Yudthana Samung - Academia.edu (original) (raw)

Papers by Yudthana Samung

The American Journal of Tropical Medicine and Hygiene

ABSTRACT. The malaria landscape in the Greater Mekong Subregion has experienced drastic changes w... more ABSTRACT. The malaria landscape in the Greater Mekong Subregion has experienced drastic changes with the ramp-up of the control efforts, revealing formidable challenges that slowed down the progress toward malaria elimination. Problems such as border malaria and cross-border malaria introduction, multidrug resistance in Plasmodium falciparum, the persistence of Plasmodium vivax, the asymptomatic parasite reservoirs, and insecticide resistance in primary vectors require integrated strategies tailored for individual nations in the region. In recognition of these challenges and the need for research, the Southeast Asian International Center of Excellence for Malaria Research has established a network of researchers and stakeholders and conducted basic and translational research to identify existing and emerging problems and develop new countermeasures. The installation of a comprehensive disease and vector surveillance system at sentinel sites in border areas with the implementation of...

Medical and Veterinary Entomology, 2020

Anopheles minimus Theobald 1901 and An. harrisoni Harbach & Manguin 2007 belong to the same speci... more Anopheles minimus Theobald 1901 and An. harrisoni Harbach & Manguin 2007 belong to the same species complex. They are morphologically similar and can exist in sympatry but have blood host preferences. The most accurate method for their identification is based on molecular techniques. Here, we measure the level of interspecific discrimination by geometric morphometry. Sixty-seven An. minimus and 22 An. harrisoni specimens were selected based on their morphological integrity and confirmed by identification polymerase chain reaction of internal transcribed spacer 2. These samples were used as reference data allowing for a morphometric identification based on geometric shape. Despite size overlap between the two species, there was a significant shape divergence allowing for differentiation of An. minimus and An. harrisoni with 90% accuracy. An intraspecific study of An. minimus showed a summer period associated to the reducing of wing size, which did not influence the shape-based differentiation of An. harrisoni. Wing venation geometry can be used to distinguish between these cryptic species mainly based on shaped divergence. This study suggests that geometric morphometrics represent a convenient low-cost method to complement morphological identification, especially concerning damaged specimens, i.e., insects having accidentally lost the anatomical features allowing a reliable morphological identification.

Insects, 2022

All members of the ant genus Odontomachus Latreille, 1804 are venomous ants. Four species in this... more All members of the ant genus Odontomachus Latreille, 1804 are venomous ants. Four species in this genus have been identified from Thailand: Odontomachus latidens Mayr, 1867; O. monticola Emery, 1892; O. rixosus Smith, 1757; and O. simillimus Smith, 1758. The three latter species are available and have been used for an outline morphometric study. They display similar morphology, which makes their distinction very difficult except for highly qualified individuals. A total of 80 worker specimens were studied, exploring the contour shapes of their head and pronotum as possible taxonomic characters. The size of each body part was estimated determining the contour perimeter, the values for which were largely overlapping between O. rixosus and O. simillimus; most O. monticola specimens exhibited a significantly larger size. In contrast to the size, each contour shape of the head or pronotum established O. rixosus as the most distinct species. An exploratory data analysis disclosed the high...

Figure 3. Classification based on harmonics. Values in percent are the proportions of correct ass... more Figure 3. Classification based on harmonics. Values in percent are the proportions of correct assignments averaged over the complete set of data, mixing the various species, but restricted to the outline-based method. Each value is shown with an error bar which is its standard deviation. The left part shows the results from the maximum likelihood method applied to the perimeter of the contour and to the shape variables. The right part shows the average scores obtained with the Mahalanobis classification. Abbreviation: first PC— the shape variables used were the few first PC of shape variables that the MLi classification selected as the most discriminant set of PC; all PC—the maximum number of PC that could be used by the Mahalanobis classification.

Figure 2. Classification based on landmarks (and semilandmarks). Values in percent are the propor... more Figure 2. Classification based on landmarks (and semilandmarks). Values in percent are the proportions of correct assignments averaged over the complete set of data, mixing the various species, but restricted to the landmark-based method (including here the combination of landmarks and semilandmarks). Each value is shown with an error bar which is its standard deviation. The left part shows the results from the maximum likelihood method applied to the centroid size and to the shape variables. The right part shows the average scores obtained with the Mahalanobis classification. Abbreviation: first PC—the shape variables used were the few first PC of shape variables that the MLi classification selected as the most discriminant set of PC; all PC—the maximum number of PC that could be used by the Mahalanobis classification.

Figure 4. Principal component analysis of sandfly data. The factor map of the two first principal... more Figure 4. Principal component analysis of sandfly data. The factor map of the two first principal components (PC) describing the morphospace of female sandfly data: S. bailyi, S. barraudi and P. stantoni. Unidentified males show a convex hull covering both female S. bailyi and S. barraudi, leaving two specimens outside the female hulls.

