Experimental infection of calves with bovine respiratory syncytial virus (Quebec strain).

An experiment was designed to evaluate the clinical, haematological, viral and serological aspects of bovine respiratory syncytial virus infection in calves. Eleven calves were inoculated intranasally with bovine respiratory syncytial virus (Quebec strain) in aerosol. Clinical, haemotological and serological responses of the calves and virus shedding were monitored. The experimentally infected animals manifested moderate to severe signs of respiratory disease. The parameters used to evaluate the severity of the disease included ocular discharge, conjunctivitis, lung sounds, nasal discharge, pyrexia and leukopenia. The animals were scored accordingly (scale infected 70.8-148.5, control 22-29.3). Highest disease scores were observed between day 6-9 after infection. Virological and serological assessment demonstrated that the observed clinical picture was due to bovine respiratory syncytial virus infection.     

Prevention of bovine respiratory syncytial virus infection and clinical disease by vaccination

A double blind field trial was carried out with a live attenuated bovine respiratory syncytial virus vaccine. The trial involved 530 calves, two to 10 months old, on 27 dairy farms, where respiratory problems due to bovine respiratory syncytial virus infections had been observed during the preceding year. In 17 herds either all calves were vaccinated (nine groups) or all calves received a placebo (eight groups). In 10 herds half the number of calves were vaccinated and the other half kept as non-vaccinated controls. Calves were vaccinated intramuscularly twice with an interval of four to five weeks. These groups were under regular clinical observation and animals were tested periodically for antibodies to bovine respiratory syncytial virus and parainfluenza type 3 virus. Serological examination indicated that no bovine respiratory syncytial virus infection had occurred prior to the first vaccination in August. Vaccination did not cause adverse reactions. Low concentrations of neutralising and complement fixing antibodies were induced by vaccination and a sharp increase of antibody titres was observed after natural infection of vaccinated animals. Infections with bovine respiratory syncytial virus occurred in six out of eight non-vaccinated groups, in nine out of 10 partly vaccinated groups and in only two out of nine completely vaccinated groups. Virus infection in completely vaccinated groups was significantly reduced compared with partly vaccinated and non-vaccinated groups. The incidence of bovine respiratory syncytial virus lower respiratory disease was significantly reduced in completely vaccinated groups compared to non-vaccinated groups. Generally only mild signs of upper respiratory disease were present in completely vaccinated groups after bovine respiratory syncytial virus infection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clenbuterol hydrochloride in calves with a natural bovine respiratory syncytial virus infection

The effect of clenbuterol hydrochloride on the course of disease in calves with a natural bovine respiratory syncytial virus infection was examined. Six calves (three to nine months of age) originating from four herds with respiratory tract disease and serological evidence of a bovine respiratory syncytial virus infection were used in this study. The calves were injected intravenously with clenbuterol hydrochloride. The effect of clenbuterol on the course of disease was measured using the PO2 in blood taken from an indwelling canula inserted in the caudal auricular artery and by clinical signs. Clenbuterol did not improve clinical signs. After clenbuterol administration arterial PO2 values decreased significantly in five out of six patients. Six to eight hours after medication the mean arterial PO2 values were higher than initial values. The moderate positive effect of clenbuterol after six to eight hours may be caused by enhancing ciliary activity and by the secretolytic activity of clenbuterol.     

The effects of Dictyocaulus viviparus infection on energy metabolism of calves

To determine the effects of lungworm infection on energy metabolism and rate of weight gain, five 3-mo-old male Friesian calves were infected orally twice each week with 640, third-stage larvae of Dictyocaulus viviparus (D.v.) over an 8-wk period. Infected calves were matched with uninfected controls on the basis of similar rates of feed consumption and weight gain during the acclimation period before infection. Infected calves were fed 2 kg of concentrates daily (88% DM), about 8.5 Mcal/d. Controls each received approximately 250 g less, about 7.5 Mcal/d. Similar amounts of hay (5.6 to 5.8 Mcal/d) were provided to all calves. Clinical, serum chemical, hematological and parasitological criteria, weight gain and utilization of energy were monitored on a weekly basis. Serum chemical and hematological analyses and clinical examinations of infected animals revealed signs typical of lungworm infection. Fecal and sputum sample examinations for infected calves were positive for D.v. larvae and ova, respectively. Control animals gained approximately 80 g.animal-1.d-1 more than infected calves. Lungworm infection had no significant effect on digestibility of energy or protein. Metabolizability of energy ingested was somewhat higher in the infected calves due to a higher dietary concentrate to roughage ratio. Utilization of metabolizable energy and protein tended to be less efficient for infected animals. Results showed that D.v.-infected calves need more feed for gain than do uninfected animals. This extra requirement is due to an increased maintenance requirement and probably to a reduced protein retention from digested protein.     

