Nosema ceranae and Nosema apis: Nosemosis, The Danger to Honey Bees and Agricultural Pollination: Difference between revisions

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==Control of Disease==
==Control of Disease==
Given the global exchange of goods, a ubiquitous mechanism of disease control is closer surveillance of shipped goods. Many virulent effectors travel along product routes on the backs of desired goods. This shipment process can be from overseas to cross county exchanges. It is important for beekeepers, farmers and naturalists to monitor honeybee populations, to make sure they are free of Nosema infection before shipment of goods. Compounding the issue of containment is the movement between bee strains of specified fungi as addressed earlier. As with most infectious disease, containment and suppression of dispersion is a broad scale but significant. [[Image:Bar graph.png|thumb|400px|]]
Given the global exchange of goods, a ubiquitous mechanism of disease control is closer surveillance of shipped goods. [[Image:Bar graph.png|thumb|300px|]]Many virulent effectors travel along product routes on the backs of desired goods. This shipment process can be from overseas to cross county exchanges. It is important for beekeepers, farmers and naturalists to monitor honeybee populations, to make sure they are free of Nosema infection before shipment of goods. Compounding the issue of containment is the movement between bee strains of specified fungi as addressed earlier. As with most infectious disease, containment and suppression of dispersion is a broad scale but significant.  


Smaller scale efforts can be made to combat the virulent nature of Nosema apis and <i>Nosema ceranae</i>. In many instances, given the importance of the Western honeybee <i>Apis mellifera</i>, the maintenance of colonial health is crucial. In organismal medicine fungal infections are often matched with an antibiotic, however given the recent discovery of <i>Nosema ceranae</i> research on possible antibiotic treatments of diseased bees is limited. Fumagilin-B or fumagillin dicyclohexylammonium, an antibiotic which is derived from the microbe Aspergillus fumigatus (Whittington et al. 2003).  This microbial produced antibiotic disrupts the DNA replication of the target parasite stopping its ability to properly reproduce. There is a methodology to inoculating an infected hive as the medicine needs to be ingested by the organisms. In N. apis Fumagilli-B has been shown to work effectively given proper drug administration (Williams et al. 2008). However in <i>Nosema ceranae</i> results are more variable. In a study done in 2010, the variability was attributed to intake methodology, and lack of knowledge about <i>Nosema ceranae</i> infection. Under the qualifications of the Williams et al. experiment, <i>Nosema ceranae</i> was not a key factor in colony health either (2010). It has become readily apparent that more research needs to be done into finding a workable antibiotic for <i>Nosema ceranae</i> infection of <i>Apis mellifera</i>.
Smaller scale efforts can be made to combat the virulent nature of Nosema apis and <i>Nosema ceranae</i>. In many instances, given the importance of the Western honeybee <i>Apis mellifera</i>, the maintenance of colonial health is crucial. In organismal medicine fungal infections are often matched with an antibiotic, however given the recent discovery of <i>Nosema ceranae</i> research on possible antibiotic treatments of diseased bees is limited. Fumagilin-B or fumagillin dicyclohexylammonium, an antibiotic which is derived from the microbe Aspergillus fumigatus (Whittington et al. 2003).  This microbial produced antibiotic disrupts the DNA replication of the target parasite stopping its ability to properly reproduce. There is a methodology to inoculating an infected hive as the medicine needs to be ingested by the organisms. In N. apis Fumagilli-B has been shown to work effectively given proper drug administration (Williams et al. 2008). However in <i>Nosema ceranae</i> results are more variable. In a study done in 2010, the variability was attributed to intake methodology, and lack of knowledge about <i>Nosema ceranae</i> infection. Under the qualifications of the Williams et al. experiment, <i>Nosema ceranae</i> was not a key factor in colony health either (2010). It has become readily apparent that more research needs to be done into finding a workable antibiotic for <i>Nosema ceranae</i> infection of <i>Apis mellifera</i>.


