Experimental respiratory syncytial virus infection in feeder-age lambs

Signs of disease, lesions, and serologic response were seen in six 6-month-old-lambs experimentally inoculated with respiratory syncytial virus (RSV). A transient febrile response, mild hyperpnea, and listlessness were seen. Multifocal areas of interstitial pneumonia and bronchiolitis were seen in lambs necropsied during the period of clinical response. A serologic response to RSV was seen in all lambs, and RSV was recovered from five lambs.     

Experimentally induced respiratory syncytial viral infection in lambs

Signs of clinical illness, lesions, and seroconversion were observed in lambs experimentally inoculated with a respiratory syncytial virus of bovine origin. Signs of clinical illness were mild and consisted of fever and hyperpnea. Multifocal areas of interstitial pneumonia were seen in lambs necropsied during the period of clinical response. All lambs seroconverted to viral antigen, and the virus was isolated from two of the lambs.     

Bovine respiratory syncytial virus infection

Bovine respiratory syncytial virus (BRSV) belongs to the pneumovirus genus within the family Paramyxoviridae and is a major cause of respiratory disease in young calves. BRSV is enveloped and contains a negative sense, single-stranded RNA genome encoding 11 proteins. The virus replicates predominantly in ciliated respiratory epithelial cells but also in type II pneumocytes. It appears to cause little or no cytopathology in ciliated epithelial cell cultures in vitro, suggesting that much of the pathology is due to the host's response to virus infection. RSV infection induces an array of pro-inflammatory chemokines and cytokines that recruit neutrophils, macrophages and lymphocytes to the respiratory tract resulting in respiratory disease. Although the mechanisms responsible for induction of these chemokines and cytokines are unclear, studies on the closely related human (H)RSV suggest that activation of NF-kappaB via TLR4 and TLR3 signalling pathways is involved. An understanding of the mechanisms by which BRSV is able to establish infection and induce an inflammatory response has been facilitated by advances in reverse genetics, which have enabled manipulation of the virus genome. These studies have demonstrated an important role for the non-structural proteins in anti-interferon activity, a role for a virokinin, released during proteolytic cleavage of the fusion protein, in the inflammatory response and a role for the SH and the secreted form of the G protein in establishing pulmonary infection. Knowledge gained from these studies has also provided the opportunity to develop safe, stable, live attenuated virus vaccine candidates.     

Reinfection of lambs with bovine respiratory syncytial virus.

Eight lambs which were experimentally infected with bovine respiratory syncytial virus (RSV) when they were six to eight weeks old were challenged with the same virus seven months later. After reinfection, lambs developed mild clinical disease and the virus was isolated from nasal swabs from three lambs and peripheral blood from two lambs. Reinfection resulted in changes in peripheral blood cell populations. There was an early increase in the number of CD8+ T lymphocytes and B (LCA p220+) lymphocytes but the proportions of CD4+ and CD4-CD8- T lymphocytes were significantly reduced. Peripheral blood mononuclear cells obtained from lambs reinfected with bovine RSV showed significantly higher responses to bovine RSV antigen in vitro than those obtained from control lambs but their responses to the mitogen phytohaemagglutinin were significantly lower than in control lambs. RSV-specific IgG, IgM and IgA levels of serum samples obtained 10 days after challenge were significantly higher than those of serum samples obtained before challenge.     

Pathogenesis of bovine respiratory syncytial virus in experimentally infected lambs

Twenty-four 6-8-week-old conventionally reared lambs were inoculated intranasally and intratracheally with bovine respiratory syncytial virus. Infected lambs showed mild clinical signs characterized by slight serous nasal discharge, coughing, lachrymation and bronchovascular sounds on the middle part of the lung 5-9 days post-inoculation (PI). Virus was isolated in nasal swabs from 9 of 24 lambs between 3 and 7 days PI. However, virus was recovered from tracheal and lung tissue of all lambs killed between 3 and 11 days PI. Virus-specific antibodies appeared as early 6 days PI but high titres were attained 14-21 days PI. Lungs of lambs killed on different days PI had multifocal areas of consolidation. There was an increase of lymphocytes with a T-suppressor cell marker and a decrease in those with a T-helper marker in lung lavages obtained 5 days PI.     

