New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

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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New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

10.21203/rs.3.rs-35716/v3 ◽

2020 ◽

Author(s):

Sebastien Marcombe ◽

Santi Maithaviphet ◽

Julie Bobichon ◽

Nothasin Phommavan ◽

Simone Nambanya ◽

...

Keyword(s):

Molecular Identification ◽

Sibling Species ◽

Rural Areas ◽

Lao Pdr ◽

Malaria Vectors ◽

Human Landing Catch ◽

Morphological Identification ◽

Anopheles Mosquitoes ◽

Malaria Burden ◽

Human Landing

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 behavior 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 P. 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 An. maculatus s.s., An. rampae , An. sawadwongporni , An. pseudowillmori , An. dravidicus , An. minimus s.s., An. aconitus , An. pampanai , An. harrisoni , An. dirus s.s., An. baimaii , An. 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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New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

10.21203/rs.3.rs-35716/v2 ◽

2020 ◽

Author(s):

Sebastien Marcombe ◽

Santi Maithaviphet ◽

Julie Bobichon ◽

Nothasin Phommavan ◽

Simone Nambanya ◽

...

Keyword(s):

Molecular Identification ◽

Sibling Species ◽

Rural Areas ◽

Lao Pdr ◽

Malaria Vectors ◽

Human Landing Catch ◽

Morphological Identification ◽

Anopheles Mosquitoes ◽

Malaria Burden ◽

Human Landing

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 behavior 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 P. 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 An. maculatus s.s., An. rampae , An. sawadwongporni , An. pseudowillmori , An. dravidicus , An. minimus s.s., An. aconitus , An. pampanai , An. harrisoni , An. dirus s.s., An. baimaii , An. 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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New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

10.21203/rs.3.rs-35716/v1 ◽

2020 ◽

Author(s):

Sebastien Marcombe ◽

Santi Maithaviphet ◽

Julie Bobichon ◽

Nothasin Phommavan ◽

Simone Nambanya ◽

...

Keyword(s):

Molecular Identification ◽

Sibling Species ◽

Rural Areas ◽

Lao Pdr ◽

Malaria Vectors ◽

Human Landing Catch ◽

Morphological Identification ◽

Malaria Burden ◽

Human Landing ◽

And Behavior

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 behavior 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 P. vivax infections in 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 13 sibling species within the main primary vector groups including An. maculatus s.s., An. rampae, An. sawadwongporni, An. pseudowillmori, An. dravidicus, An. willmori, An. minimus s.s., An. aconitus, An. pampanai, An. harrisoni, An. dirus s.s., An. baimaii, An. nemophilous. An. 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, solely 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 Anopheles 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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Anopheles Bionomics in a Malaria Endemic Area of Southern Thailand

10.21203/rs.3.rs-407027/v1 ◽

2021 ◽

Author(s):

Narenrit Wamaket ◽

Oranicha Khamprapa ◽

Sittinont Chainarin ◽

Panisa Thamsawet ◽

Ubolrat Ninsaeng ◽

...

Keyword(s):

Molecular Identification ◽

Malaria Vectors ◽

Power Calculation ◽

Chi Square ◽

Anopheles Dirus ◽

Significant Difference ◽

Southern Thailand ◽

Human Landing ◽

Greater Mekong Subregion ◽

The Impact

Abstract Background: Ivermectin mass drug administration (MDA) could accelerate malaria elimination in the Greater Mekong Subregion. This study was performed to characterize the bionomics of Anopheles in Surat Thani province, Thailand.Methods: Mosquitoes were collected via human landing collections, February - October of 2019. Anopheles were morphologically identified to species. Primary Anopheles malaria vectors were dissected to assess parity status and a subset evaluated for molecular identification and Plasmodium detection.Results: A total of 17,348 mosquitoes were collected. Of 5,777 Anopheles mosquitoes, 15 species were identified morphologically. The most abundant Anopheles were Anopheles minimus s.l. (87.87%, n = 5,035), Anopheles dirus s.l. (7.05%, n = 407), and Anopheles barbirostris s.l. (2.86%, n = 165). Molecular identification confirmed that of An. minimus s.l., 99.80% were An. minimus s.s. (n=484) and 0.2% An. aconitus (n = 1), of An. dirus s.l., 100% were An. baimaii (n = 348), and of An. maculatus s.l., 93.62% were An. maculatus s.s. (n = 44) and 6.38% An. sawadwongporni (n = 3). No Anopheles were Plasmodium positive (n = 879). An average of 11.46 Anopheles were captured per collector per night. There were differences between species in hour of collection (Kruskal-Wallis = 80.89, P < 0.0001, n = 5,666), with more An. barbirostris s.l. and An. maculatus s.l. caught earlier compared to An. minimus s.l. (P = 0.0001, P < 0.0001, respectively) and An. dirus s.l. (P = 0.0082, P < 0.001, respectively). The proportion of parous An. minimus s.l. captured by hour increased throughout the night (Wald Chi-square = 17.31, P=0.000, odds ratio = 1.0535 [1.0279 – 1.0796] 95% CI (n = 3,400). Overall, An. minimus s.l. parity was 67.68% (2,375/3,509) with an intra cluster correlation of 0.0378. A power calculation determined that an An. minimus s.l. parity reduction treatment effect size = 34%, with four clusters per treatment arm, a minimum of 300 mosquitoes dissected per cluster at an α= 0.05 will provide 82% power to detect a significant difference following ivermectin MDA. Conclusions: The study area in Surat Thani province is an ideal location to evaluate the impact of ivermectin MDA on An. minimus parity.

