08-10-2012, 05:23 PM
Electronic mosquito repellents for preventing mosquito bites and malaria infection (Review)
[attachment=35701]
B A C K G R O U N D
Malaria affects more than 250 million people and causes more
than a million deaths each year (WHO 2005). One important
control strategy against this and other mosquito-borne diseases is
mosquito control, which aims to reduce human-mosquito contact.
Different control measures are used routinely against mosquitoes
and their larvae, including chemical (eg insecticide), biological (eg
larvivorous sh or pathogenic fungi), environmental (eg land lling
or drainage), and personal protection (eg mosquito repellents
formulated as pills, coils, ointments, lotions, and sprays; and insecticide-
treated or untreated bed nets).
Electronic mosquito repellents (EMRs) are marketed in response
to a huge demand from the public for convenient, safe, and effective
antimosquito products. Female Anopheles mosquitoes transmit
malaria by sucking blood from humans, and these small handheld,
battery-powered EMRs are intended to repel them by emitting
a high frequency buzz almost inaudible to the human ear.
They can be used both indoors and outdoors, and are claimed to
repel mosquitoes within a range of up to 2.5 metres (Kutz 1974;
Helson 1977). No adverse effects have been reported in the literature.
Mobile phone companies also market a ring tone that
is claimed to repel mosquitoes within a one-metre radius (BBC
2003).
M E T H O D S O F T H E R E V I EW
AAE scanned the results of the literature search for potentially
relevant studies and then retrieved the full articles. AAE and PG
independently assessed the potentially relevant studies using an
eligibility form based on the inclusion criteria; disagreements were
resolved through discussion.
We independently extracted data from all included studies using
a data extraction form and resolved any disagreements in the
extracted data by referring to the original paper and through
discussion. We described the devices tested and the number of
observations made, and assessed the quality of the studies in
relation to whether they controlled for study locality, time of day
or night, participants (used same people to bait mosquitoes), and
whether the observers were blinded.We also assessed the number
of times observations were repeated to gain some quantitative
measure of quality and grouped this with an arbitrary cut off
into adequate (20 or more) or inadequate (less than 20). We
summarized the results of the methodological quality assessment
in Table 02.
D E S C R I P T I O N O F S T U D I E S
We identi ed 18 potentially relevant studies of EMR to prevent
mosquito bites and included 10 (see 'Characteristics of included
studies' for study details); none were randomized or quasi-randomized
controlled trials that used EMR to prevent malaria. We
excluded eight studies because they were only laboratory based or
because they did not provide any data or did not control for locality,
time, and blinding (see 'Characteristics of excluded studies').
The papers for the 10 included studies contained 22 experiments,
of which 15 were eld experiments that met the reviews inclusion
criteria; the excluded seven experiments were only laboratory
based or used chemical repellents.
Seven studies were carried out in the North America, three in
Canada (Helson 1977; Belton 1981; Lewis 1982) and four in the
USA (Gorham 1974; Kutz 1974; Garcia 1976; Schreck 1977).
Two studies were done in Africa, in Gabon (Sylla 2000) and in
The Gambia (Snow 1977). One study was undertaken in Russia
(Rasnitsyn 1974).
R E S U L T S
The number of mosquitoes landing per collection with and withoutEMRare
presented inTable 03. All 10 studies reported that the
landing rates with and without the EMR were little different and
that the EMRs failed to repel mosquitoes. These results occurred
regardless of the study location, mosquito density, mosquito genera,
or time of study (ie day or night with day-biting and nightbiting
mosquitoes).
No trials were found to assess the effects of EMRs on malaria
infection.
D I S C U S S I O N
The included studies were of good quality, had controlled for
locality, and all but one had explicitly controlled for time of day or
night, and the human bait for the mosquitoes. The results of this
review provide clear evidence from eld-based studies that there
is no hint that these devices have any effect on mosquito landing
rates. The studies reported here examined the effectiveness of the
EMRs with different methods, settings, mosquito species (since
they may respond differently to the high-pitched sounds emitted
by the EMRs), frequencies of the sound emitted by the EMRs
(since mosquitoes may respond to a particular sound wavelength),
and times of day (since day-biting and night-biting mosquitoes
may behave differently to the sound emitted by the EMRs), and
mosquito density (since this may affectEMRef cacy), but none of
them supported the claims of the EMRs' effectiveness. Although
we did not conduct a meta-analysis of the included studies, there
was no suggestion of difference in landing rates between cases and
controls in any trial. In 12 of the 15 experiments, the landing rates
in the groups with functioning EMR was actually higher than in
the control groups.
