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Matsumoto-Takahashi ELA, Iwagami M, Oyoshi K, Sasaki Y, Hongvanthong B, Kano S. Deforestation inhibits malaria transmission in Lao PDR: a spatial epidemiology using Earth observation satellites. Trop Med Health 2023; 51:60. [PMID: 37915065 PMCID: PMC10621094 DOI: 10.1186/s41182-023-00554-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Accepted: 10/26/2023] [Indexed: 11/03/2023] Open
Abstract
BACKGROUND The present study aimed to analyze the impact of deforestation on the malaria distribution in the Lao People's Democratic Republic (Lao PDR), with consideration of climate change. METHODS Malaria distribution data from 2002 to 2015 were obtained from the Ministry of Health of Lao PDR and each indicator was calculated. Earth observation satellite data (forested area, land surface temperature, and precipitation) were obtained from the Japan Aerospace Exploration Agency (JAXA). Structured equation modeling (SEM) was conducted to clarify the relationship between the malaria incidence and Earth observation satellite data. RESULTS As a result, SEM identified two factors that were independently associated with the malaria incidence: area and proportion of forest. Specifically, malaria was found to be more prevalent in the southern region, with the malaria incidence increasing as the percentage of forested land increased (both p < 0.01). With global warming steadily progressing, forested areas are expected to play an important role in the incidence of malaria in Lao PDR. This is believed because malaria in Lao PDR is mainly forest malaria transmitted by Anopheles dirus. CONCLUSION To accelerate the elimination of malaria in Lao PDR, it is important to identify, prevent, and intervene in places with increased forest coverage (e.g., plantations) and in low-temperature areas adjacent to malaria-endemic areas, where the vegetation is similar to that in malaria-endemic areas.
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Affiliation(s)
- Emilie Louise Akiko Matsumoto-Takahashi
- Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine (NCGM), 1-21-1 Toyama, Shinjuku-Ku, Tokyo, 162-8655, Japan
- Graduate School of Public Health, St. Luke's International University, Tokyo, Japan
| | - Moritoshi Iwagami
- Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine (NCGM), 1-21-1 Toyama, Shinjuku-Ku, Tokyo, 162-8655, Japan
- Parasitology Laboratory, Institut Pasteur du Laos (IPL), Ministry of Health, Vientiane, Lao People's Democratic Republic
| | - Kei Oyoshi
- Earth Observation Research Center (EORC), Japan Aerospace Exploration Agency (JAXA), Tsukuba, Japan
| | - Yoshinobu Sasaki
- Earth Observation Research Center (EORC), Japan Aerospace Exploration Agency (JAXA), Tsukuba, Japan
| | - Bouasy Hongvanthong
- Center of Malariology, Parasitology and Entomology (CMPE), Ministry of Health, Vientiane, Lao People's Democratic Republic
| | - Shigeyuki Kano
- Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine (NCGM), 1-21-1 Toyama, Shinjuku-Ku, Tokyo, 162-8655, Japan.
- Parasitology Laboratory, Institut Pasteur du Laos (IPL), Ministry of Health, Vientiane, Lao People's Democratic Republic.
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Wong ML, Zulzahrin Z, Vythilingam I, Lau YL, Sam IC, Fong MY, Lee WC. Perspectives of vector management in the control and elimination of vector-borne zoonoses. Front Microbiol 2023; 14:1135977. [PMID: 37025644 PMCID: PMC10070879 DOI: 10.3389/fmicb.2023.1135977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 02/28/2023] [Indexed: 04/08/2023] Open
Abstract
The complex transmission profiles of vector-borne zoonoses (VZB) and vector-borne infections with animal reservoirs (VBIAR) complicate efforts to break the transmission circuit of these infections. To control and eliminate VZB and VBIAR, insecticide application may not be conducted easily in all circumstances, particularly for infections with sylvatic transmission cycle. As a result, alternative approaches have been considered in the vector management against these infections. In this review, we highlighted differences among the environmental, chemical, and biological control approaches in vector management, from the perspectives of VZB and VBIAR. Concerns and knowledge gaps pertaining to the available control approaches were discussed to better understand the prospects of integrating these vector control approaches to synergistically break the transmission of VZB and VBIAR in humans, in line with the integrated vector management (IVM) developed by the World Health Organization (WHO) since 2004.
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Affiliation(s)
- Meng Li Wong
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
| | - Zulhisham Zulzahrin
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
| | - Indra Vythilingam
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
| | - Yee Ling Lau
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
| | - I-Ching Sam
- Department of Medical Microbiology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
- Department of Medical Microbiology, University Malaya Medical Centre (UMMC), Kuala Lumpur, Malaysia
| | - Mun Yik Fong
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
| | - Wenn-Chyau Lee
- Department of Parasitology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
- A*STAR Infectious Diseases Labs (A*STAR ID Labs), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
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Survey of malaria vectors on the Cambodia, Thailand and China-Laos Borders. Malar J 2022; 21:399. [PMID: 36585690 PMCID: PMC9801360 DOI: 10.1186/s12936-022-04418-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 12/15/2022] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Anopheles maculatus, Anopheles minimus and Anopheles dirus are the major vectors of malaria transmission in the Greater Mekong Subregion (GMS). The malaria burden in this region has decreased significantly in recent years as all GMS countries progress towards malaria elimination. It is necessary to investigate the Anopheles diversity and abundance status and assess the Plasmodium infection rates to understand the malaria transmission potential of these vector species in GMS countries to guide the development of up-to-date vector control strategies and interventions. METHODS A survey of mosquitoes was conducted in Stung Treng, Sainyabuli and Phongsaly Provinces on the Cambodia-Laos, Thailand-Laos and China-Laos borders, respectively. Mosquito collection was done by overnight trapping at sentinel sites in each province. After morphological identification, the 18S rRNA-based nested-PCR was performed to detect malaria parasites in the captured Anopheles mosquitoes. RESULTS A total of 18 965 mosquitoes comprising of 35 species of 2 subgenera (Subgenus Anopheles and Subgenus Cellia) and 4 tribes (Tribes Culicini, Aedini, Armigerini and Mansoniini) were captured. Tribe Culicini accounted for 85.66% of captures, followed by Subgenus Anopheles (8.15%). Anopheles sinensis dominated the Subgenus Anopheles by 99.81%. Plasmodium-infection was found in 25 out of the 1 683 individual or pooled samples of Anopheles. Among the 25 positive samples, 19, 5 and 1 were collected from Loum, Pangkhom and Siem Pang village, respectively. Eight Anopheles species were found infected with Plasmodium, i.e., An. sinensis, Anopheles kochi, Anopheles vagus, An. minimus, Anopheles annularis, Anopheles philippinensis, Anopheles tessellatus and An. dirus. The infection rates of Plasmodium falciparum, Plasmodium vivax and mixture of Plasmodium parasite species were 0.12% (2/1 683), 1.31% (22/1 683) and 0.06% (1/1 683), respectively. CONCLUSIONS Overall, this survey re-confirmed that multiple Anopheles species carry malaria parasites in the international border areas of the GMS countries. Anopheles sinensis dominated the Anopheles collections and as carriers of malaria parasites, therefore may play a significant role in malaria transmission. More extensive investigations of malaria vectors are required to reveal the detailed vector biology, ecology, behaviour, and genetics in GMS regions in order to assist with the planning and implementation of improved malaria control strategies.