==References==
==References==

Revision as of 06:34, 7 May 2014

Overview



By [Andrew Parmelee]

Apis mellifera and Apis cerana, the European and Asian honey bees respectively, not only sustain biodiversity but are of particular agricultural interest as they are essential pollinators of human maintained crops. Ecosystem health is reliant on honeybees given the necessity for primary pollinators. Studies have shown that up honey bees are accountable for 90% of commercial pollination, proving their necessity and current integration into agriculture (Klein et al. 2007). Knowing this farmers around the world allow large colonies exist to provide a necessary service to humanity. Much like most other industrial techniques and commodities many of these bee populations were introduced by Europeans for crop management. As one can see, the health of the honey bee is vital to agricultural success and sustainability. A major emphasis can be placed on pathogenic research to assure the health of the honeybee. Populations all over the world, from France to the United States are disappearing and it is of great concern. If current declines in populations persist, large scale environmental crisis will grip many developed nations, expanding the world’s hunger epidemic. Researchers, acquiring grants from agricultural based economies and large environmental firms have been working feverishly on unearthing why these colonies are failing. There are many reasons why a colony might fail. Availability of resources, predation illness, and environmental factors are considered notable stressors. Fluctuation in nest temperature destabilizes brood rearing conditions, decreasing biodiversity of a colony. A lack of diversity within the hive could prove costly given a harmful effect (Jones et al. 2004). Any of the fore mentioned burdens could play pivotal roles in lowering biodiversity within and between hives causing possible collapse.

An area of interest for slowing the extraordinary loss of world honey bee populations is the identification and comprehension of the fungal pathogens, Nosema ceranae and Nosema apis. Pathogenic factors are a concern of any colony and illness within the hive can be caused by infection of microscopic organisms. Nosema ceranae and N. apis, microsporidia, cause nosemosis. A degenerative gut disease nosemosis facilitates organism death and can expedite colony loss. Research being conducted on both parasitic fungi is relatively new and novel. Nosema ceranae, thought to be more virulent than N. apis has keystone agricultural value. Shifting from original host A. cerana to A. mellifera, Nosema ceranae illustrates the dangers lurking within in the Nosema genus as non-specific infection is hard to control. Being that A. mellifera is used quite extensively in agriculture, its worth is massive. This adaptation and move toward more generalized infection by Nosema ceranae has proved to be problematic for honey bees everywhere. There are limited techniques formulated to combat the parasitic fungi, yet methods are continuously improving. It is essential to develop a comprehensive analysis of said organisms for proper conservation of bee populations.

Organismal Structure and Development

Nosema species are a parasitic microsporidia.

Cell cycle.png

Generally these intracellular parasitic fungi infect specific host tissues, relying heavily on opportunistic relationships for proliferation. Nosema ceranae forms spores which are oval or rod shaped, consisting of 3.9-5.3µm in length and 2.0-2.5µm in width. Nosema apis produces spores that are typically 6µm in length and 3.0µm in width. As a generalized mechanism of replication, the microsporidia uses a polar filament to inject sporoplasm from a mature spore into a host cell's cytoplasm, where it reproduces (Fries, 2010). Further organismal qualities are pictured in the figure shown below from Chen et al. (2009). In conserved mechanisms, both parasitic infections are developmentally complex, maturing sequentially as follows. During early development, the microsporidia contain free ribosomes and a poorly developed rough endoplasmic reticulum in its cytoplasm. These structures form junctions with the host, integrating itself within a host cell. As a meront forms, connection with the organismal and host cytoplasm continues and a diplokarytic two nuclei is introduced into the host. Meronts replicate multiple times, and eventually give rise to the generation of oval sporonts, which are of similar size to merozoites but have a thicker plasma membrane. These sporonts eventually divide into sporoblasts, which divide and grow into mature spores (Fries et al. 1996). Matured spores incorporate a dense exospore, an anteriorly positioned anchoring disc and centralized diplokaryoticly arranged nuclei (Chen et al., 2009). A posteriorly placed polar filament coils, and the amount of coils is widely used as a determination of species type between Nosema ceranae and N. apis (Fries et al. 1996). Reproductive phases of the organism are schematically represented in the figure pictured below. Microsporidia lack proper machinery to autogenously produce energy. Utilizing host stores as supplemental material, the parasitic fungi are able to metabolize energy (Chen et al., 2010). Genomically, Nosema ceranae encompasses 2,614 protein coding genes, and contains AT biased repetitive regions increasing likelihood of genetic mutation due to error; N. apis possess smaller yet similar regions of repeats. With higher probability or mutation, these dangerous fungi are difficutl to qualify. Despite correlation in function Nosema ceranae is genetically most similar to the wasp parasite N. vespula, as N. apis and N. bombi more closely related (Chen et al., 2010). Evolutionary branching differences often

