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Article Type: Original Article
Surveillance of adult Aedes mosquitoes in Selangor, Malaysia
Sai-Ming Lau 1, Indra Vythilingam2, Jonathan Inbaraj Doss3, Shamala Devi Sekaran4, Tock H. Chua 5,
Wan Yusof Wan Sulaiman2, Karuthan Chinna3, Yvonne Ai-Lian Lim2, Balan Venugopalan1
1
State Vector Borne Disease Control Unit, Selangor State Health Department, Selangor, Malaysia
2
Department of Parasitology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
3
Julius Centre, Department of Social and Preventive Medicine, Faculty of Medicine. University of Ma-
laya, Kuala Lumpur
4
Department of Microbiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
5
Department of Pathobiology and Medical Diagnostics, Faculty of Medicine and Health Sciences,
Universiti Malaysia Sabah, Kota Kinabalu, Sabah, Malaysia.
Abstract
Objective: To determine the effectiveness of using sticky traps and the NS1 dengue antigen kit for
the surveillance of Aedes mosquitoes for dengue control.
Methods: Apartments were selected in a dengue endemic area and sticky traps were set to capture
adult Aedes mosquitoes. NS1 dengue antigen kit was used to detect dengue antigen in mosquitoes
and positive mosquitoes were serotyped using real time RT-PCR.
Results: The sticky traps were effective in capturing Aedes aegypti and a minimum of three traps per
floor was sufficient. Multiple serotypes were found in individual mosquitoes.
Conclusion: The sticky trap and the NS1 dengue antigen test kit can be used as surveillance tool in
dengue control programmes. This proactive method will be better suited for control programmes
than current reactive methods.
Keywords: Aedes aegypti; Dengue; sticky trap; NS1 antigen test kit; surveillance; Malaysia
Introduction
Dengue virus, which is transmitted primarily by the Aedes aegypti mosquito, is the most important
arbovirus affecting humans in tropical and subtropical countries (Gubler, 2001), and dengue outbreaks are spreading across more countries (Gubler, 2012;Sam et al., 2013). The number of reported
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dengue cases has increased exponentially since 2007 (WHO Western Pacific). Currently, an estimated 2.5 billion people in 100 countries are at risk (Bhatia et al., 2013). In Southeast Asia, dengue
emerged as a public health problem during and after World War II (Ooi and Gubler, 2009); in Malaysia dengue was first reported in 1902 (Skae, 1902). Epidemics of dengue have occurred in 1973, 1982
and 1998 (Teng and Singh, 2001). However, the number of reported cases in Malaysia until September 9, 2014 is above the median of 2009-2013. Current total numbers of reported cases and deaths
are 70,337 and 133, respectively (WHO Western Pacific Region 2014). In recent years the epidemics
of dengue has become critical in the state of Selangor, Malaysia. Reported cases of dengue have increased fourfold in 2014 compared to the same period in 2013 (from 8,258 to 33,564); case mortality increased fivefold from 10 in 2013 to 50 in 2014 (MoH Malaysia 2014a).
In the absence of a vaccine and drugs against dengue virus, control of the Aedes mosquito is
the main tool for the surveillance and management of dengue. In Malaysia, Ae. aegypti is the principal vector of dengue and Ae. albopictus is the secondary vector (Rudnick, 1965). Control methods for
dengue in Malaysia are environmental sanitation, house-to-house larva surveys, source reduction
and health education. Fogging and ULV are conducted when cases are reported or when Aedes indices are higher than the sensitive threshold (Ministry of Health Plan of Action for Surveillance and
Control of Dengue 2009-2013). These methods may have been effective in the past, but currently,
due to mushrooming of houses and unplanned urbanization and construction, the control of dengue
is becoming more challenging.
