The role of emerging pathogens is becoming some clear given the phenomenon now called Colony Collapse Disorder (CCD). One of the areas 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. ²
1. Allen, M. and Brenda Ball. 1996. “The Incidence and World Distribution of Honey Bee Viruses,” Bee World, Vol. 73 (3): 141-162.
2. Ball, Brenda. V. 2004. “The Trouble With Viruses,” Bee World, Vol. 85 (2): 25.
“A virus (from the Latin virus meaning “toxin” or “poison“), is a infectious agent that is unable to grow or reproduce outside a host cell. Each viral particle, or virion, consists of genetic material, DNA and 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 are taken from the Internet’s open encyclopedia.
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.
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. 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.
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. Multiple viruses can also be found in honey bee colonies.
Two viruses 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.
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 Colony Collapse Disorder or 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. Still, many remain convinced and there is evidence this virus remains an important candidate for honey bee diseases.
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. One is the promise of RNAi.
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 Argentina 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®).
Dr. Clarence Collison has provided a closer look at this important area in Bee Culture magazine and reports that honey bees appear to have relatively diminished defense systems compared to other insects. 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.
Collison, C. 2008. A Closer Look: Honey Bee Immunity. Bee Culture,Vol. 136 (6): pp. 48-50.
Evidence in the UK that some benign viruses might be excluding infestation by more virulent ones needs more study.
Updated information on viruses was provided at the 2016 meeting of the Western Apicultural Society in Hawaii:
“One emphasis was viruses. Both Dr. Stephen Martin and Ph.D. candidate Laura Brettell of the University of Salford in the United Kingdom provided their observations on the viral situation in the islands and elsewhere. Dr. Martin related an interesting history of the thinking about viruses. It could be that many of the issues affecting honey bees and reported on in the past, such as Isle of Wight and/or so-called disappearing disease might have been viral in nature, but these were not even in the discussion at that time. Viruses are also not mentioned as a major source in a more recent disease called Colony Collapse Disorder (CCD), but that is likely to change as this so-called “missing link” is being slowly becoming more recognized. As late as 1996, according to Dr. Martin only 18 viruses were known. There are many more with numerous variants, some benign. His initial predictions about viruses affecting honey honey bees were basically ignored by the scientific establishment for quite a period. However, observations that some honey bee populations with high Varroa counts did not necessarily collapse, unless the viruses were present, and technology to identify these organisms has finally given Dr. Martin’s ideas some credence that they are indeed hugely important in honey bee health. He and Ms. Brettell continue to look at them via something called quantitative polymerase chain reaction (q-PCR) as noted in a summary of a recent paper:
“Martin et al. (p. 1304) exploited this unique situation to study the mechanisms behind the emergence. Honey bee populations have long been established on the isolated Hawaiian Islands but only recently have some islands become infested with the Varroa mite. This mite has selected for a single viral pathogen-deformed wing virus among the honey bee population, with the appearance of a single dominant virus strain, which has now spread worldwide. Thus, a normally benign viral pathogen has become one of the most widely distributed and contagious insect viruses on the planet.”
The paper’s abstract says:
“Emerging diseases are among the greatest threats to honey bees. Unfortunately, where and when an emerging disease will appear are almost impossible to predict. The arrival of the parasitic Varroa mite into the Hawaiian honey bee population allowed us to investigate changes in the prevalence, load, and strain diversity of honey bee viruses. The mite increased the prevalence of a single viral species, deformed wing virus (DWV), from ~10 to 100% within honey bee populations, which was accompanied by a millionfold increase in viral titer and a massive reduction in DWV diversity, leading to the predominance of a single DWV strain. Therefore, the global spread of Varroa has selected DWV variants that have emerged to allow it to become one of the most widely distributed and contagious insect viruses on the planet.”
Ms. Brettell discussed at some length her study of the honey bees of Fernando de Noronha island off the coast of Brazil. It has long been known that this population of European honey bees has tolerated Varroa mites without much damage. Her conclusion is that both low honey bee population and mite reproductive levels have yet to allow viruses to take hold. She called the situation on the island “a ticking time bomb.” This is similar to present conditions on both Maui and Oahu. This information could turn traditional ideas about Varroa control on their head. Those looking at mite control might be able turn their attention to Viral effects instead. If this is so, perhaps an inoculation, something akin to a flu shot in humans, might have a similar effect for honey bees. A question from Treavor Weatherhead of Australia concerning the mite haplotype on the island was not answered adequately. It is known that the first mites coming to South America were of the Japanese variation; the Korean haplotype is much more destructive and was introduced later. It is not clear whether a mite haplotype analysis was conducted by Ms. Brettell. So far there are 18 total with two above being most predominant in the five-species Varroa mite complex. She will be looking further into the situation.
Jessika Santamaria, University of Hawaii, Manoa is studying something called “viral spillover.” Many of the variant viruses associated with spread of deformed wing virus (DWV) in honey bees have now been found in bumblebees. There is also evidence that these and perhaps other viruses could be spread via pollen to other insects in the islands and elsewhere. Investigations in this area continue.