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Zhang C, Luo C, Yang R, Yang Y, Guo X, Deng Y, Zhou H, Zhang Y. Morphological and molecular identification reveals a high diversity of Anopheles species in the forest region of the Cambodia-Laos border. Parasit Vectors 2022; 15:94. [PMID: 35303948 PMCID: PMC8933986 DOI: 10.1186/s13071-022-05167-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 01/17/2022] [Indexed: 11/25/2022] Open
Abstract
Background To develop an effective malaria vector intervention method in forested international border regions within the Greater Mekong Subregion (GMS), more in-depth studies should be conducted on local Anopheles species composition and bionomic features. There is a paucity of comprehensive surveys of biodiversity integrating morphological and molecular species identification conducted within the border of Laos and Cambodia. Methods A total of 2394 adult mosquitoes were trapped in the Cambodia–Laos border region. We first performed morphological identification of Anopheles mosquitoes and subsequently performed molecular identification using 412 recombinant DNA–internal transcribed spacer 2 (rDNA-ITS2) and 391 mitochondrial DNA–cytochrome c oxidase subunit 2 (mtDNA-COII) sequences. The molecular and morphological identification results were compared, and phylogenetic analysis of rDNA-ITS2 and mtDNA-COII was conducted for the sequence divergence among species. Results Thirteen distinct species of Anopheles were molecularly identified in a 26,415 km2 border region in Siem Pang (Cambodia) and Pathoomphone (Laos). According to the comparisons of morphological and molecular identity, the interpretation of local species composition for dominant species in the Cambodia–Laos border (An. dirus, An. maculatus, An. philippinensis, An. kochi and An. sinensis) achieved the highest accuracy of morphological identification, from 98.37 to 100%. In contrast, the other species which were molecularly identified were less frequently identified correctly (0–58.3%) by morphological methods. The average rDNA-ITS2 and mtDNA-COII interspecific divergence was respectively 318 times and 15 times higher than their average intraspecific divergence. The barcoding gap ranged from 0.042 to 0.193 for rDNA-ITS2, and from 0.033 to 0.047 for mtDNA-COII. Conclusions The Cambodia–Laos border hosts a high diversity of Anopheles species. The morphological identification of Anopheles species provides higher accuracy for dominant species than for other species. Molecular methods combined with morphological analysis to determine species composition, population dynamics and bionomic characteristics can facilitate a better understanding of the factors driving malaria transmission and the effects of interventions, and can aid in achieving the goal of eliminating malaria. Graphical Abstract ![]()
Supplementary Information The online version contains supplementary material available at 10.1186/s13071-022-05167-0.
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Affiliation(s)
- Canglin Zhang
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Chunhai Luo
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Rui Yang
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Yaming Yang
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Xiaofang Guo
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Yan Deng
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China
| | - Hongning Zhou
- Yunnan Provincial Key Laboratory of Vector-Borne Diseases Control and Research, Yunnan Provincial Collaborative Innovation Center for Public Health and Disease Prevention and Control, Yunnan Institute of Parasitic Diseases Innovative Team of Key Techniques for Vector Borne Disease Control and Prevention (Developing), Yunnan Institute of Parasitic Diseases, Pu'er, 665099, People's Republic of China.
| | - Yilong Zhang
- Department of Tropical Diseases, Faculty of Naval Medicine, Naval Medical University, Shanghai, 200433, China.
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Jongdeepaisal M, Inthasone S, Khonputsa P, Malaphone V, Pongsoipetch K, Pongvongsa T, Mayxay M, Chindavongsa K, Pell C, Maude RJ. Forest malaria and prospects for anti-malarial chemoprophylaxis among forest goers: findings from a qualitative study in Lao PDR. Malar J 2022; 21:8. [PMID: 34983549 PMCID: PMC8727080 DOI: 10.1186/s12936-021-04027-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 12/16/2021] [Indexed: 11/15/2022] Open
Abstract
Background Despite significant decline in malarial incidence and mortality in countries across the Greater Mekong Subregion, the disease remains a public health challenge in the region; transmission continues mainly among people who visit forests in remote areas, often along international borders, where access to primary healthcare is limited. In the absence of effective vector-control measures and limited exposure periods, malaria chemoprophylaxis has been proposed as a strategy to protect forest goers. As a rarely used approach for indigenous populations, questions remain about its feasibility and acceptability. Drawing on in-depth interviews with forest goers and stakeholders, this article examines opportunities and challenges for implementation of anti-malarial chemoprophylaxis for forest goers in Lao PDR. Methods In-depth interviews were conducted with 16 forest goers and 15 stakeholders in Savannakhet province, Lao PDR. Interview topics included experience of malaria prevention and health services, and perceptions of prophylaxis as a potential component of malaria elimination strategy. The interviews were transcribed and coded using inductive and deductive approaches for qualitative thematic analysis. Results In ethnically and geographically diverse villages, awareness of malaria risk prompts forest goers to protect themselves, albeit sub-optimally using available preventive measures. Stakeholders highlighted challenges for targeting at-risk populations and approaches to address forest malaria in southern Lao PDR. Among policymakers, choice and cost of anti-malarials, particularly their efficacy and source of funding, were key considerations for the feasibility of malaria prophylaxis. Acceptability of prophylaxis among forest goers was also influenced by the complexity of the regimen, including the number of tablets and timing of doses. Implementation of prophylaxis may be affected by a lack of transportation and communication barriers in remote communities. Conclusion Adding prophylaxis to existing malaria control activities requires strengthening the capacity of local health workers in Lao PDR. Ideally, this would be part of an integrated approach that includes strategies to address the other febrile illnesses that forest goers describe as priority health concerns. The prophylactic regimen also requires careful consideration in terms of effectiveness and simplicity of dosing. Supplementary Information The online version contains supplementary material available at 10.1186/s12936-021-04027-z.
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Affiliation(s)
- Monnaphat Jongdeepaisal
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Soulixay Inthasone
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Panarasri Khonputsa
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Vilayvone Malaphone
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Kulchada Pongsoipetch
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | | | - Mayfong Mayxay
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.,Lao-Oxford-Mahosot Hospital-Wellcome Trust Research Unit (LOMWRU), Mahosot Hospital, Ministry of Health, Vientiane, Lao PDR.,Institute of Research and Education Development (IRED), University of Health Sciences, Ministry of Health, Vientiane, Lao PDR
| | | | - Christopher Pell
- Amsterdam Institute for Global Health and Development (AIGHD), Amsterdam, The Netherlands.,Department of Global Health, Amsterdam University Medical Centers, Amsterdam, The Netherlands.,Centre for Social Science and Global Health, University of Amsterdam, Amsterdam, The Netherlands
| | - Richard J Maude
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. .,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK. .,Harvard TH Chan School of Public Health, Harvard University, Boston, USA. .,The Open University, Milton Keynes, UK.
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Hii J, Hustedt J, Bangs MJ. Residual Malaria Transmission in Select Countries of Asia-Pacific Region: Old Wine in a New Barrel. J Infect Dis 2021; 223:S111-S142. [PMID: 33906222 PMCID: PMC8079134 DOI: 10.1093/infdis/jiab004] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Background Despite substantial reductions in malaria burden and improvement in case management, malaria remains a major public health challenge in the Asia-Pacific region. Residual malaria transmission (RMT) is the fraction of total transmission that persists after achievement of full operational coverage with effective insecticide-treated bed nets (ITNs)/long-lasting insecticidal nets (LLINs) and/or indoor residual spray interventions. There is a critical need to standardize and share best practices for entomological, anthropological, and product development investigative protocols to meet the challenges of RMT and elimination goals. Methods A systematic review was conducted to describe when and where RMT is occurring, while specifically targeting ownership and usage of ITN/LLINs, indoor residual spray application, insecticide susceptibility of vectors, and human and vector biting behavior, with a focus on nighttime activities. Results Sixty-six publications from 1995 to present met the inclusion criteria for closer review. Associations between local vector control coverage and use with behaviors of human and mosquito vectors varied by locality and circumstance. Consequently, the magnitude of RMT is insufficiently studied and analyzed with sparse estimates of individual exposure in communities, insufficient or incomplete observations of ITN/LLIN use, and the local human population movement into and from high-risk areas. Conclusions This review identified significant gaps or deficiencies that require urgent attention, namely, developing standardized procedures and methods to estimate risk exposure beyond the peridomestic setting, analytical approaches to measure key human-vector interactions, and seasonal location-specific agricultural or forest use calendars, and establishing the collection of longitudinal human and vector data close in time and location.
