Science and Technology

[~ Susan ~]

Virus is likely cause of devastating bee disease
Friday, 7 September 2007
Laura Macfarlane and John Pickrell



SYDNEY: A virus, potentially imported from Australia, has been identified as the likely cause of a mysterious blight that has decimated honey bee populations across the USA.

"Our extensive study suggests the Israeli Acute Paralysis Virus (IAPV) may be a potential cause of colony collapse disorder," said one of the experts behind the discovery, epidemiologist W. Ian Lipkin of Columbia University in New York. "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."

First widely reported last year, with a few cases as early as 2004, Colony Collapse Disorder's (CCD) lethal effects have resulted in a loss of 50 to 90 per cent of hives in a quarter of beekeeping operations across the USA. The impacts of this are potentially huge because around a third of American crops, worth a total of US$14.6 billion annually, are dependent on honey bees to pollinate them.

Comprehensive survey

Theories as to the cause of the honey bee (Apis mellifera) disorder have ranged from pesticides and mites to bacteria and fungi. One suspect has been the varroa or 'vampire' mite, which sucks the blood of bees, leaving them open to other infections.

Now researchers led by Diana Cox-Foster of Pennsylvania State University, who co-chairs the CCD academic working group, have completed the first comprehensive survey of infected hives. Their method involved taking genetic samples from bees in a mixture of over 50 infected and uninfected hives across the nation from Hawaii to Pennsylvania.

As they detail online in the U.S. journal Science today, they used a rapid genome sequencing technique called pyrosequencing to catalogue the entire variety of micro-organisms that honey bees were harbouring.

"The genome of the honey bee had just been completed," said Cox-Foster. "So it was possible to do the sequencing and then eliminate the genetic material of the bees."

They found many different pathogens infecting the bees. Protozoans and fungi found were associated with both healthy and sick hives as well as many harmless bacteria, said Cox-Foster. "They represent mutualistic or symbiotic relationships with the bees, similar to those of humans and the bacteria found in the human gut."

However, hives with CCD were more heavily burdened with pathogens, especially with viruses and two microsporidian parasites. Tellingly the researchers found IAPV in 25 of 30 sick colonies samples but only in one of the 21 CCD-free colonies.

Twist in the tale

"The research gives us a very good lead to follow," said study co-author Jeffery S. Pettis, who heads the Bee Research Laboratory of the United States Department of Agriculture. "But we do not believe IAPV is acting alone – other stressors to the colony are likely involved"

The virus, first isolated by Israeli researchers at the Hebrew University in Jerusalem in 2002, includes symptoms such as shivering wings, progressive paralysis and bees dying outside the hive – some of which have been linked to CCD.

Another twist in the tale links the appearance of CCD with potentially IAPV-infected bees from Australia. The researchers said that all of the beekeeping operations in the study that were infected with IAPV had imported bees from Australia or come into contact with them – while none of the uninfected hives had.

Bees had been imported from Australia to bolster pollination efforts following a shortage in 2004, the same year that CCD started to take hold.

Further tests by Cox-Foster's team revealed that IAPV is commonly present in Australian honey bees. This posed a question as to how Australian bees could have avoided becoming sick if IAPV is the real cause of CCD. In answer to this the researchers noted that U.S. bees are typically infected with the blood-sucking varroa mite that weakens their immune systems while the Australian bees are not.

Next step

Australia's biosecurity measures have so far been able to protect the nation's honeybee industry from varroa mite, which is found across most of the rest of the world, commented entomologist Ken Walker at the Melbourne Museum in Australia.

While he agreed that some of the evidence pointed towards IAPV as the cause for CCD, Walker said multiple factors are still likely to be responsible. "The solution to this problem is urgently needed if we are to effectively manage CCD and keep it out of Australia."

Despite the compelling evidence, some experts are as yet sceptical of the connection. "This paper only adds further to the confusion surrounding CCD," Denis Anderson an entomologist with Australian national research agency the CSIRO, in Canberra, told Science in related news article. His own research has not found any link between IAPV and CCD.

Cox-Foster's team agree that the next step is to experimentally test the correlation by attempting to cause CCD by infecting hives with the virus.


http://www.cosmosmagazine.com/node/1569