Hi all 
I've had this slow spreading disease in my flock since I brought some girls home in September, I'll try to keep the story short.
I've been keeping chickens a number of years now, never had a pest or disease problem... I also don't usually buy hens elsewhere, sorta have a hatching addiction.
I bought three easter egger pullets in September. A couple weeks later, one of my free ranging roosters (I had 8) starting wheezing. I brought him indoors, to my quarantine coop, gave him Rooster Booster in his water and Vet Rx in his bedding/under his wings. He got better after a week and a half. That same week, two of my other free ranging roosters went missing, I assumed predators. None of my other chickens showed signs of illness at the time.
I had an acquaintance I sold my first chicks to years ago, and she updates me with pics every holiday season. Very sweet of her. Her update this year said she bought some pullets, around September, they had a bad case of mites and respiratory disease, a few died. I got in touch with her and it turns out we bought pullets from the same person. She thinks they have Mycoplasma Gallisepticum, and she advised injecting .1cc/lb of Tylan to the breast muscle for five days.
A week after her update, two of my serama hens start wheezing. This was the beginning of November. I bring them inside, Vet Rx in the bedding and under wings, vitamins/electrolytes in their water, kept them warm with a space heater. I gave Tylan to the sickest hen, for five days. After the Tylan injections, I swapped the vitamins/electrolytes in the water for Premoxil powder (five days). The sick hen is better but still wheezing, she is still indoors, making friends with my cat/puppy.
About mid November, my friend/acquaintance who advised the Tylan, had her favorite hen (one that I sold her as a chick) pass away suddenly. The hen acted lethargic that morning, so she brought her inside, and by that evening she passed away in her lap. No respiratory symptoms, she said her poop looked normal, she would not eat but drank some water at first.
The three pullets I originally bought seemed healthy, so a month after they came home (October) I put them with my three bigger hens. They were cooped separately from the seramas. On Wednesday, one of the pullets starts acting lethargic. I put together a large box so she would be separate from my wheezing girl, brought her inside, gave her a warm bath, put electrolytes/vitamins in her water. She wasn't breathing funny, just fluffed up like she is sick and sleeping alot. Thursday night she had passed away. It sounded very similar to the way my friend's hen passed.
I contacted the guy we both bought the pullets from, asked if he had anything similar happen to his chickens. He responded by saying he thinks it was caused by mites, and has no idea besides that. He also said he bought the pullets as chicks from Meyer's Hatchery, and they are vaccinated against Mereks. I haven't noticed mites, but I cover the runs with a mix of diaotamaceous earth/ash/soil. My friend said she had a bad case of mites from the pullets she purchased.
My questions are, can mites cause death over 48hours like that? Is there another parasite that might? The lack of symptoms has us baffled, and sad, it was so sudden. I am worried whatever it is is contagious. Would it be safe to administer a de-worming medication along with Premoxil in their water, just to try and prevent further death.
It feels like our chickens are getting hit hard in our little corner of the world, just sucks. All advise is appreciated, thanks ahead.

I've had this slow spreading disease in my flock since I brought some girls home in September, I'll try to keep the story short.
I've been keeping chickens a number of years now, never had a pest or disease problem... I also don't usually buy hens elsewhere, sorta have a hatching addiction.
I bought three easter egger pullets in September. A couple weeks later, one of my free ranging roosters (I had 8) starting wheezing. I brought him indoors, to my quarantine coop, gave him Rooster Booster in his water and Vet Rx in his bedding/under his wings. He got better after a week and a half. That same week, two of my other free ranging roosters went missing, I assumed predators. None of my other chickens showed signs of illness at the time.
I had an acquaintance I sold my first chicks to years ago, and she updates me with pics every holiday season. Very sweet of her. Her update this year said she bought some pullets, around September, they had a bad case of mites and respiratory disease, a few died. I got in touch with her and it turns out we bought pullets from the same person. She thinks they have Mycoplasma Gallisepticum, and she advised injecting .1cc/lb of Tylan to the breast muscle for five days.
A week after her update, two of my serama hens start wheezing. This was the beginning of November. I bring them inside, Vet Rx in the bedding and under wings, vitamins/electrolytes in their water, kept them warm with a space heater. I gave Tylan to the sickest hen, for five days. After the Tylan injections, I swapped the vitamins/electrolytes in the water for Premoxil powder (five days). The sick hen is better but still wheezing, she is still indoors, making friends with my cat/puppy.
About mid November, my friend/acquaintance who advised the Tylan, had her favorite hen (one that I sold her as a chick) pass away suddenly. The hen acted lethargic that morning, so she brought her inside, and by that evening she passed away in her lap. No respiratory symptoms, she said her poop looked normal, she would not eat but drank some water at first.
The three pullets I originally bought seemed healthy, so a month after they came home (October) I put them with my three bigger hens. They were cooped separately from the seramas. On Wednesday, one of the pullets starts acting lethargic. I put together a large box so she would be separate from my wheezing girl, brought her inside, gave her a warm bath, put electrolytes/vitamins in her water. She wasn't breathing funny, just fluffed up like she is sick and sleeping alot. Thursday night she had passed away. It sounded very similar to the way my friend's hen passed.
I contacted the guy we both bought the pullets from, asked if he had anything similar happen to his chickens. He responded by saying he thinks it was caused by mites, and has no idea besides that. He also said he bought the pullets as chicks from Meyer's Hatchery, and they are vaccinated against Mereks. I haven't noticed mites, but I cover the runs with a mix of diaotamaceous earth/ash/soil. My friend said she had a bad case of mites from the pullets she purchased.
My questions are, can mites cause death over 48hours like that? Is there another parasite that might? The lack of symptoms has us baffled, and sad, it was so sudden. I am worried whatever it is is contagious. Would it be safe to administer a de-worming medication along with Premoxil in their water, just to try and prevent further death.
It feels like our chickens are getting hit hard in our little corner of the world, just sucks. All advise is appreciated, thanks ahead.