SAN
JUAN, PUERTO RICO—
The United States faces its first real challenge with the
Zika virus on the island territory of Puerto Rico, a part of the nation perhaps
least prepared to cope with what is expected to be its worst outbreak. Zika, spreading rapidly in Puerto Rico, is expected to peak
in late summer and early fall. By year's end, public health officials estimate,
hundreds of thousands of people will have been infected. It is the only part of the country experiencing a major
local outbreak, but the virus is expected to reach southern U.S. states within
weeks with warmer temperatures and rising mosquito populations.
Health officials from across the United States are gathering
today at the headquarters of the Centers for Disease Control and Prevention in
Atlanta to outline a national strategy for combating Zika. In a measure of the
concern surrounding the outbreak in Puerto Rico, CDC director Tom Frieden
toured the island, meeting with top health officials and local experts
last month to assess the situation first-hand.
Conditions ripe for Zika
Puerto Rico is beset with problems already hampering the
response: abundant mosquitoes, high levels of insecticide resistance and
economic woes that have left vector control in shambles."We don't have good surveillance" here, Frieden
said in an interview at the Puerto Rican health department in San Juan during
his tour. "We don't have good control measures."First detected in Brazil last year, the Zika outbreak is
spreading through the Americas. The World Health Organization declared a global
health emergency last month because of growing evidence that Zika can cause
microcephaly, a rare birth defect defined by an unusually small head. In
adults, the virus has been linked to the typically rare autoimmune disorder, Guillain-Barre
syndrome.
Early lessons
Fighting Zika in Puerto Rico is complicated by the toll of a
decade-long recession. Nearly half of its 3.5 million residents live in
poverty, and mosquitoes are an accepted nuisance. Puerto Rico has seen repeated
outbreaks of dengue and, more recently, chikungunya. Both viruses are carried
by Aedes aegypti, the same
species of mosquito that carries Zika.
"Here in Puerto Rico, we're really starting from square
one," said Audrey Lenhart, a CDC vector control expert in an interview at
the CDC's Emergency Operations Center in San Juan.
In its latest report, the Puerto Rican health department
said there are now 350 confirmed cases of Zika infection, including 40 pregnant
women.
"We have a very serious combination of problems,"
said Dr. Alberto de la Vega, an obstetrician specializing in high-risk
pregnancies at San Juan's University Hospital at the Puerto Rico Medical
Center.
"If you don't have access to money to buy repellent, to
sleep with an air conditioner on so mosquitoes won't bite you, to have mosquito
nets around you and you live in areas where there's more stagnant water,
obviously you have higher risks," he said.
To mitigate the risk of microcephaly among newborns, the CDC
and the Puerto Rican government are distributing Zika protection kits to
pregnant women. The kits include insect repellent, bed nets, condoms to prevent
sexual transmission from an infected partner, and larvicide tablets for
standing water that cannot be drained.
De la Vega said many locals were resigned to the idea that
everyone in Puerto Rico would be infected. He said he wouldn't accept
"surrendering like that." Government mosquito abatement resources are scarce, with
fewer than a dozen trucks equipped with insecticide sprayers. Of the
municipalities that do have trucks, most are used to kill nuisance mosquitoes
that bite but do not carry disease, said Manuel Lluberas. The Puerto Rico-born
entomologist works at H.D. Hudson Manufacturing, a maker of spraying equipment.
Lluberas, who advises the WHO and the World Bank on vector
control programs, said few municipalities spray insecticide once every seven to
10 days or once every few weeks.
Spraying "needs to be done a lot more frequently"
to be effective, he said.
Scientists at CDC's Dengue Laboratory in San Juan have been
testing insecticides on mosquitoes gathered from 17 sites on the island.
Frieden said in one of the experiments, mosquitoes placed in bottles coated
with a commonly effective insecticide "were happily flying around."
Insecticide regimen
Eliminating Zika will require spraying insecticide indoors
on walls, under beds, behind furniture and inside closets, where Aedes aegypti hide. So far, only two
insecticides – deltamethrin and bifenthrin – are approved for indoor residual
spraying. Researchers have found high levels of resistance to bifenthrin in
Puerto Rico. Mosquito experts have found similar resistance in parts of
Texas and California. “You find resistance in mosquitoes in one locale, and 20
miles away they are not resistant," said Joseph Conlon, technical adviser
for the American Mosquito Control Association. It represents researchers,
public health officials and pesticide makers.
Dr. Janet McAllister, a CDC entomologist, said indoor
spraying campaigns will be carried out by local contractors, who will target
only areas where the mosquitoes hide instead of coating entire walls, as is
typically done to control mosquitoes that carry malaria.
"People would not really be coming into direct contact
with those surfaces," McAllister said.
She said the CDC does not plan to use experimental methods,
including genetically modified mosquitoes, such as those from Intrexon's Oxitec
now being tested in Brazil, or those infected with Wolbochia bacteria that
prevent Zika transmission.
Given the outbreak’s urgency, health officials need to focus
on known methods of curbing mosquitoes "rather than doing research on
things that may or may not work," she said.
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