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Yeo H, Tan CH, Chong CS, Lam-Phua SG. Identification key to the genera of adult female mosquitoes (Diptera: Culicidae) of Singapore. Zootaxa 2019; 4624:zootaxa.4624.3.9. [PMID: 31716216 DOI: 10.11646/zootaxa.4624.3.9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Indexed: 11/04/2022]
Abstract
Accurate identification of mosquitoes is crucial for the management and control of vector species. Although Singapore is a tropical country with high mosquito diversity, there are no identification keys specific to its mosquito fauna. An illustrated identification key to the genera of the adult female mosquitoes of Singapore is presented. Twenty genera are characterized and two genera found in Malaysia, Culiseta and Topomyia, are also included. The key will aid non-taxonomically trained operational officers in adult mosquito identification. The key to the genera provides the first crucial step in the process to species identification.
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Affiliation(s)
- Huiqing Yeo
- Department of Biological Sciences, National University of Singapore, Block S3, #05-01, 16 Science Drive 4, Singapore 117558. Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #06-05/08, Helios Block, Singapore 13866..
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Lam-Phua SG, Yeo H, Lee RML, Chong CS, Png AB, Foo SY, Liew C, Ng LC, Tang CS, Rueda LM, Pecor JE, Harrison BA. Mosquitoes (Diptera: Culicidae) of Singapore: Updated Checklist and New Records. J Med Entomol 2019; 56:103-119. [PMID: 30169704 PMCID: PMC6324193 DOI: 10.1093/jme/tjy154] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2018] [Indexed: 05/16/2023]
Abstract
Prior to 1965, Singapore was part of the Malaya (now Malaysia) and was usually not mentioned when mosquito records were reported for Malaya. Consequently, many species that occurred in Singapore were not listed in the world mosquito catalog, and the available checklist for Singapore since 1986 is incomplete, with some imprecise species information. In updating this checklist, we examined and verified mosquito specimens collected from Singapore in various depositories, including a thorough review of past taxonomic literature. Here, we report a checklist of 182 mosquito species, 33 new distribution records, and a consolidated status list of vectors for Singapore. As Singapore is a travel hub and hosts one of the busiest container ports in the world, there is a risk of introducing mosquito species and their associated pathogens of human disease to the country. Hence, the distribution records are important to increase our knowledge on mosquito ecology as well as to understand the risk of newly introduced vectors and their associated pathogens.
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Affiliation(s)
- Sai-Gek Lam-Phua
- Environmental Health Institute, National Environment Agency, Singapore
| | - Huiqing Yeo
- Environmental Health Institute, National Environment Agency, Singapore
| | - Ruth Mee-Lian Lee
- Environmental Health Institute, National Environment Agency, Singapore
| | - Chee-Seng Chong
- Environmental Health Institute, National Environment Agency, Singapore
| | - Ah-Bah Png
- Environmental Health Institute, National Environment Agency, Singapore
| | - Siew-Yoong Foo
- Environmental Health Institute, National Environment Agency, Singapore
| | - Christina Liew
- Environmental Health Institute, National Environment Agency, Singapore
| | - Lee-Ching Ng
- Environmental Health Institute, National Environment Agency, Singapore
- School of Biological Sciences, Nanyang Technological University, Singapore
| | - Choon-Siang Tang
- Environmental Public Health Operations, National Environment Agency, Singapore
| | - Leopoldo M Rueda
- Department of Entomology, Walter Reed Biosystematics Unit, Smithsonian Institution, Museum Support Center (MRC534), Suitland, MD
| | - James E Pecor
- Department of Entomology, Walter Reed Biosystematics Unit, Smithsonian Institution, Museum Support Center (MRC534), Suitland, MD
| | - Bruce A Harrison
- Department of Entomology, Walter Reed Biosystematics Unit, Smithsonian Institution, Museum Support Center (MRC534), Suitland, MD
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Pang SC, Andolina C, Malleret B, Christensen PR, Lam-Phua SG, Razak MABA, Chong CS, Li D, Chu CS, Russell B, Rénia L, Ng LC, Nosten F. Singapore's Anopheles sinensis Form A is susceptible to Plasmodium vivax isolates from the western Thailand-Myanmar border. Malar J 2017; 16:465. [PMID: 29145859 PMCID: PMC5689142 DOI: 10.1186/s12936-017-2114-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Accepted: 11/08/2017] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND Singapore has been certified malaria-free by the World Health Organization since November 1982. However, sporadic autochthonous malaria outbreaks do occur. In one of the most recent outbreaks of vivax malaria, an entomological investigation identified Anopheles sinensis as the most probable vector. As metaphase karyotype studies divided An. sinensis into two forms, A and B, with different vector competence: