Nosema Microsporidia can be divided into further, more distinct classifications: Nosema ceranae and Nosema apis. Nosema ceranae is currently the largest threat to bees worldwide.
Domain: Eukaryote; Phylum: Microsporidia; Class: Dihaplophasea; Order: Dissociodihaplophasida; Family: Nosematidae, Species: N. Ceranae [Others may be used. Use NCBI link to find]
Description and Significance
This microbe exists within honey bees. This microbe is parasitic and its existence in and among honey bees is resulting in the decline of bee populations. The beekeeping industry has also been severely impacted because this microbe has caused the decline of the bee population and is one of the top threats against bees. Many of these losses are attributed to Colony Collapse Disorder (CCD), characterized by high levels of mortality in bee colonies, and one of the major causes of CCD can be linked to pathogens and diseases, specifically N. ceranae. Currently, N. ceranae is the leading microsporidian parasite among North American and European bees, and it can be detected from bee samples and from bee fecal samples under a microscope. 
In the last decade, the health and population of bees have steadily been on a drastic decline due to multiple factors, with one of the most prevalent factors being Nosema. Rising nosema infections are especially potentially detrimental due to bees' extreme vitality to the survival and success of ecosystems.
This microsporidian is an obligate intracellular parasite of adult honey bees. A substantial fraction of the "diminutive N. ceranae proteome consists of novel and transposable-element proteins." The proteins that are in N. ceranae include the following: NcORF-00033, NcORF-00145, NcORF-00146, NcORF-00663, NcORF-00705, NcORF-00710, NcORF-00711, NcORF-00832, NcORF-01760, NcORF-00417, NcORF-00673, NcORF-01632, NcORF-01880, and more, all of which explain the behavior of the parasite itself and explain what causes this behavior. For example, some of the proteins descriptions are as follows: heat shock protein that plays a role in protein translocation, putative transporter of the ATP-binding cassette (ABC) family, implicated in pleiotropic drug resistance, mitochondrial superoxide dismutase and protects cells against oxygen toxicity, and a protein of the mitochondrial outer surface that binds to and promotes degradation of mRNAs for select nuclear-encoded mitochondrial proteins. Some proteins listed above interact with host proteins and host tissue. Researchers identified 2.624 putative protein-coding genes, and their predicted number of protein-coding genes is between 1,996 and 3,804. The recorded average density of genes on the 100 largest N. ceranae contigs was 0.60 genes/kb, which is lower than what was found in E. cuniculi, which is microsporidian parasite that affects rabbits, (0.94 genes/kb) and Antonospora locustae, which is another closely related microsporidian parasite, (0.97 genes/kb). In regards to gene sequence, N. ceranae is AT and relatively CCC rich and low in GC, which seems to be a common feature among microsporidians. N. ceranae also appears to be very low in G and C, individually (around 26%) and high in A and T, individually (74%). 
Cell Structure, Metabolism, and Life Cycle
Spores are ingested and invade the gut epithelium instantly following germination. Intracellular meronts thus lead to mesospores that invade nearby cells following host-cell lysis. After passing through the gut, these exospores are excreted and easily infect other hosts. Compared to N. apis, another type of nosema that affects bees and the lifespan, N. ceranae lives after it proceeds through the gut while N. apis lives in the gut, is not excreted, and moves on to infect other tissues in the bee host. 
N. ceranae has been involved in studies that seek to understand how the lifespan of the host is altered, and the parasite was shown to increase the daily mortality within a colony by a factor of 1.99. Between days 1 and 14, 75% of bees were alive. However, the number of surviving bees within the colony dropped below 50% by 16 days of age. Most of the test control bees died 9 days after infected bees, displaying that the parasite causes a much shorter lifespan for its hosts. N. ceranae was also seen to cause premature foraging among its infected hosts and mortality of worker bees. Among infected older bees, the juvenile hormone (JH) was at abnormally high levels and the yolk precursor protein (vitellogenin) was at low levels, and the opposite was true for the young infected bees, which is extremely abnormal for bees. Vitellogenin and JH put the transition from nursing as a young bee to foraging outside the hive under regulatory control, and the abnormal levels of these in bees results in abnormal behavior and might be yet another underlying factor for the premature deaths of the hosts. 
In the past, two periods displayed an extremely high prevalence of Nosema among bee populations: 1999-2002 and 2003-2005. In the 1999-2002 period, the least number of samples in which Nosema was present were recorded in the summer months. However, in 2003-2005, there was an increase with no display of any dependence on seasonality or specific months or time. 
