Getting to grips with infectious bronchitis

Infectious bronchitis is a growing problem in poultry and knowing what strains are about is crucial to developing an appropriate vaccination stratgy. Tibor Cserep of Intervet/Schering-Plough explains

Vaccination against infectious bronchitis can be complex, with many different vaccines available.

The choice of which to use is determined by the flock history, serology results and, in particular, which serotypes are circulating in the area.

So which IB strains are most commonly found in the UK and do some of the newer strains present a risk to bird health?

A recent survey by Intervet/Schering-Plough of more than 200 broiler, layer and breeding units has revealed a wide range of both known and unknown IB serotypes.

For example, across the entire sample, about two-thirds were IB positive, with IBV 793b found in 9% of flocks, followed by ARK in 8%, and D274 and H120, each accounting for 7%. In comparison, just over a third tested negative and 20% were “un-typeable” or new.

Looking at the split between layers and broilers throws up some interesting results.

Among layer flocks, 53% showed negative results and 32% were un-typed. But where typeable IB was found, IBV 4/91 accounted for half the serotypes detected.

The distribution of broiler samples, however, showed much more variation. A fifth of the flocks tested negative or were un-typeable. But of the remaining 80% of flocks, nine IB serotypes were detected, the most common of which were 793b (16%), ARK (15%), D274 (14%) and H120 (12%). (See pie chart.)

The fact that IB strains are commonly found in samples from both layer and broiler flocks is not surprising. What is more surprising is that so many of the samples – about a fifth – yielded un-typeable strains which are probably new.

This begs the question of whether a new vaccine is required for a new serotype. But the research evidence does not support this approach.

For example, cross-protection studies were carried out by well-known IB expert Jane Cook in which birds were vaccinated with two different vaccines (Nobilis Ma5 and Nobilis 4/91), both separately and in combination.

The birds were then challenged at five weeks old with 12 different IB variants. and results showed that using a combination of the Ma5 vaccine, (commonly used against classical Massachusetts IB strains), and the 4/91 vaccine, (commonly used to protect against the 793B variant), gave good protection against at least seven of the 12 IB variants.

Over 80% protection was achieved against challenge with the strains Arkansas, D274, 57/96, 890/80, A1121 and FB3.

In another study, where birds were challenged with the Italian 02 IB variant, the combination of Ma5 and 4/91 vaccines provided 90%-95% cross protection.

A more recent study from Italy looked at cross-protection of birds on a vaccination programme using Ma5 at day-old and 4/91 at 14 days. The birds were then challenged with the QX IB variant at 35 days.

Non-vaccinated infected birds showed clinical signs of varying severity, predominantly lesions in the trachea. Vaccinated birds, however, appeared healthy, apart from mild conjunctivitis in a small number of broilers. There were no signs of damage or lesions in the trachea and there was no kidney or oviduct damage either.

So for the producer, it is worth working with your vet to assemble the information that will enable the best vaccination programme to be chosen for your flock.

The vaccines should also be administered correctly. Help and advice on this is available from Intervet/Schering-Plough on a special helpline – 01908 685685.

Chinese QX – a new IB variant in the UK

One known strain indentified in the Intervet/Schering-Plough survey was IB variant QX. This was found in four samples, though since the survey was carried out, evidence has come to light which suggests it is far more widespread in the UK.

QX was first identified in China in 1996 and has now spread to the western hemisphere, where it is causing severe losses in both the broiler and layer industries across mainland Europe.

It causes false layer syndrome in layers and breeders, where the birds look and behave like laying hens, but there is irreversible damage to the oviduct. Peak egg production can fall by as much as a third.

In broilers it causes nephrosis (kidney damage), but with low mortality.

• Tibor Cserep will be providing a further update on the UK’s infectious bronchitis situation at the Poultry Meat Conference at Stoneleigh on 15 September. There will be a range of other speakers covering business and technical issues. To register for this free event, call Carole Arnold on 07801 338009 or email carole-arnold@tiscali.co.uk