Virulence

Virulent spores which exist in food, water and fecal matter, are an essential element to Nosema proliferation and infection. Being a fungus these infective agents are quite robust. Mature Nosema spores are able to exist outside a host for variable amounts of time, given different conditions. Metabolically inactive viable spores on average can persist about 25-50 days, some preserved for more than a year. The health of the spores is contingent on delivery method, concentration and temperature among other circumstances. Spores transmitted through syrup as opposed to honey display stronger virulence, producing larger densities of spores within hosts. However delivery methods are usually dependent on where the inoculation occurs. Often, laboratory inoculations take place in favorable conditions as efforts are geared toward success. Furthermore, as storage temperature increases, infection densities decrease (Malone et al. 2001). Spore health is considered sensitive up to -20oC, however germination of the spores was significantly hindered when exposed to temperature 4oC for 4 days (Gisder et al. 2010). Much like most life and infectious organisms, Nosema ceranae and Nosema apis operate ideally at host temperature. Typically higher concentrations of viable spores ingested the more confluent the malign culture becomes within host tissue. Many times a dense fungal growth has a higher probability of killing the host. Once ingested, spores go through replication in similar steps as covered previously (Malone et al. 2001).

N. apis sporulation occurs only in the host honey bee’s midgut epithelium, while N. ceranae was found to infect alimentary canals, malpighian tubules, hypopharyngeal glands, salivary glands and fat body (Chen et al. 2010). Nosema ceranae is potentially made more dangerous by the ability ot infect multiple cell types. Once localized within specific cells, spore germination occurs. The microsporidium injects sporoplasm into the host cell through a polar tube, implanting virulent machinery into the cytoplasm of the host. The proliferation and sporogonic phase follows suit, using the timeline issued previously, and illustrated in the corresponding figure. Complete reproduction of a host cell within Microsporidia infection grows within tissue types until symptoms appear. These symptoms are discussed further below, but become more prevalent given higher growth.

Research has shown seasonality could be a factor in parasitic infection by both N. apis and Nosema ceranae. A study done in Germany released in 2010 analyzed incidences of infection by season over 5 years. It was concluded that the spring months while older bees of the hive are being replaced with younger bees, contained the highest prevalence of infection. Sampled bees contained a proportion of infection (22.4% - 35.4%) in the spring while fall months accounted for a smaller frequency (5.2% - 12.7%). It should be discussed however that a higher spring time density of Nemosa spp. did not correlate with colony loss during subsequent seasons (Gisder et al. 2010). Although a promising study, more research needs to be conducted to determine a reliance on the seasons for infection. Additionally, the parasite is often transmitted in times of greater confinement. Therefore colony collapse which is linked to Nemosa infection has also been noted to occur more over the winter months. During the winter the bees are often found inside the hive, increasing contact with infected individuals (Gisder et al. 2010).

Although a virulent entity, Nosema ceranae has not conclusively been linked to colony loss. Studies have correlated the parasitic infection with the deteriorating health of a colony, eventually ending in collapse, and others have dismissed Nosema ceranae as colony threatening. For instance, in a small scale study done on controlled colonies, N. ceranae infection was found to cause colony collapse (Williams et al. 2008). However in other cases, it appears that there has been no correlation between colony loss and Nosema ceranae infection. In many areas where the parasite has been introduced, colony health remains constant, or not significantly affected. As pointed out, external or other effects may be coupling with infection, and ultimately causing complications in colony health (Fries, 2010). It is also quite possible that certain strains of bees or even fungi affect each other with different potency.