Figure 1. Measurements on Triatominae. A. Digitization of the contour of the eggs of Triatomini a... more Figure 1. Measurements on Triatominae. A. Digitization of the contour of the eggs of Triatomini and Rhodniini. B. Landmarks as digitized on the wing of Panstrongylus chinai. C. Traditional measurement of eggs of the tribe Triatomini (Panstrongylus sp. and Triatoma sp., left) and the tribe Rhodniini (Rhodnius sp., right). Abbreviation: op.dim—dimensions of the operculum; max.leng— maximum length; max.dim—maximum diameter.

Additional file 3: Table S1. Patient characteristics for the M2 migrant population*. Table S2. Pa... more Additional file 3: Table S1. Patient characteristics for the M2 migrant population*. Table S2. Patient characteristics for the M1 migrant population*. Table S3. Patient characteristics for the Thai national population. Table S4. Occupation distribution among the different population strata.

Additional file 1: Figure S1. Average number of mosquitoes monthly captured per trap.

All mosquitoes captured in the present study, their blood-fed status, percentage of females and g... more All mosquitoes captured in the present study, their blood-fed status, percentage of females and gravidity status. (DOCX 18 kb)

surveillance in a malaria endemic area on the Thai-Myanmar border

ABSTRACT The present study aimed to demonstrate the relationship of some environmental factors, v... more ABSTRACT The present study aimed to demonstrate the relationship of some environmental factors, vegetation greenness index (NDVI) and land surface temperature (LST), with the seasonal variations of Mansonia bonneae and Ma. uniformis in Khosit Subdistrict, Narathiwat Province. It was found that the Mansonia population lagged one month behind but correlated positively to NDVI, LST and rainfall. A rise in the number of mosquitoes was directly related to a rise in vegetation, temperature and rainfall.

Tropical biomedicine, 2017

Nematode infection in wild caught Phlebotomine sand flies was investigated in Thailand. Light mic... more Nematode infection in wild caught Phlebotomine sand flies was investigated in Thailand. Light microscopy (LM) and scanning electron microscopy (SEM) were used to detect and morphologically characterize entomopathogenic nematodes that presented in the sand flies. Didilia sp. nematodes were found for the first time in the body cavity of wild caught male Phlebotomus stantoni sand flies. The Didilia sp. was identified based on the morphology of the adult nematodes, from their stylet and teeth at the anterior tip, body length, and egg shell sculpture. It was noted that every infected male sand fly had unrotated genitalia, which would not allow them to mate, thus leading to the loss of their offspring. This finding provided information that might lead to study on whether or not the Didilia sp. has the potential to control sand fly population.

Medical and Veterinary Entomology, 2019

Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperatu... more Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperature has a well-known effect on insect metric properties. Can such effects blur the taxonomic signal embedded in the wing? Two strains of Aedes albopictus (laboratory and field strain) were examined under three different rearing temperatures (26, 30 and 33 ∘ C) using landmark-and outline-based morphometric approaches. The wings of each experimental line were compared with Aedes aegypti. Both approaches indicated similar associations between wing size and temperature. For the laboratory strain, the wing size significantly decreased as the temperature increased. For the field strain, the largest wings were observed at the intermediate temperature. The two morphometric approaches describing shape showed different sensibilities to temperature. For both strains and sexes, the landmark-based approach disclosed significant wing shape changes with temperature changes. The outline-based approach showed lesser effects, detecting significant changes only in laboratory females and in field males. Despite the size and shape changes induced by temperature, the two strains of Ae. albopictus were always distinguished from Ae. aegypti. The present study confirms the lability of size. However, it also suggests that, despite environmentally-induced variation, the architecture of the wing still provides a strong taxonomic signal.

Parasites & Vectors, 2016

Background: The Thai-Myanmar border is a remaining hotspot for malaria transmission. Malaria tran... more Background: The Thai-Myanmar border is a remaining hotspot for malaria transmission. Malaria transmission in this region continues year-round, with a major peak season in July-August, and a minor peak in October-November. Malaria elimination requires better knowledge of the mosquito community structure, dynamics and vectorial status to support effective vector control. Methods: Adult Anopheles mosquitoes were collected using CDC light traps and cow bait in 7 villages along the Thai-Myanmar border in January 2011-March 2013. Mosquitoes were determined to species by morphological characters. Plasmodium-positivity was determined by circumsporozoite protein ELISA. Results: The 2986 Anopheles mosquitoes collected were assigned to 26 species, with Anopheles minimus sensu lato (s.l.) (40.32 %), An. maculatus s.l. (21.43 %), An. annularis s.l. (14.43 %), An. kochi (5.39 %), An. tessellatus (5.26 %), and An. barbirostris s.l. (3.52 %) being the top six most abundant species. Plasmodium-infected mosquitoes were found in 22 positive samples from 2906 pooled samples of abdomens and heads/thoraxes. Four mosquito species were found infected with Plasmodium: An. minimus s.l., An. maculatus s.l., An. annularis s.l. and An. barbirostris s.l. The infectivity rates of these mosquitoes were 0.76, 0.37, 0.72, and 1.74 %, respectively. Consistent with a change in malaria epidemiology to the predominance of P. vivax in this area, 20 of the 22 infected mosquito samples were P. vivax-positive. The four potential vector species all displayed apparent seasonality in relative abundance. While An. minimus s.l. was collected through the entire year, its abundance peaked in the season immediately after the wet season. In comparison, An. maculatus s.l. numbers showed a major peak during the wet season. The two potential vector species, An. annularis s.l. and An. barbirostris s.l., both showed peak abundance during the transition from wet to dry season. Moreover, An. minimus s.l. was more abundant in indoor collections, whereas An. annularis s.l. and An. barbirostris s.l. were more abundant in outdoor collections, suggesting their potential role in outdoor malaria transmission. Conclusions: This survey confirmed the major vector status of An. minimus s.l. and An. maculatus s.l. and identified An. annularis s.l. and An. barbirostris s.l. as additional vectors with potential importance in malaria transmission after the wet season.