Clinical study of the disease of calves associated with Mycoplasma bovis infection

Clinical, bacteriological and serological examination of 35 calves from the age of 5 to 26 days was performed in a Holstein-Friesian dairy herd endemically infected with Mycoplasma bovis. M. bovis was isolated from 48.6% of nasal swabs taken from the calves at the age of 5 days, and from 91.4% of the same calves at the age of 26 days, indicating the gradual spread of infection. The isolation rate of Pasteurella multocida did not change much, and varied from 28.6 to 25.7%. No P. haemolytica could be detected. In addition to M. bovis and P. multocida, the herd was also infected with different viruses (including bovine viral diarrhoea virus, infectious bovine rhinotracheitis virus, bovine adenoviruses, parainfluenza-3 virus, and bovine respiratory syncytial virus) as a large proportion of the sera of newborn calves contained colostral antibodies against these viruses. In most of the newborn calves severe clinical signs (fever, depression, inappetence, hyperventilation, dyspnoea, nasal discharge and coughing) due to M. bovis infection developed. The clinical signs appeared already on the fifth day of life, and their incidence was the highest at the age of 10 to 15 days. Three calves (8.6%) died as a result of severe serofibrinous pneumonia. The surviving calves showed very poor weight gain (ranging from 1.5 to 3.5 kg) during the first two weeks of life.     

Radiographic and radionuclide lung perfusion imaging in healthy calves and calves naturally infected with bovine respiratory syncytial virus.

Nine calves between three and 18 weeks old with serologically confirmed natural bovine respiratory syncytial virus infection were examined clinically, radiographically and by radionuclide lung perfusion imaging. The results were compared with those from seven healthy calves. The diseased calves were euthanased and examined pathologically, virologically and bacteriologically. The clinical signs indicated that the disease was in an acute stage. Radiography of the diseased animals revealed cysts, corresponding morphologically with bullous emphysema, and infiltrations roughly corresponding in distribution with atelectatic and, or, pneumonic areas. Radionuclide lung perfusion imaging revealed no perfusion shifts between the left and right lungs and a normal perfusion pattern in five of the nine diseased calves. The abnormalities in the perfusion patterns of three calves were probably caused by anatomical disorders such as cysts and pleural adhesions, but no cause of the abnormality could be found in one calf. These findings suggest that in calves infected with bovine respiratory syncytial virus, the normal perfusion pattern is maintained until anatomical disorders occur. The pathological examination and radiography revealed that the cranioventral lung fields were particularly poorly ventilated. This finding and the normal perfusion pattern indicate that these parts of the lungs are probably the sites where shuntings and perfusion-ventilation mismatchings occur.     

Evaluation of severe disease induced by aerosol inoculation of calves with bovine respiratory syncytial virus

OBJECTIVE: To develop a model of bovine respiratory syncytial virus (BRSV) infection that induces severe disease similar to that seen in some cattle with naturally acquired BRSV infection. ANIMALS: 25 male Holstein calves, 8 to 16 weeks old. PROCEDURE: 17 calves were given a low-passage field isolate of BRSV by aerosolization; 8 control calves were given supernatant from noninfected cell culture. Disease was characterized by evaluating clinical signs, virus isolation and pulmonary function tests, and results of blood gas analysis, gross and histologic postmortem examination, and microbiologic testing. RESULTS: Cumulative incidence of cough, harsh lung sounds, adventitious sounds, and dyspnea and increases in rectal temperature and respiratory rate were significantly greater in infected calves. Three infected calves developed extreme respiratory distress and were euthanatized 7 days after inoculation. Virus was isolated from nasal swab specimens from all infected calves but not from mock infected calves. On day 7 after inoculation, mean PaO2 and PaCO2 were significantly lower, and pulmonary resistance was significantly higher, in infected calves. During necropsy, infected calves had varying degrees of necrotizing and proliferative bronchiolitis and alveolitis with syncytial formation. The 3 calves euthanatized on day 7 had emphysematous bullae in the caudal lung lobes; 1 had unilateral pneumothorax. CONCLUSION AND CLINICAL RELEVANCE: Severe disease similar to that seen in some cattle with naturally acquired BRSV infection can be induced in calves with a single aerosol exposure of a low-passage clinical isolate of BRSV. Our model will be useful for studying the pathogenesis of BRSV infection and for evaluating vaccines and therapeutics.     

