| Bovine immunodeficiency virus | |
|---|---|
Virus classification  | |
| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Pararnavirae |
| Phylum: | Artverviricota |
| Class: | Revtraviricetes |
| Order: | Ortervirales |
| Family: | Retroviridae |
| Genus: | Lentivirus |
| Species: | Bovine immunodeficiency virus |
Bovine immunodeficiency virus (BIV) is a retrovirus belonging to the genus Lentivirus . It is similar to the human immunodeficiency virus (HIV) and infects cattle. The cells primarily infected are lymphocytes and monocytes/macrophages. [1]
BIV was discovered in the late 1960s in the search for the infectious agent causing bovine leukemia/lymphosarcoma. This search led to the isolation and identification of three distinct classes of bovine retroviruses. BIV was specifically identified by Dr. Cameron Seger, a veterinarian of the Louisiana State University Agricultural Center, while he was studying dairy cattle at the Southeast Louisiana Experiment Station at Franklinton, Louisiana. The cows presented with high white blood cell counts, referred to as persistent lymphocytosis (PL) which is associated with the development of bovine leukemia/lymphosarcoma.[ citation needed ]
The first animal studied was an eight-year-old Holstein cow (R-29), her white blood cell count was elevated and her physical condition was steadily declining; after delivering a calf she weakened and became severely emaciated. She had to be euthanized and necropsy was performed. The diagnosis was lymphosarcoma, however, none of the tumors usually associated with the diseases were present in the postmortem gross examination. Tissue samples were sent to Dr. Van Der Maaten at the National Animal Disease Center; Dr. Van Der Maaten was able to isolate the BIV.[ citation needed ]
When the isolated BIV was inoculated into colostrum deprived young calves, they developed elevated leukocyte counts. The lymphocytosis persisted for several months and lymphadenopathy was apparent in the subcutaneous lymph nodes. This was similar to cow R-29. These calves, however, did not decline as R-29 did, which led researchers to believe that the isolated BIV was not the causative agent of the bovine leukemia/lymphosarcoma. It was put into storage and went unstudied until the discovery that acquired immunodeficiency syndrome (AIDS) was caused by HIV. [2]
One of the identifying characteristics of lentiviruses is being able to infect non-dividing cells. BIV, being a lentivirus has this characteristic. [3] BIV, like HIV, has two phases to its replication cycle. The first phase is the entry phase; it is initiated by high affinity of the virus envelope glycoprotein with a specific cell receptor. The attached virus enters the cell by one of two ways, receptor mediated endocytosis or viral envelope-cell membrane fusion. Once in the cell, the virus is uncoated and the RNA genome is reverse-transcribed into DNA. [2] Some studies have found that reverse transcriptase has a higher activity at low concentrations of Mn2+ ions when compared to Mg2+ ions; this finding is helpful in classifying the virus. [4] The DNA (provirus) is then transported into the nucleus where it integrates into the host cell genome. The second phase of the replication cycle is virus expression. During this phase the provirus is transcribed. The transcript is spliced and the viral mRNA is transported to the cytoplasm where it is then translated. After translation, the viral structural proteins assemble the virus particle at the plasma membrane and form a complex with the viral RNA as the virus buds and is released from the cell. The virus matures after proteolytic processing by the viral protease (PR). The virus is then ready to infect another cell and repeat the process. [2]
The mature virus is about 110–130 nm in size, with the genome being 8.4kb. The genome contains the usual retroviral structural genes including gag, pol, and env. These genes are surrounded by and 5’ and 3’ LTR. It also contains at least five non-structural accessory gene open reading frames (ORF). These are in the region between the pol and env ORF. Other accessory genes include vif (viral infectivity factor), tat (transcription activator), and rev (protein expression regulator). In primate lentiviruses there is usually an ORF for nef (negative factor); this is not present in BIV. BIV has a structure like all retroviruses, and contains two copies of its positive sense single stranded RNA genome. It has two compartments: the envelope and the core. The envelope comes from the host cell plasma membrane, the virus takes the membrane as it buds and then inserts viral glycoproteins into its envelope. The core of the virus contains Gag and Gag-Pol polyproteins. These polyproteins are cleaved in the mature virus to their functional forms. [4]
As mentioned before, leukocytosis and lymphadenopathy are associated with early infection. Researchers do now know how long cow R-29 was infected with BIV so some of the pathogenesis is not known. Eventually the symptoms resemble those of AIDS in humans. [3]
Like other retroviruses, BIV is spread through exchange of bodily fluids. When looking at prevalence of BIV infection, it was found that BIV is more prevalent in the southern United States and most prevalent in South America. [5] When an animal tests positive, many of the animals within the herd are also positive. Some of the spread is attributed to reuse of contaminated needles used in vaccinations, communal sharing of colostrum by calves, and failure to completely sterilize instruments after invasive treatments. [2]
The human immunodeficiency viruses (HIV) are two species of Lentivirus that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.
