There are two of my chickens who are having some abnormal behavior. The first one is Darcy, my large white pullet (unknown breed, maybe Plymouth Rock). I noticed today as she was eating, suddenly a lot of clear stuff came spilling out of her mouth. She had previously been drinking a lot of water and since it is so hot here (almost 100 degrees F), my mother says that perhaps Darcy drank too much water too quickly to try and cool off and she made herself sick. She has done this a few times before, the first time when she was about two weeks. She is currently four months.
The other is a new white Leghorn pullet who has done the same thing a few times. This new chicken spits up like that occasionally, and also, it often poops a very runny and clear liquid, much like whatever she's spitting up. Darcy has also been pooping very runny, but hers is more of a brown color. Is it possible that the new chicken has infected Darcy? I am not keeping them together and the only contact they had was when I put the new chicken in the pen with Darcy and my bantams and she was in there for only a moment - I took her out because the others began picking on her bleeding injuries. The only other way the new chicken could've possibly infected the others was when I held the new chicken and maybe some germs from it got to the others when I held them.
Also, the newest chicken is limping severely and I'm worried that she may have bumblefoot. Here's the foot she's limping on:

Another family member suggested that the new chicken may have a disease called coccidiosis. What is this, how contagious/dangerous it it, and how can I stop the spread of it in my flock? Please help!
The other is a new white Leghorn pullet who has done the same thing a few times. This new chicken spits up like that occasionally, and also, it often poops a very runny and clear liquid, much like whatever she's spitting up. Darcy has also been pooping very runny, but hers is more of a brown color. Is it possible that the new chicken has infected Darcy? I am not keeping them together and the only contact they had was when I put the new chicken in the pen with Darcy and my bantams and she was in there for only a moment - I took her out because the others began picking on her bleeding injuries. The only other way the new chicken could've possibly infected the others was when I held the new chicken and maybe some germs from it got to the others when I held them.
Also, the newest chicken is limping severely and I'm worried that she may have bumblefoot. Here's the foot she's limping on:
Another family member suggested that the new chicken may have a disease called coccidiosis. What is this, how contagious/dangerous it it, and how can I stop the spread of it in my flock? Please help!