Paenibacillus larvae and American Foulbrood – long since known and still surprising

Abstract

American foulbrood (AFB) is one of the most deleterious bacterial honey bee diseases though affecting only the larval stages of bees. The causative agent of AFB is the Grampositive bacterium Paenibacillus larvae firstly described in the beginning of the 20 th century. Since then AFB has become one of the best-studied honey bee diseases. However many aspects of AFB and the related pathogen P. larvae still remain elusive. This review will focus on three main topics by reviewing both, historical data and new results obtained with modern laboratory techniques: (i) P. larvae and the pathogenesis of AFB, (ii) transmission of P. larvae spores and AFB, and (iii) diagnosis of AFB.Zusammenfassung: Die Amerikanische Faulbrut (AFB) gehört zu den gefährlichsten bakteriellen Bruterkrankungen der Honigbienen. Der Verursacher der AFB ist das Gram-positive Bakterium Paenibacillus larvae, welches erstmals zu Beginn des 20. Jahrhunderts beschrieben wurde. Seitdem ist die AFB eine der am besten erforschten Bienenkrankheiten. Trotzdem sind immer noch viele Aspekte der AFB und des dazugehörenden Pathogens P. larvae unerforscht. Dieser Übersichtsartikel wird sich auf drei Hauptthemen beschränken und hierzu jeweils sowohl historische Daten als auch neueste Ergebnisse vorstellen, die mit modernen Labortechniken erarbeiten wurden: (i) P. larvae und Pathogenese der AFB, (ii) Übertragung der P. larvae-Sporen und der AFB und schließlich (iii) Diagnose der AFB.

The Honeybee Disease American Foulbrood — An African Perspective

“…Aristotle (384-322 BC) described in his Historia animalium a honeybee disease that 'is indicated in a lassitude on the part of the bees and in malodorousness of the hive' (cited in Genersch 2008). AFB cannot be identified with certainty from this description but it suggests that it was observed in ancient times.…”

“…AFB cannot be identified with certainty from this description but it suggests that it was observed in ancient times. In 1769, Schirach, a Saxon naturalist, gave the name 'foulbrood' to a disease among honeybees that was characterized by a foul smell of the colony (Schirach 1769;Genersch 2008). In 1882, a distinction was made between a 'mild and curable' (possibly European foulbrood) and a 'malignant and incurable' foulbrood (possibly American foulbrood) by Dzierzon (1882).…”

“…The bacterial rods then multiply in the midgut before breaking through the gut wall into the haemolymph, killing the larvae (Yue et al 2008). The larval remains degrade to a brownish, sticky substance that eventually dries down to a dark, hard scale adhering tightly to the cell wall containing millions of infective spores (reviewed in Genersch 2008).…”

“…The appearance of clinical symptoms of AFB is influenced by factors such as the age and resistance of larvae, the hygienic behaviour of adult bees that remove infected larvae as well as environmental factors such as temperature, quality and quantity of pollen and nectar (Sutter et al 1968;Rinderer & Rothenbuhler 1969;Rinderer & Rothenbuhler 1974;Brødsgaard et al 2000). AFB not only kills the infected individuals but can be lethal to the colonies if present in large quantities (Ratnieks 1992;Genersch 2008). Hives with light infections may recover but with 100 or more infected larvae the colony is unlikely to survive (Ratnieks 1992).…”

“…One of the mechanisms limiting the spread of P. larvae is filtering of AFB spores by the ventriculus in the bee honey crop so that they are not transmitted to nestmates through exchange of food. This filtering is more efficient in resistant bee strains (Genersch 2008). Hygienic behaviour of bees is another important resistance mechanism at colony level against AFB when bees rapidly detect, uncap and remove infected and dead brood (see review in Spivak & Gilliam 1998a,b;Spivak & Reuter 2001).…”