Type I Hypersensitivity in Lambs With Coughing Syndrome

Lambs from two flocks with a chronic respiratory disease characterized by paroxysmal cough and rectal prolapses were tested for their skin reactivity to Mycoplasma ovipneumoniae (MO) and M. arginini (MA) antigens (Ags). There was a marked, immediate skin reaction to intradermal injection of MO Ag in many of the tested lambs. Some of these positive lambs also reacted to MA Ag. Phosphate buffered saline (PBS) used as a negative control gave no skin reaction in any of the tested animals. In addition, simultaneous serological tests revealed low antibody levels against MO and MA. However, both agents could be routinely isolated from nasal swabs of the affected lambs. There is reason to suspect that an immediate type hypersensitivity to MO Ag and perhaps to other allergens that develops in association with the mycoplasmal infection contributes to this coughing syndrome.

Bovine Respiratory Syncytial Virus Infection in McNay Farm Calves

Clinical respiratory disease occurs almost every year in fall calves in the McNay Farm herd. Diagnostic procedures have implicated Haemophilus somnus (H. somnus) and bovine respiratory syncyial virus (BRSV) as the infectious agents primarily associated with this disease. Therefore, the 1995 calves were closely monitored after weaning and during the course of a respiratory disease. Serologic evidence indicated the involvement of the same two agents in the pathogenesis of the disease. Also, experimental evidence suggested a role for a preexisting immediate hypersensitivity to H. somnus and the development of this type of response to BRSV. We theorize that the pathogenesis of the clinical disease involved infection with H. somnus, establishment of immediate hypersensitivity in the lungs, viral infection with associated pathologic lesions, and viral exacerbation of the immediate hypersensitivity reaction with resultant clinical signs and tissue damage.