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At a recent workshop, experts discussed the benefits, risks, and research priorities associated with using genetically manipulated insects in the control of vector-borne diseases.
DOI: 10.1126/science.1078278
, 119 (2002); 298Science
et al.Luke Alphey,
Vectors
Malaria Control with Genetically Manipulated Insect
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and effectively transmit dengue virus even at
very low population densities because they pref-
erentially and frequently bite humans (23). A
successful GMM dengue control program that
falls short of vector eradication will result in a
reduction in human herd immunity and a corre-
sponding decrease in already low transmission
threshold levels. Because there is no commercial-
ly available vaccine or clinical cure for dengue,
predicting and testing transmission thresholds is
among the most important unanswered questions
in dengue epidemiology and GMM-based control
approaches.
Quantitative Analyses of Mosquito
Biology, Disease, and Control by GMM
A goal of future quantitative analyses should be
to accurately predict outcomes of proposed inter-
ventions instead of simulating events retrospec-
tively. For example, continental-scale predictions
of malaria disease burden are currently being
made on the basis of remotely sensed environ-
mental data that influence mosquito population
dynamics and, in turn, patterns of pathogen trans-
mission (24). Simulation models have been used
to predict entomological thresholds for dengue
transmission (25). Mathematical models have
been developed to identify parameters required to
predict the dynamics of transgene drive mecha-
nisms in vector populations (5, 6, 13, 26). Dif-
ferent drive strategies have been examined and
predictions made for the likely success of each
(5). An analysis of population genetics and epi-
demiology has concluded that in areas of intense
malaria transmission, GMM control programs
will have little if any effect unless mosquito
refractoriness is very close to 100% (13).
Conclusions
The meeting participants reached consensus on
four procedural issues. First, there is an urgent
need to develop uniform processes for dealing
with the ethical, legal, and social issues related to
GMM technology (27). It would be most helpful
if an international body like the World Health
Organization established guidelines, regulatory
mechanisms, and safety, containment, and con-
servation protocols. Second, for the GMM ap-
proach to be initially successful and ultimately
sustainable, its proponents must identify and de-
velop the capacity for human resources and re-
search infrastructure at sites earmarked for tech-
nology evaluation and long-term application.
Third, continued evaluation of GMM technology
will require semi-field facilities (such as large
outdoor cages), followed by release of GMM on
isolated oceanic or ecological islands that have
been thoroughly characterized with respect to the
genetic and ecological makeup of local mosquito
vector populations and site-specific patterns of
pathogen transmission and disease. Fourth, in
addition to population replacement, genetic strat-
egies for mosquito population reduction [such as
RIDL (release of insects carrying a dominant
lethal) and negative heterosis] in isolated urban
areas merit consideration (28).
Addressing these goals will require coordi-
nated interaction among scientists from diverse
disciplines. Only by studying the system in total
will we gain greater insight into the complexity
of interactions that are essential for the design,
implementation, and evaluation of progressively
more successful disease management strategies.
Such an ambitious agenda will require adequate
funding, collaboration between ecologists and
molecular geneticists, recruitment of expertise
from outside the vector-borne disease arena,
training for young scientists, and the expectation
of a sustained effort. The longitudinal field stud-
ies required to address some of the ecological
issues identified will last a decade or more. In all
these actions, people from the countries where
GMM technology is most likely to be applied
need to be more fully involved.
References and Notes
1. J. Trape, G. Pison, A. Spiegel, C. Enel, C. Rogier, Trends
Parasitol. 18, 224 (2002).
2. W. Takken, Trop. Med. Int. Health, in press.
3. A. A. James, in Insect Transgenesis: Methods and
Applications, A. M. Handler, A. A. James, Eds. (CRC
Press, Boca Raton, FL, 2000), pp. 319–333.
4. M. Enserink, Science 297, 30 (2002).
5. M. Turelli, A. A. Hoffmann, Insect Mol. Biol. 8, 243
(1999).
6. J. M. Ribeiro, M. G. Kidwell, J. Med. Entomol. 31,10
(1994).
7. F. M. Okanda et al., Malaria J. 1, 10 (2002).
8. M. J. Donnelly, F. Simard, T. Lehmann, Trends Parasi-
tol. 18, 75 (2002).
9. A. della Torre et al., Science 298, 115 (2002).
10. Y. T. Toure´ et al., Med. Vet. Entomol. 12, 74 (1998).
11. C. E. Taylor, Y. T. Toure´, M. Coluzzi, V. Petrarca, Med.
Vet. Entomol. 7, 351 (1993).
12. N. Lorimer, L. P. Lounibos, J. L. Petersen, J. Econ.
Entomol. 69, 405 (1976).
13. C. Boe¨te, J. C. Koella, Malaria J. 1, 3 (2002).
14. J. Ito, A. Ghosh, L. A. Moreira, E. A. Wimmer, M.
Jacobs-Lorena, Nature 417, 452 (2002).
15. C. Boe¨te, J. C. Koella, Trends Parasitol., in press.
16. N. J. White et al., Lancet 353, 1965 (1999).
17. I. S. Novella et al., J. Mol. Biol. 287, 459 (1999).
18. C. Boe¨te, R. E. L. Paul, J. C. Koella, Parasitology 125,93
(2002).
