My experience and research regarding Trichomonas:
This can be very complicated depending on the severity. If caught early it can be treated successfully. Without any technical is plainly a parasite (a protozoan). It is not like the internal parasites like roundworms and does not respond to normal deworming. This protozoan is transmitted from an infected bird to another through water contact. There was a lot of trouble with this in the carrier pigeon and racing pigeon world (I have a link with some techincal research info on if anyone is interested). Not only do you need to think about your flocks drinking from the water sources you have for them, but wild birds as well. If it is at all possible that they could share water sources with wild birds then it is possible to get an infected bird in your flock.
There are 2 trains of thought about the water, you can refresh the water so that it does not sit for more than 2 hours or use a sanitizer (like chlorhexidine or oxine) or Apple cidar vinegar. The ACV makes the water too acidic for the trichomonas to multiply and the oxine and chlorhexidine work in a different fashion with the same results. These water additives work on a plethera of other bacteriums and parasites that use water to mutliply or spread. So all around, a good idea. Which leads me to ponder about whether the same can be said for running water sources (like lakes vs creeks or rivers).
Signs of illness:
Yellow plaque that forms in the mouth..can be in the back of the throat, side of mouth, roof of mouth. You may see a bird that seems to have trouble eating or a misaligned beak or even a shriveled waddle or uneven look to the face when comparing one side to the other. The plaque forms as the body tries to make an immune response to the protozoan. This plaque can be the death of the bird. It can block the wind pipe or make it too difficult to get food to the back of the throat to swallow. You may only see that the bird is getting thin..this is when you MUST, no matter how difficult, look in the mouth. If this is left unnoticed or untreated it can spread to the organs and cause organ damage and eventually death. This is what makes this disease so tough, early detection is everything. I believe that my hen had been showing signs for many months before I had the right advice that lead to her diagnosis. (hind sight is 20/20) Of course, there ways to swab and culture the throat, but this can be expensive and most of the time you need to know what you suspect the problem is, to be sure you run the right test.
Metronidazole to kill the trichomonas and supportive therapy to be sure they get all the nutrients they need. This may include tube feeding or finding foods that the bird can successfully eat on it's own. The bird should be able to drink unless the beak is severely misaligned. As with any disease, it is important to provide vitamins and additional protein to help the immine system do it's job. Vitamin supplements to add to the water are available. When it comes to giving medications to a bird, like the metronidazole (in this case), should not be given in water. It is proven to decrease the amount of water intake and decrease the dosage that the bird gets. Lowered dosages of medications may not work. It is easily done if tube can simply add to the food. If not tube feeding then you will need to be creative, mix with foods that the bird will gobble up every bit.
Note on tube feeding: This should be done with instruction and can cause food to accidentally enter the lungs, in effect, suffocating the bird. Prior education is a must before attempting. Only if the bird cannot or will not eat any food on it's own.
Swab any plaque you can see with Iodine (povidone, betadine..same stuff) you may need to swab way back in the throat if you can see plaque there. Swab twice daily atleast, 3 or 4 times is better.
Treatment can be difficult since the bird will likely be doing pretty well and fighting you if you caught it early. But persistance will win over the disease. It is always easier when the birds are so ill that they don't have the energy to fight you, but that is a bad prognosis.
I have learned about this on my own, with help from several chicken vets and friends. My experience was not a good one and my beautiful hen passed away, but I learned a lot. After 2 weeks of medicating and tube feeding her body gave up and in the end, she had been ill so much longer than I thought, that it had spread to her internal organs. I have been fortunate to have learned enough to save the rest of my flock that had been with her through many months of her dealing with this (and me not knowing). I suspect that she got it form a wild bird cause I used to put their waterers out in the middle of the yard where any bird could drink out of them (and would, I thought it was cute that the wild birds would use the chicken waterers). I have now switched to plastic waterers, use oxine (and will use ACV when I run out of that) and I am always inspecting my chickens mouths. I am being very vigilant so that I do not have to go down this road again.