Why ‘vaccinated’ chickens still get infected with IBV — and what to do about it
While many vaccines and vaccination programs effectively protect against the highly contagious infectious bronchitis virus (IBV) in poultry, outbreaks of the disease still occur in vaccinated flocks — frustrating producers and, worse yet, compromising the health, welfare and performance of the birds.
Why do these breaks occur? And more importantly, how can they be prevented? Brian Jordan, PhD, associate professor at the University of Georgia, recently shared his insights and advice with Poultry Health Today.
Why disease breaks out despite vaccination
First, the vaccines used may not have been a good match for the circulating virus because new variants of IBV can arise, Jordan explained.
Secondly, he indicated that outbreaks may result from human or mechanical errors, leading to partially vaccinated flocks. That often leads to a “roll of the vaccine that was given, where it continues to replicate and cycle through a flock, which can sometimes cause disease in and of itself if that reaction is not mitigated.”
Other times breakdowns in the vaccination process “go so awry that the birds actually don’t get vaccinated at all.” In those cases, he added, “any virus that was out there that had a little bit of pathogenicity to it could come in and cause disease.”
What can make the vaccination process — a staple of poultry farming — go so badly?
Jordan pointed to the sheer volume involved. The average US hatchery processes 200,000 to 300,000 chicks a day, so vaccination is done “en masse,” with 100 chicks at a time placed in a basket and sprayed with vaccine. Problems can occur anywhere in this process, from vaccine storage and expiration dates to the mixing and handling of it.
“Sometimes just something as simple as calculating the dose can go awry,” he noted.
To counter problems in the vaccination process, Jordan stressed that producers need to make sure vaccines are properly mixed and that they are being used at the recommended dose and with the correct diluent. All aspects of the spray cabinet should be thoroughly examined as well, including the pistons, filters and nozzles. Other variables such as droplet size, distance from nozzles to cabinet, air movement and room temperature also come into play.
How to tell that a vaccine is working properly
There are several ways to check whether a vaccine is working properly, according to Jordan. One high-tech approach is thermal-imaging technology, where you “actually watch your chicks get vaccinated” and evaluate the spray coverage. Another technique involves evaluating the spray pattern on plexiglass.
“But ultimately, you have to go in and ‘ask’ the birds,” he said.
This usually involves taking swabs from the birds or euthanizing them and examining the whole trachea to determine the vaccine serotypes the birds were given. The serotypes are then examined 5 to 7 days post-vaccination through real-time polymerase chain reaction (PCR) testing.
Jordan noted that because of technology advancements, PCR testing provides evidence of which vaccines were given, how many birds actually received the vaccine and what level of vaccine they received — all good indicators of how the vaccine will perform.
The PCR testing process
The PCR test looks at those vaccine serotypes that should have been given in the hatchery, such as a Georgia/08 or a Massachusetts vaccine. Most operations vaccinate and test for two serotypes, more rarely for one or three, Jordan said.
Proper testing requires taking 15 samples per sample set, which can represent one or several houses on a farm, Jordan explained. These 15 samples are then used as six sets per one 96-well plate (“the most efficient way to run these plates”), so 90 samples total, which are all tested at once.
“Typically, producers will take samples from one house on six different farms, so we get six different take sets. We can run all those samples at once,” Jordan explained.
“They can be varied across different vaccine days, so maybe one flock was vaccinated on Monday, one flock on a Tuesday and one flock on a Thursday, so we can kind of look at a day-to-day progression within the hatchery.”
This sets the stage for three possible test results. One might reveal “both vaccines had a good take” with 90% or more of the samples positive. A second result might show that one vaccine takes but the other doesn’t — a situation that usually occurs when one vaccine is stored in liquid nitrogen and some of the vaccine is killed in the thawing process. Less often, a more highly attenuated lyophilized, freeze-dried product may not take well — especially if not given at a full dose.
In the third case, where both vaccine takes are poor, Jordan said “that usually indicates there’s a problem with the equipment, with the machinery, the syringes aren’t functioning right, maybe the application volume was too small, the nozzles are too small [or] in the cabinet you’re creating small droplets.”
Troubleshooting poor results
Where one of two vaccine takes is poor, it could be because the vaccine was frozen and was not prepared correctly. Being frozen in and of itself is not the problem ⸺ it’s the thawing and mixing of the frozen vaccine that can create an issue. Jordan said producers must examine their mixing and handling protocols. Items to be checked include the length of time the vaccine is allowed to thaw, the temperature of the water during thawing and the amount of time it takes to use all vaccine once it has been diluted.
Where both vaccines take poorly, all steps in the vaccine process must be examined, beginning with the volume of application, the nozzle flow rate and the pressure on the syringes to force out the vaccine. Producers must then make the necessary adjustments to improve the vaccine application.
In advising producers how to get the best from their vaccine, Jordan said PCR is the best indicator of whether chicks were adequately exposed to the vaccine. So, for facilities that have never done sampling at a particular location, he recommends doing PCR testing to establish a baseline before any adjustments are made in the processes.
Jordan said producers need not fear post-vaccination disease outbreaks as long as they follow proper procedures.
He noted that in well-managed hatcheries, vaccines consistently look good on sampling. Plus, in 5 years of checking vaccine takes, he has seen an improvement in numbers. Nowadays, he concluded, sampling is usually done “not to diagnose a failure but just to spot check and make sure that we’re running optimally.”
Posted on July 26, 2022