Ovitrap Surveillance in Sarawak, Malaysia: a Comprehensive Study
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Tropical Biomedicine 34(4): 795–803 (2017) Ovitrap surveillance in Sarawak, Malaysia: A comprehensive study Lau, K.W.1, Chen, C.D.1*, Lee, H.L.2, Low, V.L.3, Moh, H.H.1 and Sofian-Azirun, M.1 1Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia 2Medical Entomology Unit, WHO Collaborating Centre for Vectors, Institute for Medical Research, Jalan Pahang, 50588 Kuala Lumpur, Malaysia 3Tropical Infectious Diseases Research and Education Centre (TIDREC), University of Malaya, 50603 Kuala Lumpur, Malaysia *Corresponding author e-mail: [email protected] Received 14 May 2017; received in revised form 8 June 2017; accepted 10 June 2017 Abstract. This study reports the distribution and abundance of Aedes by using ovitrap surveillance and aims to provide the most recent information on dengue vector distribution in Sarawak State, Malaysia. The ovitrap index (OI) of Aedes larvae was found highest in urban residential area (mean OI = 90.97%), followed by suburban (69.70%), rural (65.45%) and remote (52.63%) residential areas. The mean number of Aedes larvae per ovitrap was also found to be significantly highest in urban residential area (26.47 ± 1.62) compared to other type of residential areas (p<0.05). Interestingly, no Aedes aegypti was observed in this study, but two species of Armigeres were found co-breeding with Ae. albopictus. This study reveals that Ae. albopictus is the dominant dengue vector in Sarawak State and all the surveyed residential areas are in risk of dengue transmission with OI > 10%. INTRODUCTION The two major vectors involved in these infections are Aedes aegypti and Aedes Dengue and dengue haemorrhagic fever albopictus. Both species were known to (severe dengue) remain to be an endemic adapt well to urban and suburban areas infectious disease and a serious public health where their larvae breed in artificial and problem in Malaysia. Both Aedes–borne natural containers near human dwellings diseases are frequently reported in (Chen et al., 2006). The presence of Ae. peninsular Malaysia and Borneo (Sabah and aegypti in Sarawak was first reported in Sibu Sarawak) since the first nationwide outbreak by Macdonald et al. (1965) and subsequently in 1973 (Hii, 1977; Lee & Hishamudin, 1990; in Kuching and Miri (Macdonald et al., 1967; Chang et al., 1981). The dengue outbreak in Macdonald & Rajapaksa, 1972). A sub- Sarawak occurred for the first time in 1982 sequent investigation was done by Chang and and since then, it has become public health Jute in 1982 where 73 localities in seven concern (Chang & Jute, 1994). The recent divisions of the state were surveyed. Apart report by Ministry of Health Malaysia showed from these earlier investigations, no up-to- that total accumulated reported cases of date information on the distribution pattern dengue until week 50 of year 2016 in and population of both Aedes species in Malaysia was 98,438, of which 2,688 cases Sarawak is available from the state until the were reported in Sarawak, representing an present day. increase by 43.74% compared to 2015 (MOH, 2016). 795 An ovitrap surveillance is the commonest for 24–48 hr before using) was added into sampling method to monitor Aedes mosquito the container and a small piece (10mm) of populations (Service, 1992). According to fresh beef liver was added as larval food. The Lee (1992), an ovitrap surveillance has been hatched larvae were subsequently counted shown to be a more effective and sensitive and 3rd instar-larvae were identified to technique especially when the Aedes species level according to the key by infestation rates were low. Mahadevan & Cheong (1974). The larval The aim of this study is to provide the numbers were recorded individually for latest information on the distribution of each positive ovitrap. Aedes species in different types of residential areas in Sarawak, which could help in the Data analysis local vector control programme, as well as All data obtained from this study was supplementing earlier reports. analysed as follow: (1) Ovitrap Index (OI), the percentage of positive ovitrap against the total number MATERIALS AND METHODS of ovitraps recovered from each side. Geographical description of study sites (2) Mean number of larvae per recovered An ovitrap surveillance was conducted in 21 ovitrap. residential areas across 13 districts located in 8 divisions in Sarawak, Malaysia. The All levels of statistical significance were geographical and ecological description of determined at P<0.05 by using