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Evaluation of mosquito electrocuting traps as a safe alternative to the human landing catch for measuring human exposure to malaria vectors in Burkina Faso

Malaria Journal ◽

10.1186/s12936-019-3030-5 ◽

2019 ◽

Vol 18 (1) ◽

Cited By ~ 1

Author(s):

Antoine Sanou ◽

W. Moussa Guelbéogo ◽

Luca Nelli ◽

K. Hyacinth Toé ◽

Soumanaba Zongo ◽

...

Keyword(s):

Species Composition ◽

Burkina Faso ◽

Malaria Vector ◽

Human Exposure ◽

Infected Mosquito ◽

Malaria Vectors ◽

Human Landing Catch ◽

Mosquito Vector ◽

Human Landing ◽

Biting Behaviour

Abstract Background Measuring human exposure to mosquito bites is a crucial component of vector-borne disease surveillance. For malaria vectors, the human landing catch (HLC) remains the gold standard for direct estimation of exposure. This method, however, is controversial since participants risk exposure to potentially infected mosquito bites. Recently an exposure-free mosquito electrocuting trap (MET) was developed to provide a safer alternative to the HLC. Early prototypes of the MET performed well in Tanzania but have yet to be tested in West Africa, where malaria vector species composition, ecology and behaviour are different. The performance of the MET relative to HLC for characterizing mosquito vector population dynamics and biting behaviour in Burkina Faso was evaluated. Methods A longitudinal study was initiated within 12 villages in Burkina Faso in October 2016. Host-seeking mosquitoes were sampled monthly using HLC and MET collections over 14 months. Collections were made at 4 households on each night, with METs deployed inside and outside at 2 houses, and HLC inside and outside at another two. Malaria vector abundance, species composition, sporozoite rate and location of biting (indoor versus outdoor) were recorded. Results In total, 41,800 mosquitoes were collected over 324 sampling nights, with the major malaria vector being Anopheles gambiae sensu lato (s.l.) complex. Overall the MET caught fewer An. gambiae s.l. than the HLC (mean predicted number of 0.78 versus 1.82 indoors, and 1.05 versus 2.04 outdoors). However, MET collections gave a consistent representation of seasonal dynamics in vector populations, species composition, biting behaviour (location and time) and malaria infection rates relative to HLC. As the relative performance of the MET was somewhat higher in outdoor versus indoor settings, this trapping method slightly underestimated the proportion of bites preventable by LLINs compared to the HLC (MET = 82.08%; HLC = 87.19%). Conclusions The MET collected proportionately fewer mosquitoes than the HLC. However, estimates of An. gambiae s.l. density in METs were highly correlated with HLC. Thus, although less sensitive, the MET is a safer alternative than the HLC. Its use is recommended particularly for sampling vectors in outdoor environments where it is most sensitive.

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COMPARATIVE FIELD EVALUATION OF THE MBITA TRAP, THE CENTERS FOR DISEASE CONTROL LIGHT TRAP, AND THE HUMAN LANDING CATCH FOR SAMPLING OF MALARIA VECTORS IN WESTERN KENYA

American Journal of Tropical Medicine and Hygiene ◽

10.4269/ajtmh.2004.70.33 ◽

2004 ◽

Vol 70 (1) ◽

pp. 33-37 ◽

Cited By ~ 52

Author(s):

EVAN M. MATHENGE ◽

GEORGE O. OMWERI ◽

LUCY W. IRUNGU ◽

ELIZABETH WALCZAK ◽

TOM A. SMITH ◽

...

