Biology Reference
In-Depth Information
so the trial was stopped and the area was fogged to kill the mosquitoes (Malaysian Institute for Medical
The Malaysian website noted that 46,171 dengue cases occurred in Malaysia in 2010 and larviciding,
space spraying with insecticides or fogging, public education or legally enforced breeding-site reduction have
not stopped the spread of the disease. However, the website calls the RIDL male mosquitoes “sterile,” which
is not accurate. RIDL mosquito progeny are produced, although most die at the late larval or pupal stage.
Public information was provided to the public before the releases were made, but received a “low turnout of
response from the public,” so it is not clear how informed consent was obtained from people in the affected
area. Public briefings were given to the local news media and to a variety of government officials.
Luisa Reis de Castro published an M.S. thesis on “Big Issues Around a Tiny Insect: Discussing the Release
of Genetically Modified Mosquitoes (GMM) in Brazil and Beyond.” She reported that Margareth Capurro,
a professor at the University of Sao Paolo in Brazil, has led the releases of
Ae. aegypti
containing the RIDL
construct. The mosquitoes were reared at Moscamed and permission to release the transgenic mosquitoes
in five sites was obtained on December 17, 2010. During February 2010, the first releases were made and
additional releases were made with plans to continue for 18 months.
James et al. (2011)
reviewed both the Oxitec transgenic mosquito releases and the
Wolbachia
mosquito
trials in Australia (
Box 14.3
) and pointed out, “Most vector biologists agree that success is reflected
ultimately in reduced morbidity and mortality. Some consider entomological endpoints, such as local
elimination of the principal vector species or complete introgression of a gene or symbiotic species that
causes pathogen refractoriness, as surrogate markers for impact on infection and disease. However, those
familiar with trials of conventional interventions (vaccines, drugs, and insecticides) maintain that sustained
epidemiological and clinical impact should be the primary efficacy endpoint. Observations that dengue
transmission can sometimes continue even with low mosquito population densities are cited as a reason
for vector biologists to conduct trials to measure the incidence of infection and/or disease.” They also note,
“Dengue transmission can be endemic, epidemic, multiyear episodic, and unpredictable, so that trials
may have to continue for years. Trials also must encompass large geographic areas to ensure that there
is sufficient human infection to detect differences between control and treated populations.”
Knols et al.
(2007)
discuss the potential for transgenic mosquitoes and conclude that deployment of genetically modified
mosquitoes “requires competencies beyond the field of biology, and the future of transgenic mosquitoes
will hinge on the ability to govern the process of their introduction in societies in which perceived risks may
outweigh rational and responsible involvement.”
Lavery et al. (2008)
also noted there are complex ethical,
social, and cultural considerations for the site selection for research with genetically modified mosquitoes.
For any pest-management program, it is relevant to consider all alternatives (
Gravitz 2012
). Potential
mosquito-control techniques include indoor residual spraying, insecticide-treated bed nets, odor-baited
insecticide traps, pesticides applied to water where mosquitoes breed, fungus (
Beauveria
) applications that
kill mosquitoes, infection with bacteria that preclude parasite transmission, and genetically engineered
(transgenic) mosquitoes or vaccines. Other options involved the building of more-modern houses with
solid roofs and screens on their windows and doors, as well as modifications of the landscape that result
in habitat that is less suitable for mosquito production. Each approach has advantages and disadvantages
(
Gravitz 2012
). At this point, it is unclear whether RIDL mosquitoes can provide sufficient control to
reduce dengue transmission.
Another possible solution is the development of new vaccines for prevention of dengue (
Dengue Vaccine
Initiative 2012
). The
Dengue Vaccine Initiative (2012)
reported “very substantial progress has been made in
the clinical development of several vaccines and dengue vaccine development has advanced to a point where
it now seems likely that at least one vaccine will be available for use in developing countries, perhaps as early
as 2014.” Clearly, as in all pest-management programs, reliance on a single tactic is unlikely to be sustainable
and multiple tools will be needed to manage the pest unless eradication of the vector can be achieved.