There is no correlation between the Aedes index and the number of dengue cases (Morrison
et al., 2008). Larval mortality can be high and there is a possibility that larvae may die before emergence as adults (Morrison et al., 2004). They can also be spatially dissociated from the larval development site. A more appropriate index would be the pupal index since it is the stage that directly
precedes the adult mosquito that can transmit dengue (Focks, 2003). However, to determine the
pupal index is also time consuming and labour intensive. Determining the adult density may provide
a better correlation to the number of cases (Ritchie et al., 2003;Morrison et al., 2008;Chadee and
Ritchie, 2010). The ovitrap has been used as a proxy to gauge the number of adults present from the
total number of eggs laid. This has been used to monitor the spatial and temporal analysis of the
Aedes mosquito. However, it is not an efficient tool to be used for adult density determination because Ae. aegypti exhibits skip oviposition and thus the results from ovitraps may not be accurate
(Reiter, 2007).
Many methods are available for the collection of adult Aedes mosquitoes. The BG-sentinel
can be used to collect Aedes mosquitoes and is very efficient but the only disadvantage is the cost
which may not be affordable by under developed countries where dengue is most endemic (Kroeckel
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weeks (F 4,39 = 5.82, p<0.001). However, there were significant differences in the number of eggs
recorded between the floors (F5,336=6.66, p<0.001), between the locations of the traps (F23,336=4.90,
p<0.001) and between weeks (F12,336=3.86, p<0.001). Significantly higher number of eggs were recorded on the ground floor (p<0.001). There was a significant correlation between the percentage of
positive sticky traps and density of Aedes per trap (r2=0.73, df=33, p<0.001)
The distribution of Ae. aegypti among the various floors is shown in Figure 6. In block C, the
highest percentage of Ae.aegypti was obtained on the 15th floor while in Block D it was on the
ground floor. These were the floors that had the highest number of traps. However, on a per trap
basis, there was no difference in the number caught between blocks and between floors (p>0.05),
although higher number was recorded for ground floor. Interestingly, the one trap on the ground
floor of block C caught 19% of the Ae. aegypti.
Trial 2
Relationship between Ae. aegypti caught and number of traps: There was a significant correlation
between sticky traps with Ae. aegypti and the proportion of positive ovitraps with Aedes eggs
(r2=0.43, def=17, p<0.01). The relationship between Ae. aegypti caught (y) and number of traps (x) is
best described by a non-linear model (Box-Lucas 1959). The equation obtained is y=19.92 (1-exp(0.27x) (P<0.001) (Figure 7). As the equation is asymptotic at around 20 suggesting that 20 traps per
block would be sufficient to be deployed for monitoring Aedes population.
Detection of dengue virus: A total of eight pools of Ae. aegypti were positive for dengue virus using the NS1 antigen detection kit and thus the minimum infection rate per 1000 mosquitoes
(MIR) was 38.02 (18.00-71.18). Of the 40 mosquitoes (head and thorax) tested individually using real
time RT-PCR, 15 were positive giving an infectious rate of 6.02. Of these, 10 had dual infection of
DENV2 and DENV3; two were positive for DENV3, one was positive for DENV2 and two were positive
for DENV1.
Discussion
The most important and novel finding of this project was that the virus was detected in the mosquito before a case was reported. Ten mosquitoes carried two serotypes of dengue virus. In this study,
all serotypes except DENV-4 were present. According to (Mohd-Zaki et al., 2014), DENV-4 was the
least prevalent of all serotypes and it formed less than 20 % of all serotypes detected in 2000 to
2012 in Malaysia. Thus, using sticky traps for surveillance would be more cost effective and help to
give warning before large epidemics. During this trial, we did not manage to detect dengue virus in
mosquitoes on the day of collection since the traps were sent to the main laboratory for this. How-
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the container were lined with brown disposable paper sprayed with sticky insect catcher®. This consists of synthetic solid rubber (53%), solvent (46.6%) and yellow dye (0.4%) and is produced by SR
Megah Chemicals (Taman Klang Perdana, Klang, Malaysia). The larger container was filled with 10%
hay infusion water. The smaller container containing the sticky surface was placed inside the larger
container. Ovipositing mosquitoes are trapped on the sticky surface, and if a mosquito sits on the
netting to lay eggs, the emerging adults will not be able to escape due to the netting.
