American foulbrood

American foulbrood (AFB, Histolysis infectiosa perniciosa larvae apium, Pestis americana larvae apium), caused by the spore-forming Paenibacillus larvae ssp. larvae (formerly classified as Bacillus larvae), is the most widespread and destructive of the bee brood diseases.

Paenibacillus larvae is a rod-shaped bacterium, which is visible only under a high power microscope. Larvae up to 3 days old become infected by ingesting spores that are present in their food. Young larvae less than 24 hours old are most susceptible to infection. Spores germinate in the gut of the larva and the vegetative form of the bacteria begins to grow, taking its nourishment from the larva. Spores will not germinate in larvae over 3 days old. Infected larvae normally die after their cell is sealed. The vegetative form of the bacterium will die but not before it produces many millions of spores. Each dead larva may contain as many as 100 million spores. This disease only affects the bee larvae but is highly infectious and deadly to bee brood. Infected larvae darken and die.

Until 1906 American foulbrood was not differentiated from European foulbrood, and the condition was simply referred to as foulbrood. Thereafter, the terms European and American were used to distinguish the diseases. However the designations do not refer to the geographical distributions but to the areas where they were first investigated scientifically. In 1907 it was demonstrated conclusively that a bacterium called Bacillus larvae was the cause of American foulbrood disease by fulfilling Koch's postulates. The geographical origin of AFB is unknown, but it is found almost worldwide.

Lab testing is necessary for definitive diagnosis, but a good field test is to touch a dead larva with a toothpick or twig. It will be sticky and "ropey" (drawn out). Foulbrood also has a characteristic odor, and experienced beekeepers with a good sense of smell can often detect the disease upon opening a hive. However, this odour may not be noticeable until the disease is in an advanced stage. Since response and treatment is required as early as possible to protect other colonies, absence of odour cannot be relied on as indicating absence of foulbrood. Only regular and thorough inspection of the brood can identify the disease in its early stages.

The most reliable disease diagnosis is done by sending in some possibly affected brood comb to a laboratory specialized in identifying honey bee diseases.

When cleaning infected cells, bees distribute spores throughout the entire colony. Disease spreads rapidly throughout the hive as the bees, attempting to remove the spore-laden dead larvae, contaminate brood food. Nectar stored in contaminated cells will contain spores and soon the brood chamber becomes filled with contaminated honey. As this honey is moved up into the supers, the entire hive becomes contaminated with spores. When the colony becomes weak from AFB infection, robber bees may enter and take contaminated honey back to their hives thereby spreading the disease to other colonies and apiaries. Beekeepers also may spread disease by moving equipment (frames or supers) from contaminated hives to healthy ones.

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Wikipedia