the investigation of vector competence of An. sinensis found in Singapore was thus pursued using Plasmodium vivax field isolates from the Thailand-Myanmar border. METHODS Adults and larvae An. sinensis were collected from Singapore from 14 different locations, using various trapping and collection methods between September 2013 and January 2016. Molecular identification of An. sinensis species were conducted by amplifying the ITS2 and CO1 region using PCR. Experimental infections of An. sinensis using blood from seven patients infected with P. vivax from the Thailand-Myanmar border were conducted with Anopheles cracens (An. dirus B) as control. RESULTS Phylogenetic analysis showed that An. sinensis (F22, F2 and collected from outbreak areas) found in Singapore was entirely Form A, and closely related to An. sinensis Form A from Thailand. Artificial infection of these Singapore strain An. sinensis Form A resulted in the development of oocysts in four experiments, with the number of sporozoites produced by one An. sinensis ranging from 4301 to 14,538. CONCLUSIONS Infection experiments showed that An. sinensis Form A from Singapore was susceptible to Thai-Myanmar P. vivax strain, suggesting a potential role as a malaria vector in Singapore.
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Affiliation(s)
- Sook-Cheng Pang
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Singapore, 138667 Singapore
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore, 117543 Singapore
| | - Chiara Andolina
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research Building, University of Oxford, Old Road Campus, Oxford, UK
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
| | - Benoit Malleret
- Singapore Immunology Network (SIgN), A*STAR, 8A Biomedical Grove, Singapore, 138648 Singapore
- Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, 5 Science Drive 2, Blk MD4, Level 3, Singapore, 117597 Singapore
| | - Peter R. Christensen
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
| | - Sai-Gek Lam-Phua
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Singapore, 138667 Singapore
| | | | - Chee-Seng Chong
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Singapore, 138667 Singapore
| | - Daiqin Li
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore, 117543 Singapore
| | - Cindy S. Chu
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
| | - Bruce Russell
- Department of Microbiology and Immunology, University of Otago, 720 Cumberland St, Dunedin, 9016 New Zealand
| | - Laurent Rénia
- Singapore Immunology Network (SIgN), A*STAR, 8A Biomedical Grove, Singapore, 138648 Singapore
| | - Lee-Ching Ng
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Singapore, 138667 Singapore
| | - Francois Nosten
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research Building, University of Oxford, Old Road Campus, Oxford, UK
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
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Pang SC, Chiang LP, Tan CH, Vythilingam I, Lam-Phua SG, Ng LC. Low efficacy of delthamethrin-treated net against Singapore Aedes aegypti is associated with kdr-type resistance. Trop Biomed 2015; 32:140-150. [PMID: 25801264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
There has been a worldwide surge in the number and severity of dengue in the past decades. In Singapore, relentless vector control efforts have been put in to control the disease since the 1960's. Space spraying, fogging, chemical treatment and source reduction are some commonly used methodologies for controlling its vectors, particularly Aedes aegypti. Here, as we explored the use of a commercially available delthamethrin-treated net as an alternative strategy and the efficacy of the treated net was found to be limited. Through bioassays and molecular studies, the failure of the treated net to render high mortality rate was found to be associated with the knockdown resistance (kdr) mutation. This is the first report of kdr- mutations in Singapore's Ae. aegypti. At least one point mutation, either homozygous or heterozygous, at amino acid residue V1016G of DIIS6 or F1269C of DIIIS6 was detected in 93% of field strains of Ae. aegypti. Various permutations of wild type and mutant amino acids of the four alleles were found to result in varying degree of survival rate among local field Ae. aegypti when exposed to the deltamethrin treated net. Together with the association of higher survival rate with the presence of both V1016G and F1269C, the data suggest the role of these mutations in the resistance to the deltamethrin. The high prevalence of these mutations were confirmed in a country wide survey where 70% and 72% of the 201 Ae. aegypti analysed possessed the mutations at residues 1016 and 1269 respectively. The highest mutated frequency combination was found to be heterozygous alleles (VG/FC) at both residues 1016 and 1269 (37.8%), followed by homozygous mutation at allele 1269 (24.4%) and homozygous mutation at allele 1016 (22.9%). The kdr- type of resistance among the vector is likely to undermine the effectiveness of pyrethroids treated materials against these mosquitoes.
