Viruses and Honey Bees
Bee Culture (August) Vol. 136: 19-21.
In a previous column, I discussed the role of emerging pathogens in the phenomenon now called Colony Collapse Disorder (CCD). One of those areas I listed that is becoming more and more prominent is concern about the effect of honey bee viruses. A paper in Bee World over a decade ago sought to catalog the incidence and world distribution of honey bee viruses.1 Since then, several others have come into focus as potential problems. In order to understand viruses better, it is necessary to be more informed about their origins, biology and potential treatment. :
“A virus (from the Latin virus meaning "toxin" or "poison"), is a sub-microscopic infectious agent that is unable to grow or reproduce outside a host cell. Each viral particle, or virion, consists of genetic material, DNA or RNA, within a protective protein coat called a capsid. The capsid shape varies from simple helical and icosahedral (polyhedral or near-spherical) forms, to more complex structures with tails or an envelope. Viruses infect cellular life forms and are grouped into animal, plant and bacterial types, according to the type of host infected.
“Biologists debate whether or not viruses are living organisms. Some consider them non-living as they do not meet all the criteria used in the common definitions of life. For example, unlike most organisms, viruses do not have cells. However, viruses have genes and evolve by natural selection. Others have described them as organisms at the edge of life. Viral infections in human and animal hosts usually result in an immune response and disease. Often, a virus is completely eliminated by the immune system. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat life-threatening infections. Vaccines that produce lifelong immunity can prevent viral infections.” The above two paragraphs come from the Internet’s open encyclopedia(Wikipedia.org) and the links (underlined words) are left in the document here on purpose so readers can see what other information might be available.2
To reiterate, most people talk about viruses as if they are living organisms, but this challenges in fundamental ways how biology text books define “life.” For example viruses do not respire; move nor grow. They also do not display irritability. However, viruses do reproduce and adapt to new hosts. If one considers that the only real criterion for life is the ability to replicate, then viruses must be included, even though they require another living host to do so.3
Honey bee viruses generally have not been considered problematic for bees or in beekeeping. Some, like the sacbrood virus (SBV), appeared randomly and did not cause significant damage. That all changed, however, as the Varroa mite became an integral part of the world’s honey bee colonies. “There is increasing evidence that the global spread of Varroa destructor has resulted in significant change in the type and prevalence of viruses causing mortality in honey bee colonies. This is primarily because the mite has provided new routes of transmission for naturally occurring, endemic virus infections. Adult female mites pierce the thin membranous areas of the adults bee’s body or pupal skin, to feed on the haemolypmph. At the feeding site there is some exchange of fluids between the parasite and its host, so the mite acts effectively like a hypodermic syringe.”4
Although the Varroa mite is implicated in the spread of viruses because it is a primary transporting agent or vector, it is not the only organism that can do this job. Another is the tracheal mite (Acarapis woodi). This organism also makes holes in the intersegmental membrane when feeding on bee blood or haemolymph. Mites don’t necessarily have to transport viruses. Many, it appears, are already present in honey bee populations and are benign (latent), but can be activated by mite feeding activity. Viruses can also be spread in two ways, horizontally and vertically. The former is the case with most contagious diseases where susceptible individuals are in contact with others such as in human respiratory flu viruses (spread by sneezing) or HIV (through exchange of body fluids). Honey bee viruses have been documented to spread from bee-to-bee, bee-to-mite, mite-to-mite, and mite-to-brood.
