BackgroundArboviral disease transmitted by Aedes albopictus such as dengue fever is an important threat to human health. Pyrethroid resistance raises a great challenge for mosquito control. A systematic assessment of Ae. albopictus resistance status in China is urgently needed, and the study of correlation between pyrethroid resistance and knockdown resistance (kdr) mutations would provide information to guide the control of the Ae. albopictus vector.MethodsFive field populations of Ae. albopictus were collected from Jinan (JN), Hangzhou (HZ), Baoshan (BS), Yangpu (YP) and Haikou (HK), China in 2017. Insecticide-impregnated papers were prepared with four pyrethroid chemicals, deltamethrin, permethrin, beta-cypermethrin and lambda-cyhalothrin. The susceptibility of Ae. albopictus to pyrethroids was tested by the WHO tube assay. Kdr mutations were identified by PCR and sequencing. Moreover, the correlation analysis between kdr alleles and pyrethroid resistance was performed.ResultsAll five populations of Ae. albopictus showed resistance to four pyrethroid insecticides. One kdr mutant allele at codon 1532 and three at 1534 were detected with frequency of 5.33% (I1532T), 44.20% (F1534S), 1.83% (F1534 L) and 0.87% (F1534C), respectively. Both 1532 and 1534 mutation mosquitoes were found in the BS and YP populations. Allele I1532T was negatively correlated with deltamethrin resistance phenotype (OR < 1), while F1534S mutation was positively correlated with deltamethrin and permethrin resistance (OR > 1).ConclusionsThe five field populations of Ae. albopictus adults were all resistant to deltamethrin, permethrin, beta-cypermethrin and lambda-cyhalothrin. Mutant F1534S was clearly associated with pyrethroid resistance phenotype in Ae. albopictus and this could be developed as a molecular marker to monitor the pyrethroid resistance problem in China.Electronic supplementary materialThe online version of this article (10.1186/s40249-018-0471-y) contains supplementary material, which is available to authorized users.

BackgroundAnopheles sinensis has become an important malaria vector in China. The long-term extensive utilization of pyrethroids for ITNs and IRS for mosquito control in the last three decades has resulted in the occurrence of resistant An. sinensis populations in many regions. Knockdown resistance (kdr), caused by point mutations in the VGSC gene, is one of the mechanisms that confer resistance to DDT and pyrethroids. Recently, several investigations revealed the kdr occurrence in some An. sinensis populations, however, no kdr data were available earlier than 2009. A survey tracking the dynamics of the kdr mutations in past decades would provide invaluable information to understand how the kdr alleles spread in mosquito populations temporally and spatially.MethodsA survey was conducted on the kdr alleles at condon 1014 of the VGSC gene and their distributions in 733 specimens of An. sinensis and 232 specimens of the other eight member species of the Anopheles hyrcanus group that were collected from 17 provinces in China in 1996–2014.ResultsA total of three kdr alleles, TTT (F), TTG (F) and TGT (C) were detected, and TGT (C) and TTT (F) were already present in the specimens from Jiangsu and Shandong as early as 1997. The TTT (F) was the most frequent mutant allele, and largely distributed in central China, namely Shandong, Jiangsu, Anhui, Henan, Shanghai, Jiangxi and Hubei. When data were analysed in three time intervals, 1996–2001, 2005–2009, 2010–2014, the prevalence of kdr alleles increased progressively over time in the populations in central China. In contrast, the kdr alleles were less frequent in the samples from other regions, especially in Yunnan and Hainan, despite the documented presence of pyrethroid resistant populations in those regions. Interestingly, no mutant alleles were detected in all 232 specimens of eight other species in the An. hyrcanus group.ConclusionThe survey revealed that the kdr occurrence and accumulation in the An. sinensis populations were more frequent in central China than in the other regions, suggesting that the kdr mutations may contribute significantly to the pyrethroid resistance in the mosquitoes in central China.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0644-0) contains supplementary material, which is available to authorized users.

Background Dengue virus (DENV) infection is increasingly common in southern China and can be transmitted through blood transfusion but is not currently part of donor screening throughout the region. We assessed DENV prevalence among donors at the Xishuangbanna Blood Center, Yunnan, to support development of DENV screening strategies. Methods Blood samples were collected randomly between June 2019 and August 2019. These were screened for anti-DENV IgG and IgM using enzyme-linked immunosorbent assay (ELISA). Then, all reactive samples and some randomly-chosen non-reactive samples were used to detect DENV RNAs using real-time polymerase-chain-reaction (RT-PCR) assays. After RT-PCR, samples were further tested for soluble nonstructural protein 1 (NS1) using the colloidal gold method. Donors demographics were also collected and assessed. Results Over the study period, 2254 donor samples were collected and tested for anti-DENV IgG and IgM by ELISA. This revealed 598 anti-DENV IgG and/or IgM reactive samples, a serological prevalence of 26.53%. Of these, 26 were RT-PCR positive and/or NS1 positive. Significant differences in DENV prevalence were noted by occupation (P = 0.001), education (P < 0.001), and ethnicity (P = 0.026). Conclusion The prevalence of DENV in Xishuangbanna Blood Center was higher than most other blood centers that have implemented DENV donor screening. Our study provides first-hand data about the prevalence of DENV and allows the development of a screening strategy for clinical use.

BackgroundBiting midges are hematophagus ectoparasites of insects, humans and other animals. Culicoides (Trithicoides) anophelis Edwards1922 is a predator of engorged mosquitoes.FindingsIn a field trip of wild mosquito collections, C. anophelis was found on two Anopheles mosquitoes. One mosquito with a midge clinging onto its abdomen was caught on video demonstrating the act of the midge taking blood from the engorged mosquito Anopheles vagus. The midge C. anophelis has a broad host range. Documented in the literature, the midge has been found in various mosquito species in the genera Anopheles, Culex, Aedes and Armigeres.ConclusionsA video clip was presented demonstrating a midge taking blood from an engorged mosquito. The host promiscuity of C. anophelis raises a concern about its potential as a mechanic or biological vector to spread viruses among mosquito populations.

BackgroundSand fly Phlebotomus chinensis is a principle vector for the visceral leishmaniasis (VL) in China with a wide geographic distribution. Jiuzhaigou, Sichuan is a mountain type endemic area of VL in China. Long term effective control efforts in the region have successfully reduced VL transmission. To assess the current status of the sand flies and their ecological aspects in the region, a survey was conducted in the summer of 2014 and 2015.MethodsSand fly specimens were collected by light traps in a village and blood sources were identified by PCR and sequencing of the mitochondrial cytochrome b gene.ResultsIn a rock cave, 65.2 %–79.8 % of collected sand flies were male. On a rabbit farm, 92.9 %–98.8 % of specimens were female. In pig pens, 61.1 % of specimens were female. Some females had visible blood residues. The feeding rate was 49.4 % from the pig pens, 12.3 % from the cave, and only 1.7 % from the rabbit farm. Pig, rabbit, chicken, dog, and human blood were detected in the fed specimens. Swine blood, present in all tested samples, was a preferred blood source, while chicken and dog blood were present in a third of the samples.ConclusionsIn Jiuzhaigou County, Sichuan Province of China, the considerable sandfly density and the peridomestic feeding behavior all increases the risk of VL transmission, and insecticide spraying in animal sheds could be exploited to reduce sand fly populations in human surroundings.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-016-0126-9) contains supplementary material, which is available to authorized users.