Evaluation of severe disease induced by aerosol inoculation of calves with bovine respiratory syncytial virus.
OBJECTIVE
To develop a model of bovine respiratory syncytial virus (BRSV) infection that induces severe disease similar to that seen in some cattle with naturally acquired BRSV infection.


METHODS
25 male Holstein calves, 8 to 16 weeks old.


METHODS
17 calves were given a low-passage field isolate of BRSV by aerosolization; 8 control calves were given supernatant from noninfected cell culture. Disease was characterized by evaluating clinical signs, virus isolation and pulmonary function tests, and results of blood gas analysis, gross and histologic postmortem examination, and microbiologic testing.


RESULTS
Cumulative incidence of cough, harsh lung sounds, adventitious sounds, and dyspnea and increases in rectal temperature and respiratory rate were significantly greater in infected calves. Three infected calves developed extreme respiratory distress and were euthanatized 7 days after inoculation. Virus was isolated from nasal swab specimens from all infected calves but not from mock infected calves. On day 7 after inoculation, mean PaO2 and PaCO2 were significantly lower, and pulmonary resistance was significantly higher, in infected calves. During necropsy, infected calves had varying degrees of necrotizing and proliferative bronchiolitis and alveolitis with syncytial formation. The 3 calves euthanatized on day 7 had emphysematous bullae in the caudal lung lobes; 1 had unilateral pneumothorax.


CONCLUSIONS
Severe disease similar to that seen in some cattle with naturally acquired BRSV infection can be induced in calves with a single aerosol exposure of a low-passage clinical isolate of BRSV. Our model will be useful for studying the pathogenesis of BRSV infection and for evaluating vaccines and therapeutics.
Woolums
A R
AR
Department of Pathology, School of Veterinary Medicine, University of California, Davis 95616, USA.
Anderson
M L
ML
Gunther
R A
RA
Schelegle
E S
ES
LaRochelle
D R
DR
Singer
R S
RS
Boyle
G A
GA
Friebertshauser
K E
KE
Gershwin
L J
LJ
D000336:Aerosols; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001992:Bronchoalveolar Lavage Fluid; D002417:Cattle; D002418:Cattle Diseases / Q000503:physiopathology* / Q000821:virology; D003371:Cough / Q000662:veterinary / Q000821:virology; D008297:Male; D017817:Nasal Lavage Fluid / Q000821:virology; D012129:Respiratory Function Tests / Q000662:veterinary; D018357:Respiratory Syncytial Virus Infections / Q000503:physiopathology / Q000662:veterinary*; D018112:Respiratory Syncytial Virus, Bovine / Q000472:pathogenicity*
D000336:Aerosols