Stonebrood
Scientific Beekeeping
Aspergillus spp are saprophytic filamentous fungi frequently found in soil, occasionally infecting living hosts, including plants, insects and mammals. In humans aspergillosis is most commonly seen in immunocompromised individuals. In addition, the aflatoxins produced by this fungus may be carcinogenic if ingested or inhaled, therefore when this disease occurs in bees, some precautionary actions must be taken for the protection of beekeepers. This is particularily true for people undergoing chemotherapy or other immunosuppressive regimes.

Stonebrood is a compulsorily notifiable disease in some countries (not UK). It is a rare fungal condition in brood caused by several diferent fungi including Aspergillus fumigatus (appears grey-green), Aspergillus flavus (yellow-green) and Aspergillus niger (black).

Contamination of the brood is by ingestion of the spores or or by penetration through the larval cuticle. Infected larvae become hardened and difficult to compress.

The literature states that adult bees can be affected. There appears to be no scientific evidence for this.

The best way to prevent this disease taking hold is by keeping strong uncompromised colonies and the keeping of high apiary hygiene standards.

It is interesting to note that that the old treatment for nosemosis, Fumidil B (bicyclohexyl-ammonium fumagillin) which used to be produced by Abbott Laboratories (U.S.A.) was a soluble salt of an antibiotic produced by fermentation of Aspergillus fumigatus. This product had been found to possess a specific activity against the protozoon Nosema Apis. It used to prevent the reproductive stages of the parasites from attacking the epithelial cells of the digestive stomach of the bee.
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Research Methods for Fungal Disease in Apis Mellifera

Excerpt from a comprehensive Veterinary Study on the risks to man of Zoonosis of Aspergillosis spp:
Honey bees (click for full article)
"Microbiological studies on microhabitats within bee hives have shown a high diversity and abundance of Aspergillus species in apiaries [123]. Such close association between fungi and bees within the colony, highlights their potential to cause significant stress on the health of colonies and likewise serious disease in honey bees with weakened immune systems [123]. On the other hand, nutritional limitation, particularly lack of dandelion (Taraxacum officinale plants) and polyfloral pollen, can significantly increase the susceptibility of honey bee larvae when expose to the Aspergillus species [124].

Aspergillus species are known to infect honey bee (Apis mellifera) brood, causing stonebrood disease over all larval stages [125,126]. Stonebrood is a very rare disease caused by several species of Aspergillus. The disease was first de- scribed by Massen (1906) and has since been found world- wide [127]. Aspergillus flavus has most frequently been re- ported causing the disease, followed by A. fumigatus, but also A. niger and other aspergilli can affect honey bees [128]. Species of Aspergillus producing aflatoxin have been suggested to be the primary cause of death in stonebrood- infected honey bees [129], although a negative A. flavus strain was observed to be equally active [127].

The adult bee is infected through the gut after conidial ingestion, although infection might be accounted through the cuticle surface during the larval stage. The conidia then remain in the larval gut until the first defecation event prior to pupation [123]. Infected brood, also called "mummies," can be seen in the combs. Conidia taken up by bee larva may hatch in the gut, growing rapidly to form a collar-like ring near the head. After death the larvae turn black and be- come difficult to crush, resembling small stones and hence the name stonebrood. Eventually the fungus erupts from the integument of the larvae and forms a "false skin." At this stage the larvae are covered with powdery fungal conidia [130], which are yellow, brown, green, or black depending on the species. Worker bees are unable to remove stone- brood mummies from the cells. In some cases, infected or deceased larvae appear dry, but they do not produce visible conidia within 48 h after pathogen inoculation [127].

Aspergillosis of Honey bees is relatively rare, suggesting that conidia are only infective when hives experience an unusual combination of stress factors [131]. In some countries, how- ever, stonebrood is a notifiable disease that has to be re- ported to the authorities if it occurs. Despite above described extensive diseases of Aspergillus species in honey bees and sea fan corals, aspergillosis has not been reported from any other invertebrate animal in natural conditions. This further underlines that Aspergillus is not a primary pathogen like Cordyceps or Metarrhizium but just infections to temporarily susceptible hosts. However, a variety of different insect species have been employed to study fungal pathogen-host interactions [132,133]. Experimental A. fumigatus infection has been investigated in Drosophila melanogaster and Galleria mellonella for A. fumigatus, but these infection models are beyond the scope of the present study."



123 Aspergillus spp. opportunistic parasites in hives and their pathogenicity to honey bees. Vet Microbiol 2014; 169(3–4): 203–210.

124 Foley K, Fazio G, Jensen AB et al. Nutritional limitation and resistance to opportunistic Aspergillus parasites in honey bee larvae. J Invertebr Pathol 2012; 111(1): 68–73.

125 Bailey L. Infectious Diseases in honey bee. London: Land Book; 1963.

126 Gilliam M, Vandenberg JD. Fungi. 3rd ed. In: Morse RA, Flot- tum K eds. A.I. Root Company; 1997, 79–112.

127 Jensen AB, Aronstein K, Flores JM et al. Standard methods for fungal brood disease research. J Apic Res 2013; 52(1): 1–20.

128 Illiam M, Taber S, Richardson GV. Hygienic behaviour of honey bees in relation to chalkbrood disease. Apidologie 1983; 14: 29–39.

129 Burnside CE. Fungous diseases of the honey bee. US Depart- ment of Agriculture Technical Bulletin. 1930: 149.

130 Hornitzky M, Stace P, Boulton JG. A case of stonebrood in Australian honey bees (Apis mellifera). Aust Vet J 1989; 66(2): 64

131 Vojvodic S, Jensen AB, James RR et al. Temperature dependent virulence of obligate and facultative fungal pathogens of honey bee brood. Vet Microbiol 2011; 149(1–2): 200–205.

132. Lionakis MS, Kontoyiannis DP. Drosophila melanogaster as a model organism for invasive aspergillosis. Methods Mol Biol 2012; 845: 455–468.
Definitions:
conidium (conidia pleural)
a spore produced asexually by various fungi at the tip of a specialized hypha.

saprophyte
a plant, fungus, or microorganism that lives on dead or decaying organic matter.