [[rabbit-snuffles]], different from the benign human [[snuffles]]. But it is not known whether this naturally occurring rabbit disease is linked to BLV infection. "Although several species can be infected by inoculation of the virus, natural infection occurs only in cattle (Bos taurus and Bos indicus), water buffaloes, and capybaras. Sheep are very susceptible to experimental inoculation and develop tumours more often and at a younger age than cattle. A persistent antibody response can also be detected after experimental infection in deer, rabbits, rats, guinea-pigs, cats, dogs, sheep, rhesus monkeys, chimpanzees, antelopes, pigs, goats and buffaloes." |
Natural infection of animals other than cattle and [[Bovinae|buffalo]] are rare, although many animals are susceptible to artificial infection. After artificial infection of sheep most animals succumb to leukemia. Rabbits get a fatal [[AIDS]] like disease similar to [[rabbit-snuffles]], different from the benign human [[snuffles]]. But it is not known whether this naturally occurring rabbit disease is linked to BLV infection. "Although several species can be infected by inoculation of the virus, natural infection occurs only in cattle (''Bos taurus'' and ''Bos indicus''), water buffaloes, and capybaras. Sheep are very susceptible to experimental inoculation and develop tumours more often and at a younger age than cattle. A persistent antibody response can also be detected after experimental infection in deer, rabbits, rats, guinea-pigs, cats, dogs, sheep, rhesus monkeys, chimpanzees, antelopes, pigs, goats and buffaloes."<ref name=OIE>{{cite book |author=OIE |chapter=Chapter 2.4.11 Enzootic bovine leukosis |chapterurl=http://www.oie.int/eng/normes/mmanual/2008/pdf/2.04.11_EBL.pdf |title=Manual of Diagnostic Tests and Vaccines for Terrestrial Animals |publisher=World Organisation for Animal Health (OIE) |year=2010 |url=http://www.oie.int/eng/normes/mmanual/A_summry.htm }}</ref> |
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Some long term studies may be necessary, as there appears to be a correlation in instances of cancer among butchers and slaughterhouse workers. |
Some long term studies may be necessary, as there appears to be a correlation in instances of cancer among butchers and slaughterhouse workers.<ref name=Johnson05/> "Several studies have been carried out in an attempt to determine whether BLV causes disease in humans, especially through the consumption of milk from infected cows. There is, however, no conclusive evidence of transmission, and it is now generally thought that BLV is not a hazard to humans."<ref name=OIE/> |
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==Research== |
==Research== |
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==External links== |
==External links== |
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* |
*{{cite journal |author=Kabeya H, Ohashi K, Onuma M |title=Host immune responses in the course of bovine leukemia virus infection |journal=J. Vet. Med. Sci. |volume=63 |issue=7 |pages=703–8 |year=2001 |month=July |pmid=11503896 |url=http://www.jstage.jst.go.jp/article/jvms/63/7/63_703/_article/-char/en}} |
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*{{cite journal |author=Gillet N, Florins A, Boxus M, ''et al.'' |title=Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human |journal=Retrovirology |volume=4 |issue= |pages=18 |year=2007 |pmid=17362524 |pmc=1839114 |doi=10.1186/1742-4690-4-18 |url=http://www.retrovirology.com/content/4//18}} |
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* [http://www.retrovirology.com/content/pdf/1742-4690-4-18.pdf Leukemogenesis of BLV] |
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* |
*{{cite journal |author=Takatori I, Itohara S, Yonaiyama K |title=Difficulty in detecting in vivo extracellular infective virus in cattle naturally infected with bovine leukemia virus |journal=Leuk. Res. |volume=6 |issue=4 |pages=511–7 |year=1982 |pmid=6292585 }} |
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*-1 [http://www.cellscience.com/Reviews5/Transmissible_Agents_Meat.html] |
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*-2 [http://nahms.aphis.usda.gov/dairy/dairy07/Dairy07_is_BLV.pdf] |
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*-3 [http://www.oie.int/eng/normes/mmanual/2008/pdf/2.04.11_EBL.pdf] |
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== References == |
== References == |
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Revision as of 13:08, 3 January 2011
| Bovine leukemia virus | |
|---|---|
| Virus classification | |
| Group: | Group VI (ssRNA-RT)
|
| Family: | |
| Subfamily: | Orthoretrovirinae
|
| Genus: | |
| Species: | Bovine leukemia virus
|
Bovine leukemia virus (BLV) is a bovine virus closely related to HTLV-I, a human tumour virus.