19. J. D. Charlwood et al., Am. J. Trop. Med. Hyg. 59, 243
(1998).
20. T. A. Smith, R. Leuenberger, C. Lengeler, Trends Para-
sitol. 17, 145 (2001).
21. C. A. Maxwell et al., Trop. Med. Int. Health, in press.
22. A. C. Morrison, A. Getis, T. W. Scott, unpublished
data.
23. T. W. Scott et al., J. Med. Entomol. 37, 89 (2000).
24. D. Rogers, S. E. Randolph, R. W. Snow, S. I. Hay,
Nature 415, 702 (2002).
25. D. A. Focks, R. J. Brenner, J. Hayes, E. Daniels, Am. J.
Trop. Med. Hyg. 62, 11 (2000).
26. A. E. Kiszewski, A. Spielman, J. Med. Entomol. 35, 584
(2002).
27. L. Alphey et al., Science 298, 119 (2002).
28. L. Alphey, M. Andreasen, Mol. Biochem. Parasitol.
121, 173 (2002).
29. We thank the following Wageningin meeting partic-
ipants for helpful comments: K. Aultman, P. Billings-
ley, D. Charlwood, C. Curtis, J. Edman, J. Koella, G.
Lanzaro, S. Lindsay, P. Lounibos, D. O’Brochta, S.
Randolph, W. Reisen, D. Rogers, M. Sabelis, A. Spiel-
man, C. Taylor, and Y. Toure´.
VIEWPOINT
Malaria Control with Genetically
Manipulated Insect Vectors
Luke Alphey,
1
C. Ben Beard,
2
Peter Billingsley,
3
Maureen Coetzee,
4
Andrea Crisanti,
5
Chris Curtis,
6
Paul Eggleston,
7
Charles Godfray,
5
Janet Hemingway,
8
Marcelo Jacobs-Lorena,
9
Anthony A. James,
10
Fotis C. Kafatos,
11
Louis G. Mukwaya,
12
Michael Paton,
13
Jeffrey R. Powell,
14
William Schneider,
15
Thomas W. Scott,
16
Barbara Sina,
17
Robert Sinden,
5
Steven Sinkins,
8
Andrew Spielman,
18
Yeya Toure´,
19
Frank H. Collins
20
At a recent workshop, experts discussed the benefits, risks, and research
priorities associated with using genetically manipulated insects in the
control of vector-borne diseases.
This is a partial report of a workshop—Genet-
ically Engineered Arthropod Vectors of Human
Infectious Diseases—jointly sponsored by the
World Health Organization, the MacArthur
Foundation, the National Institute of Allergy
and Infectious Diseases, and London’s Imperial
College—originally planned for 12 September
2001 in London (but reconvened in successive
sessions later in London and Atlanta). These
workshops sought to encourage communication
between the laboratory-oriented molecular bi-
ologists, whose work had suggested the poten-
tial of genetic control strategies, and the popu-
lation geneticists, ecologists, and public health
specialists, whose involvement would be cru-
cial in moving the work beyond the laboratory.
The meeting participants were charged with
considering the benefits and risks of using ge-
netically engineered arthropod vectors as public
www.sciencemag.org SCIENCE VOL 298 4 OCTOBER 2002
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T HE M OSQUITO G ENOME: A NOPHELES GAMBIAE
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health tools and mapping out a research agenda
for their development. The task of engineering
different vector species and the risks associated
with various methods of genetic engineering
are vastly different and could not be addressed
in a single report. What follows is the consen-
sus of the working group on germline-trans-
formed organisms developed for control of ma-
laria transmission (authors listed above) and
other participants. The reports of the working
groups on paratransgenesis (transformation of
obligate symbionts in insects) and on other
vector-borne diseases will be presented in the
near future.
In 1991, a scientific workshop in Arizona
assessed the prospect for malaria control by
genetic manipulation of vector populations (see
the Viewpoint by Morel et al. on page 79) (1).
The basic concept of genetic control of vector-
borne diseases was proposed by Curtis in 1968
(2), but major advances in the molecular ma-
nipulation of Drosophila melanogaster during
the 1980s encouraged reevaluation of this idea.
The WHO/TDR summary document of the
meeting laid out a clear list of research aims that
would have to be met before a genetic control
strategy could be field tested (3). These aims
fell into three categories: (i) the development of
genetic engineering tools that could be used
with malaria vectors; (ii) the identification of
effector genes that could block parasite trans-
mission; and (iii) the development of effective
methods for driving these effector genes to
fixation in natural vector populations.
The first two aims have been largely
achieved. Several different but effective
methods of germline transformation have
been developed and used in at least three
species of malaria mosquito vector (4 6);
two different laboratories have developed ge-
netic constructs that significantly reduce vec-
tor competence in experimental malaria mod-
els (7, 8). A large set of molecular markers
has been developed and is being used in
studies of gene flow and population structure
in anopheline malaria vectors (913). But
there has been no significant progress in de-
veloping methods for driving desirable genes
into wild populations and especially for en-
suring the necessary unbreakable linkage be-
tween the drive system and the gene to be
driven (see the Viewpoint by Scott et al.on
page 117) (14).
