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Table 3 In vivo studies from the scientific literature performed on young calves to study bacterial coinfections impact on BRD

From: Understanding the mechanisms of viral and bacterial coinfections in bovine respiratory disease: a comprehensive literature review of experimental evidence

Reference

Primary bacterial challenge (route of infection and dose/animal)

Time between exposure to the two pathogens

Secondary bacterial 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

Houghton and Gorlay, [154]

M. bovis (Intranasal)

Simultaneous

M. haemolytica (Intranasal)

Dually inoculated animals were more severely affected than animals inoculated with one pathogen M. bovis group: 1–6% lung consolidation M. haemolytica group: 0–1% lung consolidation Coinfected animals displayed 34 to 55% of lung consolidation

3

 

Gourlay et al. [155] (gnotobiotic calves)

M. bovis (Intranasal and intratracheal, 6 × 108 CFU)

1 day and 2 days

M. haemolytica (Intranasal and intratracheal, 7 × 108 CFU cultured for 6 h or for 18 h before inoculation)

Mannheimia group: no illness or gross lesions Coinfected group: severe clinical illness and 16% of lung consolidation at necropsy with 2-days delay, severe illness and high area of lung consolidation in dually infected calves (50–64%) inoculated with 1-day delay between pathogens, increased lesions when using 6 instead of 18 h culture of Mannheimia

3

Lack of M. bovis group

Gourlay et al. [155] (gnotobiotic calves)

M. haemolytica (Intranasal and intratracheal, 7 × 108 CFU cultured for 6 h or for 18 h before inoculation)

2 days

M. bovis (Intranasal and intratracheal, 6 × 108 CFU)

No significant increase in pneumonia in coinfected animals, mild signs in all groups

2

Lack of M. bovis group

Gourlay et al. [155] (Conventionally reared calves)

M. bovis (Intranasal and intratracheal, 6 × 108 CFU)

Simultaneous

M. haemolytica (Intranasal and intratracheal, 7 × 108 CFU cultured for 6 h or for 18 h before inoculation)

Mannheimia group: no illness and no gross lung lesions Coinfected group: only few calves displayed fever and clinical signs and 6–8% of lung consolidation at necropsy, the remaining calves displayed no clinical signs

2.5

 

Gourlay et al. [155] (Conventionally reared calves)

M. bovis (Intranasal and intratracheal, 6 × 108 CFU)

1 day

M. haemolytica (Intranasal and intratracheal, 7 × 108 CFU cultured for 6 h or for 18 h before inoculation)

M. bovis group: moderate clinical signs and reduced extent of lung consolidation (27–40%) Coinfected group: severe clinical signs resulting in the death of one calf and higher extent of lung consolidation (28 to 60%)

4