Interestingly, detrimental virulence of Nosema ceranaeinfection may be enhanced synergistically through encounters with the insecticide Fipronil. Fipronil is a general insecticide which targets harmful pests. In agriculture such an agent is sprayed on plants to avoid crop destruction; however it has been cited for a potential colony collapse instigator in bees (Aufauvre et al. 2012). In their study, both stressors were cited for having a detrimental effect on bee health; however a combination of the two proved even more lethal. The mortality rate in bees exposed to a normal commercially used level of Fipronil and then being infected by Nosema ceranae increased dramatically. After the same amount of time, 84% of co-exposed bees passed away in comparison a mortality rate of 39% in singularly burdened samples. Studies in the past using different organisms have shown a similar synergistic relationship between insecticides, outside stressors and a microbial or fungal infection. Aufauvre et al. hypothesized that exposure to alternative stressors may make it easier for microbial or fungal infections to take hold, a similar theory to being immune compromised. In the context of colony collapse, a synergistic effect between a commonly used insecticide and a growing infection is worrisome. Anytime a pesticide is used, non-target species and organisms are always in trouble. The crops in which the honeybee is responsible for pollinating may be covered with something that can increase incidence of death. This fact raises economic issues as well as the farmer now has to choose between natural pollination of crop or potential crop destruction. Artificial pollination does exist but it is not as effective as honeybee pollination.

N. apis infection has been is only potentially linked to death, but much like other types of infections, its virulence could depend such things as time of infection or dosing concentrations. Similarly Nosema ceranae infection is equally ambiguous. Given a limited database of research, experts find it hard to predict the exact implications of a Nosema ceranae infection. For instance, cage experiments conducted in 2010 produced promising results as inoculated organisms died within 8 days. Despite this however, many studies analyzing wild bees have been proved inconclusive (Fries, 2010). Further research needs to be conducted on the growing virulence of N. apis and Nosema ceranae.


Symptoms/Identification

Studies looking to mediate hive collapse for ecological and monetary gain focus on the symptoms of Nosema spp. It is important to make the distinction between an individual's health when subjected to infection, and how a particular virulent agent can affect an entire colonies health. Individuals obviously make up the entire colony, but bee hives are consisted of worker bees, larva and the queens. Infection may reach a subset of the hive as well, as not all bees come into contact with each other. It is rather difficult to properly identify nosemosis, caused by the agents in question on a living hive. Initial analysis may consist of recognition of sick or dead bees in and around the hive, brown faecal marks in the combs, done in correspondence with treatment inquiry to avoid pesticide contamination (OIE, 2008). These symptoms are also common for other general diseases which terrorize colony health. In order to fully determine the pathogen at work on any given “sick” colony, especially when dealing with Nosema, microscopy is required. Common laboratory technique is to actively look at infected abdominal tissue in order to properly identify spores within tissue, confirming infection. Much of the microscopy is seen in the figure seen above. Light microscopy and Electron microscopy are commonly used to study samples.

The downfall of individuals does not always mean the demise of a colony (Fries, 2010). N. apis and Nosema ceranae, are hypothesized to affect colony levels through individuals by atrophy of the hypopharyngeal glands. Nonetheless, despite sharing hosts, these species do not always share the same symptoms of infection. On a case by case basis, N. apis infection is not often coupled with visual signs of disease, but suffering bees may become whitish and swollen. Studies struggle to phenotypically quantify Nosema ceranae infection, displaying little to no outward symptoms. It seems the organisms get sick and die quickly

Micrographs.png

In the context of hive health, N. apis infection constitutes an increase in dysentery within the population, which as previously stated could cause higher incidence of infection. Conversely, adverse effects are more widely debated within Nosema ceranae, as it has recently transitioned from A. cerana to Apis mellifera and research is limited. Aforementioned decreases in honey production, and higher death rates among workers are both commonly thought of as large hive encompassing responses to infection when focusing on Nosema ceranae (Fries, 2010). It should be noted that experimental application of symptom study within the organisms has determined similar growth rates across the Nosema species of interest, however, germination rates could be different (Fries, 2010). This is an important concept when analyzing the spread of Nosema species. If an early detection method is developed, the rates at which infection occurs could be an important concept to harness. If a colony is deemed ill, there is a potential to save it by separating healthy parts of the colony from sickly subsets.