Consideration of the potential use of ge-
netically modified organisms (GMOs) is
driven by the realization of the enormous
human cost of diseases like malaria, and of
the inadequacy of present control measures.
Perhaps the most important theme emerging
from the workshop was the recognition that
control strategies involving GMOs could po-
tentially provoke serious public mistrust and
resistance to their implementation. Therefore
it was strongly recommended that all work
leading to the development of specific genet-
ic control strategies targeted at malaria vec-
tors should involve both public health spe-
cialists and scientists from disease-endemic
countries and (where possible) the general
public in areas where field trials could be
implemented. Because field trials of geneti-
cally modified mosquitoes would have to be
preceded by long-term, longitudinal studies
of potential field-trial sites, the local commu-
nity and its own scientists and health experts
can easily be involved.
The goal of producing GMOs intended to
benefit human health has been perceived more
favorably by the public than that of producing
GMOs for agricultural or domestic animal re-
search. However, meeting participants strongly
argued that this positive public perception could
be rapidly undermined by an actual field trial of
a transgenic arthropod that failed to provide a
significant and tangible health benefit to the
resident human community. It was therefore
recommended that all preliminary research de-
signed to lead to field trials of the efficacy of a
transgenic arthropod-based disease control
strategy should involve fully contained labora-
tory or cage environments. Release should be
permitted only when all relevant parameters
had been investigated in either contained envi-
ronments or in open field studies that did not
involve transgenic arthropods. Furthermore,
field trials involving release of transgenic ar-
thropods should take place only when all mem-
bers of both scientific and local community
review groups were assured that such trials had
a very high probability of producing a signifi-
cant and measurable public health benefit for
the local community.
Many important ecological and popula-
tion genetic issues must be understood before
any release program can be contemplated,
and such issues will be specific not only to
individual vector species but also to local
populations (see the Viewpoint by Scott et al.
on page 117) (14). Understanding the dynam-
ics of a natural population will require years
of study, with the time frame dependent on
the stability and repeatability of yearly cy-
cles. Thus, given progress in the laboratory, it
is important to start the ecological and pop-
ulation genetic study of potential target pop-
ulations soon, as this will be the biggest
scientific limitation to implementing genetic
control field trials. A large number of tech-
nical problems will have to be addressed,
ranging from the feasibility of producing an
effective release strain to the design and as-
sessment of release strategies with specifical-
ly predicted goals. To address such problems
will require the involvement of ecologists and
population geneticists. Most participants rec-
ommended that study of potential field-trial
sites should be initiated immediately at mul-
tiple different locations, recognizing that the
initial phase of fieldwork might show one or
more of the selected sites to be unsuitable.
Because the biology of vector populations at
any such site would have to be studied for
many years before field trials could be de-
signed, the community cannot investigate dif-
ferent sites sequentially.
GMOs could be used in either of two ways
for malaria control. The initial concept (ex-
pressed in the 1991 meeting) was to engineer
mosquitoes with an altered phenotype that
would be introduced into the population in such
a way that the new trait would spread and
become dominant. These strategies target the
malaria parasite, rather than the mosquito itself,
for reduction. There is an immediate research
need for the study of drive systems in Anopheles
species. These drive systems also present a po-
tential hazard because they may generate unin-
tended phenotypes and have unforeseen, poten-
tially harmful ecological effects. Autonomous
transposons, for example, could increase the
mutation rate through multiple genomic inser-
tions, leading to unanticipated alterations in the
biology of the target species. Tight linkage of
the drive system and the engineered gene is also
an important issue in that its loss in the progeny
of released mosquitoes could lead to loss of
public health efficacy and loss of the molecular
tool for future engineering efforts. Although
transposon and symbiont systems have garnered
the most attention to date, participants recog-
nized the need to explore any possible drive
system that could continue to propagate a re-
leased genetic construct through the target pop-
ulation after initial release.
An alternative use of genetic engineering for
malaria control takes a more traditional ap-
proach. This involves targeting the mosqui-
to population per se for reduction. Proposed
improvements in sterile insect techniques,
including release of insects carrying domi-
nant lethals (RIDL) (15), and other mech-
anisms of genetic sexing may alter the
prognosis for these strategies. In these sit-
uations the release of large numbers of
insects presents other specific challenges:
for example, the need to release only male
mosquitoes so as not to increase the number
or nature of mosquito bites per person per
night. In the absence of an existing drive
1
Oxford University, UK.
2
National Center for Infec-
tious Diseases, Centers for Disease Control and Pre-
vention, USA.
3
University of Aberdeen, UK.
4
South
African Institute for Medical Research, South Africa.
5
Imperial College, London, UK.
6
London School of
Tropical Medicine and Hygiene, UK.
7
Keele University,
UK.
8
Liverpool School of Tropical Medicine, UK.
9
Case
Western Reserve University, USA.
10
University of Cal-
ifornia, Irvine, USA.
11
European Molecular Biology
Laboratory, Germany.
12
Uganda Virus Research Insti-
tute, Uganda.
13
Health and Safety Executive, HSC, UK.
14
Yale University, USA.
15
Environmental Protection
Agency, USA.