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Affiliation(s)
- S C Pang
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore138667
| | - L P Chiang
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore138667
| | - C H Tan
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore138667
| | - I Vythilingam
- Parasitology Department, Faculty of medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - S G Lam-Phua
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore138667
| | - L C Ng
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore138667
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Chan A, Chiang LP, Hapuarachchi HC, Tan CH, Pang SC, Lee R, Lee KS, Ng LC, Lam-Phua SG. DNA barcoding: complementing morphological identification of mosquito species in Singapore. Parasit Vectors 2014; 7:569. [PMID: 25498759 PMCID: PMC4282734 DOI: 10.1186/s13071-014-0569-4] [Citation(s) in RCA: 109] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 11/25/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Taxonomy that utilizes morphological characteristics has been the gold standard method to identify mosquito species. However, morphological identification is challenging when the expertise is limited and external characters are damaged because of improper specimen handling. Therefore, we explored the applicability of mitochondrial cytochrome C oxidase subunit 1 (COI) gene-based DNA barcoding as an alternative tool to identify mosquito species. In the present study, we compared the morphological identification of mosquito specimens with their differentiation based on COI barcode, in order to establish a more reliable identification system for mosquito species found in Singapore. METHODS We analysed 128 adult mosquito specimens, belonging to 45 species of 13 genera. Phylogenetic trees were constructed for Aedes, Anopheles, Culex and other genera of mosquitoes and the distinctive clustering of different species was compared with their taxonomic identity. RESULTS The COI-based DNA barcoding achieved a 100% success rate in identifying the mosquito species. We also report COI barcode sequences of 16 mosquito species which were not available previously in sequence databases. CONCLUSIONS Our study utilised for the first time DNA barcoding to identify mosquito species in Singapore. COI-based DNA barcoding is a useful tool to complement taxonomy-based identification of mosquito species.
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Affiliation(s)
- Abigail Chan
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Lee-Pei Chiang
- Shizenature Pte Ltd, 3016, Eastech, Bedok North Avenue 4, #02-13, Singapore, 489947, Singapore.
| | - Hapuarachchige C Hapuarachchi
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Cheong-Huat Tan
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Sook-Cheng Pang
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Ruth Lee
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Kim-Sung Lee
- School of Life Sciences and Chemical Technology, Ngee Ann Polytechnic, 535, Clementi Road, Singapore, 599489, Singapore.
| | - Lee-Ching Ng
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
| | - Sai-Gek Lam-Phua
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Helios Block, #06-05/08, Singapore, 138667, Singapore.
