Research from Ceva Animal Health suggests that eggshell rinses may be a viable, accessible way to detect infectious bronchitis virus (IBV) infection in layer flocks experiencing egg quality abnormalities.
IBV is a ubiquitous viral pathogen of chickens that causes an upper respiratory disease, which can result in production drops and egg abnormalities in layer flocks. Infection with the virus is associated with wrinkled shells, which can mean affected eggs can’t be sold on the table egg market.
Limits to current testing
Diagnosis of IBV is usually done using tracheal or choanal swabs and reverse-transcriptase quantitative PCR (RT-qPCR). However, there are limits to this approach because, due to biosecurity requirements around avian influenza, experts are sometimes not allowed to visit farms to collect swabs.
Another issue is the large distances between facilities, particularly after the increase in free-range and pasture farming, which sometimes means technicians can’t get to acute calls immediately. Additionally, when infections are suspected on heritage breed or breeder farms, each bird is quite valuable, so euthanizing solely for diagnostic tissue samples is potentially economically damaging.
New options are needed, and Linnea Tracy, VMD, MPH, MAM, dACPV, from Ceva Animal Health, set out to determine whether egg rinses or egg components could provide an accurate diagnosis when it is not possible to visit farms experiencing acute clinical signs.
“People are already doing this as a diagnostic methodology in the field; this isn’t some wacky idea. We were just looking at this to see if we could quantify it against the more formal testing that we usually do,” Tracy said.
Testing from a range of farms
In research carried out at Ceva’s Scientific Support and Investigation Unit (SSIU) laboratories in Kansas, Tracy collaborated with Wilson Veterinary Company, receiving whole eggs and on-farm egg rinses from layer flocks experiencing shell-quality abnormalities consistent with IBV infection. Farms also submitted tracheal swab pools and some cecal tonsils from the same flocks.
The submissions came from six states and represented 11 farms, 30 total layer houses, as well as one central egg belt and one processed egg belt. All sampled flocks were previously vaccinated with both live and inactivated IBV vaccines. Veterinarians performed individual egg rinses on a total of 5 eggs by agitating eggs one at a time in a sterile Whirl-Pak bag containing 10mL of BHI broth, a medium used for culturing microorganisms, until 5 eggs had been rinsed per bag.
Rinses compare favorably
For the first part of the laboratory studies, Tracy tested the egg rinses, as well as egg membrane, albumin and yolk, for IBV by RT-qPCR, which was designed to detect eight widely circulating and vaccine strains of IBV.
She found that 95% of egg rinses were positive for IBV. All cecal tonsils from egg-rinse-positive flocks tested positive, while 69% of tracheal swabs and 39% of egg components were positive. This highlighted the sensitivity of the egg rinse approach.
“Egg rinsing is a viable testing methodology. You can’t fully correlate it to tracheal positivity, but at times when you can’t get to a farm on an acute basis, it’s a great alternative option if you need to ask someone with limited technical knowledge to sample the birds for you,” Tracy explained.
Viral passage to reproductive system
Of the 7 egg component positives, 6 shell membranes, 3 albumin samples and 1 yolk sample were positive. Tracy identified predominantly the DMV1639 strain from these samples, as well as strains not in the typing panel.
“That shows us what we expect in an acute viral infection, that the virus will go throughout the body. But it also shows us that there are viruses that are still impacting the reproductive system of these birds that are floating around in the wild,” Tracy explained.
“Layers are something of a sentinel bird for mutations and recombinations in IBV because they’re so long lived, so they have the potential to incubate various changes and cause new strains to emerge.”
Shell virus can pose threat
The second aspect of the study saw Tracy inoculating embryonating eggs with samples from positive egg rinses, then extracting from the eggs to assess virus viability. The results provided food for thought for an industry with high product movement.
“The egg industry is very complex, with a lot of egg trading going on, and diversifying systems with smaller farms funneling free range or pastured eggs into a plant that might be processing them on an inline facility. Is that a biosecurity risk? The question to ask there is, is that virus still alive?” she said.
“We were actually successful in pulling live virus out of a sample, which indicated to us that some of the virus that is landing on those shells as they’re laid may actually still be viable.”
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