16
University of California, Davis, USA.
17
Fogarty International Center, NIH, USA.
18
Harvard
School of Public Health, USA.
19
Special Programme
for Research and Training in Tropical Diseases (TDR),
WHO.
20
University of Notre Dame, USA.
4 OCTOBER 2002 VOL 298 SCIENCE www.sciencemag.org120
T HE M OSQUITO G ENOME: A NOPHELES GAMBIAE
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system, participants considered the use of
inundative release of refractory mosquitoes
as a strategy for limited field-testing of the
performance of specific genetically engi-
neered vector strains. Although considered
suitable only for a small vector population
with limited interpopulation gene flow
(such as a real or ecological island setting),
the ability to limit or quickly control un-
foreseen risks in the genetic manipulation
of an island population will be important in
early-stage trials designed to demonstrate
the efficacy of particular genetic modifica-
tions of the vector population.
Although there was support for continued,
intensive research in this area, a clear recom-
mendation emerged that there should be no pre-
cipitous releases of transgenic arthropods. The
malaria group was willing to recommend bar-
ring field trials of transgenic insects that were
designed solely for research; others felt that
initial field safety testing of the various individ-
ual elements of the engineered organism was
crucial to development. The parallel processes
of drug and vaccine development illustrate these
two views. For either product, and indeed for
engineered Anopheles mosquitoes, there is a
requirement for preliminary studies of safety
and efficacy in culture and in animal models
before the first clinical trial is initiated. With
many new drugs (other than cancer drugs), the
first human trials are performed in small num-
bers of normal healthy volunteers, and safety is
the end point examined. In these situations it
would be inappropriate to endanger patients
who are already sick by exposing them to a drug
candidate of unknown toxicity. By contrast,
when new vaccines are developed, they are most
often combined with adjuvants that improve
their potency or direct their effects to one or
more segments of the human immune system.
Under its current guidelines the U.S. Food and
Drug Administration does not allow investiga-
tion of the adjuvants alone without the vaccine
candidate being tested at the same time. The
malaria working group requires tangible bene-
fits at each phase of field testing. The other
working groupsdiscussing symbionts, trans-
ducing viruses, and other mechanisms of driving
traits into populationsdecided to follow drug-
development protocols. These differences may
be appropriate given the different nature of the
engineering tools and the different risks associ-
ated with each one.
Despite nearly universal recognition that
enormous technical and sociological problems
must be overcome before the implementation of
genetic control strategies for malaria can be field
tested, participants concluded that public health
strategies incorporating transgenic vectors offer
the potential of health benefits. Participants
from disease-endemic areas, many of whom had
limited prior exposure to transgenic arthropod
research or policy discussions, were among the
most supportive and optimistic about the public
health goals such strategies hope to achieve.
Participants also noted that the broad scope of
biological research required for the development
of genetic control strategies is likely to contrib-
ute both to the more efficient application of
currently available control tools and to the de-
velopment of new approaches.
References
1. C. M. Morel, Y. T. Toure´, B. Dobrokhotov, A. M. J.
Oduola, Science 298, 79 (2002).
2. C. F. Curtis, Nature 218, 368 (1968).
3. Prospects for malaria control by genetic manipulation
of its vectors (TDR/BCV/MAL-ENT/91.3) (World
Health Organization, Geneva, 1991).
4. C. J. Coates, N. Jasinskiene, L. Miyashiro, A. A. James,,
Proc. Natl. Acad. Sci. U.S.A. 95, 3748 (1998).)
5. F. Caterrucia et al., Nature 405, 959 (2000).
6. G. L. Grossman et al., Insect Mol. Biol. 10, 597 (2001).
7. M. de Lara Capurro, Am. J. Trop. Med. Hyg. 62, 427
(2000).
8. J. Ito et al., Nature 417, 452 (2002).
9. D. Y. Onyabe, J. E. Conn, Heredity 87, 647 (2001).
10. M. J. Donnelly, M. C. Licht, T. Lehmann, Mol. Biol.
Evol. 18, 1353 (2001).
11. W. C. Black IV, G. C. Lanzaro, Insect Mol. Biol. 10,3
(2001).
12. C. Walton et al., Mol. Ecol. 10, 569 (2001).
13. R. Wang, F. C. Kafatos, L. Zheng, Parasitol. Today 15,
33 (1999).
14. T. W. Scott, W. Takken, B. G. J. Knols, C. Boe¨te,
Science 298, 117 (2002).
15. D. D. Thomas, C. A. Donnelly, R. J. Wood, L. S. Alphey,
Science 287, 2474 (2000).
VIEWPOINT
Malaria—a Shadow over Africa
Louis H. Miller
1
and Brian Greenwood
2
Reduction in severe disease and death from falciparum malaria in Africa
requires new, more effective and inexpensive public health measures. The
completed genomes of Plasmodium falciparum and its vector Anopheles
gambiae represent a big step toward the discovery of these needed tools.
