3 Life History of American Foulbrood

3.1 Paenibacillus larvae larvae

3.2 Life Cycle

Bacterial spores can be thought of as seeds that assist the bacteria in spreading from one suitable host to another. Spores of Paenibacillus larvae larvae have a remarkably hard outer coat that protects them. The spores can survive outside the honey bee colony for more than 35 years, and are able to withstand very high temperatures, including boiling water at 100^oC. The spores are also resistant to a range of disinfectants.¹⁰

The honey bee larva is given AFB spores in brood food placed in its cell by nurse bees. The larva eats the spores, which then germinate in the larval gut, and turn into the vegetative form of the bacterium.

The vegetative form is in the shape of rods. These rods penetrate the gut wall of the larva, where they multiply, consuming the larval tissues. Death of the developing bee usually occurs either in the pre-pupal stage or just after pupation.

When the vegetative rods have consumed all of the larval tissues, they turn into spores. A single diseased larva contains more than 2.5 billion spores. House bees in the colony try to remove diseased larvae and pupae and in so doing become contaminated with spores. New larvae are infected when they are fed contaminated food.

Spores are the only form of the disease that can infect new, healthy larvae. As well, the spores can only increase in number by infecting a larva. They do not multiply in any other environment (eg., honey or beekeeping equipment).