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In a herd, BHV-1 circulation is initiated by virus reactivation and re-excretion in a latently infected animal already present, or more often by the introduction of an acutely or latently infected animal.
In a herd, BHV-1 circulation is initiated by virus reactivation and re-excretion in a latently infected animal already present, or more often by the introduction of an acutely or latently infected animal.
Between herds transmission is a major risk of BHV-1 circulation. However, it can be better controlled than within herd spread. Sanitary measures can be taken to prevent the introduction of seropositive animals or animals originating from a seropositive herd. Airborne transmission of BHV-1 has been demonstrated over short distances and can provide an explanation of between herds transmission, without the introduction of any new animal (Mars et al., 1999).
Between herds transmission is a major risk of BHV-1 circulation. However, it can be better controlled than within herd spread. Sanitary measures can be taken to prevent the introduction of seropositive animals or animals originating from a seropositive herd. Airborne transmission of BHV-1 has been demonstrated over short distances and can provide an explanation of between herds transmission, without the introduction of any new animal (Mars et al., 1999).
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In IPV, signs will include pain of the vagina or penis, reluctance to mate, mucous discharge from the vulva or penis and signs of ulcers, vesicles and erosions on the penis or vagina. The animal may be infertile and may abort or produce a stillborn calf.
In IPV, signs will include pain of the vagina or penis, reluctance to mate, mucous discharge from the vulva or penis and signs of ulcers, vesicles and erosions on the penis or vagina. The animal may be infertile and may abort or produce a stillborn calf.
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== Pathology ==
The respiratory form is the most frequently observed disease provoked by BHV-1. It affects all categories of animals. Calves are usually protected by colostral antibodies until 3-4 months of age. The severity of clinical signs varies considerably. Although BHV-1 is associated with the multifactorial respiratory disease complex of cattle, the virus is also responsible for a typical respiratory disease called infectious bovine rhinotracheitis (IBR).
The virus is excreted in the nasal secretions as early as 24 hours after infection. After an incubation period of 2 to 4 days, nasal secretions are more profuse and evolve from sero-mucous to mucopurulent discharge. Young animals show ptyalism. Around 4 days after the beginning of excretion, elevated temperatures are recorded, and animals are depressed and anorexic. In lactating cows, the milk production suddenly drops.
Ulcers and redness are visible on the nasal mucosa, in the pharynx and trachea (see pictures). Lesions are usually restricted in the upper respiratory tract. Bronchitis and pneumonia can also be observed, but usually as a consequence of secondary bacterial infections. Coughing and sneezing are observed. Conjunctivitis is associated with the respiratory form and is manifest by increased eye secretions.
Animals recover within 14 days, due to the rise of the specific immune response. Some highly virulent BHV-1 strains induce a high mortality rate.
Lesions are almost exclusively restricted to the upper respiratory tract: rhinitis, laryngitis and tracheitis. Respiratory mucosae are red and oedematous, foci of ulcers are observed and some lesions are haemorrhagic (Gibbs and Rweyemamu, 1977; Wyler et al., 1989; Straub, 1990).
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Abortion is observed between 4 and 8 months of gestation. Early embryonic death can also occur. Abortion is a consequence of respiratory infection of pregnant cows. Viraemia allows the virus to enter the uterine artery and cross the placenta. Abortion is due to a lytic infection of the fetus. All internal organs of the fetus, especially the liver and renal cortex, show foci of necrosis. A generalized multifocal necrosis is diagnosed (Smith, 1997).
Infection of cows during the last trimester of gestation can lead to neonatal death, and death of weak calves can occur during the first 2 weeks of life (Thiry et al., 1984).
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Infectious pustular vulvovaginitis (IPV) and infectious pustular balanoposthitis (IPB) is a pustular inflammation which occurs in the male or female genital mucosa, together with a rise in body temperature: up to 41.5°C. The genital mucosa is red and oedematous, and vesicles and pustules evolve into ulcers. The lesions resolve within 1 to 2 weeks (Straub, 1990).
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