All this about MS, MG, etc. got me wondering what is was. So I went to the university library for some research. I found 12,106 published papers with 2812 devoted to poultry science. I only read a few but I did find this one which pretty much says that medication after infection just eases the symptoms of the flock but doesn't cure the disease. That supports what some here have said about the hens becoming carriers.
The best solution is biosecurity which means keeping the disease out in the first place. Another paper I read describes an experimental commercial farm with over a million birds that has been disease free for over 15 years. They use dedicated apparel when going into the barns, so each of their barns has a clean changing room for the workers who can only enter thru a single point entry.
Us backyard chickeneers can do a similar thing with a little bleach and hand sanitizer. I have a dedicated pair of slip-on shoes that I wear in the coop and nowhere else. Also going to stock up on those pocket size hand sanitizers.
If anyone is interested in learning more and does have access to Web of Science or a University library, let me know and maybe I can help.
The following cited electronically from Halle Library, EMU, 18 NOV 2011.
Title: Control of Avian Mycoplasma Infections in Commercial Poultry
Author(s): Kleven S. H.
Source: AVIAN DISEASES Volume: 52 Issue: 3 Pages: 367-374 DOI: 10.1637/8323-041808-Review.1 Published: SEP 2008
Times Cited: 5 (from Web of Science)
Abstract:
"Control of pathogenic avian mycoplasmas can consist of one of three general approaches: Maintaining flocks free of infection, medication, or vaccination. Maintaining flocks free of pathogenic mycoplasmas consists of maintaining replacements from mycoplasma-free sources in a single-age, all-in all-out management system. Good biosecurity and an effective monitoring system are necessary aspects of this program. Medication can be very useful in preventing clinical signs and lesions, as well as economic losses, but cannot be used to eliminate infection from a flock and is therefore not a satisfactory long-term solution. Vaccination against Mycoplasma gallisepticum (MG) or M. synoviae (MS) can be a useful long-term solution in situations where maintaining flocks free of infection is not feasible, especially on multi-age commercial egg production sites."