Lesions in lambs experimentally infected with bovine respiratory syncytial virus

Respiratory syncytial virus was inoculated intratracheally into five 1-week-old lambs. Three of the lambs responded clinically with fever, hyperpnea, and listlessness. Pulmonary lesions consisted of multifocal areas of consolidation, with necrosis of individual epithelial cells of the airways and accumulation of necrotic debris, macrophages, and few neutrophils in terminal airways and alveoli. Pulmonary septa in affected areas were infiltrated with numerous macrophages and lymphocytes. Viral particles were seen as buds on epithelial cells and free in bronchioles and alveoli.     

Bovine respiratory syncytial virus infection: immunopathogenic mechanisms

Bovine respiratory syncytial virus (BRSV) causes severe respiratory disease in young cattle. Much like the human respiratory syncytial virus, BRSV induces immunomodulation in the infected host, favoring a Th2 response. Several groups have demonstrated IgE responses to BRSV proteins during infection and particularly in response to vaccination with formalin-inactivated vaccine in the field and experimentally. Newer vaccine modalities that favor a shift to Th1 cytokine production have provided promising results. Infection with BRSV is a major contributor to the multi-pathogen disease, bovine respiratory disease complex. This review stresses the unique immunomodulatory aspects of BRSV infection, vaccination and its interaction with the host's immune system.     

Serological studies of parainfluenza type 3 virus, bovine adenovirus type 3 and bovine respiratory syncytial virus infection in beef calves

Six serum samples were taken at monthly intervals from birth to weaning from each of 41 newborn calves in the autumn and spring calf crops of a beef cow--calf herd. The serum hemagglutination-inhibition (HI) antibody titres to parainfluenza type 3 virus (PIV-3), virus-neutralization (VN) antibody titres to bovine adenovirus type 3 (BAV-3) and bovine respiratory syncytial virus (BRSV) were determined using microtitration techniques. There was serological evidence of a significantly higher incidence of infection with BAV-3 in the fall calves than in the spring calves. Serological responses to BAV-3 were not detected in calves with VN titres of greater than 1/256. Serological evidence of subclinical infection with PIV-3 occurred mainly in late February or early March during a period of marked environmental temperature fluctuations. Serological evidence of a high incidence of infection with BRSV was obtained for both the fall and spring calf crops. Serum antibody appeared to be unable to prevent infection with BRSV. An association between infection with BRSV and clinical pneumonia was found in 3 out of 9 calves. BAV-3 infection was related to pneumonia in only 1 instance; however, there was simultaneous evidence of BRSV infection in this calf. PIV-3 infection was found to be related to pneumonia in only 1 instance. There was serological evidence of infection with BAV-3 in association with the occurrence of diarrhea in 3 calves.     

Bovine respiratory syncytial virus: first serological evidence in Uruguay

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease in calves resulting in a substantial economic loss for the cattle industry worldwide. In order to determine the presence of BRSV in Uruguay, an immunoenzymatic test was set up, using a recombinant BRSV nucleocapsid (N) protein as the antigen. The N protein was produced in Sf9 insect cells by a recombinant baculovirus expressing the N protein. Serum samples collected from one hundred cattle from four different geographic regions of Uruguay were analyzed. Antibodies against the N protein of BRSV were detected in 95% of the serum samples analyzed. These results show for the first time the presence of BRSV antibodies and suggest a widespread BRSV infection in the cattle population of Uruguay.     