Field sampling
Trial 1: For the initial study from June 2013 to September 2013, a total of 62 sticky traps were set in
blocks C and D, on floors: ground floor (GF), 3rd, 6th, 9th, 12th and 15th. In block C, the number of sticky
traps set on the respective floors starting from ground floor (GF) were 1, 2, 4, 6, 8 and 10 respectively while in Block D it was the reverse. Thus, in Block D, the ground floor had the most traps. All traps
were labelled accordingly.
All sticky traps were examined twice a week. If any insects were stuck on the surface, the
trap was replaced with a new one and taken to the laboratory for insect identification. If no insects
had caught on the surface, the sticky paper was changed once a month or as needed when dirty. The
hay infusion water was replaced once a week. The sticky traps were set inside the house or outside,
under the roof. The sticky sticky trap index was calculated as the percentage of traps positive for
Aedes. The Aedes density was calculated as the total number of Aedes divided by the number of positive sticky traps.
From July to September 2013, two ovitraps per floor per block were set to monitor the presence of Aedes. All ovitraps contained hay infusion water and were serviced twice a week. The ovitrap
index was the percentage of ovitraps positive. The egg density was calculated as the total number of
eggs divided by the number of positive traps.
Trial 2
The second trial was carried out for five weeks from 1 October 2013 until 6 November 2013. All seven blocks were included in this trial. This trial was carried out to determine the optimum number of
traps that would be needed for surveillance. Sticky traps were set on floors: GF, 3th, 6th, 9th, 12th, 15th
and 17th starting with three traps for the first week, five traps on the 2nd week, seven traps on the 3rd
week and nine traps on the 4th and 5th week respectively. Thus the total number of sticky traps set
ranged from 147 to 441. At the same time one ovitrap was placed on each of the floors mentioned
above. All traps were examined and serviced weekly.
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Identification and processing of mosquitoes
All sticky papers with insects were examined under stereomicroscope in the laboratory. Mosquitoes
were identified to species level. Only Ae. aegypti and Ae. albopictus were processed for detection of
the virus. The abdomens of the mosquitoes were pooled (five in a pool), while the head and thorax
of each mosquito were kept individually in Eppendorf tubes at -20 oC until real time RT-PCR processing.
Detection of dengue viral antigen in abdomen of mosquitoes
To each pool of mosquito abdomens, 50 µl of PBS was added and homogenized lightly using a pestle
and hand held homogenizer (Kontes Thompson Scientific). The tube was centrifuged for 3 minutes at
3,000 rpm. The SD Bioline® NS1 Ag kit (Standards Diagnostic Korea) was used to test for the dengue
antigen in the mosquito, following the manufacturer’s protocol. Briefly, the content from each tube
was pipetted using the pipet provided onto the well of the device (test kit). After 10-15 minutes, the
reading was taken. If the sample was positive, two bands will be seen. If negative, only the control
band will be seen. For all the pooled abdomens that were positive, the individual head and thorax of
the respective mosquito was tested for dengue virus by real time RT-PCR.
RNA extraction
Individual mosquitoes were ground in pre-chilled Eppendorf tubes with 0.25 ml of a growth medium
(Eagle’s minimum essential medium, EMEM). The mosquito suspensions were then centrifuged at
14000 rpm for 15 minutes at 4 °C. RNA extraction was carried out with High Pure Viral RNA Isolation
Kit (Roche Applied Science) according to the manufacturer’s protocol. The homogenate (200 μl) was
mixed with 400 μl of binding buffer and centrifuged at 8000 x g for 15 seconds. The RNA was then
washed twice with washing buffer and centrifuged at 8000 x g for 1 minute. A total of 30 µl of viral
RNA was eluted from the sample using elution buffer. The extracted RNA was collected and stored at
-80 0C for viral detection through real time RT-PCR.
