Morning Emma, yes, sadly this disease is quite prevalent, particularly in finches and we've also had chaffinches and greenfinches with the same problem of Trichomoniasis; at least you are well aware of the situation and have done the right thing by cleaning and disinfecting feeders/ tables and to take away water dishes which is a prime area for passing the parasite on to other birds. Because the finches tend to be flock birds they are more susceptible to it and it tends to rear its ugly head particular during Autumn/Winter months. So far we haven't had a problem this season but I keep a keen eye out for fluffed up appearance, damp looking plumage and particularly if the bill has bits of food stuck to it and the bird is lethargic as you saw. Sadly in smaller birds it is difficult to treat them as the medicine is too strong and usually by the time you see the bird and are able to pick it up it is too late to help it. At least it died in the warmth. According to guidelines if anyone sees this problem and there are two or more birds suffering the same disease then all food and water should be withdrawn for around 3 weeks in order to disperse the birds from the area.
Thanks for bringing this subject up Emma and I'm sorry your finch didn't survive but you did the right thing in its final hours. I had to take one chaffinch to the vet the previous year and have her euthanized as sometimes this disease can last a few weeks and they die of starvation rather than the parasite itself as the lesions block their gullet.
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Regards, Hazel
Just added these helpful pages about bird disease should anyone want more information:
Trichomonosis
Colibacillosis
Salmonellosis