By Dr Oscar Blanco (DVM, PhD), Field Technical Support Manager, Phibro Animal Health Corporation
Infectious bronchitis (IB) is a viral disease affecting poultry of different ages and diverse productive purposes.
It was initially described as a disease of broiler chickens, characterised by breathing difficulties and high mortality. It was later found in layers, causing important reduction in egg production and alteration in egg quality (discoloured eggs, brittle shells, eggs without shells, liquid egg content, et cetera).
Nothing is constant
Like with CoVID-19, the infectious bronchitis virus (IBV) can mutate, giving origin to new strains. The changes are mainly produced in the S protein on the viral surface. Sometimes such changes result in IBV variants against which the usual vaccines work less efficiently, or not at all.
What is the situation of variants in Sub-Saharan Africa?
The constant changes of the virus result in the frequent occurrence of new strains, which have been divided
in groups or lineages of similar genetic makeup. The lineages identified in Africa are presented in Table 1. Viruses inside these lineages continue changing and new variants appear.
Variant 2 (IS1494/06), the newest threat
IB variant IS/1494/06 was first isolated in the Middle East in 2006 and has spread to at least, 31 countries. Currently, IS/1494/06 is the dominant strain in the GI-23 lineage. In countries where IS/1494/06 has become established, it tends to be the dominant strain. If there is not routine vaccination against IS/1494/06, there is often co-circulation of virulent variants of G1-23, 793B and QX groups, with dominance of G1-23 viruses.
In Zambia, IS/1494/06 was detected in broilers in 2019. No new cases were reported since then, however symptoms and lesions observed in broilers and hens suggest its presence.
What does IS/1494/06 variant do to chickens?
How to protect your flock
The usual Massachusetts strain-based vaccines (for example, H120, MA5) do not properly protect chickens against many of the new variants. Ideally, one should use a vaccine strain that is closely homologous (that is very closely similar) to the field strain/s present at the farm. This would, generally, offer the best protection. Examples are offered in table 2.
There are, however, very few vaccine strains in the market that can offer homologous protection. This means that vaccination programmes need to be adjusted according to the field strains present on a farm. Some vaccine strains can offer cross protection against a range of variant field strains. For example, TAbic® IB VAR206 can also protect against 793B and some QX field strains. In other cases, however, you may need to use a combination of vaccines to give protection in the field, or you may need to adjust the timing and the interval between vaccine applications on the farm.
When facing an IB challenge in your birds it is important, therefore, to confirm the presence of the virus and identify the strain as soon as possible, so that you can apply the correct vaccination program. Your consulting veterinarian will be able to help you to confirm the presence of an IB challenge based on the symptoms and post-mortem lesions. He can also take the relevant samples for laboratory testing to confirm the diagnosis.
Please visit Phibro Academy (https://academy.pahc.com), register, and access further information on IBV variants and other poultry topics via their range of online webinars.
