USA
September 6, 2007
A comparison of healthy and
unhealthy bee colonies points to a virus contributing to Colony
Collapse Disorder (CCD), according to a report being published
by the journal Science, at the Science Express web site, on 06
September. Science
is published by The American
Association for the Advancement of Science (AAAS), the
nonprofit science society.
“Our extensive study suggests that the Israeli Acute Paralysis
Virus (IAPV) may be a potential cause of Colony Collapse
Disorder,” said W. Ian Lipkin, director of the Center for
Infection and Immunology at the Mailman School of Public Health,
Columbia University. “Our next step is to ascertain whether this
virus, alone or in concert with other factors such as microbes,
toxins and stressors, can induce CCD in healthy bees,” he added.
CCD is a puzzling phenomenon occurring in the United States –
and possibly other countries where it is not yet confirmed – in
which all adult bees disappear from the hive, leaving the honey
and pollen behind. Few, if any, dead bees are found around the
hive.
Between 50 and 90 percent of the commercial honey bee (Apis
mellifera) colonies in the United States have been afflicted by
CCD, and the disorder is making it difficult for U.S. commercial
beekeepers to pollinate crops. About a quarter of beekeeping
operations were affected by CCD during the 2006-2007 winter
alone.
Researchers including Lipkin and Diana Cox-Foster, entomology
professor at Pennsylvania State University, and colleagues have
taken a new approach to investigating infectious disease
outbreaks. To find the cause of CCD they used a rapid genome
sequencing technique called pyrosequencing to catalogue the
entire variety of microorganisms that honey bees harbor. After
comparing their sequences with known sequences held in public
databases, they identified symbiotic and pathogenic bacteria,
fungi and viruses found in both healthy and CCD-afflicted
colonies.
They tested samples collected over three years across the United
States from normal and CCD-affected hives. They also tested
royal jelly imported from China, which is fed to bee larvae to
start up a new colony, as well as apparently healthy bees
imported from Australia, in an attempt to locate a source for an
infectious agent. After detailed statistical comparison of all
the samples, the molecular signs of Israeli Acute Paralysis
Virus appeared to be associated with CCD.
“This research gives us a very good lead to follow, but we do
not believe IAPV is acting alone,” said coauthor Jeffery S.
Pettis, research leader of the Bee Research Laboratory, United
States Department of Agriculture. “Other stressors to the colony
are likely involved,” he said. Those stressors could be poor
nutrition, pesticide exposure and parasitic mites.
The next research steps include inducing CCD in healthy bees,
determining the global distribution of IAPV and CCD and studying
bees that appear to be resistant to CCD.
A Metagenomic Survey of Microbes in Honey Bee Colony Collapse
Disorder
D.L. Cox-Foster, E.C. Holmes, D.M. Geiser, D.
vanEngelsdorp, A.L. Kalkstein and L. Cui at Pennsylvania State
University in University Park, PA; S. Conlan, G. Palacios, P-L.
Quan, T. Briese, M. Hornig, A. Drysdale, J. Hui, J. Zhai and
W.I. Lipkin at Columbia University in New York, NY; E.C. Holmes
at Fogarty International Center, National Institutes of Health
in Bethesda, MD; J.D. Evans and J.S. Pettis at U.S. Department
of Agriculture (USDA) Agricultural Research Service in
Beltsville, MD; N.A. Moran and V. Martinson at University of
Arizona in Tucson, AZ; D. vanEngelsdorp at Pennsylvania
Department of Agriculture in Harrisburg, PA; S.K. Hutchison,
J.F. Simons and M. Egholm at 454 Life Sciences in Branford, CT.
The American Association for
the Advancement of Science (AAAS) is the world’s largest
general scientific society, and publisher of the journal
Science. AAAS was
founded in 1848, and serves 262 affiliated societies and
academies of science, reaching 10 million individuals. Science
has the largest paid circulation of any peer-reviewed general
science journal in the world, with an estimated total readership
of 1 million. The nonprofit AAAS (www.aaas.org) is open to all
and fulfills its mission to “advance science and serve society”
through initiatives in science policy; international programs;
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onto EurekAlert!, www.eurekalert.org, the premier science-news
Web site, a service of AAAS.
