Bovine Leukemia Virus

{Uncurated}}

Classification

Domain; Phylum; Class; Order; family [Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Genus species

Description and Significance

Describe the appearance, habitat, etc. of the organism, and why you think it is important.

Genome Structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence?

Cell Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Ecology and Pathogenesis

Pathogenesis The infection route of BLV is both through horizontal and vertical transmission. BLV is transmitted via direct contact (Kono et al., 1983), milk, and insect bites. One of the most common manners of infection is through blood in milk and flies. There are three main stages of BVL. The first begins with infection, and a cell contains the virus but is asymptomatic. The steps then begin with the Tax protein, a transcriptional activator of viral gene expression. It may inhibit DNA repair mechanisms, therefore increasing mutations within the DNA,. The next stage is known as PL, polyclonal proliferation of the virus in cells (called immortalization). Although most BLV-infected cows present no symptoms, PL is a benign form of the disease that describes an increase of untransformed B-lymphocytes in the blood of the animal. However, even after proliferation, it cannot transform cells. For lymphoma to develop, it needs a malignant transformation through a P53 mutant, TNF, or BoLa [1].

• P53 is a common tumor suppressor gene that works to control cell proliferation and apoptosis. Studies show that about half of tumors created by the BLV in cattle also contained missense mutations in p53. This suggests that p53 is one of many genetic changes that play a role in the further development of the disease.

• TNF, known as a tumor necrosis factor, TNF is a protein made by white blood cells in response to an antigen. It was found to be much higher in animals with lymphoma.

• BoLa is a bovine leukocyte antigen that determines immune responsiveness of the animal. The genetic variations of amino acids influence susceptibility. An example of this is seen in the presence of the amino acids Glu–Arg that confer resistance to PL in BLV-infected cattle.

Symptoms Only 29% of BLV-infected cattle develop persistent lymphocytosis (which are benign tumors but full of infectious potential) while <5% of BLV-infected cattle develop lymphosarcoma. Symptoms include extreme weight loss, labored breathing, lesions, tumors, bloat, fever, and loss of muscle. Lymphocytosis occurs as seen in PL, which increases B-lymphocytes past the normal range.

Significance to the Microbiome Studies show that the fecal microbial diversity differed slightly between affected and unaffected cows, and bacterial taxa that associated with rumen fermentation were more common in unaffected cows. The diversity of the microbiota was also affected, and more proliferation of BLV led to less diversity [2]. The rumen of the cow is responsible for breaking down food into useable energy and protein, so when BLV modifies the rumen's energy efficiency of this system, it causes negative effects. This may explain lessened milk production and susceptibility to other illnesses when infected with BLV.

References

Uchiyama, Jumpei et al. “Examination of the fecal microbiota in dairy cows infected with bovine leukemia virus.” Veterinary microbiology vol. 240 (2020): 108547. doi:10.1016/j.vetmic.2019.108547

Aida, Yoko, et al. “Mechanisms of Pathogenesis Induced by Bovine Leukemia Virus as a Model for Human T-Cell Leukemia Virus.” Frontiers in Microbiology, vol. 4, 2013, https://doi.org/10.3389/fmicb.2013.00328.

Author

Page authored by _____, student of Prof. Jay Lennon at IndianaUniversity.