AMERICAN SOCIETY OF TROPICAL MEDICINE AND HYGIENE, PHILADELPHIA, DECEMBER 4–8
“We’ve created the perfect habitat for this ectoparasite
that lives in mammals’ nests.” — RAJEEV VAIDYANATHAN
Inbreeding helps bedbugs’ success
By Nathan Seppa
Bedbugs that infest a room
and spread within a building
are often one big extended
family, the offspring of a
single female that begot
sons and daughters that
then interbred with impunity, researchers reported
December 6.
Other scientists reported
on mechanisms that allow bedbugs
to escape death by rapidly evolving to
detoxify insecticides thrown their way.
In that study, the researchers identified
enzymes that the insects need in this
detoxification process.
Cimex lectularius, the bedbug, has
become a scourge of slum tenements and
upscale hotels alike in the past 10 years,
staging an impressive comeback after
being knocked back to insignificance
with insecticides in the 1950s and 1960s.
But even before that there were hints
of future problems, said entomologist
Kenneth Haynes of the University
of Kentucky. The first reports of the
insecticide DDT failing to kill bedbugs
surfaced in 1948, he noted.
To get a reading on the current level
of resistance, Haynes and his colleagues tested 108 bedbug populations
and found that 88 percent had one or
two genetic mutations associated with
resistance to either DDT or pyrethroids,
a widely used family of pesticides. “
Pyrethroid resistance has facilitated in part
the resurgence and/or spread of bedbugs,” Haynes said. The group traced
this resistance to genetic changes that
enabled the bugs to produce enzymes
that detoxify insecticides. To establish
this conclusion, the researchers shut
down the enzymes’ production, which
rendered the bugs vulnerable to delta-methrin, a synthetic pyrethroid.
Bedbugs have enjoyed a resurgence in recent years,
thanks in part to resistance to pesticides.
But bedbugs do more than survive;
they reproduce like crazy. Entomologist Coby Schal of North Carolina State
University and his team investigated
apartment buildings that had reported
infestations and found bugs’ genetic
material typically showed stunning simi-larities, suggesting a single mother. “This
is an extremely high level of inbreeding,”
Schal said, and it apparently didn’t harm
the insects’ survival.
By studying dozens of infestations
from Maine to Florida, the researchers
found that diversity does exist in the
bedbug world — among infestations that
are cities apart. The difference is great
enough to indicate that the current bedbug crisis couldn’t have arisen from a
single introduction of bedbugs that then
spread like wildfire. Rather, the bugs’
clear diversity between cities suggests
many arrivals from outside the United
States, Schal said, pointing to a downside
of global interconnectedness.
While insecticide resistance and global
travel appear to have conspired to bring
on the bedbugs, humans are assisting in
other ways, says Rajeev Vaidyanathan of
SRI International in Harrisonburg, Va.
“The resurgence of these bugs didn’t happen overnight,” says Vaidyanathan. “For
the first time in the history of our species,
we are concentrated in cities. We’ve created the perfect habitat for this ectoparasite that lives in mammals’ nests.”
Averting chikungunya virus
A vaccine against the chikungunya
virus has proven protective in tests
in monkeys, researchers reported.
First identified in the 1950s in
east Africa, the mosquito-borne
virus cropped up in the democratic
republic of the congo in 1999 and
in kenya in 2004 and has since
caused major outbreaks in india
and Southeast Asia. in people, chikungunya infection can cause fever,
joint pain and other symptoms,
some severe. in the new study, scientists at tulane university and the
university of texas medical Branch
at Galveston gave a one-dose vaccine to 12 macaque monkeys, then
exposed the animals to the virus.
none developed disease. unvaccinated monkeys that were exposed
developed hypothermia and heart
and lung distress. —Nathan Seppa
Dengue vaccine tests advance
A vaccine against dengue provides
immunity against all four strains
of the virus in most recipients
and is safe to take, researchers
in Singapore reported. the preliminary results come from a trial
involving 1,200 volunteers ages
2 to 45 randomly assigned to
get either all three doses of the
dengue vaccine spaced over a year
or a control vaccination. the scientists detected signs of immunity
against three of the four dengue
subtypes in 87 percent of vaccine
recipients tested and against all
four subtypes in 67 percent. dengue can cause pain, headache and
hemorrhagic fever. other scientists
at the meeting reported that 13
clinical trials are now under way
testing various dengue vaccines.
— Nathan Seppa
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december 31, 2011 | SCIENCE NEWS | 17