Movement and Crossover

Much of the danger in the Nosema genus, particularly Nosema ceranae is expansion of virulence into new species of bees. Shipments and movements of goods around the world support world markets, international trade and global commerce, however provide a medium for transmission of parasites across before impassable boundaries. It is clear to researchers that Nosema ceranae has moved from solely infecting Eastern honey bees, to European honey bees as well. In 2007, a study investigated infectious crossover of Nosema ceranae from its native Asian host, Apis cerana, to the more pervasive Apis mellifera, within Finland. Researchers determined the ability for Nosema ceranae to disease European bees actually emerged in 1998, previously thought to be more recent and has quickly become more potent than N. apis. As seen in Figure 3 the study showed a much heavier spore count associated with Nosema ceranae infection than to that of N. apis, while a combination of the parasites an intermediate sporulation (1-158 x106, 1-34 x106, 1-83 x106 respectively). Mortality rate differed largely between species as well, Nosema ceranae accounting for 44% mortality, conversely N. apis only 8% mortality 15 days post inoculation (Paxton et al. 2007). As mentioned before, studies have shown a higher density of infection perhaps leads to higher mortality. It appears virulent forms of Nosema ceranae when introduced into European bee populations induces individualized failure, eventually destabilizing colonies.

Infectious crossover has not only occurred in Europe, but within the United States as well. The United States is home to A. mellifera, and is experiencing similar transition as European based bees. Much like the work done by Paxton et al., the Chen et al. research team concluded that Nosema ceranae had become adapted to infect European bees well before previously thought (2007, 2008). Infection of these bees were found across 12 states and analyzed throughout time (1995-2007) (Chen et al. 2008). Parasitic infectious agents are an extremely real problem, and the idea that they have spread throughout all populations is troubling.

Control of Disease

Given the global exchange of goods, a ubiquitous mechanism of disease control is closer surveillance of shipped goods.

Bar graph.png

Many virulent effectors travel along product routes on the backs of desired goods. This shipment process can be from overseas to cross county exchanges. It is important for beekeepers, farmers and naturalists to monitor honeybee populations, to make sure they are free of Nosema infection before shipment of goods. Compounding the issue of containment is the movement between bee strains of specified fungi as addressed earlier. As with most infectious disease, containment and suppression of dispersion is a broad scale but significant.

Smaller scale efforts can be made to combat the virulent nature of Nosema apis and Nosema ceranae. In many instances, given the importance of the Western honeybee Apis mellifera, the maintenance of colonial health is crucial. In organismal medicine fungal infections are often matched with an antibiotic, however given the recent discovery of Nosema ceranae research on possible antibiotic treatments of diseased bees is limited. Fumagilin-B or fumagillin dicyclohexylammonium, an antibiotic which is derived from the microbe Aspergillus fumigatus (Whittington et al. 2003). This microbial produced antibiotic disrupts the DNA replication of the target parasite stopping its ability to properly reproduce. There is a methodology to inoculating an infected hive as the medicine needs to be ingested by the organisms. In N. apis Fumagilli-B has been shown to work effectively given proper drug administration (Williams et al. 2008). However in Nosema ceranae results are more variable. In a study done in 2010, the variability was attributed to intake methodology, and lack of knowledge about Nosema ceranae infection. Under the qualifications of the Williams et al. experiment, Nosema ceranae was not a key factor in colony health either (2010). It has become readily apparent that more research needs to be done into finding a workable antibiotic for Nosema ceranae infection of Apis mellifera.

References