FLS has been reported across the world over the past decade, but it has only relatively recently been discovered in North America.

The condition was first found in Canada, and cases started to pick up in 2017, according to Karen Grogan, DVM, MAM, ACPV, clinical associate professor of avian medicine at the University of Georgia’s Poultry Diagnostic and Research Center.

It slowly spread from Canada through the primary layer-producing areas in the US like Pennsylvania, the West Coast and the Midwest, before the first case was reported in Georgia in July 2019.

The condition prevents laying hens from producing eggs, but birds display few outward signs of ill health and develop ordinary combs.

“The birds look like they’re still in production,” Grogan told Poultry Health Today. “[I like to call them] freeloaders, meaning they’re eating off the feed, but they’re not laying any eggs.”

One sign that occasionally presents is a “penguin’s stance,” where birds’ abdomens are so filled with cystic oviducts that they stand upright and waddle when they walk.

In one case Grogan uncovered on a commercial caged farm, affected birds tended to sit toward the back of cages.

During post-mortems, left oviducts were found to be very large and filled with fluid, and were no longer active.

The bird’s ovary appeared normal with follicles developing. “Sometimes those get released, and you can see secondary peritonitis that will form because the yolk material goes into the abdomen,” Grogan said.

“But there’s not a lot of extra clinical signs except for this — it’s called cystic salpingitis. So that’s the main clinical finding that we see.”

It is believed that the condition is brought about following a very early exposure to an IBV — thought to be DMV/1639 in North America — potentially in the first week.

“That virus goes in and creates changes to the epithelium of the reproductive tract. And those changes are what we feel like we were able to show in adult affected layers,” Grogan said.

“But what we don’t know exactly is sort of what that timeline is, or when birds are actually infected, and then exactly when those pathological changes occur.”

Work is now underway to try and determine the exact pathogenesis. “We’re trying to figure out exactly how it happens,” she explained. “What we do understand is that this FLS is sort of an endpoint clinical sign.”

Grogan also highlighted the importance of taking good samples to aid diagnosis. “It really helps us to go to the barn to collect samples, so we can see for ourselves. So that’s the best.”

But if that’s not possible, taking as many samples as possible and preserving in formalin or freezing is sound advice. “That’s one thing I’ve learned.

“Yes, common things are common, and most of us are pretty good at figuring out the common things, but every now and then you get something that is a zebra. So take extra samples to catch the zebras.”