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Affiliation(s)
- Jeffrey Hii
- Malaria Consortium Asia, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.,College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia
| | | | - Michael J Bangs
- Public Health and Malaria Control Department, PT Freeport Indonesia, International SOS, Jl. Kertajasa, Kuala Kencana, Papua, Indonesia.,Department of Entomology, Faculty of Agriculture, Kasertart University, Bangkok, Thailand
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Abstract
Residual malaria transmission is the actual maintained inoculation of Plasmodium, in spite of a well-designed and implemented vector control programs, and is of great concern for malaria elimination. Residual malaria transmission occurs under several possible circumstances, among which the presence of exophilic vector species, such as Anopheles dirus, or indoor- and outdoor-biting vectors, such as Anopheles nili, or specific behavior, such as feeding on humans indoors, then resting or leaving the house the same night (such as Anopheles moucheti) or also changes in behavior induced by insecticides applied inside houses, such as the well-known deterrent effect of permethrin-treated nets or the irritant effect of DDT. The use of insecticides may change the composition of local Anopheles populations, such as A. arabiensis taking up the place of A. gambiae in Senegal, A. aquasalis replacing A. darlingi in Guyana, or A. harrisoni superseding A. minimus in Vietnam. The change in behavior, such as biting activity earlier than usually reported—for example, Anopheles funestus after a large-scale distribution of long-lasting insecticidal nets—or insecticide resistance, in particular the current spread of pyrethroid resistance, could hamper the efficacy of classic pyrethroid-treated long-lasting insecticidal nets and maintained transmission. These issues must be well documented in every situation to elaborate, implement, monitor, and evaluate tailored vector control programs, keeping in mind that they must be conceived as integrated programs with several well and appropriately coordinated approaches, combining entomological but also parasitological, clinical, and social methods and analyses. A successful integrated vector control program must then be designed to reduce transmission and incidence rates of malaria morbidity and overall mortality.
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Affiliation(s)
- Pierre Carnevale
- Institut de Recherche pour le Développement, Portiragnes, France
| | - Sylvie Manguin
- HydroSciences Montpellier, Institut de Recherche pour le Développement (IRD), CNRS , Université Montpellier, Montpellier, France
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Marcombe S, Maithaviphet S, Bobichon J, Phommavan N, Nambanya S, Corbel V, Brey PT. New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey. Malar J 2020; 19:396. [PMID: 33168012 PMCID: PMC7654023 DOI: 10.1186/s12936-020-03453-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 10/18/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In Laos, the malaria burden remains high despite a significant reduction of cases during the last decade. In the context of the disease elimination by 2030, a nationwide entomological survey was conducted to better understand the distribution, abundance and behaviour of major malaria vectors (Anopheles spp.) in the country. METHODS Mosquito collections were implemented in ten villages from ten provinces during the rainy and dry seasons of 2014 and 2015 by using human landing catch (HLC) and cow bait collection (CBC) methods. After morphological identification in the field, molecular identification of the sibling species of Anopheles mosquitoes from the Funestus, Leucosphyrus, and Maculatus groups were determined using PCR specific alleles. A screening of Plasmodium falciparum and Plasmodium vivax infections in the vectors was carried out by quantitative PCR assays. RESULTS A total of 14,146 adult mosquitoes representing 25 different Anopheles species were collected and morphologically identified. Molecular identification revealed the presence of 12 sibling species within the main primary vector groups, including Anopheles maculatus, Anopheles rampae, Anopheles sawadwongporni, Anopheles pseudowillmori, Anopheles dravidicus, Anopheles minimus, Anopheles aconitus, Anopheles pampanai, Anopheles harrisoni, Anopheles dirus, Anopheles baimaii, Anopheles nemophilous. Anopheles maculatus and An. minimus were predominant during both the dry and rainy seasons, but showed highly zoophilic preferences (Zoophilic index of 98% and 95%, respectively). Overall, 22% of the total malaria vectors were collected between 10:00 PM and 5:00 AM indoors when people are sleeping. Twenty-seven percent of primary and secondary vectors were collected outdoors before 10:00 PM or after 5:00 AM, times when people are usually awake and outdoors. Only two specimens were positive for P. falciparum, one An. aconitus from Phongsaly and one An. minimus from Vientiane Province CONCLUSIONS: The results indicate that people living in rural areas in Laos are constantly exposed to malaria vectors throughout the year and specifically outdoors. The use of LLINs/IRS remains important but innovative tools and new strategies are needed to address locally, the early and outdoor malaria transmission. Lack of expertise in general entomological methods may further exacerbate the situation.
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Affiliation(s)
| | - Santi Maithaviphet
- Center for Malariology, Parasitology and Entomology, Ministry of Health, Vientiane, Lao PDR
| | - Julie Bobichon
- Institut Pasteur du Laos, Ministry of Health, Vientiane, Lao PDR
| | | | - Simone Nambanya
- Center for Malariology, Parasitology and Entomology, Ministry of Health, Vientiane, Lao PDR
| | - Vincent Corbel
- Institut de Recherche Pour Le Développement (IRD), Maladies Infectieuses et Vecteurs, Ecologie, Génétique, Evolution et Contrôle (MIVEGEC, UM1-CNRS 5290-IRD 224), Montpellier, France
| | - Paul T Brey
- Institut Pasteur du Laos, Ministry of Health, Vientiane, Lao PDR
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Tananchai C, Manguin S, Bangs MJ, Chareonviriyaphap T. Malaria Vectors and Species Complexes in Thailand: Implications for Vector Control. Trends Parasitol 2019; 35:544-558. [PMID: 31182384 DOI: 10.1016/j.pt.2019.04.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 04/25/2019] [Accepted: 04/30/2019] [Indexed: 11/18/2022]
Abstract
There are seven Anopheles species incriminated as important (primary) malaria vectors in Thailand. These vectors belong to species complexes or are in closely related groups that are difficult to separate morphologically. Precise species identification, using molecular methods, enables control operations to target only important vectors and to increase understanding of their specific ecological requirements, bionomic characteristics, and behavioral traits. This review focuses on adult mosquito behavior, vector transmission capacity, and geographical distribution of malaria vectors in Thailand identified using genetic and molecular identification methods between 1994 and 2019. A better understanding of Anopheles biodiversity, biology, behavior, vector capacity, and distribution in Thailand and neighboring countries in the Greater Mekong Subregion (GMS) will facilitate more effective and efficient vector-control strategies and consequently contribute to a further decrease in the malaria burden.
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Affiliation(s)
- Chatchai Tananchai
- Department of Entomology, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand
| | - Sylvie Manguin
- HydroSciences Montpellier (UMR-HSM), Institut de Recherche pour le Développement France (IRD), CNRS, Université Montpellier, Montpellier, France
| | - Michael J Bangs
- Department of Entomology, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand; Public Health and Malaria Control Department, PT Freeport Indonesia, International SOS, Jl. Kertajasa, Kuala Kencana, Papua 99920, Indonesia
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10
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Motoki MT, Vongphayloth K, Rueda LM, Miot EF, Hiscox A, Hertz JC, Brey PT. New records and updated checklist of mosquitoes (Diptera: Culicidae) from Lao People's Democratic Republic, with special emphasis on adult and larval surveillance in Khammuane Province. JOURNAL OF VECTOR ECOLOGY : JOURNAL OF THE SOCIETY FOR VECTOR ECOLOGY 2019; 44:76-88. [PMID: 31124228 DOI: 10.1111/jvec.12331] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 02/14/2019] [Indexed: 06/09/2023]
Abstract
A list of mosquitoes from the Nakai Nam Theun National Protected Area along the Nam Theun, Nam Mon, Nam Noy, and Nam On rivers, Nakai District, Khammuane Province, Lao People's Democratic Republic (Lao PDR) is presented. Fifty-four mosquito taxa were identified, including 15 new records in the Lao PDR. A fragment of the mtDNA cytochrome c oxidase subunit I (COI) gene, barcode region, was generated for 34 specimens, and together with four specimens already published, it represented 23 species in eight genera. In addition, an updated checklist of 170 mosquito taxa from Lao PDR is provided based on field collections from Khammuane Province, the literature, and specimens deposited in the Smithsonian Institution, National Museum of Natural History (SI-NMNH), Washington, DC, U.S.A. This paper provides additional information about the biodiversity of mosquito fauna in Lao PDR.