BLV is a retrovirus which integrates a DNA intermediate as a provirus into the DNA of B-lymphocytes of blood and milk. It contains an oncogene coding for a protein called Tax. Nevertheless in its natural host the cattle leukemia is rare. Because the oncogenic properties of the virus were discovered early, a search for evidence of pathogenicity humans started soon after discovery. Mostly farm workers drinking raw milk were tested for disease, especially for leukemia. But neither leukemia nor other signs of infection could be detected. So many in many states it was not tried to get rid of this infection**. Testing strategies have recently changed since the virus was first detected in Cows; "Only very recently have currently available and highly sensitive assays such as Western blot and ELISA been employed in testing human sera. Buehring et al (2003) detected antibodies against BLV p24 capsid antigen in 74% of human sera tested using Western blot, while none of the samples that had given the most intense reaction was positive when tested with one of the earlier techniques."[1][2]
High prevalence of virus was found from testing by USDA. "As part of the 2007 dairy study, bulk tank milk was collected from 534 operations with 30 or more dairy cows and tested with an Enzyme Linked-Immunosorbent Assay (ELISA) for the presence of antibodies against BLV. Results showed that 83.9 percent of U.S. dairy operations were positive for BLV (table 1)."[3]
Many potential routes of BLV transmission exist. Transmission through procedures that transmit blood between animals such as gouge dehorning, vaccination and ear tagging with instruments or needles that are not changed or disinfected between animals is a significant means of BLV spread. Rectal palpation with common sleeves poses a risk that is increased by inexperience and increased frequency of palpation. Transmission via colostrum, milk, and in utero exposure is generally considered to account for a relatively small proportion of infections. Embryo transfer and artificial insemination also account for a small number of new infections as long as common equipment and/or palpation sleeves are not used. While transmission has been documented via blood feeding insects, the significance of this risk is unclear. The bottom line appears to be that transmission relies primarily on the transfer of infected lymphocytes from one animal to the next and that BLV positive animals with lymphocytosis are more likely to provide a source for infection.
In general BLV causes only a benign mononucleosis-like disease in cattle. Only some animals later develop a B-cell leukemia called enzootic bovine leukosis. Under natural conditions the disease is transmitted mainly by milk to the calf. Infected lymphocytes transmit the disease too. So for artificial infection infected cells are used or the more stable and even heat resistant DNA. Virus particles are difficult to detect and not used for transmission of infection. It is possible that a natural virus reservoir exists in the water buffalo.
In Europe attempts were made to eradicate the virus by culling infected animals. The first country considered to be free of infection was Denmark**. Soon the United Kingdom followed. Like the North American states, those of the Eastern block in Europe did not try to get rid of the virus. But the Eastern Europe states started to become leukosis free after the political changes at the end of the last century. A very disturbing quote from a USDA fact sheet, "The high individual animal prevalence of BLV reported in the Dairy 1996 study suggests that testing and culling seropositive animals may not be a cost effective method to control the disease. Instead, preventing disease transmission by implementing preventive practices would likely be more cost-effective."[3]
Natural infection of animals other than cattle and buffalo are rare, although many animals are susceptible to artificial infection. After artificial infection of sheep most animals succumb to leukemia. Rabbits get a fatal AIDS like disease similar to rabbit-snuffles, different from the benign human snuffles. But it is not known whether this naturally occurring rabbit disease is linked to BLV infection. "Although several species can be infected by inoculation of the virus, natural infection occurs only in cattle (Bos taurus and Bos indicus), water buffaloes, and capybaras. Sheep are very susceptible to experimental inoculation and develop tumours more often and at a younger age than cattle. A persistent antibody response can also be detected after experimental infection in deer, rabbits, rats, guinea-pigs, cats, dogs, sheep, rhesus monkeys, chimpanzees, antelopes, pigs, goats and buffaloes."[4]
Some long term studies may be necessary, as there appears to be a correlation in instances of cancer among butchers and slaughterhouse workers.[2] "Several studies have been carried out in an attempt to determine whether BLV causes disease in humans, especially through the consumption of milk from infected cows. There is, however, no conclusive evidence of transmission, and it is now generally thought that BLV is not a hazard to humans."[4]
Research
Because of the close relationship between BLV and HTLV-I the research on BLV is important. One can use the experience with BLV for understanding HTLV-I induced diseases like ATL the adult T-cell leukemia and HMS/TSP like neurological disorders.
Clinical signs of bovine leukosis
The variety of organs where white blood cells are to be found explains the many symptoms observed by veterinarians: enlargment of superficial lymph nodes, a digestive form, a cardiac form, a nervous form, a respiratory form, etc. [5].
An unexpected clinical finding is protrusion of cunjunctival membrane, due to enlargment of retro-ocular lymph nodes.
External links
- Kabeya H, Ohashi K, Onuma M (2001). "Host immune responses in the course of bovine leukemia virus infection". J. Vet. Med. Sci. 63 (7): 703–8. PMID 11503896.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - Gillet N, Florins A, Boxus M; et al. (2007). "Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human". Retrovirology. 4: 18. doi:10.1186/1742-4690-4-18. PMC 1839114. PMID 17362524.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link) - Takatori I, Itohara S, Yonaiyama K (1982). "Difficulty in detecting in vivo extracellular infective virus in cattle naturally infected with bovine leukemia virus". Leuk. Res. 6 (4): 511–7. PMID 6292585.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
References
- ^ Buehring GC, Philpott SM, Choi KY (2003). "Humans have antibodies reactive with Bovine leukemia virus". AIDS Res. Hum. Retroviruses. 19 (12): 1105–13. doi:10.1089/088922203771881202. PMID 14709247.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ a b Johnson ES (2005). "Assessing the role of transmissible agents in human disease by studying meat workers". Cellscience Reviews. 2 (1). ISSN 1742-8130.
- ^ a b "Bovine Leukosis Virus on U.S. Dairy Operations, 2007" (PDF). NAHMS Dairy 2007. U.S. Department of Agriculture.
- ^ a b OIE (2010). "Chapter 2.4.11 Enzootic bovine leukosis". Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. World Organisation for Animal Health (OIE).
{{cite book}}: External link in|chapterurl=|chapterurl=ignored (|chapter-url=suggested) (help) - ^ Veterinary Medicine (5th ed.). London: Baillière Tindall. 1979. pp. 611 (Leucosis in cattle and other species). ISBN 0-7020-07-18-8.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)