Development of pneumonia in desert bighorn sheep after exposure to a flock of exotic wild and domestic sheep

Abstract

Summary From 1986 to 1989, 5 desert bighorn sheep (3 Ovis canadensis mexicana and 2 O c nelsoni), ranging in age from 2 to 3 years, were exposed to a flock of exotic wild and domestic sheep to potentially achieve naturally acquired pneumonia. Pasturella multocida was isolated from nasal samples from 4 of 6 sheep randomly sampled from the flock. Bighorn sheep were exposed individually and each exposure period was a trial. Treatment before and after exposure varied and included combinations of α interferon, antibiotics, anti-inflammatory drugs, and vaccines. Treatments were chosen on the basis of recommendations of others for treating pneumonia in desert bighorn sheep as well as our own experience in sheep and cattle. Regardless of treatment used, bighorn sheep in trials 1 to 4 developed signs of pneumonia within 10 to 14 days of exposure. Bighorn sheep in trials 1 to 3 died within 11 to 17 days of initial exposure. In trial 4, the bighorn sheep was isolated from the carrier sheep for treatment of pneumonia on day 14 and died on day 30. Pasteurella multocida was isolated from lung tissue in 3 of the 4 bighorn sheep. On the basis of results of trials 1 to 4, a more in depth clinical study was conducted in trial 5. Nasal and blood specimens were collected prior to and during trial 5 for bacteriologic culturing and serologic testing for bovine viral diarrhea virus, infectious bovine rhinotracheitis, parainfluenza-3 virus, and respiratory syncytial virus. The bighorn sheep was vaccinated with a modified-live Pasteurella haemolytica vaccine and allowed to habituate to its new facilities for 133 days before it was exposed to the carrier sheep. Body temperature of this bighorn sheep was monitored every hour with radiotelemetry. Pneumonia was diagnosed on day 30 of exposure to the carrier sheep. Treatment consisting of long-acting oxytetracycline, sulfadimethoxine, long-acting sulfamethazine bolus, dexamethasone, and flunixin meglumine was given for 8 days and clinical improvement was detected. Acute pneumonia was again diagnosed on day 53. The bighorn sheep was removed from contact with the carrier sheep and put in isolation for a second treatment regimen. The bighorn sheep died on day 99. Pasteurella multocida was isolated from a tracheal flush and a nasal specimen obtained during the second bout of pneumonia and from lung tissue and sinuses at necropsy. Viruses were not isolated from the tracheal flush or from tissue samples collected at necropsy. None of the carrier sheep had clinical signs of pneumonia during the trials. Bacteriologic culturing and serologic testing in the bighorn sheep and ewes prior to and during the study suggested that carrier ewes were the source of P multocida infection in the bighorn sheep. Viruses were not a predisposing factor. Chronic sinusitis following initial pneumonia was suspected to play a role in the recurrence of pneumonia in the bighorn sheep of trial 5.