Isolation and Characterization of New Variant Strains of Infectious Bronchitis Virus in Northern Egypt

Abstract

| Infectious bronchitis virus (IBV) is the causative agent of an acute and highly contagious disease affecting the respiratory, renal and/or reproductive systems of chicken called infectious bronchitis disease. Controlling of this disease needs continuous identification of the circulating strains and genotypes. In the present study, six IBV samples were isolated from different poultry farms located in northern Egypt and propagated in the allantoic cavity of specific pathogen-free embryonated chicken eggs causing curling and dwarfing of embryos at different serial egg passages. The harvested allantoic fluids were titrated by chicken embryo kidney cell cultures selecting suitable viral concentrations for investigating the ciliostasis effect of IBV on tracheal organ cell cultures. In addition, the nucleotide and protein sequences of the IBV spike glycoprotein (S) were used for molecular relationship analysing and construction of phylogenetic trees. All examined viruses induced complete ciliostasis at the fifth day post inoculation. Isolates shared total sequence identities of 99-100% on nucleotide and amino acid levels. The Egyptian strain (Eg/CLEVB-1/IBV/012) showed 99% and the Israeli strain (IS/1494/06 IBV) showed 98% with the collected isolates and recognized as the local strains with the highest total sequence identities and phylogenetic relatedness of all strains available from the Gene Bank. The Italy02 strain of IBV is the nearest relative to the collected isolates with total sequence identities of 79 and 77% at nucleotide and amino acid levels, respectively. The new variant strains currently isolated from the northern of Northern Egypt should be evaluated periodically for developing suitable autogenously based virus vaccines.

Genotyping and pathotyping of diversified strains of infectious bronchitis viruses circulating in Egypt

“…Trachea, lung and kidney were collected from infected birds after intranasal inoculation and the virus tropism was detected by rRTPCR, the results were shown in Table 5. Similarly, variants of IBV were reported as nephrogenic strains in Egypt: D274, D3896, D1559, Egypt/BeniSuef/01, 720/99 Israel, 4/91, IS/1494 [13,29] . Terregino et al [34] isolated IBV from kidney, trachea, ovary, and oviduct following infection with the QXIBV strain.…”

“…In the S1 gene, there are three HVRs located within amino acids 3867 (HVR1), 91141 (HVR2) and 274387 (HVR3) [25] . However, the outbreaks of the disease have continued to cause severe infections [13] . Usually IBV serotypes have a wide range of genetic variations in the S1 gene ranged from 2% to 25% [6,26] .…”

“…IBV targets primarily the upper respira tory tract; however the nephropathogenic strains have a predilection for the kidney of young chickens causing nephritis that can produce significant mortalities [13] . IBV targets primarily the upper respira tory tract; however the nephropathogenic strains have a predilection for the kidney of young chickens causing nephritis that can produce significant mortalities [13] .…”

“…Furthermore, S1 reveals high sequence variability than S2 subunit [8] . In Egypt, IBV strains continue to spread everywhere in the country, and have been isolated from both vacci nated and non-vaccinated flocks [13] . IBV variants are distributed worldwide, there are more than 20 IBV serotypes differentiated globally [10] .…”

“…Strong lacrimation, presence of nasal exudates, severe watery feces; 2 kidney and trachea score: No of chicks with lesion score of ≥ 1; 3 pathogenicity index: No of chicks with lesion score ≥ 1 + 1 point for every 10% mortality; 4 pathotypes: Low (pathogenicity index value 1-9), intermediate (pathogenicity index value[10][11][12][13][14][15][16][17][18], high (pathogenicity index value ≥ 19). IBV: Infectious bronchitis virus.…”