from the bench
Louisville Expands Arbovirus Surveillance,
Streamlines Mosquito Testing
By Kim Krisberg, writer
Every minute counts when trying to stop
a disease outbreak. Especially when that
disease can cause severe birth defects and
lifelong health problems.
“We knew it was coming,” said Leslie Wolf,
PhD, referring to the 2015 Zika outbreak
in Brazil. “We’re the only public health lab
in the state that tests mosquitoes. …We
needed to beef up our capacity not only to
do our own testing, but if other counties
needed help, we wanted to be ready.”
Wolf is the laboratory technical director in
Kentucky’s Louisville Metro Department
of Public Health and Wellness Laboratory,
which helps monitor hundreds of
community sites throughout the metro
area for mosquito-borne disease.
The resulting data serves as a critical
foundation for the agency’s mosquito
control efforts, essentially providing a
map of potential disease threats and
pinpointing neighborhoods at heightened
risk of transmission. Such control efforts
are hardly new for the agency—the
Louisville public health department has
been operating its Mosquito Control
Program for 60 years—but the emergence
of Zika and its associated birth defects
brought a new urgency to the need to
expand and strengthen the lab’s mosquito
surveillance capacity.
To get ready for Zika’s arrival in the
US, the Louisville lab upgraded its
instrumentation and testing protocols.
The result: the lab not only expanded
the number of mosquito-borne diseases
it monitored, it also shaved a full day
off its mosquito testing process, giving
responders a new advantage in the event
of an outbreak.
“We wanted to get results back to our
mosquito control colleagues so they
could respond in as real-time as possible,”
Wolf said.
Wolf’s colleagues in the agency’s Mosquito
Control Program typically target more
than 300 sites in the Louisville metro area
for ongoing mosquito control from March
16
LAB MATTERS Spring 2018
Before the upgrades, Wolf said
staff could test less than a dozen
pools of mosquitoes at a time for
West Nile. After the upgrades, lab
staff could test mosquitoes for
West Nile as well as Zika virus
and Saint Louis Encephalitis.
through November. Throughout that
time, specially trained staff set out and
collect mosquito traps on a weekly basis.
They then sort the mosquitoes by genus,
species, location and date collected and
deliver the vials of insects to the public
health lab for RNA extraction and testing.
Prior to implementing the new testing
methods, Wolf said the lab only screened
mosquitoes for West Nile virus, human
cases of which have been reported in
Kentucky every year for the last 15 years.
The US Centers for Disease Control and
Prevention (CDC) reports 162 cases of West
Nile virus in Kentucky between 1999 and
2016. And in August 2017, local public
health workers found West Nile-infected
mosquitoes in six Louisville ZIP code
areas. But with the advent of Zika, “we
had to boost our capacity,” Wolf said.
As funding became available, the
Louisville public health lab began
upgrading its equipment, bringing on a
higher-capacity PCR instrument in 2015
and a higher-throughput extractor in 2016.
The changes made a big difference. Before
the upgrades, Wolf said staff could test
less than a dozen pools of mosquitoes at
a time for West Nile. After the upgrades,
lab staff could test mosquitoes for West
Nile as well as Zika virus and Saint
Louis Encephalitis. As for throughput,
the lab went from having an extraction
instrument that did eight mosquito pools
at a time to one that does 96 pools at
a time; its new PCR system went from
testing 32 samples at a time to 96 at a
time. The improvements also shortened
the testing process by a day — from three
days to two.
And all that was accomplished without
putting extra stresses on lab staff. In fact,
Wolf said the old method with its low
throughput meant staff were constantly
having to load sample pools throughout
mosquito season while still keeping up
with their year-round duties. But with
the new instrumentation, Wolf said
the lab was able to both streamline the
mosquito testing process and expand its
surveillance abilities.
“Not only were we able to decrease our
turnaround time, but we’re able to do
more testing without increasing our staff,”
she said.
The new streamlined process was up and
ready to go by the 2016 mosquito season—
the first year that a locally transmitted
case of Zika virus was identified in the
US. In 2016, Wolf said the lab tested 300
mosquito pools between July and October,
with 18 positive for West Nile virus and
none positive for Zika or Saint Louis
Encephalitis. During the 2017 mosquito
season, the lab tested a bit fewer at about
250 pools, which Wolf said is likely due
to having fewer seasonal workers
available to trap, collect and sort the
insects for testing.
Beyond testing for more diseases more
quickly, the lab’s upgrades also enhanced
its verification capacity. Previously, Wolf
said the lab didn’t have the ability to
confirm its mosquito testing results—
the lab tested using validated methods
and colleagues in mosquito control and
environmental health acted on those
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