Cytotoxic T cell responses in lambs experimentally infected with bovine respiratory syncytial virus

The role of cell-mediated immune response in the immunopathogenesis of bovine respiratory syncytial virus (BRSV) infection is not well established. In the present study, cytotoxic T cell responses of BRSV-infected lambs were examined using the chromium release assay. Lambs experimentally infected with BRSV developed cytotoxic lymphocytes in the peripheral blood and the spleen, which lysed BRSV-infected but not uninfected cells. Peak cytotoxic activity occurred 10-14 days after infection. Pretreatment of mononuclear cells with anti-CD8 monoclonal antibodies and rabbit complement significantly reduced cytotoxic activity (P less than 0.05). It appears, therefore, that lambs experimentally infected with BRSV develop virus-specific, predominantly CD8+, cytotoxic lymphocytes in the peripheral blood and spleen.     

Immunology of bovine respiratory syncytial virus infection of cattle

Bovine respiratory syncytial virus (BRSV) is a respiratory pathogen of cattle that causes severe disease in calves alone and as one of several viruses and bacteria that cause bovine respiratory disease complex. Like human RSV this virus modulates the immune response to avoid stimulation of a vibrant CD8+ T cytotoxic cell response and instead promotes a Th2 response. The Th2 skew sometimes results in the production of IgE antibodies and depresses production of the Th1 cytokine interferon γ. Innate immune cells have a pivotal role in guiding the adaptive response to BRSV, with selective secretion of cytokines by pulmonary dendritic cells. Here we review some of the pertinent observations on immune responses to BRSV infection and vaccination and illustrate how experimental infection models have been used to elucidate the immunopathogenesis of BRSV infection. Recent experiments using intranasal vaccination and/or immune modulation with DNA based adjuvants show promise for effective vaccination by the stimulation of Th1 T cell responses.     

Experimental infection of calves with respiratory syncytial virus.

Three bovine isolates and one human isolate of RS virus were given intranasally to gnotobiotic, colostrum-deprived and conventional calves. All isolates produced a biphasic pyrexia associated with a serous nasal discharge. Virus was recovered from nasal secretions 4-10 days after inoculation from nasal, tracheal and bronchial mucosae and lung of animals killed 7-13 days after inoculation. Infection did not produce any macroscopic lesions, but histologically there was a focal degenerative rhinitis and a catarrhal bronchiolitis with the occasional formation of syncytia in bronchioles and alveoli.     

Lymphocyte subpopulations in peripheral blood of lambs experimentally infected with bovine respiratory syncytial virus

The lymphocyte subpopulations of peripheral blood of normal lambs and lambs experimentally infected with bovine respiratory syncytial virus (RSV) were analysed by flow cytometry, using a panel of monoclonal antibodies against specific lymphocyte epitopes. Experimental infection with bovine RSV was characterized by a significant rise in SBU-T8+ (CD8+ or cytotoxic) T cells and a significant reduction in SBU-T4+ (CD4+ or helper) T cells and B (LCA p220+) lymphocytes (P less than 0.05). The helper/suppressor (CD4/CD8) ratio was reduced from 3.91 on the day of experimental infection to 1.13 on 10 days after experimental infection (P less than 0.001). The total number of SBU-T4+ (CD4+) and B cells returned to pre-inoculation values 14 days after experimental infection but the helper/suppressor ratio remained depressed up to 21 days post-inoculation.     

Human respiratory syncytial virus infection in the pre-clinical calf model

Human respiratory syncytial virus (hRSV) is the most important respiratory pathogen in young children worldwide. Experimental modelling of hRSV disease by bovine RSV (bRSV) infection in calves provides an important tool for developing new strategies for prevention and treatment. Depending on the scientific hypothesis under investigation, this cognate host-virus model might have the disadvantage of using a highly related but not genetically identical virus. In this study, we aim to describe viral kinetics and (clinical) disease characteristics in calves inoculated with hRSV. Our results show that hRSV infects the upper and, to a lesser extent, the lower respiratory tract of calves. Infection causes upper airway clinical disease symptoms and neutrophilic infiltration of the lower airways. We conclude that a hRSV model in calves may aid future research involving distinct scientific questions related to hRSV disease in children.     