RELATED RELEASE
from Penn State
Across the nation, beekeepers
have seen hive after hive succumb to Colony Collapse Disorder
(CCD); a team of entomologists and infectious disease
researchers now report a strong correlation between the
occupancy of CCD and a virus, Israeli Acute Paralysis Virus
(IVAP).
"We have not proven a causal
relationship between any infectious agent and CCD," the
researchers report in today's (Sept. 6) issue of Science Express
online. However, they note that the prevalence of IAPV genetic
material in bees suffering from CCD, the timing of the outbreaks
and the geographical circumstances "indicate that IAPV is a
significant marker for CCD."
Many researchers are
investigating CCD because domestic honeybees are vital to a
variety of agricultural crops in the United States. Beekeepers
truck their hives cross country to pollinate almond groves in
California, field crops and forages in the Midwest, apples and
blueberries in the Northeast and citrus in Florida.
Unlike other diseases that have
plagued bees in the past, CCD leaves a hive with a few newly
hatched adults, a queen and plenty of food. Researchers suspect
a pathogen because while bees will not recolonize a CCD hive,
once the hive is irradiated and therefore sterile, bees are
happy to live there.
The disease was recognized in
2006, but beekeepers reported hive declines similar to CCD as
early as 2004. An estimated 23 percent of all beekeeping
operations in the U.S. suffered from CCD during the winter of
2006-2007.
After looking at other methods
of identifying the cause of the disease, the researchers decided
to sequence the genetic material in bees to try to find a
potential pathogen.
"The genome of the honey bee
had just been completed," said Diana Cox-Foster, professor of
entomology, Penn State. "So it was possible to do the sequencing
and then eliminate the genetic material of the bees."
W. Ian Lipkin, M.D., professor
of epidemiology, neurology and pathology at Columbia University
and director of the Center for Infection and Immunity at
Columbia University Mailman School of Public Health, and his
team prepared samples for 454 Life Science -- the company that
developed the array-based pyrosequencer -- to sequence cDNA from
the RNA of the bees.
Researchers analyzed data using
a unique set of algorithms generated at Columbia, did a large
amount of viral sequence comparison, developed real time PCR
assays and cloned the full length IAPV genome, among other
things.
The samples sequenced included
bees from four geographically separated CCD suffering
operations, apparently healthy bees imported from Australia,
non-diseased samples from Pennsylvania and Hawaii, and samples
of royal jelly imported from China. Royal jelly is secreted by
bees and used to feed all larvae, but those fed only with royal
jelly become queens.
"We chose bees from Hawaii
because at that time, those populations were free of varoa
mites, a problem in all mainland hives," says Cox-Foster. "The
royal jelly was not intended for bees, but for human consumption
and cosmetics, but some beekeepers use it to create new queens."
The researchers grouped
material for sequencing as presumed CCD positive, presumed CCD
negative and royal jelly. The pooled RNA sequences were analyzed
for bacteria, fungi, parasites and viruses matches.
Lipkin played a key role in the
search for new or reemerging pathogens, contributing unique
methods. The genetic sequences, minus that of the domestic
honeybee, were eventually matched against GenBank, a database of
genetic sequences maintained by the U.S. National Center for
Biology Information, National Institutes of Health. Ninety-six
percent of the genetic material matched that previously found in
bees.
The bacterial sequences were
those normally found in bees worldwide, analyzed by Nancy A.
Moran, the Regents' professor of ecology and evolutionary
biology, University of Arizona, and colleagues and Jay Evans,
research entomologist, Bee Research Laboratory, U.S. Department
of Agriculture, Agricultural Research Service and colleagues.
"The bacteria found were the
same as those found in two previous studies from two different
parts of the world at two different times," says Cox-Foster.