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Affiliation(s)
- Maysa T Motoki
- Medical Entomology and Vector-Borne Disease Unit, Institut Pasteur du Laos, Samsenthai Rd., Ban Kao-gnot, P.O. Box 3560, Vientiane, Lao PDR
- Walter Reed Biosystematics Unit, Entomology Department, Smithsonian Institution, MSC MRC 514, Suitland, MD, U.S.A
| | - Khamsing Vongphayloth
- Medical Entomology and Vector-Borne Disease Unit, Institut Pasteur du Laos, Samsenthai Rd., Ban Kao-gnot, P.O. Box 3560, Vientiane, Lao PDR
| | - Leopoldo M Rueda
- Walter Reed Biosystematics Unit, Entomology Department, Smithsonian Institution, MSC MRC 514, Suitland, MD, U.S.A
| | - Elliott F Miot
- Medical Entomology and Vector-Borne Disease Unit, Institut Pasteur du Laos, Samsenthai Rd., Ban Kao-gnot, P.O. Box 3560, Vientiane, Lao PDR
- Université Pierre et Marie Curie, Cellule Pasteur UPMC, Paris, France
- Insect-Virus Interactions Group, Department of Genomes and Genetics, Institut Pasteur, Paris, France
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 2000, Paris, France
| | - Alexandra Hiscox
- Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands
| | | | - Paul T Brey
- Medical Entomology and Vector-Borne Disease Unit, Institut Pasteur du Laos, Samsenthai Rd., Ban Kao-gnot, P.O. Box 3560, Vientiane, Lao PDR
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11
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Tangena JAA, Thammavong P, Malaithong N, Inthavong T, Ouanesamon P, Brey PT, Lindsay SW. Diversity of Mosquitoes (Diptera: Culicidae) Attracted to Human Subjects in Rubber Plantations, Secondary Forests, and Villages in Luang Prabang Province, Northern Lao PDR. JOURNAL OF MEDICAL ENTOMOLOGY 2017; 54:1589-1604. [PMID: 28505314 DOI: 10.1093/jme/tjx071] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Indexed: 06/07/2023]
Abstract
The impact of the rapid expansion of rubber plantations in South-East Asia on mosquito populations is uncertain. We compared the abundance and diversity of adult mosquitoes using human-baited traps in four typical rural habitats in northern Lao PDR: secondary forests, immature rubber plantations, mature rubber plantations, and villages. Generalized estimating equations were used to explore differences in mosquito abundance between habitats, and Simpson's diversity index was used to measure species diversity. Over nine months, 24,927 female mosquitoes were collected, including 51 species newly recorded in Lao PDR. A list of the 114 mosquito species identified is included. More mosquitoes, including vector species, were collected in the secondary forest than immature rubber plantations (rainy season, odds ratio [OR] 0.33, 95% confidence interval [CI] 0.31-0.36; dry season, 0.46, 95% CI 0.41-0.51), mature rubber plantations (rainy season, OR 0.25, 95% CI 0.23-0.27; dry season, OR 0.25, 95% CI 0.22-0.28), and villages (rainy season, OR 0.13, 95% CI 0.12-0.14; dry season, 0.20, 95% CI 0.18-0.23). All habitats showed high species diversity (Simpson's indexes between 0.82-0.86) with vectors of dengue, Japanese encephalitis (JE), lymphatic filariasis, and malaria. In the secondary forests and rubber plantations, Aedes albopictus (Skuse), a dengue vector, was the dominant mosquito species, while in the villages, Culex vishnui (Theobald), a JE vector, was most common. This study has increased the overall knowledge of mosquito fauna in Lao PDR. The high abundance of Ae. albopictus in natural and man-made forests warrants concern, with vector control measures currently only implemented in cities and villages.
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Affiliation(s)
- Julie-Anne A Tangena
- Department of Medical Entomology, Institut Pasteur du Laos, Samsenthai Rd, Ban Kao-gnot, PO Box 3560, Vientiane, Lao PDR
- School of Biological and Biomedical Sciences, Durham University, South Road, Durham, DH1 3LE, United Kingdom
| | - Phoutmany Thammavong
- Department of Medical Entomology, Institut Pasteur du Laos, Samsenthai Rd, Ban Kao-gnot, PO Box 3560, Vientiane, Lao PDR
| | - Naritsara Malaithong
- Department of Entomology, Kasetsart University, 50 Ngam Wong Wan Rd., Ladyaow Chatuchak Bangkok 10900, Thailand
| | - Thavone Inthavong
- Agriculture and Forestry Policy Research Center, National Agriculture and Forestry Research Institute, Nongviengkham Village, Vientiane, P.O Box 7170, Lao PDR
| | - Phuthasone Ouanesamon
- Agriculture and Forestry Policy Research Center, National Agriculture and Forestry Research Institute, Nongviengkham Village, Vientiane, P.O Box 7170, Lao PDR
| | - Paul T Brey
- Department of Medical Entomology, Institut Pasteur du Laos, Samsenthai Rd, Ban Kao-gnot, PO Box 3560, Vientiane, Lao PDR
| | - Steve W Lindsay
- School of Biological and Biomedical Sciences, Durham University, South Road, Durham, DH1 3LE, United Kingdom
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12
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Inthavong N, Nonaka D, Kounnavong S, Iwagami M, Phommala S, Kobayashi J, Hongvanthong B, Pongvongsa T, Brey PT, Kano S. Individual and household factors associated with incidences of village malaria in Xepon district, Savannakhet province, Lao PDR. Trop Med Health 2017; 45:36. [PMID: 29151802 PMCID: PMC5678595 DOI: 10.1186/s41182-017-0077-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 10/25/2017] [Indexed: 11/18/2022] Open
Abstract
Background In the Lao PDR, the incidence of malaria greatly differs among villages even within a subdistrict, and the reasons for this difference are poorly understood. The objective of this study was to identify differences in villagers’ behavior and the household environment between villages with high incidences and those with low incidences of malaria in a rural district of the Lao PDR. Methods A case-control study was conducted in Xepon district, Savannakhet province. Case villages were defined as those with a high incidence (> 10 cases per 1000 population per year), and control villages were those with a low incidence (0–10 cases per 1000 population per year). Data were collected from 178 households in the six case villages and six control villages between December 2016 and January 2017. The data collection consisted of an interview survey with the heads of households and an observational survey in and around the house. Logistic regression was used to assess the association between the case-control status and individual-level behavioral factors and household-level environmental factors adjusted for socio-demographic and economic factors. Results Compared to the household members in the control villages, household members in the case villages were significantly more likely to work at night in the forest (adjusted odds ratio 1.95; 95% confidence interval 1.28 to 2.98) and more likely to sleep overnight in the forest (adjusted odds ratio 1.94; 95% confidence interval 1.13 to 3.33). Additionally, compared to the households in the control villages, households in the case villages were significantly more likely to have an open space on the house surface (adjusted odds ratio 3.64; 95% confidence interval 1.68 to 7.84). Conclusions There were significant differences in nighttime working and sleeping behaviors in the forest and the presence of an open space on the house surface in the case versus control villages. These differences can partly explain the difference in the incidences of malaria among the villages. The Lao National Malaria Control Program should recommend that villagers use personal protection when working and sleeping in the forest and to reduce any open space on the house surfaces.
