05/25/2026
There's a virus in 85% of US backyard chicken flocks. For breeders, that number is more like 100%.
Most of the birds carrying it look completely fine. They eat, they lay, they do chicken things. The whole time, they're shedding into the air, into the dirt, onto your hands, onto every bird that comes onto your property.
It's called Marek's, and it is endemic in the US. If you have chickens, you probably have it in your coop.
Here's the part that trips people up: only 3-4% of exposed birds ever develop Marek's Disease, the clinical illness. The other 96% carry Marek's Virus their whole lives and never look sick. The virus and the disease are not the same thing, and having one doesn't mean you'll see the other. So most flock owners never see a clearly sick bird, conclude they don't have Marek's, and move on. That's not how it works.
What Marek's actually does, even in birds that never get "sick," is suppress the immune system. Symptoms may be infrequent and present like other things, such as wry neck or "failure to thrive." Your birds are running at a disadvantage their whole lives and you may never know it by looking at them.
For backyard pet flocks that might mean shorter lives and harder recoveries from other illness. For breeders it means every bird you sell, every bird you buy, every show you attend is an exposure event. The virus spreads through feather dander. It travels in a cardboard box. It comes in on the feet of passing crows. It lives in a coop long after an infected bird is gone. It is unavoidable, and if you have chickens long enough, you WILL have Marek's exposure.
There's no cure. It's a herpes virus, and once they have it, they have it for life. Vaccination reduces clinical disease but doesn't prevent infection or shedding. Once it's in your flock, it's there. Statistically, you should assume it is there, whether you see it or not.
I'm not telling you this to scare you. I'm telling you because when I figured it out, I wished someone had just said it plainly a LOT sooner.
More on what we do about it this week.
If you didn't know this, share it. Someone in your chicken groups needs to see it.
