Where the disease used to be associated with respiratory symptoms, decreased egg production and poor egg quality, some of the newer strains are also nephropathogenic, causing intestinal nephritis, according to Dr Jane Cook, a specialist on Infectious Bronchitis.

She told delegates that new variants of the disease will continue to arise, because of the nature of the virus. It has a very high mutation rate.

The type of pathology caused by these variants will differ, as well as the severity of the disease and its geological spread.

The D388 (QX) variant, for example, started in China and spread from there to Russia and Europe. Today it is of global concern and found across Asia and even in South Africa. Affected birds adopt a penguin like stance and have swollen stomachs.

The Italian O2 strain, in contrast, has been widely detected in PCR tests in birds across Europe, but it was not associated with disease, except in Spain. The disease has however now also been reported in Morocco.

Dr Cook said that one of the problems with these new strains is that they occur in well-vaccinated flocks. This might be because of vaccination biosecurity problems, but also because the vaccinations are not working against these diseases.

The question therefore arises whether new variants of vaccination are needed to prevent these diseases.

Dr Cook said she does not think so. She argued that the development of homogenous vaccines would be too costly and time consuming. The disease is also muting very fast.

She advised the industry to make use of the vaccines that are available to treat these variants.

“Success has been reported with existing vaccines on certain variant strains, such as subtypes of the Arkansas type viruses in America. The vaccine however has to be given correctly,” she said.

There has however also been cases where a single vaccine no longer did the job. In these cases, Dr Cook advised the use of two different strains of vaccine.

A study by the Animal Health Service in Deventer, for example, showed that a single application of a live vaccine did not offer sufficient protection against the D388 isolate. Better protection was achieved when other vaccines of other serotypes were included in the vaccination programme.

The vaccines could be given together or apart. “Vaccination should however be started early, preferably at day one, and it should be followed up with revaccination,” she said.