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Affiliation(s)
- Nouhak Inthavong
- Department of Global Health, Graduate School of Health Sciences, University of the Ryukyus, Uehara 207, Nishihara-cho, Okinawa, 903-0215 Japan.,SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,National Institute of Public Health, Ministry of Health, Ban Kaognot, Samsenthai Road, Sisattanak District, Vientiane, Lao People's Democratic Republic
| | - Daisuke Nonaka
- Department of Global Health, Graduate School of Health Sciences, University of the Ryukyus, Uehara 207, Nishihara-cho, Okinawa, 903-0215 Japan.,SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic
| | - Sengchanh Kounnavong
- National Institute of Public Health, Ministry of Health, Ban Kaognot, Samsenthai Road, Sisattanak District, Vientiane, Lao People's Democratic Republic
| | - Moritoshi Iwagami
- SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655 Japan.,Institut Pasteur du Laos, Ministry of Health, Sisattanak District, Vientiane, Lao People's Democratic Republic
| | - Souraxay Phommala
- National Institute of Public Health, Ministry of Health, Ban Kaognot, Samsenthai Road, Sisattanak District, Vientiane, Lao People's Democratic Republic
| | - Jun Kobayashi
- Department of Global Health, Graduate School of Health Sciences, University of the Ryukyus, Uehara 207, Nishihara-cho, Okinawa, 903-0215 Japan.,SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic
| | - Bouasy Hongvanthong
- SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,Center of Malariology, Parasitology and Entomology, Ministry of Health, Vientiane, Lao People's Democratic Republic
| | - Tiengkham Pongvongsa
- SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,Savannakhet Provincial Health Department, Thahea village, Kaysone-Phomvihan District, Savannakhet, Lao People's Democratic Republic
| | - Paul T Brey
- SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,Institut Pasteur du Laos, Ministry of Health, Sisattanak District, Vientiane, Lao People's Democratic Republic
| | - Shigeyuki Kano
- SATREPS Project for Parasitic Diseases, Vientiane, Lao People's Democratic Republic.,Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655 Japan
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13
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Tangena JAA, Thammavong P, Lindsay SW, Brey PT. Risk of exposure to potential vector mosquitoes for rural workers in Northern Lao PDR. PLoS Negl Trop Dis 2017; 11:e0005802. [PMID: 28742854 PMCID: PMC5544251 DOI: 10.1371/journal.pntd.0005802] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Revised: 08/04/2017] [Accepted: 07/12/2017] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND One major consequence of economic development in South-East Asia has been a rapid expansion of rubber plantations, in which outbreaks of dengue and malaria have occurred. Here we explored the difference in risk of exposure to potential dengue, Japanese encephalitis (JE), and malaria vectors between rubber workers and those engaged in traditional forest activities in northern Laos PDR. METHODOLOGY/PRINCIPAL FINDINGS Adult mosquitoes were collected for nine months in secondary forests, mature and immature rubber plantations, and villages. Human behavior data were collected using rapid participatory rural appraisals and surveys. Exposure risk was assessed by combining vector and human behavior and calculating the basic reproduction number (R0) in different typologies. Compared to those that stayed in the village, the risk of dengue vector exposure was higher for those that visited the secondary forests during the day (odds ratio (OR) 36.0), for those living and working in rubber plantations (OR 16.2) and for those that tapped rubber (OR 3.2). Exposure to JE vectors was also higher in the forest (OR 1.4) and, similar when working (OR 1.0) and living in the plantations (OR 0.8). Exposure to malaria vectors was greater in the forest (OR 1.3), similar when working in the plantations (OR 0.9) and lower when living in the plantations (OR 0.6). R0 for dengue was >2.8 for all habitats surveyed, except villages where R0≤0.06. The main malaria vector in all habitats was Anopheles maculatus s.l. in the rainy season and An. minimus s.l. in the dry season. CONCLUSIONS/SIGNIFICANCE The highest risk of exposure to vector mosquitoes occurred when people visit natural forests. However, since rubber workers spend long periods in the rubber plantations, their risk of exposure is increased greatly compared to those who temporarily enter natural forests or remain in the village. This study highlights the necessity of broadening mosquito control to include rubber plantations.
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Affiliation(s)
- Julie-Anne A. Tangena
- Department of Medical Entomology & Biology of Disease Vectors, Institut Pasteur du Laos, Vientiane, Lao PDR
- School of Biological and Biomedical Sciences, Durham University, Durham, United Kingdom
- * E-mail:
| | - Phoutmany Thammavong
- Department of Medical Entomology & Biology of Disease Vectors, Institut Pasteur du Laos, Vientiane, Lao PDR
| | - Steve W. Lindsay
- School of Biological and Biomedical Sciences, Durham University, Durham, United Kingdom
| | - Paul T. Brey
- Department of Medical Entomology & Biology of Disease Vectors, Institut Pasteur du Laos, Vientiane, Lao PDR
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14
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Pongvongsa T, Nonaka D, Iwagami M, Nakatsu M, Phongmany P, Nishimoto F, Kobayashi J, Hongvanthon B, Brey PT, Moji K, Mita T, Kano S. Household clustering of asymptomatic malaria infections in Xepon district, Savannakhet province, Lao PDR. Malar J 2016; 15:508. [PMID: 27756391 PMCID: PMC5069939 DOI: 10.1186/s12936-016-1552-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 10/05/2016] [Indexed: 11/10/2022] Open
Abstract
Background In the Lao PDR, malaria morbidity and mortality have remarkably decreased over the past decade. However, asymptomatic infections in rural villages contribute to the on-going local transmission. The primary objective of this study was to explore the characteristics of infections in a malaria-endemic district of the Lao PDR. The specific objectives were to investigate the prevalence and species of malaria parasites using molecular methods and to assess individual and household parasite levels and the characteristics associated with malaria infection. Methods The study population included 870 participants from 236 households in 10 villages of the Xepon district. Interviews, blood examinations and body temperature measurements were conducted between August and September 2013. A multilevel logistic regression model, with adjustment for clustering effects, was used to assess the association between predictor variables and an outcome variable (malaria infection status as principally determined by PCR). The predictive factors included individual-level factors (age, gender, past fever episode, and forest activity during night time) and household-level factors (household member size, household bed net usage/density and a household with one other malaria-infected member). Results Fifty-two participants (including 26 children) tested positive (positive rate: 6.0 %): Plasmodium falciparum mono-infection was the most common infection (n = 41, 78.8 %), followed by P. falciparum and Plasmodium vivax mixed infections (n = 9, 17.3 %). The majority of infected participants (n = 42, 80.8 %) had no fever episodes in the two previous weeks or a measurable fever (>37 °C) at the time of survey. Living in a household with one other malaria-infected member significantly increased the odds of infection (odds ratio 24.33, 95 % confidence interval 10.15–58.32). Among the 40 households that had at least one infected member, nine households were responsible for 40.4 % of the total infections. Conclusions Plasmodium vivax was detected more frequently than it was reported from the district hospital. Most infections were asymptomatic and sub-microscopic and were highly clustered within households. To further eliminate malaria in Xepon and other similar settings in the country, the National Malaria Control Programme should consider household-based strategies, including reactive case detection targeting the household members of index cases. Electronic supplementary material The online version of this article (doi:10.1186/s12936-016-1552-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Tiengkham Pongvongsa
- Savannakhet Provincial Health Department, Phonsavangnuea Village, Kaysone-Phomvihan District, Savannakhet, Lao PDR.,Department of Molecular and Cellular Parasitology, School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.,SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR
| | - Daisuke Nonaka
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR. .,Department of Global Health, School of Health Sciences, University of the Ryukyus, 207 Uehara, Nishihara-cho, Okinawa, 903-0215, Japan.
