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Bovine herpesvirus 1 (BoHV-1) is a virus of the family ''Herpesviridae'' and the subfamily ''Alphaherpesvirinae'', known to cause several diseases worldwide in cattle, including rhinotracheitis, vaginitis, balanoposthitis, abortion, conjunctivitis, and enteritis. BoHV-1 is also a contributing factor in shipping fever, also known as bovine respiratory disease (BRD). It is spread horizontally through sexual contact, artificial insemination, and aerosol transmission and it may also be transmitted vertically across the placenta. BoHV-1 can cause both clinical and subclinical infections, depending on the virulence of the strain. Although these symptoms are mainly non-life-threatening it is an economically important disease as infection may cause a drop in production and affect trade restrictions. Like other herpesviruses, BoHV-1 causes a lifelong latent infection and sporadic shedding of the virus. The sciatic nerve and trigeminal nerve are the sites of latency. A reactivated latent carrier is normally the source of infection in a herd. The clinical signs displayed are dependent on the virulence of the strain. There is a vaccine available which reduces the severity and incidence of disease. Some countries in Europe have successfully eradicated the disease by applying a strict culling policy. Infection can occur in cattle of any age, but it is most commonly seen between the ages of 6 and 18 months. ==Transmission== BoHV-1 enters the animal through the mucous membrane in the respiratory tract or genital tracts. The main mode of disease transmission is direct nose-to-nose contact between an infected and a susceptible animal.〔Muylkens B., Thiry J., Kirten P., Schynts F., Thiry E. Bovine herpes virus 1 infection and infectious bovine rhinotracheitis. Vet. Res. 2007;38:181–209.〕 This is made possible because of the virus sloughing off into the mucus. Aerosols have to be exhaled, sneezed, or coughed from an infected animal during viral shedding in order for transmission to occur.〔Mars M, Brunschke C, van Oirschot JT. Airborne transmission of BoHV-1 among cattle is possible under experimental conditions. Veterinary Microbiology 1999;66:197–207.〕 Transmission also originates from contaminated semen through use of live breeding or AI; bulls that have been affected genitally may shed the virus in their semen. Once infected it is hard for the animal to get rid of BoHV-1 because it has many mechanisms to evade the hosts’ immune systems involved in both innate immunity and adaptive immunity. The virus degrades interferon regulatory factor 3 (IRF3), effectively halting transcription of interferon type 1.〔 Interferons are a component of innate immunity involved in inhibiting viral replication in a host cell, as well as activating immune cells. BoHV-1 is also able to evade adaptive immune cells by inducing apoptosis in CD4+ cells, which assist in activating T cells when antigens are present.〔 This down regulates the number of immune cells that recognize the virus, allowing the virus to evade detection and elimination. The virus has many other evasion strategies against the host’s immune system contributing to the virus being able to maintain lifelong infection in the animal. After primary infection of BoHV-1, the latent infection is quite often found in the trigeminal ganglion of the cow, although on occasion infection can enter the central nervous system.〔Smits C, Van Maanen C, Glas R, et al. Comparison of three polymerase chain reaction methods for routine detection of bovine herpes virus 1 DNA in fresh bull semen. Journal of Virologoical Methods 2000;85:65–73.〕 These latent infections can possibly reactivate, with or without clinical symptoms, under conditions of stress or by experimental methods.〔 Infected animals will be continuous shedders throughout their lifetime when the virus reactivates; therefore, successfully propagating the disease. The virus sheds in such high titers that it will spread rapidly throughout a herd. Even though cattle might not be showing clinical signs they can still spread the disease. Aside from cattle, studies experimentally infecting animals have shown that goats and buffalo can act as reservoirs for BoHV-1, as well as red deer, sheep, swine, and reindeer.〔 Shedding begins from the nasal mucosa as soon as infection occurs, and the virus has replicated in the upper respiratory tract. During replication in the respiratory tract cells of the epithelial will undergo apoptosis.〔Nandi, S, Kumar M, Manohar M, Chauhan R. Bovine herpes virus infections in cattle. Animal Health Research Reviews 2009;10:85–98〕 The necrosis in the epithelial will result in an entry site for secondary infections that may result in shipping fever. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bovine herpesvirus 1」の詳細全文を読む スポンサード リンク
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