Project Details

Description

Bovine respiratory disease (BRD) is a cause of major economic loss in the beef and dairy industries, affecting youngstock particularly during the winter housing period [1,2]. A complex of pathogens including bovine respiratory syncytial virus (BRSV), bovine parainfluenza type-3 virus (PI3V), bovine herpesvirus type-1 (BHV-1), bovine viral diarrhoea virus (BVDV), the bacteria Mannheimia haemolytica (MH), Pasteurella multocida (PM), Histophilus somni (HS) and Arcanobacterium pyogenes and various species of Mycoplasma are regularly identified in BRD cases in the UK [3].

Typically a case of BRD involves a primary viral respiratory infection, with secondary infection of the lungs with bacteria that are often present in the nasal cavity and tonsils of healthy cattle. Whereas in the lungs they cause a serious form of pneumonia, which may cause death or disability, reduced growth and incur costs of lost productivity and veterinary treatment, in the nasal cavity (nasopharynx) these bacteria are not usually associated with disease. They may nevertheless be transmitted from one animal to another as shown in experimental field studies [4], leading to increased rates of carriage of these organisms by healthy cattle that are then at greater risk of secondary bacterial pneumonia if subjected to a predisposing factor such as viral infection or environmental stress. Uncomplicated respiratory viral infections of cattle may result in nasal discharges, thereby potentially causing increased transmission of nasopharyngeal bacteria amongst them and hence greater susceptibility to pneumonia. Conversely, we propose that vaccination to prevent respiratory viral infection may reduce the spread of nasopharyngeal bacteria and hence reduce the likelihood of secondary bacterial pneumonia in vaccinated herds over above any risk reduction conferred to animals on an individual basis.

To test this idea, we intend to conduct fieldwork in three phases. After an initial farmer recruitment phase in which preliminary data about the BRD situation on each farm will be obtained, cattle from a wide range of holdings will be investigated by collection of specimens using nasal swabs. The bacterial organisms present will be identified and typed to ascertain the levels of infection of cattle with various species and strains. Production units with suitable levels of bacterial carriage and evidence of a respiratory disease problem will be recruited into a further phase wherein the effect of vaccination targeting bovine respiratory viruses will be investigated in a longitudinal intervention cohort study. A single dose, intranasal vaccine specific for BRSV and PI3V (Rispoval RS+PI3 Intranasal) will be used in younger calves, which may have maternally-derived immunity, from 9 days of age. Two doses of an injectable vaccine against BHV-1, BVDV, BRSV and PI3V may be used in older animals from 12 weeks. Both vaccines have been shown to reduce levels of nasal discharge in animals deliberately infected with these viruses in experimental studies. The final choice of vaccine will be made considering all available information about the individual units concerned, including that obtained in the earlier phases of the study, in consultation with the farmer's own veterinary practitioner and in accordance with epidemiological principles for sound experimental design of randomised control trials. Following vaccination, cattle will once again be examined and specimens collected using nasal swabs to ascertain whether significant changes in rates of bacterial carriage and the diversity of bacterial species involved have taken place. This will be achieved using traditional bacteriological culture and multiple cutting-edge molecular techniques.

1. Barrett (1998). Cattle Pract. 6:251-5
2. Caldow & Nettleton (2000). Cattle Pract. 8:131-4
3. VLA (2009). Vet. Investig. Surveillance Report (VIDA) 2002-2009. ISBN 1 8995 1335 3
4. Briggs et al. (1998). Am. J. Vet. Res. 59:401-5
StatusFinished
Effective start/end date1/10/1230/09/16