[attachment=35701]
B A C K G R O U N D
Malaria affects more than 250 million people and causes more
than a million deaths each year (WHO 2005). One important
control strategy against this and other mosquito-borne diseases is
mosquito control, which aims to reduce human-mosquito contact.
Different control measures are used routinely against mosquitoes
and their larvae, including chemical (eg insecticide), biological (eg
larvivorous sh or pathogenic fungi), environmental (eg land lling
or drainage), and personal protection (eg mosquito repellents
formulated as pills, coils, ointments, lotions, and sprays; and insecticide-
treated or untreated bed nets).
Electronic mosquito repellents (EMRs) are marketed in response
to a huge demand from the public for convenient, safe, and effective
antimosquito products. Female Anopheles mosquitoes transmit
malaria by sucking blood from humans, and these small handheld,
battery-powered EMRs are intended to repel them by emitting
a high frequency buzz almost inaudible to the human ear.
They can be used both indoors and outdoors, and are claimed to
repel mosquitoes within a range of up to 2.5 metres (Kutz 1974;
Helson 1977). No adverse effects have been reported in the literature.
Mobile phone companies also market a ring tone that
is claimed to repel mosquitoes within a one-metre radius (BBC
2003).
M E T H O D S O F T H E R E V I EW
AAE scanned the results of the literature search for potentially
relevant studies and then retrieved the full articles. AAE and PG
independently assessed the potentially relevant studies using an
eligibility form based on the inclusion criteria; disagreements were
resolved through discussion.
We independently extracted data from all included studies using
a data extraction form and resolved any disagreements in the
extracted data by referring to the original paper and through
discussion. We described the devices tested and the number of
observations made, and assessed the quality of the studies in
relation to whether they controlled for study locality, time of day
or night, participants (used same people to bait mosquitoes), and
whether the observers were blinded.We also assessed the number
of times observations were repeated to gain some quantitative
measure of quality and grouped this with an arbitrary cut off
into adequate (20 or more) or inadequate (less than 20). We
summarized the results of the methodological quality assessment
in Table 02.
D E S C R I P T I O N O F S T U D I E S
We identi ed 18 potentially relevant studies of EMR to prevent
mosquito bites and included 10 (see 'Characteristics of included
studies' for study details); none were randomized or quasi-randomized
controlled trials that used EMR to prevent malaria. We
excluded eight studies because they were only laboratory based or
because they did not provide any data or did not control for locality,
time, and blinding (see 'Characteristics of excluded studies').
The papers for the 10 included studies contained 22 experiments,
of which 15 were eld experiments that met the reviews inclusion
criteria; the excluded seven experiments were only laboratory
based or used chemical repellents.
Seven studies were carried out in the North America, three in
Canada (Helson 1977; Belton 1981; Lewis 1982) and four in the
USA (Gorham 1974; Kutz 1974; Garcia 1976; Schreck 1977).
Two studies were done in Africa, in Gabon (Sylla 2000) and in
The Gambia (Snow 1977). One study was undertaken in Russia
(Rasnitsyn 1974).
R E S U L T S
The number of mosquitoes landing per collection with and withoutEMRare
presented inTable 03. All 10 studies reported that the
landing rates with and without the EMR were little different and
that the EMRs failed to repel mosquitoes. These results occurred
regardless of the study location, mosquito density, mosquito genera,
or time of study (ie day or night with day-biting and nightbiting
mosquitoes).
No trials were found to assess the effects of EMRs on malaria
infection.
D I S C U S S I O N
The included studies were of good quality, had controlled for
locality, and all but one had explicitly controlled for time of day or
night, and the human bait for the mosquitoes. The results of this
review provide clear evidence from eld-based studies that there
is no hint that these devices have any effect on mosquito landing
rates. The studies reported here examined the effectiveness of the
EMRs with different methods, settings, mosquito species (since
they may respond differently to the high-pitched sounds emitted
by the EMRs), frequencies of the sound emitted by the EMRs
(since mosquitoes may respond to a particular sound wavelength),
and times of day (since day-biting and night-biting mosquitoes
may behave differently to the sound emitted by the EMRs), and
mosquito density (since this may affectEMRef cacy), but none of
them supported the claims of the EMRs' effectiveness. Although
we did not conduct a meta-analysis of the included studies, there
was no suggestion of difference in landing rates between cases and
controls in any trial. In 12 of the 15 experiments, the landing rates
in the groups with functioning EMR was actually higher than in
the control groups.