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 The mosquito species Aedes aegypti has been identified as the main
transmitter of Zika infections, which have been linked to thousands
of birth defects as the virus spreads rapidly in Brazil and other
countries in Latin America and the Caribbean.
But the scientists in Brazil announced on Wednesday that they were
able to infect another species, Culex quinquefasciatus, with the
virus in a laboratory, raising concerns that Zika could be carried
by a species more prevalent than Aedes aegypti. They said much more
research is needed to learn whether the Culex mosquitoes can
transmit Zika infections.
In Brazil, Culex quinquefasciatus is 20 times more common than Aedes
aegypti, the researchers said.
The research, conducted by scientists at the government-funded
Oswaldo Cruz Foundation in the northeastern city of Recife, is part
of an ongoing trial in which researchers injected 200 of the Culex
quinquefasciatus mosquitoes with rabbit blood infected by Zika.
The virus, they said, circulated through the mosquitoes' bodies and
into their salivary glands, meaning they might be able to transmit a
Zika infection by biting a person.
"We saw an ease of infection and an ease of dissemination of the
virus to the salivary glands," Constancia Ayres, the lead scientist
in the study, told Globo, Brazil's leading television network.
Public health authorities have cited Aedes aegypti as the mosquito
overwhelming responsible for spreading Zika, with another species of
the same genus, Aedes albopictus, also transmitting the virus in
smaller numbers.
There has been evidence about other mosquitoes linked to Zika. For
example, researchers have found more than 20 mosquito species
carrying the virus in Africa, although it was unclear whether they
all transmit the disease effectively to humans.
MOSQUITOES IN THE WILD
The Brazilian research has yet to be published in a scientific
journal or reviewed by scientific peers elsewhere.
The foundation said more work was needed to determine whether Culex
mosquitoes in the wild already are carrying the virus as well as
whether they can transmit Zika infections.
Foundation spokeswoman Fabiola Tavares on Thursday said the
researchers, who will begin capturing Culex mosquitoes in areas near
Recife where the virus is known to be circulating, will now proceed
toward answering those questions. The additional research could take
up to eight months, Tavares added.
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If a mosquito besides Aedes aegypti were found to transmit Zika
infections in large numbers, it could make it more difficult to
contain the current Zika outbreak that the World Health Organization
last month declared a global public health emergency.
Much remains unknown about Zika, including whether the virus
actually causes microcephaly in babies, a condition defined by
unusually small heads that can result in developmental problems.
Brazil said it has confirmed more than 640 cases of microcephaly,
and considers most of them to be related to Zika infections in the
mothers. Brazil is investigating more than 4,200 additional
suspected cases of microcephaly.
Traces of Zika virus have been found in the bodily fluids and tissue
of mothers and babies affected by microcephaly.
Culex quinquefasciatus also exists in more temperate climes, such as
the southern United States, where it is known to carry the West Nile
virus, and can survive winters. Unlike Aedes aegypti, Culex
quinquefasciatus could keep a virus in circulation during cold
months.
Though the Culex mosquitoes prefer to feed on the blood of birds,
they also commonly bite humans, especially in rural areas. That
means that targeted pesticide use and other mosquito control efforts
for that species, which rests in trees and other high areas, would
need to be different from those for Aedes aegypti, which rests in
low spots, often indoors.
"You can't spray up high the way you can around buildings," said
Grayson Brown, director of the University of Kentucky's public
health entomology laboratory who was not involved in the Oswaldo
Cruz Foundation research.
If Culex mosquitoes were indeed proven to transmit Zika, Brown said,
"it would really complicate the public health issue."
(Reporting by Paulo Prada; Additional reporting by Ben Hirschler in
London; Editing by Will Dunham)
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