Bovine respiratory syncytial virus infection influences the impact of alpha- and beta-integrin-mediated adhesion of peripheral blood neutrophils

Effect of aerosolized bacterial lysate on development of naturally occurring respiratory disease in beef calves

Background

Bovine respiratory disease (BRD) is a major problem affecting beef cattle after arrival to feedlots. Alternatives to antibiotics are needed for prevention.

Hypothesis

Stimulation of pulmonary innate immune responses at the time of arrival to a feedlot reduces the occurrence and severity of BRD.

Animals

Sixty beef steers at high risk of BRD.

Methods

Randomized, double‐blinded, placebo‐controlled study. Calves received saline or a lysate of Staphylococcus aureus and Escherichia coli by aerosol, at 16 hours after feedlot arrival. Calves were monitored for 28 days for disease outcomes and levels of Mycoplasma bovis and Mannheimia haemolytica in nasal swabs.

Results

Death from M bovis pneumonia was significantly greater in lysate‐treated animals (6/29, 24%) compared to controls (1/29, 3%; odds ratio = 10.2; 95% confidence interval [CI] = 1.1‐96.0; P = .04). By 28 days after arrival, 29/29 lysate‐treated calves had ultrasonographic pulmonary consolidation compared to 24/29 control calves (P = .05). Lysate‐treated calves had lower weight gain compared to control calves (−8.8 kg, 95% CI = −17.1 to −0.5; P = .04), and higher body temperatures on days 4, 7, and 21 (0.19°C; 95% CI = 0.01‐0.37; P = .04). Nasal M bovis numbers increased over time and were higher in lysate‐treated calves (0.76 log CFU, 95% CI = 0.3‐1.2; P = .001).

Conclusions and Clinical Importance

Aerosol administration of a bacterial lysate exacerbated BRD in healthy high‐risk beef calves, suggesting that respiratory tract inflammation adversely affects how calves respond to subsequent natural infection with M bovis and other respiratory pathogens.

Age-dependent differences in the pathogenesis of bovine respiratory syncytial virus infections related to the development of natural immunocompetence

The severity of respiratory syncytial virus (RSV) infections appears to differ with age in both humans and bovines. A primary RSV infection in naïve infants and in young calves runs a more severe course when they are 1-6 months old than in their first month of life. The relative lack of clinical signs in the first month of age may be due to high levels of maternally derived neutralizing antibodies or low exposure to infectious virus. This study examined whether age-dependent differences in the pathogenesis of bovine RSV (bRSV) between neonatal and young calves may be due to differences in age-dependent immunocompetence. To study the effect of age and immune parameters on bRSV disease in neonatal and young calves, neonatal (1-day-old) calves without maternally derived antibodies were infected experimentally with bRSV and the severity of disease and immune responses were evaluated in comparison with disease in similar 6-week-old infected calves. Neonatal calves had more extensive virus replication and lung consolidation, but lower pro-inflammatory [in particular tumour necrosis factor alpha (TNF-α)] responses, specific humoral immune responses, lung neutrophilic infiltration and clinical signs of disease than 6-week-old calves. The lack of correlation between virus replication and clinical signs suggests an important role of pro-inflammatory cytokines, in particular TNF-α, in the disease. The capacity to produce pro-inflammatory TNF-α appeared to increase with age, and may explain the age-dependent differences in RSV pathogenesis.