Going to be a little long. Let me preface this by saying I am not a poultry expert. Far from it. Just my recent experience. Nearly two years ago the family and I drove 2 hours to a hatchery to pick up some chicks that were not your common variety tractor supply chicks. Got some Ayem Cemani's, Mille d'Uccles, Apenzeller Spitzhauben and Easter Egger/Ayem Cemani mix. Ended up getting a few more locally over the last few months for a total of 15. No problems so far. These are more pets than anything else. They stay in a 10X20 dog fence with wire on the top to keep out predators. They are not let out to free range. 2 weeks ago I bought 19 different breeds for Tractor Supply for mainly egg purposes. 10 days ago I noticed one of the Spitz's had tracheal rales and and a cough. The Mille d'Uccle rooster had a sneeze and sounded like he had laryngitis. Quarantined them two. I wanted to know what is going on. None of the local vets are poultry experts, but one of them has a few chickens and said she will look at them. Carried them in. She took a swab to send off to the state lab, checked a fecal sample, and prescribe Tylan to mix in the water. Told me to let them free range some to improve their diet. Got a call later in the week. They were positive for mycoplasma gallisepticum. A bacterial infection that is treated with antibiotics, but also makes them lifetime carriers even after antibiotic. And it is easily passed to other poultry and birds. Her words were "It is no big deal. They will need to be quarantined and I did speak with someone at the state to ask about when you can start back eating the eggs. There is a 28 day wait period after the last day of antibiotics. You can however scramble the eggs in the meantime and give it to the chickens for protein. I also asked him about the chicks you bought and he said more than likely they have already been exposed. It's also a reportable disease to the department of agriculture so she told me someone from the state would be in contact." Guy called Saturday to arrange a meet time. More on that later. A couple of days later the vet called back and said to start treating the whole flock with the Tylan as they were most likely already exposed.
Back on February 9, my wife sent me text saying my chickens had competition along with a picture of hundreds of migratory black birds in the trees, on the ground etc. This was along the time we had all those days of rain. Chickens can have mycoplasma gallisepticum (MG) for a long time and not have any symptoms. Stress is a triggering event. It can be as simple as a change in weather or relocation. MG has an incubation period of 4 to 21 days. Remember me saying it is easily passed along to other poultry, birds? What I *think* happened is that some of those black birds passed it along. It can be as simple as flying over the pen and taking a crap that lands inside or sneezing . To quote the poultry site, "Transmission may be transovarian, or by direct contact with birds, exudates, aerosols, airborne dust and feathers, and to a lesser extent fomites." Either way, I'll never know for sure. Also noticed that one of the hens inside the fence has a sneeze. That makes 3 with symptoms. Having said that, my neighbor 4 houses down has chickens as well. He bought them within the last year. Could have been them too. Don't know. I have a friend that owns chicken houses. He's said some diseases could be transmitted by something as simple as a fly coming in on the chicken truck to deliver chickens to the houses that can cause a lot of problems.
Having been told what they had, of course I used Google Fu to find out more even though the vet filled me in on most of it. It's not zoonotic. No harm to humans. You can eat the eggs (unless they had antibiotic then you have a wait period) and the chicken. Again, they will be lifelong carriers and it is easy to pass on to other poultry and birds. It's common in backyard flocks. One website stated around 30%. Guy from the agriculture department calls Saturday and arranges a time to come out. Comes out after lunch. I thought he would come to the chicken coop/fence. He didn't as he had been around chicken houses. Chickens are quarantined for 45 days after the end of symptoms. After that I could let them free range if I wanted as the vet recommended. I took the opportunity to ask and reaffirm what I had read. He stated "You can eat the eggs and the chicken. It doesn't affect humans. It's one of the more common infections in backyard flocks." I mentioned the 30% number in backyard flocks I had read and he stated "It's probably more than that. Most people don't carry their chickens to the vet because if they have something it may reportable and their flock is quarantined so most people won't even go to the vet to avoid that. Let me tell you what the department did about 20 years ago right after Hurricane Floyd. They did this behind the scenes because they didn't want people to get mad and upset that their chickens were being tested. We went to the State Fair where people show their animals and swabbed poultry. 70% came back positive for mycoplasma gallisepticum." I asked him if I could put the two chickens in quarantine back with the other since I was treating the whole flock. He said "I would because they most likely have it anyway." I also told him these were more pets than meals so he asked if one died what I would do with it. I told him bury it. He said you could "bury it or incinerate it if you don't want to eat it. Either one is fine."
Bringing this to a close. When the chicks are fully feathered they will be outside in their own coop. As the vet said the man from the state she spoke with stated, more than likely they have already been exposed. So, these will be closed flocks. All in- All out. No new ones in and none out. They will die here. I don't sell hatching eggs or chickens. As stated they are mostly pets, but my original intent (and still is) is that if the SHTF I would have a source of food. I had read on Backyardchickens.com that a lot of people culled their entire flock and started new after cleaning and waiting a few weeks. I didn't know why until I investigated further. Those that chose to do that were either selling hatching eggs or sell chickens for profit and didn't want to expose other birds to MG. YOU DO NOT HAVE TO DO THIS IF YOU ONLY WANT YOUR CHICKENS FOR EGGS AND MEAT. This is for MG only. I do not know about other diseases. For those of you that are interested in starting a flock AND MAY BE INTERESTED IN SELLING HATCHING EGGS OR CHICKENS, I suggest you do NOT go to the local auction house, the local farmer/neighbor/Craigslist, etc selling/giving away chickens. Go to a local hatchery (Dragonfly farms in Hillsborough is AWESOME). Tractor Supply chicks are fine I would think but buy them in the store, not the parking lot. Having said that, you can take all the biosecurity measures you can to protect your flock, but all it takes is a wild bird that has MG fly over your flock and take a dump on it, drop a feather, or sneeze nearby.
Addendum- Also meant to state that MG does not live in the environment long. Typically about 3 days.