There could be several weeks or months between the actual infection and outbreak (= first visible symptoms), depending on the condition of the colony and the bacteria strain; there are five different documented genotypes in Austria).
American foulbrood (AFB) is a highly contagious, bacterial infection of the bee brood, which leads to the death of the brood, Typical clinical symptoms are: patchy hive; sunken, holey, moist, shimmering cell caps; left over, closed brood cells; light to dark brown, thread-like, slimy substance in the cell; sticky scabs in the lower channel of the cell; and the possible characteristic of a glue-like odour to the slimy substance.
Progression of Disease
The larvae are infected by ingesting the spores together with their food. Larvae that are one to two days old can be infected. The spores develop into rod-shaped bacteria in the larvae’s mi-gut area after 24 hours. There, the bacteria reproduce on a massive scale for one to four days after the infection. They subsequently manage to break through the intestinal epithelium in some places, moving between the intestinal epithelial cells into the larvae’s body cavity in large numbers. Should this happen, the larvae will die. The rod-shaped bacteria then turn into spores. Spores may already be produced in limited numbers at the beginning of the infection.
Depending on the foulbrood strain, the larvae that already die at an early stage (prior to cell capping) are removed by worker bees responsible for cleaning the hive to differing levels. Thus, the disease’s symptoms could become apparent through more or less extensive breeding holes, depending on how much of the infected brood has been removed before cell capping. Should this be the case, it can be difficult to diagnose American foulbrood in the colony (thus, always look out for a brood nest with holes!). The typical symptoms for American foulbrood only become visible when the larvae die after the cell closes: the slimy substance, which can dry later and form scabs.