One-step TaqMan real-time RT-PCR
The one-step TaqMan real-time RT-PCR was carried out in a CFX96 Thermocycler (BioRad) (Kong et
al., 2006). Briefly, 5 μl of the sample RNA, 0.5 μM of each primer, four TaqMan probes (0.25 μM
each), and 5.0 mM of MgCl2 in final concentration were used in a 25 μl reaction containing the onestep RT-PCR premix (BioNeer). The thermal cycling profile of this assay consisted of an initial RT step
at 50 0C for 30 min, and Taq polymerase activation at 95 0C for 15 min, followed by 40 cycles of PCR
with the following conditions: denaturation at 95 0C for 30 s, annealing/extension at 60 0C for 1 min.
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Statistical analysis
All statistical analyses were performed using R (Team, 2008) (R Development Core Team 2008) programming language for statistical analysis (version 3.1) and Excel 2010. Data were subjected to analysis of variance (ANOVA), t-test, non-parametric tests (, Pearson’s χ2 test), non-linear regression
(Box-Lucas) and general linearized modelling. The minimum infectious rate (MIR) was calculated by
maximum likelihood estimation method (Chiang and Reeves, 1962) based on 45 pools of 5 mosquitoes each.
Results
Trial 1
A total of 249 Ae. aegypti and eight Ae. albopictus was obtained from the two blocks for the 18
weeks of the first trial while a total of 35 dengue cases was reported for the same period for the two
blocks. Figure 3 shows the distribution of the dengue cases, Aedes mosquitoes and the positive
mosquitoes throughout the study period. It would appear that the positive mosquito was detected
(6-10 June 2013) before a case was reported (8 June 2013). There was no correlation between number of cases and number caught for Ae. aegypti (r2=0.013) and Ae. albopictus (r2=0.012).
Also further correlation analysis on the lag time (2, 3 and 4 weeks) of occurrence of cases
and number of Aedes caught did not show significant relationship between the two variables. However, the relationship between number of cases and Aedes caught yielded significant relationship using general linearized model (GLM). The relationship can be described with the equation:
y=1.1517+0.0404x (F 1,20=3.95,p<0.001).
Analysis of distribution of cases recorded during the study period among the 17 floors (Supplementary table) in the seven blocks showed that the cases occurred independently of floor and
block (Pearson’s χ2=112.22, df = 102, p-value >0.05). The sticky trap index and the ovitrap index are
shown in Figure 4. The ovitrap index seemed to follow the same trend as the sticky trap index. However, the ovitrap index was higher than sticky trap which was to be expected because a single mosquito can lay eggs in many containers. ANOVA indicated there was no statistical difference in the index values recorded between the blocks, between the floors and between locations (P>0.05). Besides Ae. aegypti and Ae. albopictus, the sticky trap also collected a large number of Culex
quinquefasciatus (results not shown).
The density of Ae. aegypti and the egg density per trap are shown in Figure 5. Both show the
same trend. ANOVA indicated there was no difference in egg density per trap between blocks
(F6,216=1.70, p>0.05) nor between weeks (F4,216=1.66, p>0.05). Similarly, there was no difference in
positive sticky traps between blocks (F7,39 =1.52, p>0.05) but a significant difference existed between
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weeks (F 4,39 = 5.82, p<0.001). However, there were significant differences in the number of eggs
recorded between the floors (F5,336=6.66, p<0.001), between the locations of the traps (F23,336=4.90,
p<0.001) and between weeks (F12,336=3.86, p<0.001). Significantly higher number of eggs were recorded on the ground floor (p<0.001). There was a significant correlation between the percentage of
positive sticky traps and density of Aedes per trap (r2=0.73, df=33, p<0.001)
The distribution of Ae. aegypti among the various floors is shown in Figure 6. In block C, the
highest percentage of Ae.aegypti was obtained on the 15th floor while in Block D it was on the
ground floor. These were the floors that had the highest number of traps. However, on a per trap
basis, there was no difference in the number caught between blocks and between floors (p>0.05),
although higher number was recorded for ground floor. Interestingly, the one trap on the ground
floor of block C caught 19% of the Ae. aegypti.
