Long-term trends in housefly (Musca domestica L.) insecticide resistance in China.

Controlling housefly populations relies on the use of insecticides, which inevitably leads to the development of resistance. A better and more comprehensive understanding of the spatial and temporal distribution of resistance could guide the control of houseflies. However, most studies on housefly resistance in China are scattered and poorly coordinated. We collected resistance data from houseflies in the published literature and from the vector biomonitoring system of the Chinese Center for Disease Control and Prevention. A 5- or 10-year resolution was used to study the temporal dynamics of resistance to five commonly used insecticides: deltamethrin, permethrin, beta-cypermethrin, dichlorvos, and propoxur. ArcGIS was used to visualize their spatial distributions. The correlation between year and resistance coefficient was determined using SPSS 26.0 and RStudio to explore the changes in resistance over the years. A total of 2128 data were included in this study, ranging from 1982 to 2022, based on which we found significant increases in resistance over the past forty years for the five studied insecticides. Among them, pyrethroids had the most strikingly elevated resistance level and were mainly distributed in the northern and southeastern coastal areas. Dichlorvos and propoxur had intermediate increases in resistance, and most of these increases were identified in North China and the Yangtze River. Housefly resistance to commonly used insecticides in China is increasing and spatially heterogeneous. This finding also highlights the necessity of continuous routine surveillance of housefly resistance, which could guide future housefly control operations and slow the development of resistance.

Climate heterogeneity, season variation, and sexual dimorphism modulate the association between MHC II diversity and parasite variation in striped hamster.

Parasite-mediated selection is widely believed to play a crucial role in maintaining the diversity of the major histocompatibility complex (MHC) genes, which is thought to be maintained through heterozygote advantage, rare-allele advantage, and fluctuating selection. However, the relationship between parasite pressure and MHC diversity has yielded inconsistent findings. These inconsistencies may arise from the influence of environmental factors and individual variations in traits on host-parasite interactions. To address these issues, our study extensively investigated populations of striped hamsters inhabiting regions characterized by environmental heterogeneity. The primary objective was to examine the universality of parasite-mediated selection mechanisms. Our observations revealed the presence of multiple parasite infections, accompanied by spatial and temporal variations in parasite communities and infection patterns among individual hamsters. Specifically, the temperature was found to influence all four parasite indices, while the presence of gamasid mites and parasite richness decreased with increasing precipitation. We also noted significant seasonal variation in parasite dynamics. Moreover, a significant sexual dimorphism was observed with males exhibiting a considerably higher parasite burden compared to their female counterparts. Lastly, we identified the maintenance of MHC polymorphism in striped hamsters as being driven by the heterozygote advantage and fluctuating selection mechanisms. This study underscores the significance of ecological processes in comprehending host-parasite systems and highlights the necessity of considering environmental factors and individual traits when elucidating the mechanisms underlying MHC diversity mediated by parasites.

Effects of the source of information and knowledge of dengue fever on the mosquito control behavior of residents of border areas of Yunnan, China.

BACKGROUND: Strengthening the mosquito control measures undertaken by residents of an area where dengue fever is present can significantly decrease the spread of this disease. The aim of this study was to explore the effects of the source of information and knowledge of dengue fever on the mosquito control behavior of residents of areas at high risk of this disease to determine effective ways of enhancing this behavior. METHODS: A survey was conducted via face-to-face interviews or questionnaires between March and May 2021 in three regions of the province of Yunnan, China. The survey included basic information about the respondents, the source(s) of their dengue fever information, the level of their dengue fever knowledge, and the measures they had implemented to control mosquitoes. Principal component analysis was used to extract the main components of the sources of information. Correlation analysis and structural equation analysis were used to explore the impact of the sources of information and residents' dengue fever knowledge on their mosquito control behavior. RESULTS: Publicity achieved through mass media, including official WeChat accounts, magazines/newspapers, poster leaflets, television/radio and the Internet, had a direct effect on dengue fever knowledge and mosquito control behavior, and indirectly affected mosquito control behavior through dengue fever knowledge. Organized publicity campaigns, including information provided by medical staff and through community publicity, had a direct effect on dengue fever knowledge and indirectly affected mosquito control behavior through dengue fever knowledge. The residents' level of dengue fever knowledge had a significant, positive, direct effect on their mosquito control behavior. CONCLUSIONS: Mosquito control is an important measure for the prevention and control of outbreaks of dengue fever. An effective source of information can improve the level of dengue fever knowledge among residents and thus enhance their mosquito control behavior.

