P. larvae is a rod-shaped bacterium that causes American foulbrood (AFB), a destructive disease of honey bee colonies. The origin of AFB is unknown, but it is found worldwide. Bees move spores around the hive a...
P. larvae is a rod-shaped bacterium that causes American foulbrood (AFB), a destructive disease of honey bee colonies. The origin of AFB is unknown, but it is found worldwide. Bees move spores around the hive and robber bees can assist in the transmission of spores between hives. Beekeepers may also spread the disease by moving equipment from contaminated hives to healthy ones (Lindstrom et al., 2008; OIE, 2013a; Ministry for Primary Industries, 2013).
This disease is on the list of diseases notifiable to the World Organisation for Animal Health (OIE) and is a notifiable pest according to DEFRA (DEFRA, 2011; FERA, 2013). The disease and pathogen are included in the Invasive Species Compendium because of the OIE listing.
Paenibacillus is a genus of Gram-positive, facultative anaerobic, endospore-forming bacteria. Members of this genus were originally included in Bacillus, until reclassification separated them into a distinct genus in 1993 (Ash et al., 1993).
Paenibacillus larvae causes American foulbrood in honeybees (Apis mellifera). Previously, American foulbrood and powdery scale disease were considered distinct (Graaf et al., 2006), but this is no longer valid and the pathogenic agents, Paenibacillus larvae subsp. larvae and Paenibacillus larvae subsp. pulvifaciens, were reclassified as one species, Paenibacillus larvae (Genersch et al., 2006), although the subspecies are still referred to in the literature.
American foulbrood has a worldwide distribution (D’Alessandro et al., 2007) and cases have been reported in almost all the beekeeping regions of the five continents (Antúnez et al., 2004). It appears to be uncommon or even absent in significant parts of sub-Saharan Africa (Fries and Raina, 2003), but has been reported from some countries there (Hansen et al., 2003).
Studies have shown geographical clustering of different genotypes; for example Peters et al. (2006) reported non-random distribution of five different genotypes in the district of Arnsberg, Germany.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
P. larvae is already present in most regions where honey bees are kept, but spread on a more local level is still a concern.
It is the spores that are the infectious agent; they can be spread from colony to colony by transfer of wax, queens, combs or honey (OIE, 2013a).
Recent studies have also shown that small hive beetles (Aethina tumida) are vectors of P. larvae and should be considered in control programmes for American foulbrood where both pests are present (Schäfer et al., 2010).
Robber bees may enter a hive that has become weakened by AFB infection and take contaminated honey back to their hives, so assisting disease spread to other colonies and apiaries. Studies have shown that transmission of AFB between apiaries can occur within 1 km from clinically-diseased colonies in the absence of robber bees, but over longer distances when they are present (Lindström et al., 2008).
The movement of bees, equipment and supplies worldwide has assisted in spreading bee diseases to all areas where bees are raised (OIE, undated).
P. larvae are Gram-positive, rod-shaped, round-ended and spore-forming bacteria. They are only visible under a high-power microscope. They vary greatly in size, being 0.5 μm wide and between 1.5 and 6 μm long; they occur both singly and in chains and filaments. Some strains are motile. Spores contaminate bee larval food and larvae ingest and become infected by the spores. The spores germinate in the larval gut and the vegetative bacteria are nourished by the larvae. Before the vegetative form of the bacterium dies, millions of spores are produced and can be spread to other bees. (OIE, 2013a; Pennsylvania Department of Agriculture, undated).
Studies have shown geographical clustering of different genotypes. Peters et al. (2006) reported five different genotypes (AB, Ab, ab, aβ and A) in Arnsberg, Germany in studies between March 2003 and October 2004. Two genotypes were found in one hive and it was reported that the five genotypes were not randomly distributed in the district.
American foulbrood is a serious disease of honey bees worldwide and causes considerable economic losses (Basualdo et al., 2008). This disease has caused a significant decrease in honeybee populations, beekeeping industries and agricultural production (Antúnez et al., 2010). Honey bees are important to the agricultural and horticultural sectors as pollinators -- the value of pollination is estimated to exceed the value of products from beehives many-fold (Delaplane and Mayer, 2000) -- so any disease causing decline in bee populations will have a significant impact on their role in these industries.
A decline in bee numbers has been attributed to American foulbrood, amongst other bee diseases. Bee decline will have a significantly negative affect on pollination within habitats that rely on these insects for development (Delaplane and Mayer, 2000).
Impact on Biodiversity
A decline in native bees due to the spread of American foulbrood will have a negative effect on bee biodiversity (Cuthbertson and Brown, 2009).
The effect of American foulbrood outbreaks on honeybee health will also have a significant impact on honey products and thus the livelihood of beekeepers.
Chirila F; Fit N; Rapuntean S; Nadas G; Nistor AC, 2011. A study regarding the Paenibacillus larvae strains sensitivity isolated from some counties in Transylvania to different antibiotics and vegetal essential oils. Cluj Veterinary Journal, 19(1):60-64.
OIE, 2009. World Animal Health Information Database - Version: 1.4. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int
Roussenova NV, 2011. Antibacterial activity of essential oils against the etiology agent of American foulbrood disease (Paenibacillus larvae). Bulgarian Journal of Veterinary Medicine, 14(1):17-24.
