Infectious bronchitis virus variants - History, current situation and control measures

Overview & Synopsis

Infectious bronchitis virus (IBV) is ubiquitous in most parts of the world where poultry are reared and is able to spread very rapidly in non-protected birds. It is shed via both the respiratory tract and the faeces and can persist in the birds and the intestinal tract for several weeks or months. Outdoors, survival of IBV for 56 days in litter has been reported. Although strict biosecurity and working with a one-age system are essential control measures, normally vaccination is required to increase the resistance of the chickens against challenge with IBV strains. This is made more difficult to achieve because IBV exists in the form of many different antigenic or genotypic types, commonly referred to as variants. Being a coronavirus and therefore a single stranded RNA virus, IBV has the enormous capacity to change both by spontaneous mutation and by genetic recombination. Both these events occur with IBV and are most likely to result in the emergence of new variants if they occur in the hypervariable regions of the spike gene. Whilst many new variants are unable to replicate or survive for only a short time, a few emerge which become of economic importance either world wide or in restricted geographic areas. This paper presents an overview of the history and current situation of IBV worldwide, including the measures necessary to control the many IB variants found throughout the world .