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Biol Open. 2016 Jun 15;5(6):745-55. doi: 10.1242/bio.018234.

Role of carriers in the transmission of pneumonia in bighorn sheep (Ovis canadensis).

Author information

1
Department of Veterinary Microbiology & Pathology, Washington State University, Pullman, WA 99163, USA.
2
Paul G. Allen School for Global Animal Health, Washington State University, Pullman, WA 99163, USA.
3
Department of Veterinary Microbiology & Pathology, Washington State University, Pullman, WA 99163, USA ssrikumaran@vetmed.wsu.edu.

Abstract

In the absence of livestock contact, recurring lamb mortality in bighorn sheep (Ovis canadensis) populations previously exposed to pneumonia indicates the likely presence of carriers of pneumonia-causing pathogens, and possibly inadequate maternally derived immunity. To investigate this problem we commingled naïve, pregnant ewes (n=3) with previously exposed rams (n=2). Post-commingling, all ewes and lambs born to them acquired pneumonia-causing pathogens (leukotoxin-producing Pasteurellaceae and Mycoplasma ovipneumoniae), with subsequent lamb mortality between 4-9 weeks of age. Infected ewes became carriers for two subsequent years and lambs born to them succumbed to pneumonia. In another experiment, we attempted to suppress the carriage of leukotoxin-producing Pasteurellaceae by administering an antibiotic to carrier ewes, and evaluated lamb survival. Lambs born to both treatment and control ewes (n=4 each) acquired pneumonia and died. Antibody titers against leukotoxin-producing Pasteurellaceae in all eight ewes were 'protective' (>1:800 and no apparent respiratory disease); however their lambs were either born with comparatively low titers, or with high (but non-protective) titers that declined rapidly within 2-8 weeks of age, rendering them susceptible to fatal disease. Thus, exposure to pneumonia-causing pathogens from carrier ewes, and inadequate titers of maternally derived protective antibodies, are likely to render bighorn lambs susceptible to fatal pneumonia.

KEYWORDS:

Antibodies; Bighorn sheep; Carrier; Mycoplasma; Pasteurellaceae; Pneumonia

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