A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus.
Feline immunodeficiency virus (FIV) is a Lentivirus that affects cats worldwide, with 2.5% to 4.4% of felines being infected.
Lentivirus is a genus of retroviruses that cause chronic and deadly diseases characterized by long incubation periods, in humans and other mammalian species. The genus includes the human immunodeficiency virus (HIV), which causes AIDS. Lentiviruses are distributed worldwide, and are known to be hosted in apes, cows, goats, horses, cats, and sheep as well as several other mammals.
Gammaretrovirus is a genus in the Retroviridae family. Example species are the murine leukemia virus and the feline leukemia virus. They cause various sarcomas, leukemias and immune deficiencies in mammals, reptiles and birds.
The genome and proteins of HIV have been the subject of extensive research since the discovery of the virus in 1983. "In the search for the causative agent, it was initially believed that the virus was a form of the Human T-cell leukemia virus (HTLV), which was known at the time to affect the human immune system and cause certain leukemias. However, researchers at the Pasteur Institute in Paris isolated a previously unknown and genetically distinct retrovirus in patients with AIDS which was later named HIV." Each virion comprises a viral envelope and associated matrix enclosing a capsid, which itself encloses two copies of the single-stranded RNA genome and several enzymes. The discovery of the virus itself occurred two years following the report of the first major cases of AIDS-associated illnesses.
The murine leukemia viruses are retroviruses named for their ability to cause cancer in murine (mouse) hosts. Some MLVs may infect other vertebrates. MLVs include both exogenous and endogenous viruses. Replicating MLVs have a positive sense, single-stranded RNA (ssRNA) genome that replicates through a DNA intermediate via the process of reverse transcription.
Viral vectors are tools commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism or in cell culture. Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect. Delivery of genes or other genetic material by a vector is termed transduction and the infected cells are described as transduced. Molecular biologists first harnessed this machinery in the 1970s. Paul Berg used a modified SV40 virus containing DNA from the bacteriophage λ to infect monkey kidney cells maintained in culture.
Group-specific antigen, or gag, is the polyprotein that contains the core structural proteins of an Ortervirus. It was named as such because scientists used to believe it was antigenic. Now it is known that it makes up the inner shell, not the envelope exposed outside. It makes up all the structural units of viral conformation and provides supportive framework for mature virion.
Env is a viral gene that encodes the protein forming the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane.
Visna-maedi virus from the genus Lentivirus and subfamily Orthoretrovirinae, is a retrovirus that causes encephalitis and chronic pneumonitis in sheep. It is known as visna when found in the brain, and maedi when infecting the lungs. Lifelong, persistent infections in sheep occur in the lungs, lymph nodes, spleen, joints, central nervous system, and mammary glands; The condition is sometimes known as ovine progressive pneumonia (OPP), particularly in the United States, or Montana sheep disease. White blood cells of the monocyte/macrophage lineage are the main target of the virus.
Bovine leukemia virus (BLV) is a retrovirus which causes enzootic bovine leukosis in cattle. It is closely related to the human T‑lymphotropic virus type 1 (HTLV-I). BLV may integrate into the genomic DNA of B‑lymphocytes as a DNA intermediate, or exist as unintegrated circular or linear forms. Besides structural and enzymatic genes required for virion production, BLV contains an oncogene coding for a protein called Tax and expresses microRNAs of unknown function. In cattle, most infected animals are asymptomatic; leukemia is rare, but lymphoproliferation is more frequent (30%).
