BHV-1 has a restricted host range (i.e. bovids) and seldom crosses the species barrier (Brake & Studdert 1985). BHV-1.1 infections are most common in feedlot cattle (Merck, 2005). Infection is usually for life and carriers are asymptomatic unless the virus is reactivated (i.e. by stress). The duration of shedding is approximately 10-14 days during acute respiratory infection (Gibbs & Rweyemamu 1977) and also occurs following stress-induced reactivation of latent virus. Horizontal transmission can occur via contact with infected nasal droplets or contaminated semen (Mars et al., 2000; Kahrs, 2001). BHV-1 is also vertically transmitted between pregnant dams and their fetuses (Miller et al., 1991).BHV-1 is not abundant in the environment. It is very susceptible to changes in temperature and humidity (Elazhary and Derbyshire 1979; Mars et al. 1999) and easily eliminated by common disinfectants and solvents (Gibbs, and Rweyemamum, 1997). Although, infection can occur via inhalation of aerosolized virus, this is not likely a major cause of infection. Aerosolized virus does not appear to be able to travel greater than two cow-lengths (Wetlink et al., 1993).
Although Whetstone and Evermann
(1988), reported that BHV-1 infection caused clinical disease in sheep
goats, this may have been specific to a certain strain of virus. As a
rule, clinical BHV-1 disease does not occur in sheep under natural or
experimental conditions (personal communication with Dr. Philip
1993), despite the presence of BHV-1 cross-reactive antibodies in most
BHV-1 is not zoonotic and
at this time,
BHV-1 entry occurs at mucosal surfaces. BHV-1 receptors are expressed on the surface of epithelial cells of the upper respiratory tract, vaginal or prepuce mucous membranes, and the tonsils and conjunctivae (Tikoo et al. 1995a), as well as CD4+ T cells (Lovato et al. 2003), monocytes and macrophages (Nyaga & McKercher 1979; Forman et al. 1982).
Cell-mediated immune pathology
occurs approximately 7 days post-infection (Engels and Ackermann,
Infected cells can also undergo virus-induced apoptosis (Lovato et al.,
Denuding of the respiratory mucosal epithelium by apoptosis or immune
results in increased susceptibility to secondary bacterial infections
can result in pneumonia and even death (Hanon et al., 1998; Lovato et
BHV-1 also has immunosuppressive
properties. Infection of monocytes and macrophages interferes with
antigen-processing and presentation as well impairing phagocytosis
(Nyaga & McKercher 1979; Forman et al. 1982). BHV-1 also expresses
protein that binds complement factor C3, thus inhibiting the complement
(Huemer et al., 1993). With respect to neutrophils, there is a decrease
circulating number in blood and their activity is diminished (Tikoo et
1995; Forman et al., 1982). Infection of CD4+ T cells results in lower
of cells in the circulating lymphocyte pool, decreased IL-2 expression
decreased cytokine secretion following stimulation with mitogen (Forman
1982; Winkler et al., 1999). BHV-1 gG has the ability to bind and
number of chemokines, thus contributing to suppression of the host
response (Bryant et al., 2003).
Regardless of whether the initial
infection is symptomatic or asymptomatic, infection always results in
is another method of evading the immune response and most often occurs
peripheral nervous tissue, specifically the sciatic and trigeminal
is immune-privileged and do not express class I MHC molecules (Rock et
1992; Rock, 1994). Latency may also occur in tonsillar-resident
peripheral blood lymphocytes (Mweene et al., 1996). Cattle with latent
infection may be seronegative for BHV-1-specific antibodies (Hage et
1998). Re-activation of latent virus by stress, such as shipping,
shedding within 1 to 4 days and may also result in the appearance of
symptoms within 1 week of the stress event (Thiry et al., 1987).
The severity of BHV-1 infection in cattle relates to the subtype and strain of virus. Respiratory disease is the most common clinical form of infection in non-breeding cattle, whereas, abortion and genital infections are more common in breeding cattle. BHV-1 can also be characterized as either uncomplicated or complicated. Uncomplicated infections do not result in death in healthy, mature cattle (Kahrs, 2001). Complicated infections occur when there is secondary bacterial infection or systemic spread of virus resulting in viremia, and can result in death (Engels and Ackermann, 1996). Fatal viremia also occurs in newborn calves with failed passive transfer of maternal antibodies (Mechor et al. 1987).
Infectious Bovine Rhinotracheitis (IBR)Most common clinical manifestation of BHV-1 infection in feedlot cattle.
1. Uncomplicated IBR - Viral infection alone; is not life-threatening. Most lesions are restricted to the upper respiratory tract and trachea. Recovery occurs approximately 4 – 5 days after onset of clinical signs.
2. Complicated IBR - Viral infection is followed by secondary bacterial pneumonia, which may result in death. Mortality may reach 10 %. “Shipping fever” is a severe pneumonic condition, that occurs when infection with BHV-1, BVD, parainfluenzae-3 virus, or respiratory synctial virus, is followed by secondary bacterial infection with Mannheimia hemolytica and/or Pasteurella multocida (Yates, 1982).
Genital infectionPredominant subtype: BHV-1.2
forms of disease:
Generalized infection in calves
BHV-1 infection can be severe in young calves and cause a generalized disease, characterized by enteritis and death. Pyrexia, diarrhea, ocular discharge, incoordination, and eventually convulsions and death may occur in a short period after generalized viral infection. Calves might present with a respiratory component that is characterized by: respiratory distress, petechial to ecchymotic hemorrhages in the mucous membranes of the nasal cavity and the paranasal sinuses and focal areas of necrosis in the nose, pharynx, larynx, and trachea. The sinuses and nasal cavity are often filled with a serous or serofibrinous exudate. As the disease progresses, the pharynx becomes covered with a serofibrinous exudate, and blood-tinged fluid may be found in the trachea. The pharyngeal and pulmonary lymph nodes may be acutely swollen and hemorrhagic. The tracheitis may extend into the bronchi and bronchioles; when this occurs, epithelium is sloughed in the airways. The viral lesions are often masked by secondary bacterial infections. In young animals with generalized BHV-1 infection, erosions and ulcers overlaid with debris may be found in the nose, esophagus, and forestomachs. In addition, white foci may be found in the liver, kidney, spleen, and lymph nodes.
Other clinical signs
Conjunctivitis, mastitis, enteric disease and dermal disease may also occur. Any of these signs may occur in isolation or concurrently with other forms of disease (Kahrs, 2001; Wellenberg, 2002).