A novel strategy for screening mutations in the voltage-gated sodium channel gene of Aedes albopictus based on multiplex PCR-mass spectrometry minisequencing technology.

BACKGROUND: The current prevention and control strategy for Aedes albopictus heavily relies on comprehensive management, such as environmental management and chemical control. However, the wide application of pyrethroids has facilitated the development of insecticide resistance, primarily via mutations in the voltage-gated sodium channel (VGSC) gene. This study aims to develop a novel strategy for detecting mutations in the VGSC gene in Ae. albopictus using multiplex PCR-mass spectrometry (MPCR-MS) minisequencing technology. METHODS: We established a new strategy for detecting mutations in the VGSC gene in Ae. albopictus using MPCR-MS minisequencing technology. MPCR amplification and mass probe extension (MPE) were first used, followed by single nucleotide polymorphism (SNP) typing mass spectrometry, which allows the simultaneous detection of multiple mutation sites of the VGSC gene in 96 samples of Ae. albopictus. A total of 70 wild-collected Ae. albopictus were used to evaluate the performance of the method by comparing it with other methods. RESULTS: Three target sites (1016, 1532, 1534) in the VGSC gene can be detected simultaneously by double PCR amplification combined with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, achieving a detection limit of 20 fg/µl. We applied this method to 70 wild-collected Ae. albopictus, and the obtained genotypes were consistent with the routine sequencing results, suggesting the accuracy of our method. CONCLUSIONS: MPCR-MS minisequencing technology provides a sensitive and high-throughput approach to Ae. albopictus VGSC gene mutation screening. Compared with conventional sequencing, this method is economical and time-saving. It is of great value for insecticide resistance surveillance in areas with a high risk of vector-borne disease.

Epidemiological characteristics and temporal-spatial analysis of overseas imported dengue fever cases in outbreak provinces of China, 2005-2019.

BACKGROUND: Overseas imported dengue fever is an important factor in local outbreaks of this disease in the mainland of China. To better prevent and control such local outbreaks, the epidemiological characteristics and temporal-spatial distribution of overseas imported dengue fever cases in provincial-level administrative divisions (PLADs) where dengue fever is outbreak in the mainland of China were explored. METHODS: Using the Chinese National Notifiable Infectious Disease Reporting Information System (CNNDS), we identified overseas imported dengue fever cases in dengue fever outbreak areas in the mainland of China from 2005 to 2019 to draw the epidemic curve and population characteristic distribution of overseas imported cases in each PLAD. Based on spatial autocorrelation analysis of ArcGIS 10.5 and temporal-spatial scanning analysis of SaTScan 9.5, we analyzed the temporal-spatial distribution of overseas imported dengue fever in dengue fever outbreak areas in the mainland of China. RESULTS: A total of 11,407 imported cases, mainly from Southeast Asia, were recorded from 2005 to 2019 in these 13 PLADs. Of which 62.1% were imported into Yunnan and Guangdong Provinces. Among the imported cases, there were more males than females, mainly from the 21-50 age group. The hot spots were concentrated in parts of Yunnan, Guangdong and Fujian Provinces. We found the cluster of infected areas were expanding northward. CONCLUSIONS: Based on the analysis of overseas imported dengue cases in 13 PLADs of the mainland of China from 2005 to 2019, we obtained the epidemiological characteristics and spatial distribution of imported dengue cases. Border controls need to pay attention to key population sectors, such as 21-50 years old men and education of key populations on dengue prevention. There is a need to improve the awareness of the prevention and control of imported cases in border areas. At the same time, northern regions cannot relax their vigilance.

Knockdown resistance mutations distribution and characteristics of Aedes albopictus field populations within eleven dengue local epidemic provinces in China.

