Infectious Disease
Infectious disease is a broad category encompassing many likely agents assisting in the documented effects associated with Colony Collapse Disorder. For the purpose of this discussion, we will cover the topics of parasitism, as well as bacterial, and fungal diseases.
Parasitism has had a long-standing relationship with the honeybee industry, and the presence of such mites as the Varroa and Acarapis genera have caused great damage to honeybee brood, “...threatening the survival of managed and feral honey bees, the beekeeping industry and, due to the role of bees in pollination, the future of many agricultural crops” (Sammataro, Gerson & Needham 2000:519). Though “Relatively harmless on its natural host, the Eastern honeybee, Apis cerana, the varroa mite has crossed onto the Western honeybee, Apis mellifera, and spread from its Asian origins throughout most of the world” (Allsopp 2007:2). The varroa mite, Varroa jacobsoni, appears to have a clear preference for infesting “...older bee larvae and pupae, with the mite preferring drone brood to worker brood” (Shimanuki, Hachiro & Knox 2000:23). Those honeybees infested with the varroa mite often do not complete their development cycle and die in the pupae stage. Those that do emerge from that state, “...may have shortened abdomens, misshapen wings, and deformed legs and may weigh less than healthy bees” (Shimanuki, Hachiro & Knox 2000:23). It is 
believed that the varroa mite, while directly causing damage to the developing bee, indirectly affects wing shape, as it is thought to be a host to the virus known for causing such specific damage. The varroa mite can significantly impact the livelihood of the hive, as their preference for drone honeybees affects the availability of reproductive males, thereby weakening the overall genetic diversity of the species.
The honeybee tracheal mite, Acarapis woodi, lives exclusively within the trachea of infected honeybees. Symptoms vary, and often mimic those of the varroa mite. Often, the “...affected bee could have disjointed wings and be unable to fly, have a distended abdomen, or both” (Shimanuki, Hachiro & Knox 2000:28). Ultimately, a positive diagnosis of A. woodi is made upon microscopy observation of the trachea. Both parasitic mites have caused great damage to the Western honeybee, Apis mellifera, but have had less of an affect on the European honeybee, leading one to believe that environmental conditions such as temperature and humidity may serve to increase or decrease the mites’ activity. In most cases, beekeepers and scientists use a variety of means to destroy the mite, however such measures often have an adverse affect on the hive as well, since “...bees and mites are both arthropods, [and] many of their basic physiological processes are similar, narrowing the possibilities for finding suitable toxicants” (Sammataro, Gerson & Needham 2000:22).
Bacterial diseases are also of particular concern amongst agricultural entomologists. In American foulbrood disease, Paenibacillus larvae, Infected larvae and pupae, die after their cells have been capped...they may be sunken, concave, dark and at times greasy-looking” (Goodman 2008:1). As a brood related disease, development is arrested before the honeybee has a chance to contribute to the dynamic of the hive, making such a disease severely detrimental to population growth and colony sufficiency. American foulbrood is transmitted through spores, which have been documented as being still being viable even within several decades since release. Because of the spores’ hardy nature, “one method of controlling AFB is to destroy the viability of the spores in contaminated bee equipment. This can be accomplished by gamma or electron beam irradiation or by fumigation with a sterilant gas such as ethylene oxide” (Shimanuki, Hachiro & Knox 2000:6).
Fungal diseases are extremely detrimental, and rather difficult to eliminate once in the hive. Larvae afflicted with the fungal disease, chalkbrood, are easily identified upon gross observation, “...becoming fluffy and swelling to expand and take on the hexagonal shape of the cell” (Goodman 2008:2). The fungus, Ascosphaera apis, causes Chalkbrood and is a disease specifically associated with the brood, in which larvae turn into "mummy-like" casings. While other fungi exist in adult honeybees, and may affect their ability to efficiently collect pollen, diseases affecting the brood are of more immediate concern to scientists, due to the potential for an entire colony collapse from lack of viable offspring.