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Lee RML, Choong CTH, Goh BPL, Ng LC, Lam-Phua SG. Bioassay and biochemical studies of the status of pirimiphos-methyl and cypermethrin resistance in Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae) in Singapore. Trop Biomed 2014; 31:670-679. [PMID: 25776592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Aedes (Stegomyia) aegypti (Linnaeus) and Ae. (Stegomyia) albopictus (Skuse) were sampled from five regions of Singapore (Central, North East, North West, South East and South West) and tested with diagnostic concentrations of the technical grade insecticides, pirimiphos-methyl and cypermethrin. Biochemical assays were performed on the same populations of Ae. aegypti and Ae. albopictus to determine activities of detoxifying enzymes, including non-specific esterase (EST), monooxygenase (MFO) and acetylcholinesterase (AChE). The diagnostic test showed that all Ae. aegypti populations were susceptible to pirimiphos-methyl (mortality = 99 to 100%), but resistant to cypermethrin (mortality = 11 to 76%). Resistance to pirimiphos-methyl was observed in all Ae. albopictus populations (mortality = 49 to 74%) while cypermethrin resistance was detected in most Ae. albopictus populations (mortality = 40 to 75%), except those from Central (mortality = 86%) and South East (mortality = 94%) showing incipient resistance. The biochemical assays showed that there was significant enhancement (P < 0.001) of MFO activity in pyrethroid-resistant Ae. albopictus populations and most Ae. aegypti populations. The biochemical assay results suggested that AChE could play a role in pirimiphos-methyl resistance of Ae. albopictus in South West, South East and North East regions. The small but significant increase in EST activities in Ae. aegypti from all regions suggest that it may play a role in the observed cypermethrin resistance.
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Affiliation(s)
- R M L Lee
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore 138667
| | - C T H Choong
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore 138667
| | - B P L Goh
- National Institute of Education, Nanyang Technological University, 50 Nanyang Avenue, Singapore 638798
| | - L C Ng
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore 138667
| | - S G Lam-Phua
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, Singapore 138667
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Deng L, Koou SY, Png AB, Ng LC, Lam-Phua SG. A novel mosquito feeding system for routine blood-feeding of Aedes aegypti and Aedes albopictus. Trop Biomed 2012; 29:169-174. [PMID: 22543617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A novel mosquito feeding system for routine blood-feeding of Aedes aegypti and Aedes albopictus was developed and evaluated. The system consisted of a collagen membrane casing filled with specific pathogen free (SPF) mini-pig blood, which is warmed by a simple in-house designed heating device. Blood feeding rate, fecundity, survival rate and hatchability of Ae. aegypti and Ae. albopictus colonies maintained by the feeding system were compared with those raised by conventional guinea pig feeding method. Aedes aegypti, displayed a significant difference in the feeding rate when offered blood meal using the membrane feeding (85.3%) and the guinea pig feeding (96.2%) methods (P=0.012). Though the feeding rate was reduced, the level was acceptable for maintenance of laboratory colonies. There was no significant difference in the fecundity (P=0.556), survival rate (P=0.715), and hatchability (P=0.932) between the two methods. For Ae. albopictus, the two feeding methods yielded no significant difference for the three parameters (fecundity, survival rate and hatchability=0.887, 0.580 and 0.564, respectively). Hence, we conclude that this simple collagen based membrane blood feeding system can be used for routine colonization of laboratory strains of Ae. aegypti and Ae. albopictus.