statistical the study sites are given in Table 1. The 21 programme, student t-test and one-way residential areas were categorized according ANOVA (SPSS® version 21.0; IBM, Armonk, to their landscapes into urban, suburban, NY). rural and remote areas. Ovitrap surveillance RESULTS The ovitrap as described by Lee (1992) was used in this surveillance. Each ovitrap Table 2 shows the ovitrap index (OI) and consisted of a 300 ml black plastic container the mean number of larvae per ovitrap of with 6.5 cm in diameter, 9.0 cm in height and Ae. albopictus and Armigeres sp. obtained the opening measures 7.8cm in diameter. The from 21 residential areas across 13 districts outer wall of the container was coated with in Sarawak. All residential areas were a layer of black oil paint. Fresh water was categorized into urban, suburban, rural and added to a level of 5.5 cm and an oviposition remote according to their landscapes as paddle made form hardboard (10 cm x 2.5 shown in Table 1. Aedes albopictus was cm x 0.3cm) was placed diagonally with the present in all localities with the OI ranging rough surface upwards into each ovitrap. from 35.00% to 100% and mean number of Ovitraps were placed in not less than 10% larvae per ovitrap ranged from 2.74 ± 1.15 to of the houses in all residential areas. The 29.41 ± 6.64. ovitraps were placed outside the house but Comparisons between OI according to confined to the immediate vicinity of the landscapes show that the OI of the urban house, i.e. car porch and corridor under the residential area was significantly higher than eave. The houses were chosen randomly. rural, suburban and remote residential area (p < 0.05) with mean OI at 90.97 ± 1.59%, 69.76 Identification of larvae ± 8.34%, 65.91 ± 3.88% and 52.63 ± 15.79%, The ovitraps were collected after 5 days respectively. In addition, significantly highest and transported back to laboratory and the Ae. albopictus mean number of larvae per contents were poured individually into a ovitrap was obtained from urban residential labelled plastic container, together with the areas (26.47 ± 1.62) compared to rural areas paddle. Overnight water (tap water exposed (14.73 ± 2.95), suburban areas (13.55 ± 2.22) 796 Table 1. Geographical description of study sites in Sarawak, Malaysia Division District Study Sites Coordinates Elevation (meter a.s.l.) Type of residential area Kuching Kuching Lorong Siol Kandis N 1º 34’ 31.8"; E 110º 21’ 50.6" 5 Urban Petra Jaya N 1º 34’ 43.0"; E 110º 20’ 25.8" 7 Urban Bau Kampung Atas N 1º 28’ 44.7"; E 110º 11’ 11.5" 46 Remote Kampung Apar N 1º 28’ 30.8"; E 110º 08’ 55.7" 20 Remote Samarahan Samarahan Kampung Merdang Gayam N 1º 27’ 34.4"; E 110º 24’ 59.5" 14 Rural Kampung Merdang Lumut N 1º 27’ 02.5"; E 110º 23’ 52.6" 7 Rural Kampung Bukit Brangan N 1º 26’ 40.4"; E 110º 23’ 16.7" 17 Suburban Serian Kampung Melayu Tebakang N 1º 12’ 27.8"; E 110º 33’ 57.2" 19 Suburban Sibu Sibu Kiew Nang N 2º 15’ 47.4"; E 111º 51’ 48.6" 8 Suburban 797 Selangau Pekan Selangau N 2º 31’ 24.1"; E 112º 19’ 33.2" 25 Rural Mukah Mukah Kampung Kuala Lama N 2º 53’ 44.4"; E 112º 05’ 33.4" 4 Suburban Bandar Baru Mukah N 2º 53’ 34.0"; E 112º 05’ 33.9" 3 Suburban Dalat Pekan Dalat N 2º 44’ 20.7"; E 111º 56’ 14.9" 6 Rural Miri Miri Kampung Siwa Jaya N 4º 13’ 40.7"; E 113º 54’ 59.3" 22 Rural Bandar Miri N 4º 28’ 02.4"; E 114º 00’ 15.6" 6 Urban Lutong, Kg. Tulang N 4º 22’ 59.2"; E 113º 58’ 56.9" 9 Suburban Bintulu Bintulu Kemena Jaya N 3º 10’ 26.6"; E 113º 02’ 53.9" 11 Suburban JKR Quarters N 3º 10’ 42.4"; E 113º 02’ 55.3" 19 Suburban Tatau Kampung Dagang Tatau N 2º 52’ 33.7"; E 112º 51’ 12.6" 7 Rural Sarikei Sarikei Pekan Sarikei N 2º 07’ 40.9"; E 111º 31’ 7.85" 3 Suburban Kapit Kapit Pekan Kapit N 2º 01’ 1.11"; E 112º 56’ 14.9" 18 Rural 798 and remote areas (7.06 ± 4.32) (p < 0.05). residential areas, with mean ovitrap index There difference in larval numbers was 90.97 ± 1.59% and mean number of larvae significant among all residential areas per ovitrap 26.47 ± 1.62. (p < 0.05). The differences in OI and mean number Aedes aegypti was not detected of larvae per ovitrap of Ae. albopictus throughout the surveillance. On the other between landscapes can possibly be the hand, Armigeres sp. was found co-breeding results of geo-physical and socio- with Ae. albopictus from 5 residential areas, environmental set up of the residential area namely Kampung Melayu Tebakang (District: with reference to location and basic amenities Serian, Division: Samarahan), Kampung (Chang & Jute, 1982). According to Chang & Merdang Lumut (Samarahan, Samarahan), Jute (1982), the density of Ae.