| | - Moritoshi Iwagami
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655, Japan.,Institut Pasteur du Laos, Sisattanak District, Vientiane, Lao PDR
| | - Masami Nakatsu
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655, Japan
| | - Panom Phongmany
- Savannakhet Provincial Health Department, Phonsavangnuea Village, Kaysone-Phomvihan District, Savannakhet, Lao PDR
| | - Futoshi Nishimoto
- Graduate School of Tropical Medicine and Global Health, Nagasaki University, 1-12-4 Sakamoto, Nagasaki-shi, Nagasaki, 852-8523, Japan
| | - Jun Kobayashi
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Department of Global Health, School of Health Sciences, University of the Ryukyus, 207 Uehara, Nishihara-cho, Okinawa, 903-0215, Japan
| | - Bouasy Hongvanthon
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Center of Malariology, Parasitology and Entomology, Ministry of Health, Vientiane, Lao PDR
| | - Paul T Brey
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Institut Pasteur du Laos, Sisattanak District, Vientiane, Lao PDR
| | - Kazuhiko Moji
- Graduate School of Tropical Medicine and Global Health, Nagasaki University, 1-12-4 Sakamoto, Nagasaki-shi, Nagasaki, 852-8523, Japan
| | - Toshihiro Mita
- Department of Molecular and Cellular Parasitology, School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.,SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR
| | - Shigeyuki Kano
- SATREPS Project for Parasitic Diseases, Vientiane, Lao PDR.,Department of Tropical Medicine and Malaria, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655, Japan.,Institut Pasteur du Laos, Sisattanak District, Vientiane, Lao PDR
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15
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Killeen GF. Characterizing, controlling and eliminating residual malaria transmission. Malar J 2014; 13:330. [PMID: 25149656 PMCID: PMC4159526 DOI: 10.1186/1475-2875-13-330] [Citation(s) in RCA: 303] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 08/16/2014] [Indexed: 12/02/2022] Open
Abstract
Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) interventions can reduce malaria transmission by targeting mosquitoes when they feed upon sleeping humans and/or rest inside houses, livestock shelters or other man-made structures. However, many malaria vector species can maintain robust transmission, despite high coverage of LLINs/IRS containing insecticides to which they are physiologically fully susceptible, because they exhibit one or more behaviours that define the biological limits of achievable impact with these interventions: (1) Natural or insecticide-induced avoidance of contact with treated surfaces within houses and early exit from them, thus minimizing exposure hazard of vectors which feed indoors upon humans; (2) Feeding upon humans when they are active and unprotected outdoors, thereby attenuating personal protection and any consequent community-wide suppression of transmission; (3) Feeding upon animals, thus minimizing contact with insecticides targeted at humans or houses; (4) Resting outdoors, away from insecticide-treated surfaces of nets, walls and roofs. Residual malaria transmission is, therefore, defined as all forms of transmission that can persist after achieving full universal coverage with effective LLINs and/or IRS containing active ingredients to which local vector populations are fully susceptible. Residual transmission is sufficiently intense across most of the tropics to render malaria elimination infeasible without new or improved vector control methods. Many novel or improved vector control strategies to address residual transmission are emerging that either: (1) Enhance control of adult vectors that enter houses to feed and/or rest by killing, repelling or excluding them; (2) Kill or repel adult mosquitoes when they attack people outdoors; (3) Kill adult mosquitoes when they attack livestock; (4) Kill adult mosquitoes when they feed upon sugar or; (5) Kill immature mosquitoes in aquatic habitats. To date, none of these options has sufficient supporting evidence to justify full-scale programmatic implementation. Concerted investment in their rigorous selection, development and evaluation is required over the coming decade to enable control and, ultimately, elimination of residual malaria transmission. In the meantime, national programmes may assess options for addressing residual transmission under programmatic conditions through pilot studies with strong monitoring, evaluation and operational research components, similar to the Onchocerciasis Control Programme.
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Affiliation(s)
- Gerry F Killeen
- Ifakara Health Institute, Environmental Health and Ecological Sciences Thematic Group, Ifakara, Morogoro, United Republic of Tanzania.
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16
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Chen-Hussey V, Carneiro I, Keomanila H, Gray R, Bannavong S, Phanalasy S, Lindsay SW. Can topical insect repellents reduce malaria? A cluster-randomised controlled trial of the insect repellent N,N-diethyl-m-toluamide (DEET) in Lao PDR. PLoS One 2013; 8:e70664. [PMID: 23967083 PMCID: PMC3743820 DOI: 10.1371/journal.pone.0070664] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Accepted: 06/13/2013] [Indexed: 11/23/2022] Open
Abstract
Background Mosquito vectors of malaria in Southeast Asia readily feed outdoors making malaria control through indoor insecticides such as long-lasting insecticidal nets (LLINs) and indoor residual spraying more difficult. Topical insect repellents may be able to protect users from outdoor biting, thereby providing additional protection above the current best practice of LLINs. Methods and Findings A double blind, household randomised, placebo-controlled trial of insect repellent to reduce malaria was carried out in southern Lao PDR to determine whether the use of repellent and long-lasting insecticidal nets (LLINs) could reduce malaria more than LLINs alone. A total of 1,597 households, including 7,979 participants, were recruited in June 2009 and April 2010. Equal group allocation, stratified by village, was used to randomise 795 households to a 15% DEET lotion and the remainder were given a placebo lotion. Participants, field staff and data analysts were blinded to the group assignment until data analysis had been completed. All households received new LLINs. Participants were asked to apply their lotion to exposed skin every evening and sleep under the LLINs each night. Plasmodium falciparum and P. vivax cases were actively identified by monthly rapid diagnostic tests. Intention to treat analysis found no effect from the use of repellent on malaria incidence (hazard ratio: 1.00, 95% CI: 0.99–1.01, p = 0.868). A higher socio-economic score was found to significantly decrease malaria risk (hazard ratio: 0.72, 95% CI: 0.58–0.90, p = 0.004). Women were also found to have a reduced risk of infection (hazard ratio: 0.59, 95% CI: 0.37–0.92, p = 0.020). According to protocol analysis which excluded participants using the lotions less than 90% of the time found similar results with no effect from the use of repellent. Conclusions This randomised controlled trial suggests that topical repellents are not a suitable intervention in addition to LLINs against malaria amongst agricultural populations in southern Lao PDR. These results are also likely to be applicable to much of the Greater Mekong Sub-region. Trial Registration This trial is registered with number NCT00938379
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Affiliation(s)
- Vanessa Chen-Hussey
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom.
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17
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Khaminsou N, Kritpetcharat O, Daduang J, Charerntanyarak L, Kritpetcharat P. Genetic analysis of the merozoite surface protein-1 block 2 allelic types in Plasmodium falciparum clinical isolates from Lao PDR. Malar J 2011; 10:371. [PMID: 22177111 PMCID: PMC3281801 DOI: 10.1186/1475-2875-10-371] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Accepted: 12/17/2011] [Indexed: 11/14/2022] Open
Abstract
Background MSP-1 is one of the potential malarial vaccine candidate antigens. However, extensive genetic polymorphism of this antigen in the field isolates of Plasmodium falciparum represents a major hindrance for the development of an effective vaccine. Therefore, this study aimed to establish the prevalence and genetic polymorphisms of K1, MAD20 and RO33 allelic types of msp-1 block 2 among P. falciparum clinical isolates from Lao PDR. Methods Plasmodium falciparum isolates were collected from 230 P. falciparum-infected blood samples from three regions of Lao PDR. K1, MAD20 and RO33 were detected by nested PCR; SSCP was used for polymorphism screening. The nested PCR products of each K1, MAD20 and RO33 allelic types that had different banding patterns by SSCP, were sequenced. Results The overall prevalence of K1, MAD20 and RO33 allelic types in P. falciparum isolates from Lao PDR were 66.95%, 46.52% and 31.30%, respectively, of samples under study. Single infections with K1, MAD20 and RO33 allelic types were 27.83%, 11.74% and 5.22%, respectively; the remainders were multiple clonal infections. Neither parasite density nor age was related to MOI. Sequence analysis revealed that there were 11 different types of K1, eight different types of MAD20, and 7 different types of RO33. Most of them were regional specific, except type 1 of each allelic type was common found in 3 regions under study. Conclusions Genetic polymorphism with diverse allele types was identified in msp-1 block 2 among P. falciparum clinical isolates in Lao PDR. A rather high level of multiple clonal infections was also observed but the multiplicity of infection was rather low as not exceed 2.0. This basic data are useful for treatment and malaria control program in Lao PDR.
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Affiliation(s)
- Naly Khaminsou
- Faculty of Medical Technology, University of Health Science, Vientiane, Lao PDR
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18
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Is staying overnight in a farming hut a risk factor for malaria infection in a setting with insecticide-treated bed nets in rural Laos? Malar J 2010; 9:372. [PMID: 21176242 PMCID: PMC3224235 DOI: 10.1186/1475-2875-9-372] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Accepted: 12/23/2010] [Indexed: 11/25/2022] Open
Abstract
Background Overnight stays in farming huts are known to pose a risk of malaria infection. However, studies reporting the risk were conducted in the settings of poor net coverage. This study sought to assess whether an overnight stay in a farming hut is associated with an increased risk of malaria infection if insecticide-treated bed nets (ITNs) are properly used. Methods A pair of cross-sectional surveys was carried out in the Lamarm district of Sekong province, Laos, in March (dry season) and August (rainy season) in 2008. Questionnaire-based interviews and blood examinations were conducted with farmers and their household members from three randomly selected villages in March (127 households, 891 people) and August (128 households, 919 people). Logistic regression analysis, adjusted for potential confounding factors, was used to assess the association between malaria infection status and frequency of overnight stays for the two weeks prior to the study in both the seasons. Results In March, 13.7% of participants reported staying overnight in a farming hut at least once in the previous two weeks. The percentage increased to 74.6% in August. Not only adults but also young children stayed overnight as often as adults. The use of an ITN the preceding night was common both in farming huts (66.3% in March, 95.2% in August), and in main residences (85.8% in March, 92.5% in August). Logistic regression analysis showed no statistical association between malaria infection status and frequency of overnight stays in farming huts in either study period. However, people sharing one family type net with five people or more were significantly more likely to have malaria than those sharing a net with up to two people in the dry season. Conclusions This study showed that staying overnight in farming huts was not associated with an increased risk of malaria infection in the setting where ITNs were widely used in farming huts. It suggests that malaria infection during overnight stays in farming huts might be preventable if ITNs are properly used in rural Laos.
