IB and IB variants – what’s a variant and what’s all the fuss about?

IB and IB variants – what’s a variant and what’s all the fuss about?

Nov 12, 2012

Infectious bronchitis (IB) is a common poultry virus affecting the upper respiratory tract of birds With the increasing stocking densities in today’s modern poultry production systems, its effects are becoming more and more significant.

The virus was first identified in 1931 and based on serological tests certain classic serotypes were identified such as the Massachusetts and Connecticut strains. Using these original virus strains the first vaccines were manufactured.

What has become apparent since then is that this virus is evolving all the time (its characteristics, against which the vaccines are targeted, are changing all the time) and that within the serotype there are strains with varying ability to cause damage (so called pathotypes).

In the field this resulted in some IB strains causing upper respiratory tract problems with decreased growth and increased mortality in broilers. While in layers and breeders drops in egg production, egg quality and hatchability have occurred. All of this despite having been vaccinated with the classic vaccines.

These strains that caused problems in classically vaccinated birds were called variant strains, examples of such strains are 4/91 and QX. QX is the latest in the hit parade, first identified in China and now causing problems in many parts of the world, including South Africa.

As we know the virus is always changing (a moving target for the vaccine manufacturers), so a lot of research has gone into finding out the best method to combat this in the field. Work done several years ago by Jane Cook from the UK showed that vaccinating with an MA5 and a 4/91 vaccine provided the broadest protection against the varying seroptypes.

In South Africa we have only had access to Massachusetts and closely related vaccines so  we have not been able to implement this approach. This is getting addressed as we speak, and hopefully will be resolved in the near future.