The current focus of malaria control programs in
Africa is rightly on the management of sick
children through early treatment with effective
antimalarial drugs. However, this cannot be the
final strategy. The two first-line drugs, chloro-
quine and sulfadoxine/pyrimethamine (Fan-
sidar), are no longer effective in many parts of
East Africa where chloroquine resistance (intro-
duced from Asia) is rampant. Combinations of
new drugs may help to slow the emergence and
spread of resistant parasites (1), but control strat-
egies based on early treatment mean a never-
ending struggle to develop and deploy new drugs
before the Plasmodium malaria parasites become
resistant to existing drugs. Thus, the long-term
control strategy must be to interrupt the trans-
mission of this parasite. Unfortunately, this will
be extremely difficult in parts of Africa where
people may be bitten as many as 1000 times a
year by infected mosquitoes. Insecticide-treated
bed netsnow being vigorously promoted in
many parts of Africareduce bites from infect-
ed mosquitoes by as much as 90% (2). However,
their effectiveness is already under threat as a
result of the emergence of pyrethroid resistance
in Anopheles funestus in Mozambique and in A.
gambiae in agricultural areas of West Africa (3).
Household spraying with residual insecticides is
highly effective in reducing malaria in some
parts of Africa, but it is logistically demand-
ing, costly, and may have adverse environ-
mental effects.
There are many ways to reduce malaria
transmission, but none can provide a complete
block in transmission, particularly in the highly
endemic areas of Africa (4), and new approaches
are desperately needed (5). Publication of the
Plasmodium falciparum (6) and Anopheles gam-
biae genomes (7) represents a big step forward
in our search for new tools for controlling ma-
laria. Combined deployment of three strategies
that each have the potential to reduce malaria
transmission by 90% drug treatment, vaccina-
tion, and vector controlshould be sufficient to
stop transmission, even in highly endemic areas
of Africa. We will need to first test such strate-
gies in areas with a low intensity of transmission
before attempting the challenging task of pre-
venting malaria transmission in the highly en-
demic areas of Africa.
Anyone who has thought deeply about the
problem of reducing severe disease and death
from malaria in Africa realizes the crucial need
for a malaria vaccine. Pre-erythrocytic, blood-
stage, and transmission-blocking vaccines have
recently been developed by a number of groups
(8). Each type of vaccine has a part to play in
the complex, highly diverse epidemiology of
malaria and the associated variety of patterns of
1
Laboratory of Malaria and Vector Research, National
Institute of Allergy and Infectious Diseases, Bethesda,
MD 20892, USA.
2
Department of Infectious and Trop-
ical Diseases, London School of Hygiene and Tropical
Medicine, London WC1B 3DP, UK.
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... One of the promising methods under development is the sex-specific expression of fluorescent markers at an early developmental stage, ideally Keywords: Malaria, Vector control, COPAS embryonic or first instar larval [24,27,28]. Such methods can be used to produce a male-only population very early in development, either by conditionally killing the females or by removing them using sex-specific differential expression of fluorescent transgenic markers [24,29,30]. Sex separation in early development minimizes rearing costs and facilitates the handling and processing of male-only based releases. ...
Article
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Background South Africa has set a mandate to eliminate local malaria transmission by 2023. In pursuit of this objective a Sterile Insect Technique programme targeting the main vector Anopheles arabiensis is currently under development. Significant progress has been made towards operationalizing the technology. However, one of the main limitations being faced is the absence of an efficient genetic sexing system. This study is an assessment of an An. arabiensis (AY-2) strain carrying the full Y chromosome from Anopheles gambiae , including a transgenic red fluorescent marker, being introgressed into a South African genetic background as a potential tool for a reliable sexing system. Methods Adult, virgin males from the An. arabiensis AY-2 strain were outcrossed to virgin females from the South African, Kwazulu-Natal An. arabiensis (KWAG strain) over three generations. Anopheles arabiensis AY-2 fluorescent males were sorted as first instar larvae (L1) using the Complex Object Parametric Analyzer and Sorter (COPAS) and later screened as pupae to verify the sex. Life history traits of the novel hybrid KWAG-AY2 strain were compared to the original fluorescent AY-2 strain, the South African wild-type KWAG strain and a standard laboratory An. arabiensis (Dongola reference strain). Results The genetic stability of the sex-linked fluorescent marker and the integrity and high level of sexing efficiency of the system were confirmed. No recombination events in respect to the fluorescent marker were detected over three rounds of introgression crosses. KWAG-AY2 had higher hatch rates and survival of L1 to pupae and L1 to adult than the founding strains. AY-2 showed faster development time of immature stages and larger adult body size, but lower larval survival rates. Adult KWAG males had significantly higher survival rates. There was no significant difference between the strains in fecundity and proportion of males. KWAG-AY2 males performed better than reference strains in flight ability tests. Conclusion The life history traits of KWAG-AY2, its rearing efficiency under laboratory conditions, the preservation of the sex-linked fluorescence and perfect sexing efficiency after three rounds of introgression crosses, indicate that it has potential for mass rearing. The potential risks and benefits associated to the use of this strain within the Sterile Insect Technique programme in South Africa are discussed.
... Although An. arabiensis is known to be a less efficient vector compared to An. gambiae and An. (Eckhof et al., 2017;Alphey et al., 2002;Deredec et al., 2011;Burt, 2003;James, 2005;. Another novel approach is to reduce the mosquito lifespan by introducing a lethal gene or a pathogen in the mosquito population Pumpuni et al., 1996). ...
