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First evidence of pyrethroid resistance in Italian populations of West Nile virus vector Culex pipiens.

ABSTRACT: Culex pipiens (Linnaeus), one of the most abundant mosquito species in Europe, plays a crucial role in the endemic transmission of West Nile virus and caused the large outbreak with >1600 human cases in 2018. Although evidence of resistance to pyrethroids has been reported for Cx. pipiens populations from Spain and Greece, resistance monitoring has been largely neglected in Italy. Herein, we investigate susceptibility of Italian Cx. pipiens populations to the pyrethroids permethrin and deltamethrin. Results from WHO-tube-bioassays revealed mortalities ranging from 14-54%, indicating high levels of resistance, in four out of 10 populations exposed to permethrin (0.75%) and of 63% in one of three populations exposed to deltamethrin (0.05%). Reduced susceptibility (mortality<98%) was detected in almost all other populations. A clear association is shown between the resistant phenotype and the presence of kdr-alleles in position 1014 of the VSSC, strongly suggesting its role in reducing susceptibility. The study provides the first evidence of pyrethroid-resistance in Italian Cx. pipiens populations and reports levels of resistance paralleled in the European region only in Turkey. This highlights the urgent need to implement insecticide-resistance management plans to restore the efficacy of the nowadays only chemical weapon available to control arbovirus transmission in Europe.

SUBMITTER: Pichler V

PROVIDER: S-EPMC9540436 | biostudies-literature | 2022 Sep

REPOSITORIES: biostudies-literature

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First evidence of pyrethroid resistance in Italian populations of West Nile virus vector Culex pipiens.

Pichler Verena V Giammarioli Carola C Bellini Romeo R Veronesi Rodolfo R Arnoldi Daniele D Rizzoli Annapaola A Lia Riccardo Paolo RP Otranto Domenico D Ballardini Marco M Cobre Pietro P Serini Paola P Della Torre Alessandra A Caputo Beniamino B

Medical and veterinary entomology 20220409 3

Culex pipiens (Linnaeus), one of the most abundant mosquito species in Europe, plays a crucial role in the endemic transmission of West Nile virus and caused the large outbreak with >1600 human cases in 2018. Although evidence of resistance to pyrethroids has been reported for Cx. pipiens populations from Spain and Greece, resistance monitoring has been largely neglected in Italy. Herein, we investigate susceptibility of Italian Cx. pipiens populations to the pyrethroids permethrin and deltameth ...[more]

PMID: 35396754

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Project description:BackgroundUnderstanding mechanisms that contribute to viral dissemination in mosquito vectors will contribute to our ability to interfere with the transmission of viral pathogens that impact public health. The expression of genes in two Culex pipiens quinquefasciatus populations from Florida with known differences in vector competence to West Nile virus (WNV) were compared using high throughput sequencing.ResultsA total of 15,176 transcripts were combined for comparison of expression differences between the two populations and 118 transcripts were differentially expressed (p < 0.05). The fold change in expression of the differentially expressed genes ranged from -7.5 - 6.13. The more competent population for WNV (Gainesville) over expressed 77 genes and down regulated 44 genes, compared with the less competent population for WNV (Vero Beach). Also, splicing analysis identified 3 transcripts with significantly different splice forms between the two populations. The functional analysis showed that the largest proportion of transcripts was included in the catalytic activity and transporter activity groups except for those in the unknown group. Interestingly, the up- regulated gene set contained most of the catalytic activity function and the down- regulated gene set had a notable proportion of transcripts with transporter activity function. Immune response category was shown in only the down regulated gene set, although those represent a relatively small portion of the function. Several different vitellogenin genes were expressed differentially. Based on the RNAseq data analysis, ovary development was compared across the populations and following WNV infection. There were significant differences among the compared groups.ConclusionsThis study suggests that ovary development is correlated to vector competence in two Culex populations in Florida. Both populations control energy allocations to reproduction as a response to WNV. This result provides novel insight into the defense mechanism used by Culex spp. mosquitoes against WNV.

