Table 2 In vivo studies from the scientific literature performed on young calves to assess viral coinfections impact on BRD
Reference | Primary viral challenge (route of infection and dose/animal) | Time between exposure to the two pathogens | Secondary viral challenge (route of infection and dose/animal) | Main results of the clinical trials | Impact of the coinfection on BRD (score 1 to 4) | Study limitations |
|---|---|---|---|---|---|---|
Pollreisz et al. [142] | BVDV-1 (Intranasal and intratracheal, 5 mL of 2 × 108 TCID50) | Simultaneous, 1 day and 2 days | BRSV (Intranasal and intratracheal, 5 mL of 106 TCID50/mL) | BVDV group: mild signs BRSV group: serous nasal discharge, rapid and shallow respiration and depression Coinfected group: excessive serous or mucopurulent nasal discharge, rapid breathing, diarrhoea, severe depression, one calf had to be euthanized | 4 | |
Brodersen et al. [143] | BVDV | Simultaneous | BRSV | Coinfected group: increased clinical signs, higher viral shedding and increased lung lesions than infection with either virus alone | 3 | |
Elvander et al. [138] | BVDV (non-cytopathogenic) (Intratracheal, 105 TCID50/mL) | Simultaneous | BRSV (Intratracheal, BRSV group: 10 mL of 104 TCID50/mL, coinfected group: 10 mL of BRSV 105 TCID50/mL) | No increase in clinical signs in coinfected group | 2 | Lack of BVDV group; different BRSV dose in mono-infected and coinfected groups |
Risalde et al. [145] | BVDV-1 (non-cytopathogenic) (Intranasal, 1 mL/nostril of 105 TCID50/mL) | 12 days | BoHV-1.1 (Intranasal,1 mL/nostril of BoHV-1.1 × 107 TCID50/mL) | Appearance of clinical signs in all groups but increase in severity in coinfected group; increase in pro-inflammatory cytokines and APPs in coinfected group (IL-1β) and more severe inflammatory lesions | 3 | Lack of BVDV group |
Ridpath et al. [140] | BVDV-2a (Intranasal aerosol, 4 mL of 106 TCID50/mL) | 3, 6 and 9 days | BCoV (Intranasal aerosol) | BCoV group: pyrexia but no gross lesions Coinfected group: higher fever, lung lesions present in all infected groups but more pronounced in 6-day delay group; peripheral blood lymphocytes count returned to baseline in 6-day delay group but not in 9-day delay group | 3 | BCoV dose is not reported |
Ridpath et al. [140] | BCoV (Intranasal aerosol) | 3 days | BVDV-2a (Intranasal aerosol, 4 mL of 106 TCID50/mL) | BCoV group: pyrexia but no gross lesions Coinfected group: pyrexia and lung lesions in some coinfected calves consisting in pale, firm foci randomly scattered throughout the lungs but particularly obvious in the ventral caudal lobes | 2 | BCoV dose is not reported |