Each year about this time something infects my flocks. Less than 1 in 20 birds are involved each time and the transmission does not appear horizontal. Some of the flocks are free ranging and some are confined in pens or coops. By time of infection, birds are at least 20 weeks post-hatch and some birds affected are > 2 years old. Both sexes are affected at roughly equal frequency. Affected birds appear drunk as normal leg, wing and tail function is lost. While affected birds are not able to fly up to roost and when I place them there they fall off before night is over. They are also prone to deficate on themselves but much of that appears to due to roosting / sleeping on ground. They show normal interest in food and water although feed intake is slowed. Until recently my birds were kept almost excleusively free range with minimal monitoring so I did not notice and let nature take its course. We had hogs so affected birds were usually culled by hogs. Now that many birds are kept confined and hogs are no longer part of picture so I am taking note. Last three years running I have isolated affected birds and all seem to recover although fullness of recovery has not been evaluated. What are some possible diseases that show such signs?