Background: Aedes albopictus, commonly known as the tiger mosquito, has attracted global attention because its bite can transmit several viruses, such as dengue virus. With the absence of an effective therapy and vaccine, mosquito control is the sole method for dengue fever control. However, Ae. albopictus has developed resistance to most insecticides, especially pyrethroids. Many scholars have conducted thorough research for the target-site of pyrethroids. The main target-site is the voltage-gated sodium channel gene (VGSC) whose mutation causes knockdown resistance (kdr). The spatial distribution of three locus kdr mutations in Ae. albopictus has not been comprehensively analyzed nationwide in China. In addition, the relationship between the frequency of kdr mutations and dengue fever has not yet been explored. Methods: A total of 2,241 Ae. albopictus samples from 49 populations from 11 provinces of mainland China were collected in 2020 and analyzed for mutations in the VGSC gene. DNAstar 7.1. Seqman and Mega-X were used to compare the sequences and read the peak map to confirm the genotypes and alleles of each mutation. ArcGIS 10.6 software was used to make interpolation and extract meteorological data of collection sites and to conduct spatial autocorrelation analysis. R 4.1.2 software was used to conduct a chi-square test for kdr mutations and dengue area and to analyze the correlation between meteorological factors and kdr mutations. Results: The overall frequencies of mutant alleles at 1016G, 1532T, and 1534S/C/L were 13.19%, 4.89%, and 46.90%, respectively. Mutations at the three loci were found at 89.80% (44/49), 44.90% (22/49), and 97.96% (48/49) of the field populations. At each of the loci V1016 and I1532, only one allele was detected, which was GGA(G) and ACC(T), respectively. Five mutant alleles were found at codon 1534: TCC/S (33.49%), TGC/C (11.96%), TTG/L (0.60%), CTC/L (0.49%), and TTA/L (0.58%). In total, 31 triple-locus genotype combinations were found, and the single locus mutation was the most common. We also found firstly triple-locus mutant individuals, whose genotypes were V/G+I/T+F/S and V/G+I/T+S/S. The 1016 and 1532 mutation rates were significantly negatively related to the annual average temperature (AAT), but the 1534 mutation rate was significantly positively related to AAT. The 1532 mutation rate was significantly positively related to the 1016 mutation rate but negatively related to the 1534 mutation rate. A relationship was observed between the 1534 codon mutation rate and dengue epidemic areas in this study. Furthermore, spatial autocorrelation analysis results showed that the mutation rates of different codons in different geographical areas had spatial aggregation and positive spatial correlation. Conclusion: This study showed that the multiple kdr mutations at codon 1016, 1532 and 1534 of Ae. albopictus were found in most areas of China. Two novel triple-locus genotype combinations, V/G+I/T+F/S and V/G+I/T+S/S, were detected in this study. In addition, the relationship between mosquito resistance and dengue fever outbreak should be further explored, especially considering the insecticide-usage history in different areas. The characteristic of spatial aggregation of VGSC gene mutation rates reminds us to notice the gene exchange and similarity of insecticide usage in the adjacent areas. The use of pyrethroids should be restricted to delay resistance development. New-type insecticides should be developed to adjust the changes in the resistance spectrum. Our study provides abundant data on the Ae. albopictus kdr gene mutation in China; these findings will be useful for the correlation analysis of molecular mechanism of insecticide resistance.

Predicting the Potential Global Distribution of Amblyomma americanum (Acari: Ixodidae) under Near Current and Future Climatic Conditions, Using the Maximum Entropy Model.

Amblyomma americanum (the lone star tick) is a pathogen vector, mainly from eastern North America, that bites humans. With global integration and climate change, some ticks that are currently confined to a certain place may begin to spread out; some reports have shown that they are undergoing rapid range expansion. The difference in the potential geographic distribution of A. americanum under current and future climatic conditions is dependent on environment variables such as temperature and precipitation, which can affect their survival. In this study, we used a maximum entropy (MaxEnt) model to predict the potential geographic distribution of A. americanum. The MaxEnt model was calibrated at the native range of A. americanum using occurrence data and the current climatic conditions. Seven WorldClim climatic variables were selected by the jackknife method and tested in MaxEnt using different combinations of model feature class functions and regularization multiplier values. The best model was chosen based on the omission rate and the lowest Akaike information criterion. The resulting model was then projected onto the global scale using the current and future climate conditions modeled under four greenhouse gas emission scenarios.

Severe Case of Rickettsiosis Identified by Metagenomic Sequencing, China.

A case of Rickettsia sibirica subspecies sibirica BJ-90 infection in China was identified by metagenomic analysis of an eschar biopsy specimen and confirmed by nested PCR. Seroprevalence of spotted fever group Rickettsia was ≈17.4% among the local population. This report highlights the threat of rickettsioses to public health in the Qinghai-Tibet Plateau.