"They represent mutualistic or symbiotic relationships with the
bees, similar to those of humans and the bacteria found in the
human gut."
Protozoans and fungi analyzed
by Liwang Cui, associate professor of entomology, and David M.
Geiser, associate professor of plant pathology, Penn State
respectively, were associated with both CCD and non CCD
populations.
"We knew before we started that
we would find a boatload of viruses in the bees given our
preliminary research," says Cox-Foster. "Eighteen different
types are known from serology and antibody work in England."
Cox-Foster's and Lipkin's
groups analyzed the viruses. They found the expected viruses,
and they found one that, while identified by researchers at
Hebrew University in 2004, has just now appeared in scientific
publication. This virus, IAPV, along with Kashmir bee virus
(KBV), was found only in CCD populations. In the initial
experiments, the researchers report that "IAPV was found in all
four affected operations sampled, in two of four royal jelly
samples and in the Australian sample. KBV was present in three
of four CCD operations, but not in the royal jelly."
Other viruses and Nosema
parasites had been suggested as the cause of CCD, but the
researchers found that those pathogens appear in both CCD and
non-CCD samples. Only KBV and IAPV correlated with CCD in the
genetic survey. In a recently published study, Jeffery S.
Pettis, research leader, Bee Reseach Laboratory, and colleagues
reported that Nosema ceranae had been in the U.S. for at least
10 years, along with Nosema apis.
Researchers then analyzed
samples collected from 30 CCD colonies and 21 healthy colonies
in the past three years for four pathogens: KBV, IAPV and Nosema
apis and Nosema ceranae -- both fungi that infect bees. They
found that all samples that had IAPV had KBV, but KBV also
occurred in both sick and healthy samples.
"IAPV was found to increase the
risk of CCD with a trend for increased CCD risk in samples
positive for Nosema apis," the researchers said. "Neither KBV
nor N. ceranae contributed significantly to the risk for CCD nor
did they alter the influence of IAPV on CCD."
However, while IAPV may be a
marker for CCD, proving that any organism is the cause of CCD is
somewhat more difficult. The researchers will now try to infect
bee colonies with CCD. Beside general health stress from the
heavy load of pathogens normally carried by bees, other
suggested contributors to CCD include pesticides, drought and
nutritional stress.
Timing also may be the key to
pinpointing the cause. The United States began allowing
importation of bees from Australia in 2004, which coincides with
early reports of CCD. The same year, IAPV, described by Israeli
researchers with symptoms of shivering wings, progressed
paralysis and bees dying outside the hive appeared. While CCD
does not seem to have the same symptoms, this may reflect a
different strain of the virus, co-infection with another
pathogen or the presence of other stressors.
The researchers note that "the
varroa mite, for example, absent in Australia, immunosuppresses
bees, making them more susceptible to infection by other
organisms." Beekeepers used mitocides, chemicals used to control
varroa, on both CCD and healthy colonies.
Edward C. Holmes, professor of
biology, Penn State, and Gustavo Palacios, Columbia University,
were instrumental in determining the evolutionary relationships
of the viruses found in CCD colonies compared to previously
known viruses and isolates from Australia.
While unquestionably it is
important to identify the cause of CCD, this total genetic study
of bees and their fellow travelers also may lead to a better
understanding of other disease causing agents in the population
and to an understanding of the beneficial organisms that reside
within the bee.
Other researchers on the
Penn State team include Dennis vanEngelsdorp, senior extension
associate and State Apiarist for the Pennsylvania Department of
Agriculture, and Abby Kalkstein, research technologist. Other
researchers at Columbia University include Sean Conlan,
Phenix-Lan Quan, Thomas Briese, Mady Hornig, Andrew Drysdale,
Jeffrey Hui and Junhui Zhai. Vince Martinson, University of
Arizona and Stephen K. Hutchison, Jan Fredrik Simons and Michael
Eghom, at 454 Life Sciences, also contributed.
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