Harrogate and Ripon Beekeepers Association has a microscopist and Disease Liaison Officer, Dave Rennison, who will examine samples of your bees for adult bee diseases (i.e. not brood diseases like EFB and AFB!) if you are concerned about them. Acarine and nosema are the most common, and micro examination of samples is the usual method of diagnosis.
The service operates by post and is free to HRBKA members, but please ensure that your sample of bees is packed in paper and cardboard, not plastic and also that your package carries the correct postage. A sample of about 30 bees is required; preferably alive but if dead, as fresh as possible. If alive, put a couple of sugar lumps in with the package.
Please telephone Dave (contact details in the Members' Handbook) before posting to ensure that he is at home. A big matchbox makes the ideal packing and if sending more than one sample you should mark each with the hive that it came from. Your e-mail address would also assist communication. Advice on disease prevention and treatment and also sample collection method is available if you need it.
Articles on bee health regularly appear in The Apiarist - the association's quarterly magazine. The February 2014 issue contains an article by Joe Dod discussing thymol in feed given to bees, which makes reference to a paper on the subject of the effect of thymol on nosema, which you can download.