Trial 2
Relationship between Ae. aegypti caught and number of traps: There was a significant correlation
between sticky traps with Ae. aegypti and the proportion of positive ovitraps with Aedes eggs
(r2=0.43, def=17, p<0.01). The relationship between Ae. aegypti caught (y) and number of traps (x) is
best described by a non-linear model (Box-Lucas 1959). The equation obtained is y=19.92 (1-exp(0.27x) (P<0.001) (Figure 7). As the equation is asymptotic at around 20 suggesting that 20 traps per
block would be sufficient to be deployed for monitoring Aedes population.
Detection of dengue virus: A total of eight pools of Ae. aegypti were positive for dengue virus using the NS1 antigen detection kit and thus the minimum infection rate per 1000 mosquitoes
(MIR) was 38.02 (18.00-71.18). Of the 40 mosquitoes (head and thorax) tested individually using real
time RT-PCR, 15 were positive giving an infectious rate of 6.02. Of these, 10 had dual infection of
DENV2 and DENV3; two were positive for DENV3, one was positive for DENV2 and two were positive
for DENV1.
Discussion
The most important and novel finding of this project was that the virus was detected in the mosquito before a case was reported. Ten mosquitoes carried two serotypes of dengue virus. In this study,
all serotypes except DENV-4 were present. According to (Mohd-Zaki et al., 2014), DENV-4 was the
least prevalent of all serotypes and it formed less than 20 % of all serotypes detected in 2000 to
2012 in Malaysia. Thus, using sticky traps for surveillance would be more cost effective and help to
give warning before large epidemics. During this trial, we did not manage to detect dengue virus in
mosquitoes on the day of collection since the traps were sent to the main laboratory for this. How-
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ever, this is a simple procedure that can be carried out by health staff at the ground level. Studies in
Singapore have also shown that the antigen detection NS1 kit was useful in detecting the dengue viral antigen in field-collected mosquitoes (Tan et al., 2011;Lee et al., 2013).
Adult mosquitoes can be used for estimating dengue transmission risk (Ritchie et al., 2004)
and dengue virus has been found in field-collected Aedes mosquitoes in Mexico (Garcia-Rejon et al.,
2008), Southeast Asia (Chow et al., 1998;Chung and Pang, 2002) and India (Tewari et al., 2004). The
peak entomological inoculation seems to precede the human dengue cases by several weeks to a
month (Garcia-Rejon et al., 2008). However, although these studies showed evidence that the monitoring of adult population would be a useful tool for dengue surveillance, it is not being implemented as a surveillance tool. One reason could be due to the use of RT-PCR for the detection of dengue
virus in mosquitoes. This requires expertise and laboratory support and would be very expensive for
dengue endemic countries. However, since the NS1 antigen kit is effective and simple to use, it could
be used in future dengue control programmes.
Our trials have also shown that it is unnecessary to set large numbers of traps. Our sticky
trap numbers ranged from 147 to 441 and setting as few as three traps in each floor or about 20
traps per block - also supported by the Box-Lucas equation - were sufficient to collect and monitor
the adult Ae. aegypti population for control programmes purposes. Similar studies in Brazil also
showed that setting as many as four traps in their study area was sufficient (Resende et al., 2012).
However, before the introduction of sticky traps, it will be necessary to determine the number
needed for each house type and location.
