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Journal of Clinical Microbiology, September 2000, p. 3291-3298, Vol. 38, No. 9
Department of Veterinary Microbiology and
Parasitology, School of Veterinary Medicine, Louisiana State
University,1 and Department of
Veterinary Science, LSU Agricultural Center, Baton
Rouge,3 Louisiana; Conservation and
Production Research Laboratory, USDA, Agricultural Research Service,
Bushland,2 Texas Veterinary Diagnostic
Laboratory, Amarillo,4 and Department of
Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M
University, College Station,6 Texas; and
National Animal Disease Center, Ames,
Iowa5
Received 18 April 2000/Returned for modification 31 May
2000/Accepted 29 June 2000
Respiratory tract infections with viruses and
Pasteurella spp. were determined sequentially among 26 cattle that died during two severe epizootics of shipping fever
pneumonia. Nasal swab and serum samples were collected prior to onset
of the epizootics, during disease progression, and after death, when
necropsies were performed and lung samples were collected. Eighteen
normal control cattle also were sampled at the beginning of the
epizootics as well as at weekly intervals for 4 weeks. Respiratory
bovine coronaviruses (RBCV) were isolated from nasal secretions of 21 and 25 cattle before and after transport. Two and 17 cattle nasally
shed Pasteurella spp. before and after transport,
respectively. RBCV were isolated at titers of 1 × 103
to 1.2 × 107 PFU per g of lung tissue from 18 cattle
that died within 7 days of the epizootics, but not from the lungs of
the remaining cattle that died on days 9 to 36. Twenty-five of the 26 lung samples were positive for Pasteurella spp., and their
CFU ranged between 4.0 × 105 and 2.3 × 109 per g. Acute and subacute exudative, necrotizing lobar
pneumonia characterized the lung lesions of these cattle with a
majority of pneumonic lung lobes exhibiting fibronecrotic and exudative changes typical of pneumonic pasteurellosis, but other lung lobules had
histological changes consisting of bronchiolitis and alveolitis typical
of virus-induced changes. These cattle were immunologically naive to
both infectious agents at the onset of the epizootics, but those that
died after day 7 had rising antibody titers against RBCV and
Pasteurella haemolytica. In contrast, the 18 clinically normal and RBCV isolation-negative cattle had high hemagglutinin inhibition antibody titers to RBCV from the beginning, while their antibody responses to P. haemolytica antigens were delayed.
Evans' criteria for causation were applied to our findings because of the multifactorial nature of shipping fever pneumonia. This analysis identified RBCV as the primary inciting cause in these two epizootics. These viruses were previously not recognized as a causative agent in
this complex respiratory tract disease of cattle.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Coronavirus and Pasteurella Infections
in Bovine Shipping Fever Pneumonia and Evans' Criteria for
Causation
*
Corresponding author. Mailing address: Department of
Veterinary Microbiology & Parasitology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803. Phone: (225) 346-3311. Fax: (225) 346-5715. E-mail:
jstorz{at}mail.vetmed.lsu.edu.
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