Large lump on two chickens

[00lduncan]

Hi we noticed one of our elderly ex batts was looking quiet and limping two days ago. We checked her over and immediately noticed a big crusty lump/cavity by her tail swollen round the outside and then hollow). We've isolated her and cleaned her wound and we're seeing how she goes. She was passing a lot of fluid yesterday but her appetite has improved and she's eating more solid feed again today. We've just checked the rest of the flock and found a similar lump below the vent/ on the lower belly of another chicken (who is otherwise very well, active and eating, she is a 4 year old Thuringian). We've given Epsom salt baths and palliative care. We thought it was Staphylococcus in the first chicken but now think it might be Marek's. We also had a fairly sudden mystery death about 2 weeks ago. Has anyone seen anything like this before.

 

[KaseySnow]

There was another thread that had a similar looking wound posted a few weeks back. Check it out:
https://www.backyardchickens.com/threads/help-my-chicken-is-poorly.1459322/

Where are you located? That post above was from someone in the UK. Do you have access to an avian vet or maybe have one you could call or e-mail these photos to? Could be tumors, could be a bacteria...perhaps even more likely the latter if you are noticing it spreading.