Biology subjects

Saeung, A.

Publications and source records attributed to Saeung, A..

4 recordsLinked to original sources

bioRxiv2025

Natural salivary gland barrier curtails Zika virus transmission in Thai Aedes aegypti

BackgroundVector competence is a critical determinant of arbovirus transmission dynamics, yet most studies in Thailand have primarily examined Aedes aegypti susceptibility to infection and systemic viral dissemination rather than the mosquitos potential to transmit infectious virions. Given that transmission potential varies among mosquito populations, identifying population-specific transmission barriers is crucial for optimizing vector control strategies especially under budget and resource constrains. Methodology/Principal FindingsThis study assessed the Zika virus (ZIKV) transmission potential of three Ae. aegypti populations from Thailand: two field-derived populations from Chiang Mai (CSP) and Nakhon Sawan (NAK) and a long-established laboratory strain (DMSC). Following oral exposure to a locally circulating ZIKV strain, viral transmission potential was evaluated. CSP mosquitoes demonstrated the earliest and highest ZIKV prevalence in salivary glands at 7 days post-infectious blood meal (dpibm), with DMSC and NAK populations reaching comparable infection levels at later time points. Despite this, NAK mosquitoes exhibited a strong barrier, resulting in significantly lower transmission potential. Genetic crosses revealed that this phenotype is inherited as an autosomal dominant trait and is similarly effective against dengue virus serotype 2 (DENV2), underscoring the broad-spectrum potential of NAK Ae. aegypti for transmission suppression. Furthermore, male NAK mosquitoes exhibited superior mating competitiveness, reinforcing their viability as a tool for vector control by population replacement. Conclusions/SignificanceOur findings highlight significant variability in ZIKV vector competence among Thai Ae. aegypti populations, emphasizing the importance of direct transmission assessments in vector competence studies. The discovery of a naturally occurring, heritable salivary gland escape barrier presents an opportunity for vector control strategies through NAK-based population replacement approaches. With their strong mating capability and broad arbovirus-blocking ability, NAK mosquitoes provide a natural alternative to Wolbachia-based and genetically modified mosquito interventions. Author summaryAedes aegypti is the primary vector of arboviruses such as Zika virus (ZIKV) and dengue virus (DENV), but not all mosquitoes that become infected successfully transmit the virus. While most research in Thailand has focused on mosquito infection and virus dissemination, fewer studies have examined the ability of mosquitoes to transmit infectious virus through their saliva. We discovered a mosquito population from Nakhon Sawan (NAK) that exhibits a natural barrier to virus release from the salivary glands, leading to significant blocking of virus transmission in ZIKV-infected mosquitoes. This salivary gland escape barrier of NAK is a heritable autosomal dominant characteristic that also restricts DENV transmission. Given their high mating competitiveness, NAK mosquitoes present a promising candidate for population replacement strategies aimed at reducing arbovirus transmission. Our findings emphasize the importance of assessing transmission rates rather than relying solely on infection and dissemination rates. Furthermore, the discovery of a naturally occurring mosquito population with reduced transmission potential offers a practical and sustainable vector control approach. The implementation of NAK-based population replacement strategies could serve as an alternative to traditional control methods, such as insecticide application or genetically modified mosquito releases. Future research should focus on field trials to validate the efficacy of this approach in real-world settings and assess its long-term impact on virus transmission dynamics.

microbiology↗

bioRxiv2023

Dirus Complex Species Identification PCR (DiCSIP) improves identification of Anopheles dirus complex from Greater Mekong Subregion