... This has led to global recognition of an urgent need for additional methods in malaria control (WHO 2015, Alonso andNoor 2017). Genetic technologies hold great promise as an important addition to an integrated approach to reduction and, over time, elimination of malaria (Alphey et al. 2002, Matthews 2011, Gabrieli et al. 2014, Adelman 2015, Gantz et al. 2015. Target Malaria aims to develop and share innovative, costeffective, and sustainable genetic technologies for malaria control. ...
Article
The Institut de Recherche en Sciences de la Santé (IRSS) of Burkina Faso, West Africa, was the first African institution to import transgenic mosquitoes for research purposes. A shift from the culture of mosquito research to regulated biotechnology research and considerable management capacity is needed to set up and run the first insectary for transgenic insects in a country that applied and adapted the existing biosafety framework, first developed for genetically modified (GM) crops, to this new area of research. The additional demands arise from the separate regulatory framework for biotechnology, referencing the Cartagena Protocol on Biosafety, and the novelty of the research strain, making public understanding and acceptance early in the research pathway important. The IRSS team carried out extensive preparations following recommendations for containment of GM arthropods and invested efforts in local community engagement and training with scientific colleagues throughout the region. Record keeping beyond routine practice was established to maintain evidence related to regulatory requirements and risk assumptions. The National Biosafety Agency of Burkina Faso, Agence Nationale de Biosécurité (ANB), granted the permits for import of the self-limiting transgenic mosquito strain, which took place in November 2016, and for conducting studies in the IRSS facility in Bobo-Dioulasso. Compliance with permit terms and conditions of the permits and study protocols continued until the conclusion of studies, when the transgenic colonies were terminated. All this required close coordination between management and the insectary teams, as well as others. This article outlines the experiences of the IRSS to support others undertaking such studies. The IRSS is contributing to the ongoing development of genetic technologies for malaria control, as a partner of Target Malaria (https://targetmalaria.org). The ultimate objective of the innovation is to reduce malaria transmission by using GM mosquitoes of the same species released to reduce the disease-vectoring native populations of Anopheles gambiae s.l.
... Additionally, physical confinement can be used to research modified mosquitoes incorporating gene drive (Alphey et al. 2002;Benedict et al. 2008). There should have been a test outside the laboratory for GMM to reproduce or spread the modification to wild mosquitoes. ...
Chapter
Advancements in genetic engineering have resulted in the development of mosquitoes with impaired vector competence, thereby limiting acquisition and transmission of pathogens. The main dengue (DENV) vector, Aedes aegypti, is an invasive species that have spread unwittingly across the world as a result of human trade and travel. The Ae. aegypti mosquito species has spread across tropical and subtropical regions, with higher presence in urban regions where rapid breeding patterns have shown in artificial containers. Identification of and treating an adequate number of mosquito breeding sites as a control measure have been done for the past couple of years, and yet improvement is far from the expectations, even with well-funded and well-organized initiatives. In order to stop the pathogen transmission, genetically modified mosquitoes (GMM) needs to be created and released. Despite many Aedes-related achievements, GMM creation has been challenging. The spread of particular genetic elements that impair vector competence, trigger deleterious recessive mutations, or skew a population's sex ratio can be used to prevent the spread of vector disease, or eradicate invasive organisms in a species-specific and eco-friendly manner. In recent years, genome editing strategies have evolved to make use of a variety of nucleases, ranging from sequence-specific zinc finger nucleases to modular TALENs (transcription activator-like effector nucleases) and most recently, RNA-guided nucleases adapted from bacterial adaptive immune systems, dubbed CRISPR/Cas (clustered regularly interspaced palindromic repeats/CRISPR associated systems). By combining these methods, a new era in gene editing had emerged. Generally, both of these gene editing technologies utilize sequence-specific nucleases to generate double-stranded DNA breaks (or nicks) in the target sequence, resulting in desired DNA modifications using endogenous DNA repair mechanisms. Since cells with DNA lesions are unable to divide further, the nuclease-generated strand breaks must be rapidly repaired by the cell to maintain the viability. CRISPR/Cas has been widely accepted for use in a variety of organisms, including insect species, with only minor optimization steps needed thus far. CRISPR/Cas9 technology transformed the process of engineering nucleases capable of cleaving complex genomic sequences. A complementary guide RNA (gRNA) directs the Cas9 endonuclease's operation to the specific DNA target site, enabling the editing of virtually any DNA sequence without complex protein engineering and selection procedures. Apart from genome editing, the specificity and flexibility of the CRISPR/Cas9 method enables unprecedented rapid development of genetically modified organisms with mutation systems for disease vector insect control. The stability and expression of the gene construct generated by CRISPR/Cas9 or any other method must be addressed before GMM are released, in order to make sure that pathogen transmission and formulation are interrupted robustly and completely. Spreading foreign antipathogen genes through gene drive strategies among wild mosquito populations strengthens the case for a more streamlined approach. Major fields that must be adequately assessed include risk evaluation and management, conducting studies to ensure human and environmental protection, developing effective control strategies built on comprehensive gene-driving systems, and adequately addressing the ethical, legal, and social consequences of GMM release. Although GMM is theoretically feasible as a disease control method, field releases should be made only when strong scientific evidence of human and environmental protection and effectiveness are presented, and public acceptance is addressed appropriately. This chapter discusses the diverse technological advances in generating Ae. aegypti mosquitoes which are resistant to dengue virus (DENV) and other diseases, as well as the biosafety and risk assessment of these procedures. Additionally, the chapter outlines a convincing path forward for developing successful genetic-based DENV control strategies based on CRISPR/Cas9, which could be expanded to control other arboviruses while maintaining biosafety.