Failure to spread bovine virus diarrhoea virus infection from primarily infected calves despite concurrent infection with bovine coronavirus

Previous reports on the spread of bovine virus diarrhoea virus (BVDV) from animals primarily infected with the agent are contradictory. In this study, the possibility of transmission of BVDV from calves simultaneously subjected to acute BVDV and bovine coronavirus (BCV) infection was investigated. Ten calves were inoculated intranasally with BVDV Type 1. Each of the 10 calves was then randomly allocated to one of two groups. In each group there were four additional calves, resulting in five infected and four susceptible calves per group. Virulent BCV was actively introduced in one of the groups by means of a transmitter calf. Two calves, susceptible to both BVDV and BCV, were kept in a separate group, as controls. All ten calves actively inoculated with BVDV became infected as shown by seroconversions, and six of them also shed the virus in nasal secretions. However, none of the other eight calves in the two groups (four in each) seroconverted to this agent. In contrast, it proved impossible to prevent the spread of BCV infection between the experimental groups and consequently all 20 study calves became infected with the virus. Following infection, BCV was detected in nasal secretions and in faeces of the calves and, after three weeks in the study, all had seroconverted to this virus. All calves, including the controls, showed at least one of the following clinical signs during days 3-15 after the trial started: fever (> or =40 degrees C), depressed general condition, diarrhoea, and cough. The study showed that BVDV primarily infected cattle, even when co-infected with an enteric and respiratory pathogen, are inefficient transmitters of BVDV. This finding supports the principle of the Scandinavian BVDV control programmes that elimination of BVDV infection from cattle populations can be achieved by identifying and removing persistently infected (PI) animals, i.e. that long-term circulation of the virus without the presence of PI animals is highly unlikely.     

犊牛呼吸道合胞体病毒和巴氏杆菌混合感染的调查研究

为了对疑似牛呼吸道合胞体病毒和巴氏杆菌混合感染的犊牛进行病原鉴定,本研究采用常规病毒经细菌分离鉴定和PCR方法分别进行分离与鉴定。结果表明,该病毒株能在BT细胞上增殖并产生特征性合胞体形态的细胞病变;无血凝性和血吸附特性;能被牛呼吸道合胞体病毒(bovine respiratory syncytial virus,BRSV)标准阳性血清中和;分离的病毒经RT-PCR鉴定为牛呼吸道合胞体病毒;根据菌落形态、细菌染色特性及生化特性,鉴定分离的细菌为巴氏杆菌。提示,该牛场为牛呼吸道合胞体病毒和巴氏杆菌混合感染。     

Pestivirus in cattle: experimentally induced persistent infection in calves

Twenty-two heifers were infected intranasally with non-cytopathic bovine viral diarrhoea virus (BVDV) between days 74 and 82 of pregnancy. All animals had developed serum antibodies against BVDV 5 weeks later. No clinical effects were seen in the heifers, and they all delivered a live calf. The newborn calves were generally small, appeared unthrifty as typical 'poor doers', and some developed secondary infections with diarrhoea and signs of respiratory disease. Eighteen of the 22 calves were born without antibodies against BVDV and were persistently infected (PI) with the virus. One was weak at birth and died the following day. Four calves were born with serum antibodies against BVDV and with no detectable virus. Three of these showed signs and/or pathological changes indicating disease in the central nervous system. Otherwise, there were no obvious clinical differences between these calves and the PI calves, nor were there any apparent significant differences in blood parameters between these groups. In general, the calves showed low gamma-globulin values and thrombocytopaenia, but moderately increased fibrinogen values and relatively normal lymphocyte numbers.     

Interferon, fluorescent antibody, and neutralizing antibody responses in sera of calves inoculated with bovine respiratory syncytial virus

Interferon, fluorescent antibody, and neutralizing antibody responses were studied in sera of 9 calves inoculated with bovine respiratory syncytial virus, in relation to viral shedding and clinical signs of disease. The calves (5.5 to 6.5 weeks of age) were assigned to 3 groups. Group I was inoculated once with the virus, and groups II and III were challenge exposed at postinoculation day (PID) 15 or 37. Serum-neutralizing and indirect fluorescent antibody techniques were used to measure antibody responses. The plaque-inhibition technique, using vesicular stomatitis virus, was applied to measure serum interferon titers. The virus was recovered by inoculation of nasal secretions onto cell cultures. Fluorescent antibody was detected in all calves on PID 3, with maximum titers appearing approximately on PID 10. Low neutralizing antibody was detected in most animals on PID 3, and titers peaked approximately 4.5 weeks after inoculation and then decreased. Interferon titers were high in all calves during the early stage of infection, dropped to undetectable amounts by PID 6, and reappeared in low amounts at least 1 week later. All infected calves manifested clinical signs of disease by PID 4 to 9. Clinical signs of disease were not observed after challenge exposure at PID 15 or 37, and anamnestic responses were not detected. Virus was recovered after challenge exposure at PID 15, but not at PID 37.     