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19
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Phommanivong V, Thongkham K, Deyer G, Rene JP, Barennes H. An assessment of early diagnosis and treatment of malaria by village health volunteers in the Lao PDR. Malar J 2010; 9:347. [PMID: 21122128 PMCID: PMC3014971 DOI: 10.1186/1475-2875-9-347] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Accepted: 12/01/2010] [Indexed: 11/15/2022] Open
Abstract
Background Early diagnosis and treatment (EDAT) is crucial to reducing the burden of malaria in low-income countries. In the Lao PDR, this strategy was introduced in 2004-2005 and an assessment was performed at the community level in January 2007. Methods EDAT with malaria rapid diagnostic test (MRDT) and artemisinin combination therapy (ACT) was prospectively assessed among 36 randomized village health volunteers (VHVs) and 720 patients in six malaria-endemic provinces of Laos (three pilot provinces (PP), and three non-pilots provinces (NPP)). ACT was also retrospectively assessed among 2188 patients within the same areas from June to November 2006. Two checklists were used and scores were calculated. Results EDAT performance of the VHVs was rated better in PP than in NPP (16.67% versus 38.89%, respectively, p = 0.004). Nearly all VHVs could diagnose malaria but only 16 (44%) could describe the symptoms of severe malaria. In January 2007, 31/720 (4%) patients tested positive using the Paracheck® test, 35 (5%) with microscopy (sensibility: 74.3%, specificity 99.3%, positive and negative predictive values: 83.9% and 98.7%, respectively). Patients from June to November were at higher risk of malaria: 35.19% of 2,188 febrile patients were positive (OR: 10.6, 95%CI: 7.4-15.5, p < 0.000). VHVs reported the MRDT easy to use, and yielded a satisfactory performance score. EDAT performance was rated as poor despite satisfactory results regarding ACT treatment, duration and dosages. Pre-referral treatment of severe malaria was infrequent and often inadequate, with 20% of these patients dying. Results suggest a higher mortality from severe malaria than officially reported. Shortage of ACT was frequent. Discussion and conclusion MRDT and ACT are useful and efficient and can be used by VHVs. VHVs' global EDAT performance is enhanced through training and monitoring. Persistent gaps in knowledge, care of patients and wrong treatment have to be addressed.
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Do Manh C, Beebe NW, Thi Van VN, Le Quang T, Lein CT, Van Nguyen D, Xuan TN, Le Ngoc A, Cooper RD. Vectors and malaria transmission in deforested, rural communities in north-central Vietnam. Malar J 2010; 9:259. [PMID: 20846447 PMCID: PMC2945362 DOI: 10.1186/1475-2875-9-259] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Accepted: 09/16/2010] [Indexed: 12/02/2022] Open
Abstract
BACKGROUND Malaria is still prevalent in rural communities of central Vietnam even though, due to deforestation, the primary vector Anopheles dirus is uncommon. In these situations little is known about the secondary vectors which are responsible for maintaining transmission. Basic information on the identification of the species in these rural communities is required so that transmission parameters, such as ecology, behaviour and vectorial status can be assigned to the appropriate species. METHODS In two rural villages--Khe Ngang and Hang Chuon--in Truong Xuan Commune, Quang Binh Province, north central Vietnam, a series of longitudinal entomological surveys were conducted during the wet and dry seasons from 2003-2007. In these surveys anopheline mosquitoes were collected in human landing catches, paired human and animal bait collections, and from larval surveys. Specimens belonging to species complexes were identified by PCR and sequence analysis, incrimination of vectors was by detection of circumsporozoite protein using an enzyme-linked immunosorbent assay. RESULTS Over 80% of the anopheline fauna was made up of Anopheles sinensis, Anopheles aconitus, Anopheles harrisoni, Anopheles maculatus, Anopheles sawadwongporni, and Anopheles philippinensis. PCR and sequence analysis resolved identification issues in the Funestus Group, Maculatus Group, Hyrcanus Group and Dirus Complex. Most species were zoophilic and while all species could be collected biting humans significantly higher densities were attracted to cattle and buffalo. Anopheles dirus was the most anthropophilic species but was uncommon making up only 1.24% of all anophelines collected. Anopheles sinensis, An. aconitus, An. harrisoni, An. maculatus, An. sawadwongporni, Anopheles peditaeniatus and An. philippinensis were all found positive for circumsporozoite protein. Heterogeneity in oviposition site preference between species enabled vector densities to be high in both the wet and dry seasons allowing for year round transmission. CONCLUSIONS In rural communities in north central Vietnam, malaria transmission was maintained by a number of anopheline species which though collected feeding on humans were predominantly zoophilic, this behaviour allows for low level but persistent malaria transmission. The important animal baits--cattle and buffalo--were kept in the village and barrier spraying around these animals may be more effective at reducing vector densities and longevity than the currently used indoor residual spraying.
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Affiliation(s)
- Cuong Do Manh
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Nigel W Beebe
- School of Biological Sciences, University of Queensland, St Lucia, Queensland, 4072, Australia
- CSIRO Entomology, Long Pocket Laboratories, Indooroopilly, Queensland, 4068, Australia
| | - Van Nguyen Thi Van
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Tao Le Quang
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Chau Tran Lein
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Dung Van Nguyen
- Military Preventive Medicine Centre, Ho Chi Minh City, Vietnam
| | - Thanh Nguyen Xuan
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Anh Le Ngoc
- Entomology Department, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Robert D Cooper
- Australian Army Malaria Institute, Gallipoli Barracks, Enoggera, Queensland 4051, Australia
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Jorgensen P, Nambanya S, Gopinath D, Hongvanthong B, Luangphengsouk K, Bell D, Phompida S, Phetsouvanh R. High heterogeneity in Plasmodium falciparum risk illustrates the need for detailed mapping to guide resource allocation: a new malaria risk map of the Lao People's Democratic Republic. Malar J 2010; 9:59. [PMID: 20181273 PMCID: PMC2841197 DOI: 10.1186/1475-2875-9-59] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2009] [Accepted: 02/24/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Accurate information on the geographical distribution of malaria is important for efficient resource allocation. The Lao People's Democratic Republic has experienced a major decline in malaria morbidity and mortality in the past decade. However, efforts to respond effectively to these changes have been impeded by lack of detailed data on malaria distribution. In 2008, a countrywide survey on Plasmodium falciparum diagnosed in health centres and villages was initiated to develop a detailed P. falciparum risk map with the aim to identify priority areas for malaria control, estimate population at risk, and guide resource allocation in the Lao People's Democratic Republic. METHODS P. falciparum incidence data were collected from point-referenced villages and health centres for the period 2006-2008 during a country-wide survey between December 2008 and January 2009. Using the highest recorded annual rate, continuous surfaces of P. falciparum incidence were produced by the inverse distance weighted interpolation technique. RESULTS Incidence rates were obtained from 3,876 villages and 685 health centres. The risk map shows that P. falciparum is highly heterogeneous in the northern and central regions of the country with large areas of no transmission. In the southern part, transmission is pervasive and the risk of P. falciparum is high. It was estimated that 3.4 million people (60% of the population) live at risk of malaria. CONCLUSIONS This paper presents the first comprehensive malaria risk map of the Lao People's Democratic Republic based entirely on empirical data. The estimated population at risk is substantially lower than previous estimates, reflecting the presence of vast areas with focal or no malaria transmission as identified in this study. These findings provide important guidance for malaria control interventions in the Lao People's Democratic Republic, and underline the need for detailed data on malaria to accurately predict risk in countries with heterogeneous transmission.