Vertical transmission is a special case where a virus may be spread within a colony from the queen to her offspring, affecting the next generation. A recent study concludes: “:Our work has provided substantial evidence for the vertical transmission of viruses in honeybees, but a number of factors that may play important roles in the efficiency of virus transmission are far from being understood. For example, the host immune responses and virus pathological features that facilitate the vertical transmission of individual viruses are not known. The roles of vertical transmission of viruses in bee disease epidemiology need to be determined. This will be especially relevant for honeybees, where viruses normally persist as latent infections and group living can possibly drive high levels of horizontal transmission or amplification of existing infections. Further studies of host-virus interactions might give some insight into these issues.”5
Multiple viruses can also be found in honey bee colonies. “Using uniplex RT-PCR we screened honey bee colonies for the presence of several bee viruses, including Black Queen Cell virus (BQCV), Deformed Wing virus (DWV), Kashmir Bee virus (KBV), and Sacbrood virus (SBV), and described the detection of mixed virus infections in bees from these colonies. We report for the first time that individual bees can harbor four viruses simultaneously. Results from field surveys of these viruses indicate that mixed infections of BQCV, DWV, KBV, and SBV in the honey bee probably arise due to broad geographic distribution of viruses.6
As noted elsewhere, the spread of viruses appears to be continuing around the globe helped along by mite vectors and other risk factors. Recently, two are of particular concern and are thought to be associated with significant bee losses.
The first is deformed wing virus (DWV), which by most accounts has become ubiquitous in European honey bee populations. Beekeepers can often recognize symptoms of DWV by simply examining affected worker bees, the wings of which are not well developed or abnormal in some way. At one time these symptoms were thought to be simply the result of feeding by parasitic mites. Deformed wing virus is endemic among honey bees in the U.S., although when the European bees became historically infested with this virus, is unknown. However, simply having deformed wing virus does not appear to cause bees to emerge from the pupal state with deformed wings, nor does it cause colony deaths. In addition, a group of Japanese researchers found that a virus that is 99 percent the same as deformed wing, appears in the brains of aggressive guard bees so there may be some positive effect in this virus that allows it to persist in a colony.7
The other virus that is becoming of interest to researchers is Israeli acute paralysis virus (IAPV). It burst onto the scene when it was given wide publicity at the World Apicultural Congress in Melbourne, Australia (Apimondia 2007) as “strongly correlated with CCD.” Australian package bees that had just begun to be imported into the U.S. the last few years, therefore, were implicated. This brought a storm of protest from Australian scientists and package producers, concluding that the virus had also been found in hives not suffering from CCD, and asking why if it was so closely linked to the phenomenon, that there are no hives in Australia suffering from
CCD.8 Still, as one U.S. researcher has said, “…the stats are very convincing, with literally every colony showing symptoms of CCD also harboring the virus. We don't find data that plain usually."9
Ian Parnell, a professional biologist and environmental writer, provides an intensive analysis of the controversy on his blog, which is mandatory reading for anyone interested in this issue.10
A subsequent U.S. investigation concluded: “Our results show that IAPV in the U.S. predates both the latest incarnation of CCD and the importation of Australian package bees. Nevertheless, we caution that much work is still needed to absolve or implicate this virus, or specific imports, in CCD. Most importantly, experimental studies are ongoing to determine the relative virulence of imported or domestic IAPV strains, and such studies will provide the best evidence for making importation and management choices. Viruses with minimal genome sequence differences can show greatly different levels of virulence, and all isolates of IAPV we studied showed at least some sequence variation. Given its observed association with CCD, this virus remains an important candidate for honey bee disease.”11
Besides being inconspicuous to beekeepers, other reasons exist for the relatively little work on honey bee viruses by scientists over the years. They are not easy to detect, and even if there was any evidence viruses were doing harm to honey bee colonies, there were few if any treatment options.
