8 month old pullet lost interest in roosting, eating, drinking- six others seemingly not infected

[Chikinlovin]

I have 7 pullets all together. They are egg layers and I've had them since they were chicks. Mornings ago I noticed one pullet did not leave the roost when I brought scraps out. Later I noticed it just hunched on floor of coop. This morning it was in a nesting box but this evening while six others were roosting it was sitting on floor. All seven were once laying but now only four with darker days and colder weather. I am thinking this is an infection from unclean and slightly crowded conditions. I will be disinfecting everything tomorrow. I never expected having 7 at this point. So I am weary of them all doing well together. Do I think this is an infection and treat with corid? Do I treat all of the chickens. I do not have a lot of options available but I want to do what is right for the chickens. Any thoughts would be greatly appreciated!!

 

[Chikinlovin]

UPDATE... I've cleaned the coop entirely. We've had a lot of wet conditions lately. The ill pullet passed away today while I was cleaning. I had placed her under a warm light in a nesting box while I cleaned, but she didn't last long. The other chickens all seem fine. I haven't done any sort of treatment with them. Is this isolated? I never found blood in stool, but the ill pullet did have a lot of white liquid/diarrhea seemingly leaking out. Any one have any ideas? Am getting ready for winter and want happy chickens!

 

[Smoochie]

Did it look normal?

http://chat.allotment.org.uk/index.php?topic=17568.0

 

[Chikinlovin]

She looked mostly normal... I thought maybe her comb was getting a little shriveled. But she didn't eat/drink for a few days either. She was hunched for the two days prior.

 

[Smoochie]

I would treat the flock for coccidiosis just to be safe.