A 10-month study of healthy honey bees by University of California, San Francisco scientists has identified four new viruses that infect bees, while revealing that each of the viruses or bacteria previously linked to colony collapse is present in healthy hives as well.

The study followed 20 colonies in a commercial beekeeping operation of more than 70,000 hives as they were transported across the country pollinating crops, to answer one basic question: what viruses and bacteria exist in a normal colony throughout the year?

The results depict a distinct pattern of infections through the seasons and provide a normal baseline for researchers studying a colony – the bee population within a hive – that has collapsed. Findings are reported in the June 7 issue of the Public Library of Science ONE (PLoS ONE) at www.PLoSone.org.

The study tracked 27 unique viruses that afflict honey bees, including four that previously were unknown and others proposed as causes of the Colony Collapse Disorder that has been wiping out colonies for the past five years, according to senior author Joe DeRisi, PhD, a Howard Hughes Medical Institute investigator and professor of biochemistry and biophysics at UCSF.

“We brought a quantitative view of what real migrating populations look like in terms of disease,” DeRisi said. “You can’t begin to understand colony die-off without understanding what normal is.”

Because the colonies in this study remained healthy despite these pathogens, the research supports the theory that colony collapse may be caused by factors working alone or in combination, said Michelle Flenniken, PhD, who jointly led the research.

“Clearly, there is more than just exposure involved,” said Flenniken, a postdoctoral scholar in the laboratory of UCSF microbiologist Raul Andino, PhD. “We noticed that specific viruses dominated in some seasons, but also found that not all of the colonies tested positively for a virus at the same time, even after long-distance transport in close proximity.”