Nosema and dysentery are not the same
Yesterday I read the following statement on the blog of a well-known beekeeper. “First I looked at the hive entrances which had signs of nosema the last time I visited. The hive looked just the same – no new nosema on the side of the hive.”
Whoa! There are at least two things wrong with this statement. First off, you cannot see Nosema on the side of a hive. What you can see on the side of a hive is bee feces, which may or may not contain Nosema. More often than not, an accumulation of runny brown feces at the entrance to a hive in spring is honey bee dysentery. Unlike human dysentery, honey bee dysentery is not caused by a pathogen but by poor diet.
It is true that Nosema apis also causes diarrhea-like feces to be deposited in or on the hive, but it cannot be distinguished from dysentery without a laboratory analysis—or at least a microscope and some training.
Secondly, Nosema ceranae, which also can infect honey bees, does not cause the bees to defecate in or on the hive. Most often bees become infected with Nosema ceranae in the summer and die in the field while out foraging. In any case, bees infected with Nosema ceranae do not leave diarrhea-like feces as a clue.
In summary, seeing no feces does not mean the bees are free of Nosema anymore than seeing feces means they are.