Correlation of a disease scoring system with arterial PO2 values in respiratory syncytial virus infection in calves

The mean arterial PO2 value measured in blood obtained by puncture of the brachial artery of 20 calves with acute clinical signs of a bovine respiratory syncytial virus (BRSV) infection was 8.4 +/- 1.9 kPa. The values differed significantly from arterial PO2 values of eleven healthy calves (mean 14.2 +/- 1.5 kPa). A disease scoring system is presented based on the type of respiration and the findings on auscultation. A high correlation (r = -0.87) was found between disease scores and arterial PO2 values. This indicates that the described disease scoring system can be a useful tool in the evaluation of the severity and course of BRSV infections in calves, and could be used for evaluating the efficacy of BRSV vaccines in the field. The course of disease was studied in 127 calves with clinical signs of serologically proven BRSV infection. Animals with mild respiratory signs during the acute phase of disease remained free of severe respiratory problems until the end of a 35-day examination period. Mean disease scores indicated that animals with severe signs in the acute phase often developed persistent respiratory problems.     

Associations between viral infection and respiratory disease in young beef bulls

Blood samples were taken from bull calves at two Meat and Livestock Commission performance testing centres, just after weaning at six months of age and at six weekly intervals until the end of the performance test seven months later. Sera were assayed by specific ELISAS for antibodies to bovine herpes virus 1 (BHV1), respiratory syncytial virus, parainfluenza 3 (Pi3) and adenoviruses A and B. Seroconversions between each sampling were related to the occurrence of clinical respiratory disease using chi-squared (chi 2) and relative risk (RR) analyses. In 294 bulls there were 123 cases of respiratory disease. Seroconversion to bovine respiratory syncytial virus (RR = 4.7, chi 2 = 96.3, P less than 0.001) and adenovirus A (RR = 1.8, chi 2 = 8.9, P less than 0.001) and adenovirus B (RR = 1.9, chi 2 = 5.6, P less than 0.05) were significantly associated with clinical respiratory disease. There was evidence that prior exposure to respiratory syncytial virus (RR = 0.4, chi 2 = 9.8, P less than 0.01) Pi3 (RR = 0.4, chi 2 = 12.8, P less than 0.01) and adenovirus A (RR = 0.7, chi 2 = 7.5, P less than 0.01) conferred some protection against respiratory disease after arrival at the centre. It is concluded that vaccination before weaning, at least against bovine respiratory syncytial virus, would be beneficial.     

Characterization and identification of a bovine respiratory syncytial virus isolated from young calves.

Two identical viruses designated 371 and 375 were recovered from nasal secretions of 2 of 7 calves in a beef cow-calf herd in which calves (45 to 105 days of age) had signs of acute respiratory tract disease. The cytopathic, morphologic and physico-chemical characteristics of the isolates were those of bovine respiratory syncytial virus. Although a humoral antibody response to bovine respiratory syncytial virus was not observed, it was concluded that this virus probably had a part in the respiratory tract disease in these calves.     

Association of bovine viral diarrhea virus with multiple viral infections in bovine respiratory disease outbreaks

We investigated eleven outbreaks of naturally occurring bovine respiratory diseases in calves and adult animals in the St-Hyacinthe area of Quebec. Specific antibodies to bovine herpesvirus-1, bovine viral diarrhea virus, respiratory syncytial virus, parainfluenza type 3 virus, reovirus type 3, and serotypes 1 to 7 of bovine adenovirus were found in paired sera from diseased animals. Several bovine viruses with respiratory tropism were involved concomitantly in herds during an outbreak of bovine respiratory disease. In addition, concomitant fourfold rises of antibody titers were frequently observed to two or more viral agents in seroconverted calves (61%) or adult animals (38%). Bovine viral diarrhea virus was found to be the most frequent viral agent associated with multiple viral infection in calves only (92%).     

