The role of voltage-gated sodium channel genotypes in pyrethroid resistance in Aedes aegypti in Taiwan

Background

Aedes aegypti is the major vector of dengue that threatens public health in tropical and subtropical regions. Pyrethroid-based control strategies effectively control this vector, but the repeated usage of the same insecticides leads to resistance and hampers control efforts. Therefore, efficient and prompt monitoring of insecticide resistance in local mosquito populations is critical for dengue control.

Methodology/Principal finding

We collected Ae. aegypti in southern Taiwan in March and October 2016. We analyzed the voltage-gated sodium channel (vgsc) genotypes of parentals (G0) and G1 adults after cypermethrin insecticide bioassay. Our results showed that four VGSC mutations (S989P, V1016G, F1534C, and D1763Y) associated with resistance were commonly detected in field-collected Ae. aegypti. The frequencies of these four mutations in the local mosquito population were significantly higher in October (0.29, 0.4, 0.27 and 0.11) than in March (0.09, 0.16, 0.18 and 0.03). Specific vgsc combined genotypes composed of the one to four such mutations (SGFY/SGFY, SVCD/SVCD, SGFY/PGFD, SVCD/SGFY, PGFD/PGFD, and SVCD/PGFD) shifted towards higher frequencies in October, implying their resistance role. In addition, the cypermethrin exposure bioassay data supported the field observations. Moreover, our study observed an association between the resistance level and the proportion of resistance genotypes in the population.

Conclusions/Significance

This is the first study to demonstrate the role of four-locus vgsc genotypes in resistance evaluation in a local Ae. aegypti population in Taiwan. This alternative method using resistance-associated genotypes as an indicator of practically insecticide resistance monitoring is a useful tool for providing precise and real-time information for decision makers.

Dengue outbreaks occur annually in Taiwan, and pyrethroid insecticides are commonly used to reduce mosquito density. Insecticide resistance of mosquitoes is commonly observed in the field and threatens vector control programs. Here, we analyzed the association between the combined vgsc genotype and resistance phenotype based on field surveillance data in March and October and a cypermethrin exposure bioassay. Resistance-attributable specific vgsc genotypes were proposed. Using the combined vgsc genotype rather than each vgsc allele is recommended for better resistance prediction to provide real-time information for control program managers.

Impact of heavy precipitation events on pathogen occurrence in estuarine areas of the Puzi River in Taiwan

Pathogen populations in estuarine areas are dynamic, as they are subject to multiple natural and anthropogenic challenges. Heavy rainfall events bring instability to the aquatic environment in estuaries, causing changes in pathogen populations and increased environmental sanitation and public health concerns. In this study, we investigated the effects of heavy precipitation on the occurrence of pathogens in the Puzi River estuary, which is adjacent to the largest inshore oyster farming area in Taiwan. Our results indicated that Vibrio parahaemolyticus and adenovirus were the most frequently detected pathogens in the area. There was a significant difference (Mann-Whitney U test, p < 0.01) in water quality parameters, including total coliform, Escherichia coli, water temperature, turbidity, salinity, and dissolved oxygen, between groups with and without V. parahaemolyticus. In addition, the detection rate was negatively correlated with the average daily rainfall (r2 > 0.8). There was no significant difference between water quality parameters and the presence/absence of adenovirus, but a positive correlation was observed between the average daily rainfall and the detection rate of adenovirus (r2 ≥ 0.75). We conclude that heavy precipitation changes estuarine water quality, causing variations in microbial composition, including pathogens. As extreme weather events become more frequent due to climate change, the potential impacts of severe weather events on estuarine environments require further investigation.

Comparison of two rapid diagnostic tests during a large dengue virus serotype 3 outbreak in the Solomon Islands in 2013

Dengue virus (DENV) infection causes various clinical presentations, including asymptomatic infection, dengue with or without warning signs and severe dengue. An early and accurate diagnosis of DENV infection during the first few days of illness supports clinical management and significantly reduces dengue-associated mortality and morbidity. However, it is very difficult to confirm DENV infection in endemic regions without qualified dengue diagnostic laboratories. In this study, we evaluated the performance of two commercially available rapid diagnostic tests (RDTs) using serum samples collected in the Solomon Islands during the 2013 DENV-3 outbreak. The sensitivity and specificity of the tests were calculated by comparing the results of DENV nonstructural protein 1 (NS1), IgM and IgG RDTs with those obtained by qRT-PCR. We also compared the results of the DENV IgM/IgG RDT with those obtained using an IgM/IgG capture enzyme-linked immune-sorbent assay (ELISA). The sensitivities of the SD and CTK NS1 RDTs were similar (90.9% and 92.6%), and the specificity of the SD NS1 RDT was significantly higher than that of the CTK NS1 RDT (100% versus 78.8%). The inclusion of IgM and IgG in the RDT did not significantly increase the sensitivity for DENV diagnosis. Compared with the SD IgM RDT, IgM capture ELISA had the same specificity but higher sensitivity. User-friendly RDTs remain the first choice and the most convenient tool in dengue endemic regions, where laboratory facilities and the corresponding infrastructure are lacking. Our study provided important and practical information for comparing the performance and validity of the different RDTs for rapid dengue detection.

Tigecycline resistance among carbapenem-resistant Klebsiella Pneumoniae: Clinical characteristics and expression levels of efflux pump genes

Objectives

Tigecycline is a treatment option for infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). Emerging tigecycline resistance in CRKP represents a growing threat. Knowledge of the clinical, microbiological, and molecular characteristics of tigecycline- and carbapenem-resistant Klebsiella pneumoniae (TCRKP) is limited.

Methods

Patients infected with TCRKP were identified from a Taiwanese national surveillance study. Clinical data were collected from medical records. We performed susceptibility tests, carbapenemase gene detection, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Furthermore, we performed quantitative real-time polymerase chain reaction (qRT-PCR) analyses to assess the expression levels of the efflux pump genes acrB and oqxB.

Results

We identified 16 patients infected with TCRKP, with urinary tract infection (UTI) being the most common type of infection (63%). The all-cause 30-day mortality rate was 44% in patients with TCRKP infection. Patients with a site of infection other than the urinary tract had a significantly higher mortality rate than patients with UTIs (83% vs. 20%, p = 0.035). PFGE and MLST revealed no dominant clone or sequence type. Using qRT-PCR, overexpression of both the acrB and oqxB genes was identified in seven isolates, and overexpression of the oqxB gene was observed in another seven. There was poor correlation between acrB or oqxB expression and tigecycline MICs (r = -0.038 and -0.166, respectively).

Conclusions

The mortality rate in patients infected with TCRKP in this study was 44% and this is an important subset of patients. The absence of a linear relationship between efflux pump genes expression and MICs indicates that tigecycline resistance may be mediated by other factors. Continuous monitoring of tigecycline resistance among CRKP isolates and resistance mechanisms are necessary.