Abstract
In the present study, the replication kinetics of nephropathogenic (B1648) and respiratory (Massachusetts-M41) IBV strains were compared in vitro in respiratory mucosa explants and blood monocytes (KUL01+ cells), and in vivo in chickens to understand why some IBV strains have a kidney tropism. B1648 was replicating somewhat better than M41 in the epithelium of the respiratory mucosa explants and used more KUL01+ cells to penetrate the deeper layers of the respiratory tract. B1648 was productively replicating in KUL01+ monocytic cells in contrast with M41. In B1648 inoculated animals, 102.7–6.8 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8, 10 and 12 days post inoculation (dpi), 102.4–4.5 viral RNA copies/mL in plasma at 2, 4, 6, 8, 10 and 12 dpi and 101.8–4.4 viral RNA copies/106 mononuclear cells in blood at 2, 4, 6 and 8 dpi. In M41 inoculated animals, 102.6–7.0 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8 and 10 dpi, but viral RNA was not demonstrated in plasma and mononuclear cells (except in one chicken at 6 dpi). Infectious virus was detected only in plasma and mononuclear cells of the B1648 group. At euthanasia (12 dpi), viral RNA and antigen positive cells were detected in lungs, liver, spleen and kidneys of only the B1648 group and in tracheas of both the B1648 and M41 group. In conclusion, only B1648 can easily disseminate to internal organs via a cell-free and -associated viremia with KUL01+ cells as important carrier cells.
Highlights
Avian infectious bronchitis virus (IBV) causes mild to acute respiratory disease in chickens, characterized by coughing, sneezing, tracheal rales and dyspnea [1]
IBV B1648 and M41 replication characteristics in respiratory mucosa and KUL01+ cells B1648 and M41 replication in tracheal mucosa explants Inoculation of chicken tracheal mucosa explants with IBV B1648 and M41 led to the appearance of viral antigen positive cells in the epithelium and lamina propria of the tracheal mucosa starting from 6 hpi (Figure 1)
The number of B1648 infected cells in the epithelium was significantly higher than M41 infected cells at 6 [B1648: 2856.3 ± 217.2, M41: 877.0 ± 142.7 (11.2 ± 2.9%), P = 0.0002)], 12 [B1648: 6490.3 ± 298.9 (82.5 ± 4.1%), M41: 4380.0 ± 203.1 (57.6 ± 3.4%), P = 0.0005] and 24 hpi [B1648: 4077.3 ± 225.4 (51.8 ± 4.8%), M41: 3064.3 ± 144.9 (38.9 ± 3.0%), P = 0.0028]
Summary
Avian infectious bronchitis virus (IBV) causes mild to acute respiratory disease in chickens, characterized by coughing, sneezing, tracheal rales and dyspnea [1]. IBV causes huge economic losses in both broilers and layers. IBV has a tropism for the epithelium of the respiratory tract and for the epithelium of kidneys, oviduct, gastrointestinal tract (oesophagus, proventriculus, duodenum, jejunum, bursa of Fabricius, caecal tonsils, rectum and cloaca) and testes [3, 4]. IBV is clinically associated with poor performance of birds, reduced egg production and quality, as well as increased predisposition to other secondary bacterial infection [5]. Multiple serotypes of IBV exist, and new variants emerge due to frequent point mutations and recombination events in the viral genome [4]. Vaccination failure is very common against IBV due to poor or no cross-protection between different IBV serotypes
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