Experimental bovine respiratory tract disease with Haemophilus somnus

Eight calves were inoculated into the bronchus with H. somnus. Thirteen calves were inoculated with bovine respiratory syncytial virus (BRSV) and 8 days later with H. somnus. All calves developed necrotizing, suppurative, lobular bronchopneumonia and pleuritis. Clinical signs of disease and pneumonic lesions were significantly more severe in calves that were sequentially inoculated with BRSV followed by H. somnus. Pneumonic lesions in the inoculated calves were similar to those described for naturally occurring H. somnus-associated respiratory tract disease. Control calves inoculated with BRSV alone or sham-inoculated with medium did not develop clinical signs of respiratory tract disease. The BRSV-inoculated control calves developed minimal pneumonic lesions.     

Experimental bovine respiratory syncytial virus infection in conventional calves: light microscopic lesions, microbiology, and studies on lavaged lung cells

Conventionally raised male Holstein calves, 1 month of age, were infected by intranasal and intratracheal inoculation with bovine respiratory syncytial virus. Viral antigen was identified by fluorescence microscopy most commonly in the cytoplasm of tracheal and bronchial epithelial cells 3 to 5 days after inoculation. Cytoplasmic viral antigen was identified also in nasal, nasopharyngeal, bronchiolar, and alveolar epithelial cells and in alveolar macrophages. Bronchitis and tracheitis, characterized in part by epithelial necrosis, formation of syncytial epithelial cells and epithelial hyperplasia, were the most common lesions observed histologically. Rhinitis, bronchiolitis, and interstitial pneumonia were observed less frequently. Alterations were not detected in the numbers of cells recovered by bronchoalveolar lavage after inoculation. An increase in the phagocytic rate of latex beads occurred in macrophages 5 days after inoculation. Viral-induced lesions were resolved by 30 days after inoculation. The results indicated that bovine respiratory syncytial virus inoculation of calves results in reversible alterations in airway epithelial structure and in the phagocytic function of alveolar macrophages.     

Epidemiological study of bovine respiratory syncytial virus infections in calves: influence of maternal antibodies on the outcome of disease

A prospective epidemiological survey on bovine respiratory syncytial virus (BRSV) infections in calves was carried out on 21 dairy farms during one BRSV epidemic season. Special attention was paid to the role of maternal antibodies. On 15 farms the spread of the virus was demonstrated during the investigation period and on eight farms this was accompanied by an outbreak of acute respiratory disease. Disease seldom occurred in calves younger than two weeks old and the most severe disease was observed in calves from one to three months old. Although maternal antibodies did not effectively prevent the disease, both the incidence and severity of disease were inversely related to the level of specific maternal antibodies. Two serodiagnostic techniques were compared. In calves older than three months from herds with disease outbreaks associated with bovine respiratory syncytial virus the diagnosis was established in 80 per cent of the animals by an increase in IgG titre against BRSV and in 77 per cent by the detection of BRSV specific IgM. In comparison, only 10 per cent of the calves younger than three months were positive by IgG serodiagnosis, and 51 per cent by IgM serodiagnosis. On farms where the spread of the virus was accompanied by an outbreak of clinical disease more calves were present, a higher proportion of the calves was younger than three months, and calves of all ages were more often housed together.     

High mortality rate associated with bovine respiratory syncytial virus (BRSV) infection in Belgian white blue calves previously vaccinated with an inactivated BRSV vaccine

In a group of 60 Belgian White Blue calves less than 8 months old still housed in barns, a bovine respiratory syncytial virus (BRSV) outbreak was revealed on the basis of a direct diagnosis (immunofluorescence and virus isolation) performed on the lungs of dead animals, and the kinetics of BRSV neutralizing antibodies. Clinical signs, macroscopical and microscopical pulmonary lesions were also compatible with a BRSV infection. This outbreak is peculiar because the 35 oldest calves (204 +/- 29 days old) had been vaccinated 3-4 months before with an inactivated BRSV vaccine and 30% of these animals had died of respiratory distress. While they experienced a mild respiratory symptomatology, no death was recorded among the 25 youngest calves (69 +/- 29 days old) which had been left unvaccinated. Another peculiarity was found at the histological level where a massive infiltration of eosinophils was demonstrated in the pulmonary tissues of the dead animals. Together these data parallel the dramatic story described 30 years ago in children previously vaccinated with a formalin-inactivated human RSV (HRSV) vaccine upon a natural HRSV challenge. This illustrates that an immunopathological phenomenon also takes place after BRSV vaccination in cattle.