The ovitrap results also showed that the number of Aedes was falling since the egg density
decreased over time. Since the Aedes mosquito performs skip oviposition (Reiter, 2007) the positivity of the ovitrap may not have fallen as expected compared to the sticky trap. Researchers have
tried to correlate the adult density from sticky traps and egg counts from ovitraps (Facchinelli et al.,
2007). In some studies, a poor correlation was detected when comparing collections from ovitraps
and mosquiTrap (Gama et al., 2007). However, similar percentages of positive ovitraps and sticky
traps were reported in Australia (Ritchie et al., 2003) and in Italy (Facchinelli et al., 2007). In our
study, there was significant correlation between sticky trap and ovitrap index.
The Aedes larva survey has been the hallmark of the surveillance programme for decades
(Azil et al., 2011) but it has shown that it is currently not sustainable due to the mushrooming of
houses and apartments in the urban areas. Health personal have not increased in proportion to the
number of housing estates that have developed over the years, thus leading to shortage of manpower to carry out surveys. In most urban areas, people are at work during the day and accessibility
to houses for larva surveys is a major problem. However, it would be easier and more effective to
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use the sticky traps as a surveillance tool. A larger area can be covered by a smaller number of personnel. The true incidence of the disease in Malaysia may be underestimated due to the use of passive reporting system and low levels of reporting from the private sector (Beatty et al., 2010). Thus,
there is the additional benefit of detecting the virus in the mosquito and taking necessary control
measures to break the chain of transmission. This would be a more proactive measure for a control
program.
Although many studies have been conducted in different countries (Ritchie et al.,
2004;Gama et al., 2007;Honório et al., 2009;Chadee and Ritchie, 2010;de Santos et al.,
2012;Resende et al., 2013) to show the effectiveness of the sticky trap in collecting the Aedes mosquitoes and its importance in a surveillance program, this has not been implemented in any control
program in Southeast Asia (Azil et al., 2011) with the exception of Singapore where it is used for
dengue cluster management (Lee et al., 2013). However, in Brazil, besides using larval surveys, some
municipalities are using Intelligent Dengue Monitoring (MI Dengue) which consists of using
MosquiTRAP (a sticky trap with a synthetic attractant), palmtops/cell phones, and GIS software
(Geo-Dengue). The adult indices are used for larviciding and source reduction (Eiras and Resende,
2009). Our initial trial has encouraged health workers who worked in this study to observe the benefits of using the sticky trap compared to carrying out house to house larval surveys.
New paradigms are wanting for surveillance of dengue since it is the fundamental for setting
goals and evaluating success. Reliable surveillance tools for dengue vectors are greatly needed. An
inexpensive and effective Ae. aegypti-specific adult trap would be a significant surveillance breakthrough, and could also allow for virus testing (Sivagnaname and Gunasekaran, 2012). Thus, we feel
strongly that this simple sticky trap and the NS1 antigen diagnostic kit will serve as a good tool for
surveillance of dengue. This needs to be tested in many different ecotypes.
Another important aspect of this trap is that a female Ae. aegypti will have to lay eggs after a
blood meal (with or without virus) and thus if it selects the sticky trap it will be caught. If it had selected some other container to lay her eggs, there is another opportunity for it to select this sticky
trap for its 2nd oviposition and thus will not be able to transmit the virus.
But the major limitation of the sticky trap is that it targets only gravid females seeking ovipositing sites rather than host-seeking ones and its efficacy could be reduced by nearby natural
oviposition sites (Ritchie et al., 2003). That is the reason why hay infusion water was used to make
the sticky trap containers more attractive than the surrounding containers. Ideally, attractant would
be used instead of preparing hay infusion every week. These sticky traps also have the advantage
over other traps that were used for collection for adult mosquitoes, because they do not need to be
serviced daily. It would not be practical for a control programme to use a tool that has to be serviced
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daily. Commercial traps are also very expensive.
It is also important that the sticky adult trap has some mechanism which prevents
immatures from developing into adults. Chadee and Ritchie (2010) found that due to death stress
oviposition, female Ae. aegypti shoot out eggs directly into the water when caught on the sticky surface. Thus, either larvicides can be applied to kill the emerging larvae or a netting can be placed at
the bottom of the inner container so as to prevent the escape of the adult mosquitoes.