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Affiliation(s)
- L Deng
- Environmental Health Institute (EHI) of National Environment Agency, 11 Biopolis Way, #06-05/08, Helios Block, Singapore
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Ng LC, Lee KS, Tan CH, Ooi PL, Lam-Phua SG, Lin R, Pang SC, Lai YL, Solhan S, Chan PP, Wong KY, Ho ST, Vythilingam I. Entomologic and molecular investigation into Plasmodium vivax transmission in Singapore, 2009. Malar J 2010; 9:305. [PMID: 21029478 PMCID: PMC2988040 DOI: 10.1186/1475-2875-9-305] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Accepted: 10/29/2010] [Indexed: 11/10/2022] Open
Abstract
Background Singapore has been certified malaria free since November 1982 by the World Health Organization and despite occasional local transmission, the country has maintained the standing. In 2009, three clusters of malaria cases were reported in Singapore. Methods Epidemiological, entomological and molecular studies were carried out to investigate the three clusters, namely Mandai-Sungei Kadut, Jurong Island and Sembawang. Results A total of 29 malaria patients, with no recent travel history, were reported in the three clusters. Molecular analysis based on the msp3α and msp1 genes showed two independent local transmissions: one in Mandai-Sungei Kadut and another in Sembawang. Almost all cases within each cluster were epidemiologically linked. In Jurong Island cluster, epidemiological link remains uncertain, as almost all cases had a unique genetic profile. Only two cases shared a common profile and were found to be linked to the Mandai-Sungei Kadut cluster. Entomological investigation found Anopheles sinensis to be the predominant Anopheline in the two areas where local transmission of P. vivax was confirmed. Anopheles sinensis was found to be attracted to human bait and bites as early as 19:45 hrs. However, all Anopheles mosquitoes caught were negative for sporozoites and oocysts by dissection. Conclusion Investigation of P. vivax cases from the three cluster areas confirmed the occurrence of local transmission in two areas. Although An. sinensis was the predominant Anopheline found in areas with confirmed transmission, the vector/s responsible for the outbreaks still remains cryptic.
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Affiliation(s)
- Lee-Ching Ng
- Environmental Health Institute, National Environment Agency, 11 Biopolis Way, Singapore 138667.
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Jeffery J, Lee RML, Tan SY, Liew C, Ng LC, Lam-Phua SG. New mosquito species records (Diptera: Culicidae) from Singapore. Trop Biomed 2010; 27:138-142. [PMID: 20562825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Nine species of mosquitoes in eight genera are recorded for the first time in Singapore. An additional two species were overlooked in a 1986 checklist for mosquitoes in Singapore, and one was described after 1986. Location and habitat data are provided for the nine new records. With the inclusion of these new records the number of species reported from Singapore is 137.
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Affiliation(s)
- John Jeffery
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
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Ng LC, Tan LK, Tan CH, Tan SSY, Hapuarachchi HC, Pok KY, Lai YL, Lam-Phua SG, Bucht G, Lin RTP, Leo YS, Tan BH, Han HK, Ooi PLS, James L, Khoo SP. Entomologic and virologic investigation of Chikungunya, Singapore. Emerg Infect Dis 2009; 15:1243-9. [PMID: 19751586 PMCID: PMC2815960 DOI: 10.3201/eid1508.081486] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Local transmission of chikungunya, a debilitating mosquito-borne viral disease, was first reported in Singapore in January 2008. After 3 months of absence, locally acquired Chikungunya cases resurfaced in May 2008, causing an outbreak that resulted in a total of 231 cases by September 2008. The circulating viruses were related to East, Central, and South African genotypes that emerged in the Indian Ocean region in 2005. The first local outbreak was due to a wild-type virus (alanine at codon 226 of the envelope 1 gene) and occurred in an area where Aedes aegypti mosquitoes were the primary vector. Strains isolated during subsequent outbreaks showed alanine to valine substitution (A226V) and largely spread in areas predominated by Ae. albopictus mosquitoes. These findings led to a revision of the current vector control strategy in Singapore. This report highlights the use of entomologic and virologic data to assist in the control of chikungunya in disease-endemic areas.
