Page 66 - Poultry-Punch April 2020 edition

POULTRY PUNCH ARTICLE

turkey coronavirus (TCoV) and avian infectious bronchitis virus
(AIBV) have also been demonstrated. Antibodies to IBV have been
demonstrated in humans with close contact to poultry, but the
virus has not been reported to cause human clinical disease
The Corona Virus

Coronaviruses are a group of viruses that have a halo, or
crown-like (corona) appearance when viewed under an electron
microscope.( Photo courtesy of the CDC)

Avian Coronaviruses are enveloped positive-strand RNA viruses
that replicate in the cytoplasm.They have a distinctive set of club- Schematic diagram of evolution of possible pathways and
shaped spikes on their envelope, and the spike protein (S) is the emergens of new antigenic variant / serotype from parental strain
primary determinant of cell tropism and pathogenesis, being of IBV(Adopted from Lee2002)
responsible (and apparently sufficient) for receptor binding and
fusion . However, other envelope proteins are present: the M Infectious bronchitis virus (IBV)
protein, the E protein, and (in some coronaviruses) an HE protein . IBVis a coronavirus that causes an acute and highly contagious
The coronavirus S protein is categorized as a class I fusion protein, disease in chickens. The virus can cause substantial economic losses
based on the presence of characteristic heptad repeats as such, throughout the poultry industry worldwide. It can affect the upper
it shows features of the fusion proteins of influenza virus (HA), respiratory tract and the reproductive tract, and some strains can
retroviruses (Env), and paramyxoviruses (F and HN), for which there cause nephritis.
is extensive characterization at the structural and biophysical levels.
Genetic and phenotypic variations are common features in
the evolution processes of Infectious bronchitis virus strains
lead to evolution of important antigenic and pathogenic variable
strains. The role of mutation, recombination and selection in the
generationmand evolution of Quasis species production in IBV

IBV is the prototype species of the Coronavirus family, Gamma
coronavirus genus, classified in the order Nidovirales, and it is the
type species of the genus coronavirus of the domestic chicken
(Gallus gallus). Infectious bronchitis (IB) was first observed
by Schalk and Hawn (1931) in North Dakota in the United States
in 2- to 3-week-old chickens. However, the nature of the infectious
agent was not determined at that time and was assumed that IB
was mainly a disease of young chickens.
Hence, the disease was named “infectious bronchitis of young
chicks.” Five years later, it was demonstrated that the causative
agent of this disease is a virus, which was named IBV (Beach and
Schalm, 1936). Since that initial discovery, many different serotypes,
defined by neutralizing antibodies, and genetic types, based on the
deduced amino acid sequence (from the nucleic acid sequence) of
the spike gene, have been described around the world.

66 April, 2020