... Currently, there are no specific drugs or vaccines against ZIKV infection, with vector control being the only viable method for alleviating the diseases caused by this virus. Genetic manipulation of vectors to modulate vector competence is also a potential novel approach for controlling vector-borne diseases [8][9][10]. Therefore, knowledge of molecular interactions between viruses and mosquito hosts is critical to manipulating vector competence. ...
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Background Zika virus (ZIKV) is transmitted to humans primarily by Aedes aegypti . Previous studies on Ae. aegypti from Jiegao (JG) and Mengding (MD) in Yunnan province, China have shown that these mosquitoes are able to transmit ZIKV to their offspring through vertical transmission, indicating that these two Ae. aegypti strains pose a potential risk for ZIKV transmission. However, the vector competence of these two Ae. aegypti strains to ZIKV has not been evaluated and the molecular mechanisms influencing vector competence are still unclear. Methods Aedes aegypti mosquitoes from JG and MD were orally infected with ZIKV, and the infection rate (IR), dissemination rate (DR), transmission rate (TR) and transmission efficiency (TE) of these two mosquito strains were explored to evaluate their vector competence to ZIKV. On 2, 4 and 6 days post-infection (dpi), the small RNA profiles between ZIKV-infected and non-infected Ae. aegypti midgut and salivary gland tissues were compared to gain insights into the molecular interactions between ZIKV and Ae. aegypti . Results There were no significant differences in the IR, DR, TR and TE between the two Ae. aegypti strains ( P > 0.05). However, ZIKV RNA appeared 2 days earlier in saliva of the JG strain, which indicated a higher competence of the JG strain to transmit ZIKV. Significant differences in the microRNA (miRNA) expression profiles between ZIKV-infected and non-infected Ae. aegypti were found in the 2-dpi libraries of both the midgut and salivary gland tissues from the two strains. In addition, 27 and 74 miRNAs (|log2 fold change| > 2) were selected from the miRNA expression profiles of ZIKV-infected and non-infected midgut and salivary gland tissues from the JG and MD strains, respectively. Conclusions Our results provide novel insights into the ZIKV–mosquito interactions and build a foundation for future research on how miRNAs regulate the vector competence of mosquitoes to this arbovirus. Graphical abstract
Chapter
The emerging and re-emerging vector-borne diseases are a serious public health problem throughout the world. It has been observed that more than 100 countries and approximately half of the world’s population are at risk on vector-borne diseases (VBDs). The global burden of the vector-borne diseases is unacceptably high. It alludes toward their functional inappropriateness, untimeliness, and irrelevance in controlling vectors and vector-borne diseases. Modern technologies, coupled with other appropriate ones within the precincts of integrated vector management (IVM), can tide over this situation posed by conventional, mostly insecticide-based, methodologies. A lot of challenges, obstacles, and interruptive factors have warranted urgent deployment of new approaches for the control of VBDs keeping in mind the inbuilt ethical, social, and regulatory issues. Genetically modified mosquito (GMM) technology is a complex and highly sophisticated biotechnological intervention for suppression of vector populations. Wolbachia-associated sterile insect technique (SIT) has been proved highly significant and effective for replacement of mosquito populations. Adopting a highly sophisticated GMM technology to suppress or replace the mosquito populations’ density is a big question in developing countries because their priority is directed to foremost fulfill the basic human rights to sustain. Yet, notwithstanding foreseeable bottlenecks, of paramount importance is the need to deploy GMM technology with due consideration to socioeconomic factors and availability of advanced biotechnological facilities during the application of GMM in the developing countries.
Chapter
In Northern State, Sudan, a feasibility study for sterile insect technique (SIT) in an area-wide integrated pest management was established for the first time in an African country. The aim of the study was to see whether it is feasible, from a technical, an economical and a biological perspective, to use sterile male mosquitoes to control mosquito populations in designated areas in the African context. The project was focussed on Anopheles arabiensis, one of the major malaria vectors. Meteorological data, larval surveillance and population genetic studies were carried out on the disease vectors. The first phase of the study focussed on the development of an efficient sex-separation system, development of dose-sterility curves for the pupal and adult stages and testing of a range of doses in competition experiments to determine effective sterility dose. This stage was followed by a semi-field phase that monitored their swarming and mating behaviours, effectiveness of irradiated males in competitive experiments with wild males and insemination rates. Information regarding irradiation and transportation of irradiated males were also obtained during the study. Unfortunately, the SIT study was terminated in 2017 before starting field release of irradiated males. In spite of the challenges, such investment need not be totally abandoned as valuable experience has been gained and capacity built, which are of high value to malaria control program in Sudan.