Project description:BackgroundIn cool-temperate regions, mosquitoes face winter conditions that hinder their development. To cope with cold temperatures, species like Culex pipiens, a major vector of West Nile virus (WNV), diapause as adult females in overwintering shelters known as hibernacula. This study aimed to identify and characterize the overwintering sites of Cx. pipiens in central Italy, analyzing the environmental factors influencing the abundance of the two biological forms, Cx. pipiens pipiens and Cx. pipiens molestus.MethodsField surveys were conducted in Lazio and Tuscany over two consecutive winters (2022/2023 and 2023/2024). Overwintering mosquitoes were collected from different hibernacula types, including natural caves, artificial cavities and buildings. Environmental variables such as temperature, humidity, light intensity and vapor pressure deficit (VPD) were recorded in the entrance and inner rooms of each hibernaculum. Mosquito species and Cx. pipiens forms were identified through morphological and molecular analyses. A beta regression model was applied to assess the relationship between environmental factors and Cx. pipiens abundance. Redundancy analysis (RDA) was used to explore the impact of small- and landscape-scale variables on biological forms distribution.ResultsCulex pipiens presence was confirmed in 24 hibernacula and represented the most abundant species, with Anopheles maculipennis s.l., Culiseta annulata and Culex hortensis accounting for 0.4% of the collected individuals. Comparing the entrance and inner rooms, a higher abundance of Cx. pipiens s.s. was observed in the darker environments, characterized by a humidity of 50-75%, a temperature of 10-20 °C and a VPD of 0.3-0.8 kPa. Inside the inner rooms, Cx. pipiens females preferred lower temperatures, light intensity and humidity, combined with higher VPD. The RDA highlighted that Cx. pipiens pipiens was associated with low temperatures and VPD and high humidity levels, preferring semi-natural areas. Culex pipiens molestus was positively associated with artificial areas. Hybrids were observed in several types of hibernacula.ConclusionsThis study provides insights into the overwintering ecology of Cx. pipiens in southern Europe, highlighting the environmental factors driving its abundance. These results may inform future vector control strategies aimed at reducing mosquito populations and limiting WNV diffusion in temperate regions.

Project description:BackgroundCulex spp. mosquitoes are considered to be the most important vectors of West Nile virus (WNV) detected in at least 34 species of mosquitoes in the United States. In North America, Culex pipiens pipiens, Culex pipiens quinquefasciatus, and Culex tarsalis are all competent vectors of WNV, which is considered to be enzootic in the United States and has also been detected in equines and birds in many states of Mexico and in humans in Nuevo Leon. There is potential for WNV to be introduced into Mexico City by various means including infected mosquitoes on airplanes, migrating birds, ground transportation and infected humans. Little is known of the geographic distribution of Culex pipiens complex mosquitoes and hybrids in Mexico City. Culex pipiens pipiens preferentially feed on avian hosts; Culex pipiens quinquefasciatus have historically been considered to prefer mammalian hosts; and hybrids of these two species could theoretically serve as bridge vectors to transmit WNV from avian hosts to humans and other mammalian hosts. In order to address the potential of WNV being introduced into Mexico City, we have determined the identity and spatial distribution of Culex pipiens complex mosquitoes and their hybrids.ResultsMosquito larvae collected from 103 sites throughout Mexico City during 2004-2005 were identified as Culex, Culiseta or Ochlerotatus by morphological analysis. Within the genus Culex, specimens were further identified as Culex tarsalis or as belonging to the Culex pipiens complex. Members of the Culex pipiens complex were separated by measuring the ratio of the dorsal and ventral arms (DV/D ratio) of the male genitalia and also by using diagnostic primers designed for the Ace.2 gene. Culex pipiens quinquefasciatus was the most abundant form collected.ConclusionsImportant WNV vectors species, Cx. p. pipiens, Cx. p. quinquefasciatus and Cx. tarsalis, are all present in Mexico City. Hybrids of Cx. p. pipiens and Cx. p. quinquefasciatus were also collected and identified. The presence and abundance of these WNV competent vectors is a cause for concern. Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.

Dataset Information

First evidence of pyrethroid resistance in Italian populations of West Nile virus vector Culex pipiens.

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First evidence of pyrethroid resistance in Italian populations of West Nile virus vector Culex pipiens.

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