Penn State
A newly discovered virus infecting the fungus that causes white-nose syndrome in bats could help scientists and wildlife agencies track the spread of the disease that is decimating bat populations in the United States, a new study suggests.
Regional variations in
this virus could provide clues that would help researchers better understand
the epidemiology of white-nose syndrome, according to Marilyn Roossinck,
professor of plant pathology and environmental microbiology, College of
Agricultural Sciences, Penn State.
White-nose syndrome is
a particularly lethal wildlife disease, killing an estimated 6 million bats in
North America since it was identified in 2006. The disease, caused by the
fungus Pseudogymnoascus destructans, first was found in New York
and now has spread to 29 states and four Canadian provinces.
Although several species of bats have been affected, some of the most prevalent species in the Northeast -- such as little brown bats -- have suffered estimated mortality as high as 99 percent.
These losses have serious ecological implications. For
instance, bats have a voracious appetite for insects and are credited with
helping to control populations of mosquitoes and some agricultural pests.
The researchers
examined 62 isolates of the fungus, including 35 from the United States, 10
from Canada and 17 from Europe, with the virus infection found only in North
American samples.
P. destructans is clonal, meaning it is essentially
identical everywhere it has been found in North America, making it difficult to
determine how it is moving, said Roossinck, who also is affiliated with Penn
State's Center for Infectious Disease Dynamics.
"But the virus it
harbors has quite a bit of variation," she said. "For example, in all
the fungal isolates from Pennsylvania we analyzed, the viruses are similar. But
those viruses differ from the ones we found in isolates from Canada, New York
and so forth."
Roossinck explained
that fungal viruses are not readily transmitted among fungi, so the variation
in the viral genome probably is occurring as the virus evolves within each
fungal isolate, providing a marker.
"So we believe
the differences in the viruses reflect the movement of the fungus, and this
viral variability should enable us to get a better handle on how the disease is
spreading," she said.
The virus is not
thought to cause disease, but researchers don't yet know whether it influences
the virulence of the fungus, Roossinck noted.
"It's very
difficult to study virulence in terms of infection in the bats in part because
there are almost no bats left to study, and we don't have an experimental
system that works."
The researchers, who
reported their results online in PLOS Pathogens, were able to
eliminate the virus from one fungal isolate, which provided a virus-free
isolate that they could compare to wild isolates that harbor the virus to look
for biochemical changes.
"Although we
didn't look directly at the role of the virus in white-nose syndrome, there is
evidence of a close biological relationship between the fungus and the
virus," Roossinck said. "We found that the virus-free isolate makes
many fewer spores than an isolate with the virus, suggesting that the virus may
be beneficial to the fungus in reproduction.
"We don't know
whether the fungus spreads through spores or through direct contact between
bats," she said. "But if it spreads via spores, the virus actually
could be enhancing the spread of white-nose syndrome as a result of this
increased spore production."
Roossinck said the
study has important implications in the search for ways to save the bats of
North America.
"There's a lot we don't know about white-nose syndrome, and
before we can develop control strategies, we have to better understand the
biology of the system. We now have a tool that can be used in broader studies
to examine the epidemiology of the disease."