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Novel malaria control strategies using genetically engineered mosquitoes (GEMs) are on the horizon. Population modification is one approach wherein mosquitoes are engineered with genes rendering them refractory to the malaria parasite coupled with a low-threshold, Cas9-based gene drive. When released into a wild vector population, GEMs preferentially transmit these beneficial genes to their offspring, ultimately modifying a vector population into a non-vector one. Deploying this technology awaits evaluation including ecologically contained field trials. Here, we consider a process for site selection, the first critical step in designing a trial. Our goal is to identify a site that maximizes prospects for success, minimizes risk, and serves as a fair, valid, and convincing test of efficacy and impacts of a GEM product intended for large-scale deployment in Africa. We base site selection on geographical, geological, and biological, rather than social or legal, criteria. We recognize the latter as critically important but not preeminent. We propose physical islands as being the best candidates for a GEM field trial and present an evaluation of 22 African islands. We consider geographic and genetic isolation, biological complexity, island size, topography, and identify two island groups that satisfy key criteria for ideal GEM field trial sites.
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In insects, cuticular pigmentation genes have been exploited as potential visible markers for constructing genetic manipulation systems. Here, we cloned cysteine sulfinic acid decarboxylase (CSAD), an orthologue of melanin metabolism pathway genes, and performed RNAi experiments in the brown planthopper Nilaparvata lugens (Hemiptera: Delphacidae). The results showed that a decrease in the level of transcription of NlCSAD increased melanin deposition in the body compared to the control group, resulting in darker cuticle pigmentation. Female adults treated with dsNlCSAD and mated with wild-type males laid significantly fewer eggs than the dsGFP-treated group, and lower hatchability of the eggs was also observed. In addition, two melanic mutant N. lugens strains (NlCSAD−/+ and NlCSAD−/−) constructed by the CRISPR/Cas9 genome editing system showed darker cuticular melanisation and a reduced oviposition and hatching rate, but the homozygotes had a darker body colour, fewer eggs and lower hatchability than heterozygotes or individuals after RNAi. Thus, we have provided the first evidence that NlCSAD is required for normal body pigmentation in adults and has a role in the fecundity of females and hatchability of eggs in N. lugens via a combination of RNAi and knockout of target genes based on the CRISPR/Cas9 genome editing system. Our results suggest that NlCSAD is a candidate visual reference gene for genetic manipulation of this important crop pest.
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A major modification to the sterile insect technique is described, in which transgenic insects homozygous for a dominant, repressible, female-specific lethal gene system are used. We demonstrate two methods that give the required genetic characteristics in an otherwise wild-type genetic background. The first system uses a sex-specific promoter or enhancer to drive the expression of a repressible transcription factor, which in turn controls the expression of a toxic gene product. The second system uses non–sex-specific expression of the repressible transcription factor to regulate a selectively lethal gene product. Both methods work efficiently inDrosophila melanogaster, and we expect these principles to be widely applicable to more economically important organisms.
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Anopheline mosquito species are obligatory vectors for human malaria, an infectious disease that affects hundreds of millions of people living in tropical and subtropical countries. The lack of a suitable gene transfer technology for these mosquitoes has hampered the molecular genetic analysis of their physiology, including the molecular interactions between the vector and the malaria parasite. Here we show that a transposon, based on the Minos element1 and bearing exogenous DNA, can integrate efficiently and stably into the germ line of the human malaria vector Anopheles stephensi , through a transposase-mediated process.
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Transgenic mosquitoes resistant to malaria parasites are being developed to test the hypothesis that they may be used to control disease transmission. We have developed an effector portion of an antiparasite gene that can be used to test malaria resistance in transgenic mosquitoes. Mouse monoclonal antibodies that recognize the circumsporozoite protein of Plasmodium gallinaceum can block sporozoite invasion of Aedes aegypti salivary glands. An anti-circumsporozoite monoclonal antibody, N2H6D5, whose corresponding heavy- and light-chain gene variable regions were engineered as a single-chain antibody construct, binds to P. gallinaceum sporozoites and prevents infection of Ae. aegypti salivary glands when expressed from a Sindbis virus. Mean intensities of sporozoite infections of salivary glands in mosquitoes expressing N2scFv were reduced as much as 99.9% when compared to controls.
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The mariner transposable element is capable of interplasmid transposition in the embryonic soma of the yellow fever mosquito, Aedes aegypti. To determine if this demonstrated mobility could be utilized to genetically transform the mosquito, a modified mariner element marked with a wild-type allele of the Drosophila melanogaster cinnabar gene was microinjected into embryos of a kynurenine hydroxylase-deficient, white-eyed recipient strain. Three of 69 fertile male founders resulting from the microinjected embryos produced families with colored-eyed progeny individuals, a transformation rate of 4%. The transgene-mediated complementation of eye color was observed to segregate in a Mendelian manner, although one insertion segregates with the recessive allele (female-determining) of the sex-determining locus, and a separate insertion is homozygous lethal. Molecular analysis of selected transformed families demonstrated that a single complete copy of the construct had integrated independently in each case and that it had done so in a transposase-mediated manner. The availability of a mariner transformation system greatly enhances our ability to study and manipulate this important vector species.
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