Bovine respiratory syncytial virus infection in an ontario cattle herd

Bovine respiratory syncytial virus was recovered from the lung of a six month old calf that died during an outbreak of respiratory disease in a cattle herd in Ontario. Lung tissue removed from the calf at necropsy, performed within two hours of death, was frozen at -70°C prior to virus isolation attempts. Syncytia and intracytoplasmic inclusions were demonstrated both in histological sections of the calf's lung and in stained cell culture preparations infected with the bovine respiratory syncytial virus isolate. Direct fluorescent antibody and virus neutralization tests serologically confirmed the identity of the isolate.     

Serological evidence of Mycoplasma cynos infection in canine infectious respiratory disease

A high proportion of dogs suffer from respiratory disease when they are placed in kennels for vacation or re-homing. The role of Mycoplasma cynos as an initiating agent in canine infectious respiratory disease was investigated by examining the serological response of dogs to this organism at the time of entry into a large re-homing kennel. Forty-two paired serum samples from dogs (21-day interval) were examined for antibody to M. cynos using Western blotting. The development of antibody in the serum was related to clinical disease recorded over the same period. Sixty seven per cent of the dogs showed a two-fold or greater rise in antibody to M. cynos during the first 3 weeks in the kennel. Reactivity with a 45 kDa antigen was dominant. Of those showing a positive serological reaction, 80% had recorded clinical respiratory disease while 20% remained healthy. The findings of this study show that an antibody response to M. cynos is common in dogs entering the re-homing kennel and is positively related to the development of clinical respiratory disease.     

Experimental bovine respiratory syncytial virus infection in conventional calves: ultrastructural respiratory lesions

The morphogenesis and repair of airway and alveolar injury induced by bovine respiratory syncytial virus (BRSV) was studied ultrastructurally in conventional calves to characterize pulmonary cell types susceptible to viral infection and cytopathologic changes associated with infection. Viral nucleocapsids and budding virions were present in tracheal and bronchial ciliated and nonciliated epithelial cells and mucous cells 3, 5, and 7 days after inoculation and in bronchiolar ciliated and nonciliated epithelial cells 5 days after inoculation. Mild interstitial pneumonia was observed 5 days after inoculation and was characterized by swelling of type 1 and type 2 alveolar epithelial cells, interstitial edema, and infiltration by lymphocytes and macrophages. Viral assembly and release in tracheal and bronchial epithelial cells was associated with loss of cilia from ciliated cells, formation of syncytial epithelial cells, swelling of mitochondria and endoplasmic reticulum, and cell necrosis. Neutrophils, lymphocytes, and macrophages were present in close association with the viral-infected and damaged epithelial cells. There was intercurrent hyperplasia of basal epithelial cells that, in association with other epithelial lesions, resulted in the loss of normal ciliated epithelium in these airways 5 and 7 days after inoculation. Regeneration of airway epithelium was largely completed by 10 days after inoculation, except in 1 of 4 calves that had failure of epithelial repair and that developed secondary bacterial pneumonia. Pulmonary ultrastructure in BRSV-inoculated calves 30 days after inoculation was indistinguishable from that in controls. The results demonstrated that BRSV can induce reversible alterations in airway epithelium, which may cause depression of mucociliary clearance and thereby enhance susceptibility to bacterial infection.     

An epizootic of respiratory syncytial virus infection in a dairy herd

Respiratory syncytial virus was the cause of a severe epizootic of bovine respiratory tract disease. The virus, isolated from a sick cow during the epizootic, produced cytopathic effect in a bovine turbinate cell line 14 days after it was inoculated. Additional support for the diagnosis came from the results of pathologic and serologic examinations. Lesions consistently present were severe necrotizing bronchiolitis and epithelial syncytia projecting from bronchiolar and alveolar walls. Also, in the cow from which the virus was isolated, there was tracheitis with a syncytial-like change involving the mucosal epithelium.