Journal of vector ecology : journal of the Society for Vector Ecology, 2003

The vector competence of Aedes aegypti (L.) mosquitoes, collected during the hot, rainy and cool ... more The vector competence of Aedes aegypti (L.) mosquitoes, collected during the hot, rainy and cool seasons from different localities in Thailand, was tested for a correlation with a seasonal cyclic pattern of dengue incidence. Under laboratory conditions, some groups of mosquitoes exhibited differences in susceptibility to oral infection but showed no correlation to dengue cases that peak during the rainy season. Thus, the environmental conditions of each season, although they might affect a temporal change of mosquito vector competence, they might not have any direct effects on virus transmission patterns. Mosquito populations from different parts of Thailand were also likely to be homogeneous in their susceptibility to dengue virus during the study period. Other factors, such as characteristics of the virus, vector density and frequency of host-vector contact, should be considered for seasonal pattern of dengue diseases.

Parasites & Vectors

Background Anopheles sawadwongporni Rattanarithikul & Green, Anopheles maculatus Theobald and Ano... more Background Anopheles sawadwongporni Rattanarithikul & Green, Anopheles maculatus Theobald and Anopheles pseudowillmori (Theobald) of the Anopheles maculatus group (Diptera: Culicidae) are recognized as potential malaria vectors in many countries from the Indian subcontinent through Southeast Asia to Taiwan. A number of malaria vectors in malaria hotspot areas along the Thai-Myanmar border belong to this complex. However, the species distribution and dynamic trends remain understudied in this malaria endemic region. Methods Mosquitoes of the Maculatus group were collected using CDC light traps every other week from four villages in Tha Song Yang District, Tak Province, Thailand from January to December 2015. Adult female mosquitoes were morphologically identified on site using taxonomic keys. Molecular species identification was performed by multiplex PCR based on the internal transcribed spacer 2 (ITS2) region of ribosomal DNA (rDNA) and sequencing of the cox1 gene at a DNA barcodin...

Scientific Reports

Microscopic observation of mosquito species, which is the basis of morphological identification, ... more Microscopic observation of mosquito species, which is the basis of morphological identification, is a time-consuming and challenging process, particularly owing to the different skills and experience of public health personnel. We present deep learning models based on the well-known you-only-look-once (YOLO) algorithm. This model can be used to simultaneously classify and localize the images to identify the species of the gender of field-caught mosquitoes. The results indicated that the concatenated two YOLO v3 model exhibited the optimal performance in identifying the mosquitoes, as the mosquitoes were relatively small objects compared with the large proportional environment image. The robustness testing of the proposed model yielded a mean average precision and sensitivity of 99% and 92.4%, respectively. The model exhibited high performance in terms of the specificity and accuracy, with an extremely low rate of misclassification. The area under the receiver operating characteristi...

Journal of Vector Ecology

We investigated the nocturnal activity of cave-dwelling sand flies at different time intervals an... more We investigated the nocturnal activity of cave-dwelling sand flies at different time intervals and determined their species composition and seasonal variation. Sand flies were captured on one night each month using CDC light traps from 18:00-06:00 with the collecting bag being changed every two h between February, 2010 and January, 2011. A total of 18,709 individuals, including 10,740 males and 7,969 females, was collected. The overall ratio between male and female specimens was 1:0.74. The collected specimens included 14 species from four genera, Chinius, Idiophlebotomus, Phlebotomus, and Sergentomyia. Sergentomyia phadangensis was the most abundant species (comprising 31.9% of the collected individuals), followed by Se. anodontis (22.8%) and Ph. mascomai (18.2%). The highest number of specimens was collected in July (15.6%), followed by May (15.5%) with the peak of collection recorded at the time interval of 00:01-02:00, followed by 22:01-00:00. However, there were no significant differences observed among time intervals of sand fly collections (p=0.154). Observations of the nocturnal activity of male and female sand flies throughout the night suggest that phlebotomine sand flies show the greatest activity level after midnight.