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Abstract
The Asia-Pacific region has at least 50% of its population at risk for malaria. In Malaysia, indigenous malaria is largely concentrated among the Orang Asli in Peninsular Malaysia. A cross-sectional study was conducted in an Orang Asli community in the district of Raub, Pahang, to determine the predictors of malaria. Age, seldom/never wearing protective clothing while in the jungle, going out at night, ever staying in another village, and living in bamboo-walled homes were found to be associated with malaria (crude odds ratio = 1.8-4.5; 95% confidence interval [CI] = 1.1-9.1) After adjusting for confounding, major predictors of malaria were age ≤12 years (adjusted odds ratio [aOR] = 4.3;95% CI = 2.2-8.4),), never/seldom wearing protective clothing while in the jungle (aOR = 3.8; 95% CI = 1.8-8.0), and going out at night (aOR = 2.5; 95% CI = 1.4-4.8). The findings lend support for intensifying behaviour modification in this population.
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Affiliation(s)
- Gurpreet Kaur
- Institute for Public Health, Ministry of Health, Jalan
Bangsar, Kuala Lumpur, Malaysia,
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Moore SJ, Min X, Hill N, Jones C, Zaixing Z, Cameron MM. Border malaria in China: knowledge and use of personal protection by minority populations and implications for malaria control: a questionnaire-based survey. BMC Public Health 2008; 8:344. [PMID: 18828901 PMCID: PMC2576233 DOI: 10.1186/1471-2458-8-344] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Accepted: 10/01/2008] [Indexed: 11/10/2022] Open
Abstract
Background Malaria control in remote, forested areas of the Mekong region relies on personal protection from mosquito bites. Uptake of these methods may be limited by knowledge of the link between mosquitoes and malaria as well as social and economic aspects. Understanding barriers to uptake will inform malaria control programmes on targets for improvement of delivery. Methods A total 748 key respondents: health providers and village heads, from 187 villages and 25 different ethnic groups, were interviewed using structured questionnaires. Differences in use of personal protection, and knowledge of malaria between groups were analysed using chi-square; and binary logistic regression used for multivariate analysis. Results Malaria knowledge was poor with 19.4% of women and 37.5% of men linking mosquitoes with malaria, although 95.6% knew one or more methods of mosquito control. Virtually all respondents used personal protection at some time during the year; and understanding of malaria transmission was strongly associated with bednet use. Those working in forest agriculture were significantly more likely to know that mosquitoes transmit malaria but this did not translate into a significantly greater likelihood of using bednets. Furthermore, use of personal protection while woing outdoors was rare, and less than 3% of respondents knew about the insecticide impregnation of bednets. The use of bednets, synthetic repellents and mosquito coils varied between ethnic groups, but was significantly more frequent among those with higher income, more years of education and permanent housing. The reported use of repellents and coils was also more common among women despite their low knowledge of malaria transmission, and low likelihood of having heard information on malaria within the last year. Conclusion The use of personal protection must be increased, particularly among outdoor workers that have higher malaria risk. However, personal protection is widely used and widely accepted to prevent nuisance biting mosquitoes, with the major barrier to use being affordability. Therefore, social marketing campaigns aimed at women and those that work outdoors that provide highly subsidised products, especially insecticide impregnation kits for bednets and hammock nets are most likely to succeed in lowering malaria morbidity among non Han-Chinese groups in rural China.
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Affiliation(s)
- Sarah J Moore
- DCVBU, London School of Hygiene and Tropical Medicine, London, UK.
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Khaminsou N, Kritpetcharat O, Daduang J, Kritpetcharat P. A survey of malarial infection in endemic areas of Savannakhet province, Lao PDR and comparative diagnostic efficiencies of Giemsa staining, acridine orange staining, and semi-nested multiplex PCR. Parasitol Int 2007; 57:143-9. [PMID: 18160336 DOI: 10.1016/j.parint.2007.11.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 11/09/2007] [Accepted: 11/17/2007] [Indexed: 10/22/2022]
Abstract
Malaria remains one of the most important parasitic diseases in Lao PDR, especially in forested rural areas. Knowing the rate of infection using highly sensitive and specific methods, and the factors related to malarial infection, may be helpful in reducing the infection and mortality rates. We aimed to study the malarial infection rate by comparing three detection methods, i.e., Giemsa staining, acridine orange (AO) staining and semi-nested multiplex PCR. The study also included some factors related to malarial infection in the endemic areas of Savannakhet province, Lao PDR. The respective malarial infection rates by Giemsa staining, AO staining and semi-nested multiplex PCR in Houy Jang vs. Keng Thong villages were 13.1 vs. 20.8, 16.2 vs. 25.4 and 20.8 vs. 30.8%. The infection rate among children not over 10 years of age was higher than infection rate among the older ages (p=0.002, Z-test for two proportions). The higher infection rates by semi-nested multiplex PCR over Giemsa and AO staining suggest the existence of many subclinical cases with low level parasitemia, undetected by microscopic techniques. We found no mixed infections using Giemsa or AO staining, but using semi-nested multiplex PCR we found 1.2% (3/260) mixed P. falciparum and P. vivax infections, suggesting that semi-nested multiplex PCR is suitable for detecting malarial infection from endemic areas whose cases may have low parasitemia and/or mixed infection. The factors significantly related to malarial infection from 260 questionnaires were: (1) children and young adults, (2) not having lived in the area more than 5 years, and (3) not using a mosquito net over the bed, indicating an increased risk of new residents of contracting malaria and a need to promote bed nets.
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Affiliation(s)
- Naly Khaminsou
- College of Health Technology, Vientiane, Lao Democratic People's Republic
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Large-scale malaria survey in Cambodia: novel insights on species distribution and risk factors. Malar J 2007; 6:37. [PMID: 17389041 PMCID: PMC1847522 DOI: 10.1186/1475-2875-6-37] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Accepted: 03/27/2007] [Indexed: 11/17/2022] Open
Abstract
Background In Cambodia, estimates of the malaria burden rely on a public health information system that does not record cases occurring among remote populations, neither malaria cases treated in the private sector nor asymptomatic carriers. A global estimate of the current malaria situation and associated risk factors is, therefore, still lacking. Methods A large cross-sectional survey was carried out in three areas of multidrug resistant malaria in Cambodia, enrolling 11,652 individuals. Fever and splenomegaly were recorded. Malaria prevalence, parasite densities and spatial distribution of infection were determined to identify parasitological profiles and the associated risk factors useful for improving malaria control programmes in the country. Results Malaria prevalence was 3.0%, 7.0% and 12.3% in Sampovloun, Koh Kong and Preah Vihear areas. Prevalences and Plasmodium species were heterogeneously distributed, with higher Plasmodium vivax rates in areas of low transmission. Malaria-attributable fevers accounted only for 10–33% of malaria cases, and 23–33% of parasite carriers were febrile. Multivariate multilevel regression analysis identified adults and males, mostly involved in forest activities, as high risk groups in Sampovloun, with additional risks for children in forest-fringe villages in the other areas along with an increased risk with distance from health facilities. Conclusion These observations point to a more complex malaria situation than suspected from official reports. A large asymptomatic reservoir was observed. The rates of P. vivax infections were higher than recorded in several areas. In remote areas, malaria prevalence was high. This indicates that additional health facilities should be implemented in areas at higher risk, such as remote rural and forested parts of the country, which are not adequately served by health services. Precise malaria risk mapping all over the country is needed to assess the extensive geographical heterogeneity of malaria endemicity and risk populations, so that current malaria control measures can be reinforced accordingly.
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Khamlome B, Eto H, Mita T, Sakurai M, Saito T, Tsuzuki A, Kobayashi J, Phompida S, Kobayakawa T. The status of malaria before and after distribution of ITNs from 1999 to 2006 in two districts of Khammouanne Province, Lao P.D.R. Trop Med Health 2007. [DOI: 10.2149/tmh.35.343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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