Keyword(s):

Disease Control ◽

Light Trap ◽

Field Evaluation ◽

Malaria Vectors ◽

Human Landing Catch ◽

Western Kenya ◽

Human Landing ◽

Centers For Disease Control ◽

Control Light

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Low-density genetically diverse natural Wolbachia infections in malaria vectors in Kayin state, Myanmar

Wellcome Open Research ◽

10.12688/wellcomeopenres.15005.3 ◽

2019 ◽

Vol 4 ◽

pp. 11

Author(s):

Sunisa Sawasdichai ◽

Victor Chaumeau ◽

Tee Dah ◽

Thithiworada Kulabkeeree ◽

Ladda Kajeechiwa ◽

...

Keyword(s):

Malaria Vectors ◽

Human Landing Catch ◽

Low Density ◽

Mosquito Vectors ◽

Infection Rates ◽

Vector Species ◽

Closely Related Species ◽

Human Landing ◽

Malaria Mosquitoes ◽

Rrna Sequences

Background: Natural Wolbachia infections in malaria mosquitoes were recently reported in Africa, and negatively correlated with the development of Plasmodium falciparum in the vectors. The occurrence and effects of Wolbachia infections outside Africa have not been described and may have been underestimated. Methods: Mosquitoes were collected by human-landing catch during May and June 2017 in ten villages in Kayin state, Myanmar. Closely related species of malaria vectors were identified with molecular assays. Wolbachia infection rates were assessed with quantitative real-time PCR. Results: Low titer of Wolbachia DNA was detected in 13/370 samples in six malaria vector species. Phylogenetic analysis based on 16S rRNA sequences revealed a high diversity of Wolbachia strains and identified lineages different from those described in the African malaria mosquitoes. Conclusion: These low-density genetically diverse natural Wolbachia infections question the ecology and biology of Wolbachia-Anopheles interactions in Southeast Asia. Their effects on malaria transmission and mosquito vectors are yet to be determined.

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Semi Field Evaluation of Freestanding Transfluthrin Passive Emanators and the BG Sentinel Trap as a “Push-Pull control Strategy” Against Aedes aegypti Mosquitoes

10.21203/rs.3.rs-26088/v1 ◽

2020 ◽

Author(s):

Mgeni Mohamed Tambwe ◽

Sarah Moore ◽

Hassan Chilumba ◽

Johnson Kyeba Swai ◽

Jason Moore ◽

...

Keyword(s):

Aedes Aegypti ◽

Field Experiments ◽

Protective Efficacy ◽

Malaria Vectors ◽

Human Landing Catch ◽

Regular User ◽

Pull System ◽

Significant Difference ◽

Human Landing ◽

Bg Sentinel

Abstract Background The use of volatile pyrethroids and odor-baited traps in a push-pull system has been shown to reduce house entry and outdoor bites for malaria vectors. This technology has the potential to control other outdoor biting mosquitoes such as Aedes aegypti that transmit arboviral diseases. In this study, semi-field experiments were conducted to evaluate whether a push-pull system could be used to reduce bites from Aedes.Methods The push and pull under investigation consisted of two freestanding transfluthrin passive emanators (FTPE), and a BG sentinel trap (BGS) respectively. The FTPE contained hessian strips treated with 5.25 g of transfluthrin active ingredient. The efficacies of FTPE and BGS alone and in combination were evaluated by human landing catch in a large semi-field system in Tanzania. We also investigated the protection of FTPE over six months. The data was analyzed using generalized linear mixed models with binomial distribution.Results Two FTPE have a protective efficacy (PE) of 61% (95% Confidence interval (CI): 52.18–69.91) against human landing rate of Aedes aegypti. The BGS did not significantly reduce mosquito landings; the PE was 2.14% (95% CI: -2.87-7.16). The combination of FTPE and BGS (push-pull) provided the PE of 64.46% (95% CI: 59.06–69.85). However, there was no significant difference in the protective efficacy between the push-pull and the two FTPE against Ae. aegypti (p = 0.286). The FTPE offered significant protection against Ae. aegypti at month three, with a PE of 46.44% (95% CI: 41.12–51.76), but not at six months with a PE of 2.20% (95% CI: -9.00-14.02).Conclusions The protective efficacy of the FTPE and the full push-pull system are similar, indicative that bite prevention is primarily due to the activity of the FTPE. While these results are encouraging for the FTPE, further work is needed for a push-pull system to be recommended for Ae. aegypti control. The three-month protection provided by the FTPE against Ae. aegypti bites suggests it would be a useful additional personal protection tool during dengue outbreaks, that does not require regular user compliance.

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