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Chung YK, Lam-Phua SG, Chua YT, Yatiman R. Evaluation of biological and chemical insecticide mixture against Aedes aegypti larvae and adults by thermal fogging in Singapore. Med Vet Entomol 2001; 15:321-327. [PMID: 11583451 DOI: 10.1046/j.0269-283x.2001.00311.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
To improve the operational efficiency of dengue vector control in Singapore, larvicide and adulticide were applied together by thermal fog generator (Agrofog AF40). The mixture consisted of Bacillus thuringiensis var. israelensis (Vectobac 12 AS) as biological larvicide at 1.5 L/ha and pirimiphos-methyl (Actellic 50 EC) as adulticide at 100 g ai/ha, diluted 10-fold with water. Aerosol of this mixture was evaluated against the mosquito Aedes aegypti (L.) (Diptera: Culicidae) in bioassays using cages of 10 adult females exposed at heights of 0.3-2.4 m and distances of 3-12 m from the hand-held generator. Cups containing 200 mL water were treated at ground level by exposure to the aerosol application at the same distances from the generator. Subsequent larval bioassays on days 1, 7, 14, 21 and 28 post-spray involved exposing 20 larvae/cup for 48 h. Droplets had VMD 57 microm and female mosquitoes were killed by 2 s exposure to the aerosol at 3 m. We obtained 92-100% mortality of the adult mosquitoes and 100% control of larvae at 3 m distance, but only 10-13% mortality at 12 m from the fogger. In treated cups, larvae showed high mortality (92%) when exposed for 48 h even 1 month post-treatment. Results demonstrate the practical advantage of using this mixture of Vectobac 12AS and Actellic 50 EC for simultaneous control of Aedes adults and larvae, with prolonged larvicidal efficacy in treated containers.
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Affiliation(s)
- Y K Chung
- Vector Control & Research Department, Ministry of the Environment, Singapore.
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Chow VT, Chan YC, Yong R, Lee KM, Lim LK, Chung YK, Lam-Phua SG, Tan BT. Monitoring of dengue viruses in field-caught Aedes aegypti and Aedes albopictus mosquitoes by a type-specific polymerase chain reaction and cycle sequencing. Am J Trop Med Hyg 1998; 58:578-86. [PMID: 9598444 DOI: 10.4269/ajtmh.1998.58.578] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Virologic surveillance for dengue through the detection of the prevalent serotype(s) circulating in the human population during inter- and intra-epidemic periods constitutes a reliable sentinel system for dengue outbreaks. We have applied a rapid and sensitive, semi-nested, reverse transcription-polymerase chain reaction (RT-PCR) assay using nonstructural protein 3 gene primers for the type-specific-detection of dengue viruses in artificially infected and in field-caught adult Aedes mosquitoes. In laboratory experiments, the assay was sensitive enough to detect one virus-infected mosquito head in pools of up to 59 uninfected heads. In a prospective field study conducted from April 1995 to July 1996, female adult Ae. aegypti and Ae. albopictus mosquitoes were caught from selected dengue-sensitive areas in Singapore and assayed by RT-PCR. Approximately 20% of 309 mosquito pools were positive for dengue viruses. Of the 23 RT-PCR-positive Ae. aegypti pools (containing 1-17 mosquitoes each), 18 pools (78.3%) were positive for dengue 1 virus. There were 40 RT-PCR-positive Ae. albopictus pools (containing 1-33 mosquitoes each) of which 31 (77.5%) were positive for dengue 1 virus. The predominant virus type responsible for the current dengue epidemic since 1995 was also dengue 1. The geographic locations of the virus-infected mosquitoes correlated with the residences or workplaces of patients within dengue outbreak areas. A total of 43.5% of the positive Ae. aegypti pools and 25.0% of the positive Ae. albopictus pools contained only a single mosquito. Both Aedes species showed similar overall minimum infection rates of 57.6 and 50 per 1,000 mosquitoes. Infected Ae. aegypti were detected as early as six weeks before the start of the dengue outbreaks in 1995 and 1996. However, infected Ae. albopictus appeared later, when the number of cases was increasing. Virologic surveillance by RT-PCR for detecting dengue virus-infected Aedes mosquitoes in the field may serve as an early warning monitoring system for dengue outbreaks.
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Affiliation(s)
- V T Chow
- Department of Microbiology, Faculty of Medicine, National University of Singapore, Kent Ridge
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