The human T-lymphotropic virus, human T-cell lymphotropic virus, or human T-cell leukemia-lymphoma virus (HTLV) family of viruses are a group of human retroviruses that are known to cause a type of cancer called adult T-cell leukemia/lymphoma and a demyelinating disease called HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLVs belong to a larger group of primate T-lymphotropic viruses (PTLVs). Members of this family that infect humans are called HTLVs, and the ones that infect Old World monkeys are called Simian T-lymphotropic viruses (STLVs). To date, four types of HTLVs and four types of STLVs have been identified. HTLV types HTLV-1 and HTLV-2 viruses are the first retroviruses discovered. Both belong to the oncovirus subfamily of retroviruses and can transform human lymphocytes so that they are self-sustaining in vitro. The HTLVs are believed to originate from interspecies transmission of STLVs. The HTLV-1 genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus. A closely related virus is bovine leukemia virus BLV. The original name for HIV, the virus that causes AIDS, was HTLV-3.
Retroviral matrix proteins are components of envelope-associated capsids of retroviruses. These proteins line the inner surface of viral envelopes and are associated with viral membranes.
Mason-Pfizer monkey virus (M-PMV), formerly Simian retrovirus (SRV), is a species of retroviruses that usually infect and cause a fatal immune deficiency in Asian macaques. The ssRNA virus appears sporadically in mammary carcinoma of captive macaques at breeding facilities which expected as the natural host, but the prevalence of this virus in feral macaques remains unknown. M-PMV was transmitted naturally by virus-containing body fluids, via biting, scratching, grooming, and fighting. Cross contaminated instruments or equipment (fomite) can also spread this virus among animals.
Lentiviral vectors in gene therapy is a method by which genes can be inserted, modified, or deleted in organisms using lentivirus.
Bovine foamy virus (BFV) is a ss(+)RNA retrovirus that belongs to the genus spumaviridae. Spumaviruses differ from the other six members of family retroviridae, both structurally and in pathogenic nature. Spumaviruses derive their name from spuma the latin for "foam". The 'foam' aspect of 'foamy virus' comes from syncytium formation and the rapid vacuolization of infected cells, creating a 'foamy' appearance.
Feline foamy virus or Feline syncytial virus is a retrovirus and belongs to the family Retroviridae and the subfamily Spumaretrovirinae. It shares the genus Felispumavirus with only Puma feline foamy virus. There has been controversy on whether FeFV is nonpathogenic as the virus is generally asymptomatic in affected cats and does not cause disease. However, some changes in kidney and lung tissue have been observed over time in cats affected with FeFV, which may or may not be directly affiliated. This virus is fairly common and infection rates gradually increase with a cat's age. Study results from antibody examinations and PCR analysis have shown that over 70% of felines over 9 years old were seropositive for Feline foamy virus. Viral infections are similar between male and female domesticated cats whereas in the wild, more feral females cats are affected with FeFV.
Equine foamy virus (EFV), also called foamy virus (FV), is virus in the genus Equispumavirus. It shares similarities, with respect to replication, with lentiviruses. EFV, along with other FVs are from the family Retroviridae and subfamily Spumaretrovirinae. Spumarivuses, such as EFV, are complicated retroviruses that have been characterized in many animals including nonhuman primates, cattle, cats. Additionally, these viruses have been identified in animals that most often carry lentiviruses.
Gibbon-ape leukemia virus (GaLV) is an oncogenic, type C retrovirus that has been isolated from primate neoplasms, including the white-handed gibbon and woolly monkey. The virus was identified as the etiological agent of hematopoietic neoplasms, leukemias, and immune deficiencies within gibbons in 1971, during the epidemic of the late 1960s and early 1970s. Epidemiological research into the origins of GaLV has developed two hypotheses for the virus' emergence. These include cross-species transmission of the retrovirus present within a species of East Asian rodent or bat, and the inoculation or blood transfusion of a MbRV-related virus into captured gibbons populations housed at medical research institutions. The virus was subsequently identified in captive gibbon populations in Thailand, the US and Bermuda.