The number of infected mosquitoes obtained in the study was high. This shows that the survival of these old females was important because they have to survive at least 6-9 days (incubation
period) after feeding on an infected blood meal. Indirectly the sticky trap prevented the humanvector contact, which would reduce the infective bites and also eliminate all mosquito progeny.
Studies have also indicated that abundance of larvae or pupae was not predictive of abundance of
Ae. aegypti females (Morrison et al., 2008). The relationship between vector abundance and dengue
transmission needs to be elucidated (Bowman et al., 2014); to introduce adult mosquito sampling as
a routine and current indices like Breteau are not reliable universal dengue transmission thresholds.
A recent study in Thailand (Yoon et al., 2012) demonstrated a positive association between infected
Ae. aegypti and dengue-infected children in the same and neighbouring houses. The positive mosquito was obtained before the index case was reported.
Conclusion
This preliminary trial has shown that the sticky trap is a cheap and effective way to collect Aedes
mosquito. Dengue virus was detected in Ae. aegypti before the epidemic. The NS1 antigen test kit is
a simple tool that can be used by public health staff to demonstrate the presence of an infected
mosquito and thus preventive action can be taken before an epidemic occurs. A shift to this toolkit
would be more efficient for a control programme than the current practice of house-to-house larval
surveys.
Acknowledgements
We thank the staff of the Entomology Unit of the Selangor State Health Department for their help in
setting and collecting traps. The project was funded by University of Malaya/ Ministry of Higher Education.
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Corresponding author: Indra Vythilingam, Department of Parasitology, Faculty of Medicine,
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Figure Legends
Figure 1. Map of peninsular Malaysia showing the different states. Insert is the map of Selangor,
showing all districts. The study was carried out in Mentrai court apartments which is situated in
Petaling district
Figure 2. Picture of the sticky trap. A) the small container which has the sticky surface and netting at
the bottom. B) this is the larger container containing the hay infusion water and the smaller container will be placed inside this larger container C) cover which is used when the containers are transported to the field and laboratory.
Figure 3. Total Aedes aegypti, Ae. albopictus, total number of cases and pooled positive mosquito.
Data for block C and D have been combined and used for the above. Denotes pools of positive Ae.
aegypti. Week 8 had two pools of mosquitoes positive. Purple line denotes median number of cases
Figure 4. Sticky trap index and ovitrap index (percentage positive) for the 18 weeks
Figure 5. Density of Ae. aegypti and density of eggs per trap for 18 weeks
Figure 6. Percentage of Ae. aegypti caught in each floor. This is calculated based on the total Ae.
aegypti captured in each block.
Figure 7. Total number of Ae. aegypti captured using different densities of sticky traps over 5 weeks.
The equation for Box-Lucas function is y=19.92 (1-exp(-0.27x) (P<0.001).
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Accepted Article
Figure 1
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Accepted Article
Figure 2
30
5
+
4
25
+
+
+
3
15
2
Median
10
+
+
1
5
+
0
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Weeks
No. of cases
No. of Aedes albopictus
No. of Aedes aegypti
+
Figure 3
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Positif in NS1
No. of Aedes mosquitoes
20
Number of dengue cases
Accepted Article
35
6
Ovitrap index
% Trap positif
100.0%
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
Weeks
Figure 4
Ae.aegypti
70
0.6
60
0.5
50
0.4
40
0.3
30
0.2
20
0.1
10
0
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Weeks
Figure5
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Density of Aedes per trap
Eggs
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0.0%
Density of eggs per trap
Accepted Article
Sticky trap index
Accepted Article
15th
% of Aedes aegypti in Block D
% of Aedes aegypti in Block C
12th
9th
6th
3rd
GF
0.0%
10.0%
20.0%
30.0%
40.0%
Figure 6
Figure 7
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50.0%
60.0%
70.0%