Background: Imported falciparum malaria from Africa has become a key public health challenge in Guizhou Province since 2012. Understanding the polymorphisms of molecular markers of drug resistance can guide selection of antimalarial drugs for the treatment of malaria. This study was aimed to analyze the polymorphisms of pfcrt, pfmdr1, and K13-propeller among imported falciparum malaria cases in Guizhou Province, China. Method: Fifty-five imported falciparum malaria cases in Guizhou Province during 2012-2016 were included in this study. Their demographic information and filter paper blood samples were collected. Genomic DNA of Plasmodium falciparum was extracted from the blood samples, and polymorphisms of pfcrt, pfmdr1, and K13-propeller were analyzed with nested PCR amplification followed by sequencing. Data were analyzed with the SPSS17.0 software. Results: The prevalence of pfcrt K76T, pfmdr1 N86Y, and pfmdr1 Y184F mutation was 56.6, 22.2, and 72.2%, respectively, in imported falciparum malaria cases in Guizhou Province. We detected two mutant haplotypes of pfcrt, IET and MNT, with IET being more commonly found (54.7%), and five mutant haplotypes of pfmdr1, of which NFD was the most frequent (53.7%). There were totally 10 combined haplotypes of pfcrt and pfmdr1, of which the haplotype IETNFD possessed a predominance of 28.8%. In addition, three nonsynonymous mutations (S459T, C469F, and V692L) and two synonymous mutations (R471R and V589V) were detected in K13-propeller, all having prevalence less than 6.0%. In particular, a candidate K13 resistance mutation, C469F, was identified for the first time from Democratic Republic of the Congo with the prevalence of 2.0%. Conclusions: The high prevalence of IET haplotype of pfcrt and NFD haplotype of pfmdr1 suggests the presence of chloroquine, artemether/lumefantrine, and dihydroartemisinin/piperaquine resistance in these cases. Therefore cautions should be made to artemisinin therapy for P. falciparum in Africa. Continuous monitoring of anti-malarial drug efficacy in imported malaria cases is helpful for optimizing antimalarial drug therapy in Guizhou Province, China.

Acetylcholinesterase is the primary target of organophosphates (OPs) and carbamates in insects. As gene mutation has been verified as an important mechanism of insecticide resistance in insects, in this study, we investigated the status of OPs resistance and the polymorphism of ace gene (that encodes acetylcholinesterase) in housefly (Musca domestica L) field populations in Guizhou Province, China. Bioassays showed that the houseflies had 142.16–303.54-fold resistance to dichlorvos (DDVP) and 122.13–363.98-fold resistance to temephos. Molecular analysis revealed resistance-causing mutations of ace gene at loci of 260, 342 and 407 in the housefly populations, with a total frequency of 55%, 100% and 94%, respectively. In addition, 11 combinations of ace mutation were observed across the detected populations. The most frequently detected combination was L/V+A/V+Y, followed by L+A+Y and L/V+A+Y. No significant relationship was found between single mutation/combination mutations and DDVP resistance. These results indicate that the OPs resistance is prevalent among the housefly populations in Guizhou Province, with a similar pattern of allele mutation of ace across China. The target resistance can not fully account for the resistance of houseflies to OPs in Guizhou.

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Background： The campaign to establish the national sanitary city has been launched across major places in Guizhou Province, which leads to the extensive use of insecticide to eradicate the disease-carrier Musca domestica found everywhere while keeping the cleanliness of environment.Methods: In order to perceive the resistance of houseflies to the commonly used organophosphate insecticides in 7 housefly populations belonging to Guizhou province (China), the susceptibility bioassays, detection of resistance-associated mutations, and the carboxylesterase activity assay were conducted.Results: The bioassays exhibited 142.16~303.54-fold to dichlorvos (DDVP) and 122.13~363.98-fold to temephos. The molecular analysis unveiled mutant ACE gene at loci of 260, 342 and 407 in all populations, which led to high frequencies at 27.4~73.8% of 260L, 59.1~76.7% of 342A, 23.7~40.9% of 342V, and 83.4~100.0% of 407Y, with inclusion of 8 genotypes and 10 mutant combinations. Further analysis of mutations showed a linkage disequilibrium of L/V+A+Y at locus 260 & 342, indicating a significant association with the DDVP resistance. The Hardy-Weinberg equilibrium test demonstrated that the observed ACE heterozygosity mostly exceeded 0.5 and deviated from the equilibrium. In the fixation index, an insignificant differentiation was noted among the 7 housefly populations. Conclusions: However, further research should concentrate on the use of insecticides to avoid the abuse of insecticides, and to regularly monitor the resistance of houseflies using novel methods.