Virus detection methods are now becoming much more available given new genetic technologies. Researchers at the U.S. Department of Agriculture have reported on their efforts in this arena: “We also developed a multiplex RT-PCR assay for the simultaneous detection of multiple bee viruses. The feasibility and specificity of the multiplex RT-PCR assay suggests that this assay is an effective tool for simultaneous examination of mixed virus infections in bee colonies and would be useful for the diagnosis and surveillance of honey bee viral diseases in the field and laboratory. Phylogenetic analysis of putative helicase and RNA-dependent RNA polymerase (RdRp) encoded by viruses reveal that DWV and SBV (sacbrood virus) fall into a distinct group, whereas KBV (Kashmir Bee Virus) and BQCV (black queen cell virus) belong to a distinct lineage with other picorna-like viruses that infect plants, insects and vertebrates.”12
Another detection method described at the January 2008 National Beekeeping Conference in Sacramento, CA is the Integrated Virus Detection System (IVDS), pioneered by the military, but now being used by civilian scientists in a number of disciplines. “This new invention utilizes the physical properties of virus, virus-like and other nanometer (nm) particles to determine a concentration, distribution and information for discrimination and characterization of nanometer particles (1 nm equals one billionth of a meter). This analysis can identify many known virus families pathogenic to man, as well as a new means for detecting unknown and emerging viruses. Another great advantage is that the IVDS instrument does not require complicated chemistry or reagents.”13
Potential treatment of honey bee viruses in many ways seems to parallel the human situation. It is unfortunate that many people confuse bacterial infections with those produced by viruses. The symptoms are often similar, and modern human culture has produced a belief that antibiotics are a “silver bullet” cure for most ailments. Physicians may have some of the same perceptions and also are often under the gun by patients who demand treatment by antibiotics no matter the cause or cost. As a consequence, antibiotics are often prescribed for relatively common conditions that often clear up by themselves. This practice and the improper use of the materials by patients (not taking the full dose as prescribed) create a favorable environment for bacterial resistance. Antibiotics only target bacteria and so viral conditions (common colds, influenza).are not affected. In extreme conditions, antibiotics may be taken as preventatives, causing an escalation of antibacterial resistance such that whole classes of antibiotics may become useless. This has in fact happened in honey bees where presumed overuse of the antibiotic Terramycin® has resulted in American foulbrood (Paenibacillus larvae larvae) bacterial resistance and led to the development of another treatment based on tylosin (Tylan®).
The best way to ward off virus infection is to use the patient's own immune system. As one authority says, “it may be hard to accept when the doctor says the only cure is for 'nature to take its course'.”14 The treatment of virus infections in humans usually involves: drinking plenty of water, staying at home so as not the spread the bug, and perhaps taking something to alleviate pain or reduce temperature. Vaccines are routinely developed to provide the body some help in quickly and effectively fighting viruses. This is the philosophy behind the annual flu shot that is recommended each fall for a large part of the U.S. human population.
The realization that viruses are more and more important in honey bee health has led to a more intense examination of the insect’s immune system. “Viral infections induce unspecific cell defense reactions such as phagocytosis and nodule formation. A small number of viruses or viruses of a low virulence infecting the insect are killed by haemocytes whereas heavy infections or virulent strains can replicate and kill a specific types of haemocytes involved in antiviral defensive reactions.”15
Dr. Clarence Collison has provided a closer look at this important area and reports that honey bees appear to have relatively diminished defense systems compared to other insects.16 It seems reasonable to suggest that creative researchers should come up with a vaccine(s) to help bees develop stronger immune systems to ward off current and future viral threats.
References: All URLs accessed June 14, 2008.
Allen, M. and Brenda Ball. 1996. “The Incidence and World Distribution of Honey Bee Viruses,” Bee World, Vol. 73 (3): 141-162.
Ball, Brenda. V. 2004. “The Trouble With Viruses,” Bee World, Vol. 85 (2): 25.
Chen, Y.P., et al. 2006. Prevalence and Transmission of Honeybee Viruses, APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 2006, p. 606–611 Vol. 72, No. 1 http://aem.asm.org/cgi/reprint/72/1/606.pdf
Chen, Y. and J. Evans. Historical presence of Israeli Acute Paralysis Virus in the United States, submitted toAmerican Bee Journal 10/29/07 http://www.in.gov/dnr/files/IAPV.pdf
Collison, C. 2008. A Closer Look: Honey Bee Immunity. Bee Culture,Vol. 136 (6): pp. 48-50.