The effects of simultaneous respiratory infections on the nasal shedding of Mycoplasmopsis bovirhinis in dairy calves.

Although there are several studies that described the possible participation of Mycoplasmopsis bovirhinis (formerly, Mycoplasma bovirhinis) in respiratory disease in calves worldwide, none of these evaluated the effects of concomitant infections on the shedding of this organism. Accordingly, this study evaluated the effects of simultaneous respiratory infections in dairy calves on the nasal shedding of M. bovirhinis. A statistical two-step model, using univariable and multivariable with logistic regression was developed to investigate and predict the possible effects of simultaneous infections by Histophilus somni, Mannheimia haemolytica, Pasteurella multocida, bovine coronavirus (BCoV), and ovine gammaherpesvirus 2 (OvGHV2) in dairy calves on the nasal shedding of M. bovirhinis. The multivariable analysis demonstrated that dairy calves infected with OvGHV2 have 2.59 times likelihood of nasal shedding of M. bovirhinis relative to calves not infected by OvGHV2, while the odds of nasal shedding of M. bovirhinis was 3.46 times higher in dairy calves infected by M. haemolytica. In contrast, simultaneous respiratory infections in dairy calves by H. somni, P. multocida, and BCoV had no direct effect on the nasal shedding of M. bovirhinis. Consequently, infections by OvGHV2 and M. haemolytica may be possible risk factors for the nasal shedding of M. bovirhinis in dairy calves. These results demonstrated the importance of disease modeling in veterinary medicine to predict and understand the complex outcomes of associations in animals concomitantly infected by several disease pathogens.

The Role of Mycoplasma bovirhinis in the Development of Singular and Concomitant Respiratory Infections in Dairy Calves from Southern Brazil.

The role of Mycoplasma bovirhinis in the development of pulmonary disease in cattle is controversial and was never evaluated in cattle from Latin America. This study investigated the respiratory infection dynamics associated with M. bovirhinis in suckling calves from 15 dairy cattle herds in Southern Brazil. Nasal swabs were obtained from asymptomatic (n = 102) and calves with clinical manifestations (n = 103) of bovine respiratory disease (BRD) and used in molecular assays to identify the specific genes of viral and bacterial disease pathogens of BRD. Only M. bovirhinis, bovine coronavirus (BCoV), ovine gammaherpesvirus 2 (OvGHV2), Histophilus somni, Pasteurella multocida, and Mannheimia haemolytica were detected. M. bovirhinis was the most frequently diagnosed pathogen in diseased (57.8%; 59/102) and asymptomatic (55.3%; 57/103) calves at all farms. BCoV-related infections were diagnosed in diseased (52%; 53/102) and asymptomatic (51.4%; 53/103) calves and occurred in 93.3% (14/15) of all farms. Similarly, infectious due to OvGHV2 occurred in diseased (37.2%; 38/102) and asymptomatic (27.2%; /28/103) calves and were diagnosed in 80% (12/15) of all farms investigated. Significant statistical differences were not identified when the two groups of calves were compared at most farms, except for infections due to OvGHV2 that affected five calves at one farm. These results demonstrated that the respiratory infection dynamics of M. bovirhinis identified in Southern Brazil are similar to those observed worldwide, suggesting that there is not enough sufficient collected data to consider M. bovirhinis as a pathogen of respiratory infections in cattle. Additionally, the possible roles of BCoV and OvGHV2 in the development of BRD are discussed.

The Participation of a Malignant Catarrhal Fever Virus and Mycoplasma bovis in the Development of Single and Mixed Infections in Beef and Dairy Cattle With Bovine Respiratory Disease.

The bovine respiratory disease (BRD) complex is a multietiological and multifactorial disease associated with a wide range of viral and bacterial pathogens. This study evaluated the contribution of specific infectious disease agents in the development of BRD in cattle from Brazil and determined if a virus within the malignant catarrhal fever virus (MCFV) group and Mycoplasma bovis, acting individually or in conjunction, can be associated with the development of BRD. Formalin-fixed paraffin-embedded pulmonary sections were used in immunohistochemical assays to determine the intralesional presence of six antigens associated with BRD: bovine alphaherpesvirus 1 (BoHV-1), bovine parainfluenza virus 3 (BPIV-3), bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), MCFV, and M. bovis. Pneumonia was diagnosed in 82.7% (120/145) of all cattle evaluated. Interstitial pneumonia (60%, 72/120) and suppurative bronchopneumonia (25.8%, 31/120) were the most frequent patterns of pneumonia identified. Intralesional antigens of MCFV (53.3%, 64/120) were the most frequently associated with BRD, followed by M. bovis (47.5%, 57/120), BVDV (42.5%, 51/120), BoHV-1 (28.3%, 34/120), BRSV (24.2%, 29/120), and BPIV-3 (8.3%, 10/120). Additionally, antigens of BVDV, MCFV, and M. bovis were the most frequently identified agents associated with singular and concomitant infections. The MCFV identified during this study is more likely to be ovine gammaherpesvirus 2 (OvHV-2), since OvHV-2 is the only MCFV identified within the geographical region of this study. Interstitial pneumonia with proliferative vascular lesions may be a useful histologic feature to differentiate MCFV-induced pneumonia from other viral pneumonias of cattle. These results demonstrate that MCFV and M. bovis, in single or mixed infections, can produce pneumonia in cattle and should therefore be considered as primary agents in the development of BRD.

A review of the epidemiological, clinical, and pathological aspects of malignant catarrhal fever in Brazil.

Sheep-associated malignant catarrhal fever (SA-MCF), the form of MCF that occurs in Brazil, is a severe, frequently fatal, infectious disease caused by ovine gammaherpesvirus-2 (OvHV-2), in which sheep are the asymptomatic hosts and cattle and other cloven-hoofed animals are the accidental hosts. This review provides a critical analysis of the historical, epidemiological aspects and the estimated economic impacts associated with SA-MCF in Brazil. Moreover, the clinical manifestations and pathological lesions associated with SA-MCF in cattle are reviewed and discussed and the phylogenetic distribution of OvHV-2 in Brazil is presented. OvHV-2 is the only MCF virus identified in animals from Brazil. It is recommended that a histopathologic diagnosis of SA-MCF be based on all aspects of vascular disease in the affected animal and not only lymphocytic/necrotizing vasculitis and/or fibrinoid change. Conformation of the intralesional participation of OvHV-2 in these alterations can be achieved by immunohistochemistry and/or in situ hybridization assays. Additionally, it is proposed that OvHV-2 should be considered as a possible infectious disease agent associated with the development of bovine respiratory disease in cattle. Furthermore, the possible role of the small intestine in the dissemination of OvHV-2 is discussed.