Samples were collected from most countries worldwide, and between N. ceranae and N. apis, N. ceranae was the most prevalent Nosema parasite found. 38% of samples did not contain any form of Nosema, but N. Ceranae was found in 53.8% of all samples. However, N. apis and N. ceranae were discovered in all countries studied. Most samples from France and Germany had infected samples. Samples from Switzerland did not show N. apis and N. ceranae occurring together, and in samples from France, N. apis was always detected alongside N. ceranae. Also, N. ceranae was detected in 75% of Spanish samples collected while N. apis was in 38.1% of those samples. 
Ecology and Known Roles in Symbiosis
In regards to how these parasites affect the health of honey bees, N. ceranae decreases the infected bee's ability to acquire nutrients from its environment and thus shortens the bee's lifespan by causing starvation. This parasite also affects the bee's colony in that the colony will struggle with growth since the parasite will spread among the bees and in that the colony will struggle with surviving the winter season. Since infected bees struggle with finding nutrients and winter is characterized by less growth and abundance of nutrients, infected bees and colonies have poor winter survivorship. However, despite the abundance of N. ceranae, this parasite can be found not only in declining bee colonies but in healthy be colonies as well. 
N. ceranae has grown to become a worldwide pathogen rather than a parasite restricted to one region and has branched out from the western hemisphere to eastern hemisphere colonies and bees populations in Asia. 
In a study by Martín-Hernández, Nosema was present in samples collected from most of Europe and most countries worldwide, meaning that bees could potentially be on a drastic decline in most countries worldwide and most European countries. Because of this and because of the vitality of bees in every day life and in the survival of ecosystems, certain systems must be edging closer to collapse with the rapid decline of bee health ad bee populations. 
Nosema ceranae and Nosema apis are both parasites that negatively affect honey bees and ultimately result in higher mortality rates among bees. Nosema ceranae is deadlier to bees; however, when analyzing the genome sequences of both parasites, there is less than 1% diversity between the two species. Another difference between the two is that Nosema ceranae is excreted by the bee in fecal matter and Nosema apis remains in the gut of the host.
When trying to detect parasites in bees, the PCR technique works extremely well since it is a delicate and very sensitive test used for detecting microsporidian infection, and it enables detection of the parasite at very low levels of infection and can reveal all the stages of the parasite's life cycle, which is typically difficult to accomplish.
 Huang, Wei-Fone & Leellen F. Solter. (2013). Nosema apis and Nosema ceranae: A comparative study in the honey bee host. Bee Culture and American Bee Journal, (https://bee-health.extension.org/managed-pollinator-cap-update-nosema-apis-and-nosema-ceranae-a-comparative-study-in-the-honey-bee-host/).
 Chen, Y., Evans, J., Murphy, C., Gutell, R., Zuker, M., Gundensen-Rindal, D and Pettis, J. (2009). Morphological, molecular, and phylogenetic characterization of Nosema ceranae, a microsporidian parasite isolated from the European honey bee, Apis mellifera. Journal of Eukaryotic Microbiology 56: 142-147. (https://www.ncbi.nlm.nih.gov/pubmed/19457054)
 Cornman, R. S., Chen, Y. P., Schatz, M. C., Street, C., Zhao, Y., Desany, B., … Evans, J. D. (2009). Genomic Analyses of the Microsporidian Nosema ceranae, an Emergent Pathogen of Honey Bees. PLoS Pathogens, 5(6). (https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.100046)
 Martín-Hernández, R., Higes, M., Salvador, A., Garrido-Bailón, E., Meana, A. and Prieto, L. 2007. Outcome of Colonization of Nosema ceranae by Apis mellifera. Applied and Environmental Microbiology 73(20):6331. (https://www.ncbi.nlm.nih.gov/pubmed/17675417)
 Smith, M. L. (2012). The Honey Bee Parasite Nosema ceranae: Transmissible via Food Exchange? PLoS One, 7(8).
 Jack, C. J., Lucas, H. M., Webster, T. C., & Sagili, R. R. (2016). Colony Level Prevalence and Intensity of Nosema ceranae in Honey Bees (Apis mellifera L.). PLoS One, 11(9).
 Goblirsch, M., Huang, Z. Y., & Spivak, M. (2013). Physiological and Behavioral Changes in Honey Bees (Apis mellifera) Induced by Nosema ceranae Infection. PLoS One, 8(3).
This page was authored by Kristin Barnett as part of the 2020 UM Study USA led by Dr. Erik Hom at the University of Mississippi.