Evaluating Aouad (Ammotragus lervia) as a Pneumonia Risk to Texas Bighorn Sheep (Ovis canadensis)

Abstract

Conserving bighorn sheep (Ovis canadensis) in their native range is challenged by pneumonia epizootics. Mycoplasma ovipneumoniae and Pasteurellaceae family bacteria are strongly implicated in these epizootics. Domestic sheep (Ovis aries) and domestic goats (Capra aegagrus) frequently carry these agents, and frequently cause bighorn sheep epizootics. However, the southwestern United States and northern Mexico host feral populations of aoudad (Ammotragus lervia). Aoudad are native to the Barbary coast of northern Africa and were introduced to the United States in the 1950s to provide hunting opportunities. Their habitat and diet requirements are apparently like those of bighorn sheep. Further, aoudad are within the Caprinae subfamily, within which most species are competent carriers of respiratory pathogens. Wildlife managers suspect that aoudad may negatively impact bighorn sheep populations through competition and potential disease transmission. To address these concerns, we investigated the host competency of aoudad, their ability to transmit important respiratory pathogens to bighorn sheep, and the clinical pathological effects of these agents in aoudad. These questions were answered through a two-phase study.

In phase 1, we experimentally inoculated aoudad with leukotoxigenic Pasteurellaceae and/or Mycoplasma ovipneumoniae. We found that aoudad were competent hosts of these pathogens for extended time-periods. Aoudad did develop clinical and pathological signs consistent with pneumonia, but stress was a significant contributor. Taken together, phase 1 provided evidence that aoudad are conceptually a respiratory pathogen transmission risk to bighorn sheep.

The phase 2 study involved exposing bighorn sheep to indirect and direct contacts with aoudad experimentally infected with leukotoxigenic Pasteurellaceae and/or Mycoplasma ovipneumoniae. Bighorn sheep contacting infected aoudad had moderate to rapid pathogenesis and mortalities. Aoudad experienced no fatal pneumonia and had mild disease without gross respiratory lesions. Aoudad can transmit respiratory pathogens intra and interspecifically indirectly and directly. Aoudad pose a conceptual disease threat to bighorn sheep and this requires future research on: 1) the virulence, transmissibility, and sources of Mycoplasma ovipneumoniae strains in aoudad, 2) how shared water sources may serve as a transmission risk, 3) behaviors of sympatric aoudad and bighorn sheep populations, and 4) the efficacy of diagnostic assays in free-ranging aoudad.