Plant Virus Makes Bizarre Kingdom Jump to Honeybees

Heather Callaghan
Activist Post

Another explanation for Colony Collapse Disorder and the rapid decline of honeybees follows a surprising discovery involving a virus that typically infects the Plant Kingdom – Tobacco Ringspot Virus (TRSV).

U.S. and Chinese researchers report their findings in mBio, the online open-access journal of the American Society for Microbiology.

The plant virus has somehow jumped to the Animal Kingdom, now infecting honeybees.

The first two sentences of the study abstract hold unsettling implications:

Emerging and reemerging diseases that result from pathogen host shifts are a threat to the health of humans and their domesticates. RNA viruses have extremely high mutation rates and thus represent a significant source of these infectious diseases.

Lead author Ji Lian Li, at the Chinese Academy of Agricultural Science in Beijing, says:

The results of our study provide the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies.

More Bizarre Findings

They already knew that bees could spread the disease to other plants through pollination. But how did it spread from the plants to the bees?

From the abstract:

The tree topology indicated that the TRSVs from arthropod hosts shared a common ancestor with those from plant hosts and subsequently evolved as a distinct lineage after transkingdom host alteration. This study represents a unique example of viruses with host ranges spanning both the plant and animal kingdoms.

Another finding sounds similar to the Bubonic Plague scenario, except instead of fleas carrying the sickness, it could be a little mite. Varroa mites, vampiric parasites, are associated with CCD or weakened colonies. TRSV was found in their bodies but did not lead to an infection in the mites.

Mutating RNA Viruses

EurekaAlert! relays:

Notably, about 5% of known plant viruses are pollen-transmitted and thus potential sources of host-jumping viruses. RNA viruses tend to be particularly dangerous because they lack the 3′-5′ proofreading function which edits out errors in replicated genomes. As a result, viruses such as TRSV generate a flood of variant copies with differing infective properties. 

One consequence of such high replication rates are populations of RNA viruses thought to exist as “quasispecies,” clouds of genetically related variants that appear to work together to determine the pathology of their hosts. These sources of genetic diversity, coupled with large population sizes, further facilitate the adaption of RNA viruses to new selective conditions such as those imposed by novel hosts. “Thus, RNA viruses are a likely source of emerging and reemerging infectious diseases,” explain these researchers.

Other diseases associated with CCD, known to wipe out hives as early as 2006 include; Israel Acute Paralysis Virus (IAPV), Acute Bee Paralysis Virus (ABPV), Chronic Paralysis Virus (CPV), Kashmir Bee Virus (KBV), Deformed Wing Bee Virus (DWV), Black Queen Cell Virus (BQCV) and Sacbrood Virus (SBV).

So – do findings like this serve to mitigate the responsibility of chemical pesticides on environmental health, or could they further implicate them in the results thereof?

It turns out…

…when they studied different colonies classified as either “weak” or “strong,” TRSV and other viruses were more prevalent in the weakened colonies. During their studies, the strong colonies could effectively ward off most disease and, unlike their weaker counterparts, could survive the cold winters into February.

Something has weakened modern bee generations…

One study, with contradictory terms appeared to detract attention from chemicals on bee health by emphasizing that the bees are not directly killed, but are stressed.

Recently, another study, showing that chemicals did not directly kill the colony, proved that pesticides were creating smaller worker bees by retarding their growth, ultimately leading to the untimely end of a colony.

The researchers called for more surveillance of potential host-jumping events as part of insect pollinator management programs and concluded:

The increasing prevalence of TRSV in conjunction with other bee viruses is associated with a gradual decline of host populations and supports the view that viral infections have a significant negative impact on colony survival.

Regardless of the cause, the collective immunity of pollinators is weakening at a rapid pace and bees are falling prey to invaders that previously posed less harm. Imagine the sheer disease-state of honeybees, weakened enough to become susceptible to diseases in the Plant Kingdom….

Please check out the study here for more information:
Systemic Spread and Propagation of a Plant-Pathogenic Virus in European Honeybees, Apis mellifera

Image: Wikimedia Commons honeybee with superimposed TRSV microbes

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