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Georgia 08 IB variant remains threat to US poultry

by Timothy S. Cummings, DVM, DACPV
Senior Technical Services Veterinarian
Zoetis Inc.

 

In my part of the country, infectious bronchitis due to the Georgia 2008 (GA 08) variant strain has been a huge problem for the broiler industry.  As the name implies, the disease was first identified in Georgia back in the winter of 2007-08 but since then has been isolated in Tennessee, Kentucky, Alabama, North and South Carolina and in my state, Mississippi.

Most of the poultry industry in Mississippi is concentrated in the mid to lower region of the state.  In 2013, we isolated GA 08 from a few farms in Mississippi, so it was around but it wasn’t causing any significant problems.

Extremely cold weather at the beginning of this year, however, seemed to “jump start” the disease.  The field experience has been very variable among poultry companies, with some complexes experiencing significant processing plant condemnations and others having minimal issues.

This isn’t a typical bronchitis that ostensibly affects the upper respiratory tract, causing the usual coughing, swollen sinuses and other respiratory signs. Initially, we didn’t see many clinical signs at all.  Over time, though, the challenge increased and clinical signs such as snicking or “rattling” became more apparent in some flocks.  Mortality has typically been low, as certain houses of affected flocks get treated.

Condemnations

Ga 08 primarily affects the lower respiratory tract and results in abdominal airsacculitis (Figure 1).

Figure 1.  Airsacculitis typically doesn’t cause problems in the field but leads to condemnation at the processing plant.

Figure 1. Airsacculitis typically doesn’t cause problems in the field but leads to condemnation at the processing plant.

It tends to be a disease primarily of older broiler birds, but you can find airsac lesions in the field if you are looking.  Condemnation at the processing plant is the main consequence and cause of loss for producers, although in some of the more severely affected flocks, secondary infections such as Escherichia coli develop and are an additional cause of mortality in the field that can be attributed to GA 08.

With airsacculitis, the interior of the birds becomes infected, resulting in a lot of cheesy material that just can’t be cleaned out.  Part of the problem is that many companies don’t have the personnel or facilities at their processing plants to handle this kind of clean up, which takes time and slows down the processing line.  The result is that entire birds may be discarded.

When mortality does occur because the disease has progressed, pericarditis (Figure 2) or perihepatitis is likely to be found upon necropsy.

Figure 2.  Pericarditis due to GA 08

Figure 2. Pericarditis due to GA 08

When GA 08 first emerged, there obviously wasn’t a vaccine for it, and there wasn’t any good cross-protection from existing infectious bronchitis vaccines.  One of the veterinarians at a leading poultry company made his own attenuated, live autogenous vaccine, which he used for a while and it helped.

Vaccination

The vaccine is frozen and comes in liquid nitrogen.  It is applied by coarse spray at the hatchery.  In heavily challenged areas, a second dose can be given in the field at 14 to 18 days of age by spray.  There’s a better chance of knocking down the field challenge with two doses.

In my experience, most of the producers I’ve talked to who have had problems with GA 08 and used the vaccine last winter and spring are reporting a positive response.  In these anecdotal reports, they’ve told me they are seeing fewer signs of the disease and fewer condemnations.

The vaccine has not completely eliminated problems due to GA 08 — especially where field isolates have shown evidence of genetic drift.

Some producers have used the vaccine throughout the summer and plan to use it into the next year.  Some didn’t use it during hot weather to see if the virus is gone but will restart if GA 08 reappears.  There is no “one size fits all” strategy for all producers with regard to this disease, so each company must weigh the risk it is willing to take.

Increased risk with cooler weather

If producers haven’t been vaccinating against GA 08 and the disease starts to show up in their operations, I would urge them to consider vaccinating before cooler weather arrives because that’s when this disease usually turns ugly.  It starts subtly and seems to be triggered by cold weather.  Once the disease cranks up, it can cost a lot in condemnations — a lot more than the cost of the vaccine.

We really need to think more about how to help prevent disease outbreaks of GA 08 rather than waiting for it to strike hard, especially because the signs it produces are often not obvious.  Look for an uptick in condemnations and, if GA 08 is suspected, get samples from affected birds.

The gold-standard test is isolation of the virus from tracheal samples (ideally) or cecal tonsils, followed by identification using polymerase chain reaction/sequencing analysis of the S1 gene.  There is already some evidence of field virus drift in some regions (< 95% similarity to reference virus), so we will need to be vigilant in monitoring for the presence of this virus in the field.

Personally, I think this virus is going to persist and that we need to continue vaccinating in some areas for the foreseeable future.  We also need to combine vaccination with ramped-up biosecurity procedures and good bird management.

Infectious bronchitis viruses can be tracked around by almost anything — footwear, equipment and vehicles.  The wind can take it certain distances, and if farms are close together, it can literally blow across the road.  I tell growers to be especially vigilant about adhering to biosecurity procedures if GA 08 is a threat in their area — particularly if their birds aren’t vaccinated.  They also need to manage birds well to minimize stress because if GA 08 emerges, it will be less severe if birds aren’t stressed.

With the combination of vaccination, biosecurity and good bird management, however, it’s my belief that we can minimize the effects of GA 08 on performance and condemnations.  And maybe in time, this virus will move out of our poultry industry.

 


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