BackgroundThe Anopheles dirus complex plays a significant role as malaria vectors in the Greater Mekong Subregion (GMS), with varying degrees of vector competence among species. Accurate identification of sibling species in this complex is essential for understanding malaria transmission dynamics and deployment of effective vector control measures. This becomes increasingly crucial as the GMS advances towards malaria elimination while facing with the emergence of zoonotic simian malaria transmission. However, the original molecular identification assay, Dirus Allele Specific PCR (AS-PCR) targeting the ITS2 region have pronounced non-specific amplifications leading to ambiguous results and misidentification of the sibling species. This study investigates the underlying causes of these inconsistencies and develops new primers for accurate identification of species within the Anopheles dirus complex. Methodology/Principal findingsDespite several optimizations by reducing primer concentration, decreasing thermal cycling time, and increasing annealing temperature, the Dirus AS-PCR continued to produce inaccurate identifications, particularly for Anopheles dirus, Anopheles scanloni, and Anopheles nemophilous. Subsequently, in silico analyses pinpointed problematic primers with high GC content and multiple off-target binding sites. Through a series of in silico analyses and laboratory validation, a new set of primers for Dirus Complex Species Identification PCR (DiCSIP) has been developed. DiCSIP primers improve specificity, operational range, and sensitivity for accurate identification of five complex member species found in the GMS. Validation with laboratory and field An. dirus complex specimens demonstrated that DiCSIP could correctly identify all samples while the original Dirus AS-PCR misidentify An. dirus as other species when used with different thermocyclers. Conclusion/SignificanceThe DiCSIP assay offers a significant improvement in An. dirus complex identification, addressing challenges in specificity and efficiency of the previous ITS2-based assay. This new primer set provides a valuable tool for accurate entomological surveys, supporting effective vector control strategies to reduce transmission, and prevent the re-introduction of malaria in the GMS. Author SummarySeveral species of Anopheles mosquitoes belong to species complexes due to their indistinguishable morphology from closely related sibling species. However, members of the same species complex may exhibit varied vectorial capability, i.e. the ability to spread human pathogens, in this case malaria parasites, ranging from dominant vector to non-vector. The Dirus AS-PCR molecular assay to identify species within the An. dirus complex, a significant malaria vector species in the GMS, can produce inconsistent PCR results leading to misidentification. Furthermore, our analysis of An. dirus ITS2 sequences in the NCBI database indicated misidentification between these sibling species suggesting the need for a new set of primers to improve reproducibility and sensitivity in identifying members of the An. dirus complex. This study presents thorough analyses of the existing primers that cause difficulties in correct amplification and a development of a new set of primers for Dirus Complex Species Identification PCR (DiCSIP) assay. The DiCSIP assay offers several advantages over the original Dirus AS-PCR. It provides a higher specificity, sensitivity and wider operational range allowing for the use of the DNAzol direct reagent to process mosquito samples without the need for DNA extraction, saving both time and cost in sample processing. Our study provides a valuable molecular tool for entomological surveys, which is crucial for effective vector control measures in the GMS.

molecular biology↗

bioRxiv2021

New insights into antimalarial chemopreventive activity of antifolates

Antifolates targeting dihydrofolate reductase (DHFR) are antimalarial compounds that have long been used for malaria treatment and chemoprevention (inhibition of infection from mosquitoes to humans). Despite their extensive applications, the thorough understanding of antifolate activity against hepatic malaria parasites, especially resistant parasites, have yet to be achieved. Using a transgenic P. berghei harboring quadruple mutant dhfr from P. falciparum (Pb::Pfdhfr-4M), we demonstrate that quadruple mutations on Pfdhfr confer complete chemoprevention resistance to pyrimethamine, the previous generation of antifolate, but not a new class of antifolate designed to overcome the resistance such as P218. Detailed investigation to pin-point stage-specific chemoprevention further demonstrated that it is unnecessary for the drug to be present throughout hepatic development. The drug is most potent against the developmental stages from early hepatic trophozoite to late hepatic trophozoite, but is not effective at inhibiting sporozoite and early hepatic stage development from sporozoite to early trophozoite. Our data shows that P218 also inhibited the late hepatic stage development, from trophozoite to mature schizonts to a lesser extent. With a single dose of 15 mg/kg, P218 prevented infection from up to 25,000 pyrimentamine-resistant sporozoites, a number equal to thousands of infectious mosquito bites. Additionally, the hepatic stage of malaria parasite is much more susceptible to antifolates than the asexual blood stage. This study provides important insights into the activity of antifolates, as a chemopreventive therapeutic which could lead to a more efficient and cost effective treatment regime.

microbiology↗

bioRxiv2020

Serratia marcescens secretes proteases and chitinases with larvicidal activity against Anopheles dirus

Vector control, the most efficient tool to reduce mosquito-borne disease transmission, has been compromised by the rise of insecticide resistance. Recent studies suggest the potential of mosquito-associated microbiota as a source for new biocontrol agents or new insecticidal chemotypes. In this study, we identified a strain of Serratia marcescens that has larvicidal activity against Anopheles dirus, an important malaria vector in Southeast Asia. This bacterium secretes heat-labile larvicidal macromolecules when cultured under static condition at 25{degrees}C but not 37{degrees}C. Two major protein bands of approximately 55 kDa and 110 kDa were present in spent medium cultured at 25{degrees}C but not at 37{degrees}C. The Liquid Chromatography-Mass Spectrometry (LC-MS) analyses of these two protein bands identified several proteases and chitinases that were previously reported for insecticidal properties against agricultural insect pests. The treatment with protease and chitinase inhibitors led to a reduction in larvicidal activity, confirming that these two groups of enzymes are responsible for the macromolecules toxicity. Taken together, our results suggest a potential use of these enzymes in the development of larvicidal agents against Anopheles mosquitoes.

microbiology↗