Assessment of insecticide resistance in primary dengue vector, Aedes aegypti (Linn.) from Northern Districts of West Bengal, India

Insecticide susceptibility status on Aedes aegypti (Linn) and Aedes albopictus (Skuse) of Chittorgarh district, Rajasthan, India

Vector-borne diseases are a major burden to human health. It accounts for more than 17% of the total infectious diseases and causes more than 0.7 million deaths annually. Mosquitoes are potential vectors for many vector-borne diseases that cause illness to public health, globally. Vector species of the genus Aedes i.e., Aedes aegypti and Aedes albopictus are the vector for many arboviruses such as dengue, chikungunya, yellow fever, and Zika in India. Dengue is one of the most prevalent viral infections causing a high number of cases throughout the world and resistance to insecticides can be a reason for the failure of vector control strategies. This study was carried out to check the degree of resistance among these vectors in the Chittorgarh district of Rajasthan, India through standard World Health Organization protocol. The resistance was monitored to pyrethroids i.e., deltamethrin (0.05%), permethrin (0.75%), alphacypermethrin (0.05%); organochlorine i.e., DDT (4%), and an organophosphate larvicide i.e., temephos (0.02 mg/L) in both vector species. Complete resistance to DDT was observed among all tested populations of both species. All tested populations of Aedes albopictus were found susceptible to pyrethroids. Aedes aegypti was found resistant in the Mangalwad population, unconfirmed resistant in Bhopalsagar and Rashmi populations while the remaining are susceptible to permethrin. The Mangalwad population was also found unconfirmed resistant to deltamethrin and alphacypermethrin. Larvae of both species were found susceptible to temephos. Decreasing the use of DDT will help to reduce the impact on human health and environmental contamination. However, temephos as a larvicide, deltamethrin, and alphacypermethrin as an adulticide can be used in critical disease outbreaks at a minimum concentration as mosquitoes are found susceptible in the study area.

Genetic characterization of dengue virus from patients presenting multi-serotypic infections in the Northern West Bengal, India

Northern West Bengal, popularly known as North Bengal, is a dengue-endemic area, which has been severely affected by Dengue in the past few years resulting in massive hospitalizations and deaths. Genetic characterization of the circulating endemic dengue virus (DENV) serotypes is of paramount importance for the epidemiological understanding of the infection and subsequent vaccine development. The present study was conceived to characterize circulating dengue serotypes and to undertake phylogenetic study. EDTA blood samples of all (N = 83) NS1-positive cases of patients with acute febrile illness referred to different health care facilities were collected and processed for RNA isolation followed by the complementary DNA (cDNA) preparation. Serotype determination of dengue infection was done using conventional PCR by targeting the viral C-prM region. Phylogenetic tree was constructed by implementing the Maximum likelihood method. Out of 83 blood samples 17 were detected to be positive for the presence of dengue viral RNA. DENV3 was found to be the predominant serotype in the single-infection cases; however, we have detected multi-serotypic co-infections throughout the study. Joint pain was found to be the most valuable symptom for the prognosis of dengue. Sequence analyses suggested that both DENV1- and DENV3-circulating genotypes are in the genotype III group and remain closely related to the Indian clade. To the best of our knowledge, this is the first report on the genetic characterization of circulating DENVs in North Bengal, which may contribute to the study of dengue epidemic and pathogenesis.

Expansive and Diverse Phenotypic Landscape of Field Aedes aegypti (Diptera: Culicidae) Larvae with Differential Susceptibility to Temephos: Beyond Metabolic Detoxification

Arboviruses including dengue, Zika, and chikungunya are amongst the most significant public health concerns worldwide. Arbovirus control relies on the use of insecticides to control the vector mosquito Aedes aegypti (Linnaeus), the success of which is threatened by widespread insecticide resistance. The work presented here profiled the gene expression of Ae. aegypti larvae from field populations of Ae. aegypti with differential susceptibility to temephos originating from two Colombian urban locations, Bello and Cúcuta, previously reported to have distinctive disease incidence, socioeconomics, and climate. We demonstrated that an exclusive field-to-lab (Ae. aegypti strain New Orleans) comparison generates an over estimation of differential gene expression (DGE) and that the inclusion of a geographically relevant field control yields a more discrete, and likely, more specific set of genes. The composition of the obtained DGE profiles is varied, with commonly reported resistance associated genes including detoxifying enzymes having only a small representation. We identify cuticle biosynthesis, ion exchange homeostasis, an extensive number of long noncoding RNAs, and chromatin modelling among the differentially expressed genes in field resistant Ae. aegypti larvae. It was also shown that temephos resistant larvae undertake further gene expression responses when temporarily exposed to temephos. The results from the sampling triangulation approach here contribute a discrete DGE profiling with reduced noise that permitted the observation of a greater gene diversity, increasing the number of potential targets for the control of insecticide resistant mosquitoes and widening our knowledge base on the complex phenotypic network of the Ae. aegypti response to insecticides.

A new knockdown resistance (kdr) mutation, F1534L, in the voltage-gated sodium channel of Aedes aegypti, co-occurring with F1534C, S989P and V1016G

BACKGROUND

Aedes aegypti is a primary vector of dengue, chikungunya and Zika infections in India. In the absence of specific drugs or safe and effective vaccines for these infections, their control relies mainly on vector control measures. The emergence of insecticide resistance in vectors, especially against pyrethroids, is a serious threat to the insecticide-based vector control programme. This study reports the presence of multiple knockdown resistance (kdr) mutations present in an Ae. aegypti population from Bengaluru (India), including a new mutation F1534L.

METHODS

Aedes aegypti collected from Bengaluru were subjected to insecticide susceptibility tests with DDT, deltamethrin and permethrin. The DNA sequencing of partial domain II, III and IV of the voltage-gated sodium channel (VGSC) was performed to screen kdr mutations present in the population and PCR-based assays were developed for their detection. Genotyping of kdr mutations was done using PCR-based assays, allelic frequencies were determined, and tests of genetic association of kdr mutations with the insecticide resistance phenotype were performed.

RESULTS

The Ae. aegypti population was resistant to DDT, deltamethrin and permethrin. The DNA sequencing of the VGSC revealed the presence of four kdr mutations, i.e. S989P and V1016G in domain II and two alternative kdr mutations F1534C and F1534L in domain III. Allele-specific PCR assays (ASPCR) were developed for the detection of kdr mutations S989P and V1016G and an existing PCR-RFLP based strategy was modified for the genotyping of all three known kdr mutations in domain III (F1534L, F1534C and T1520I). Genotyping of Ae. aegypti samples revealed a moderate frequency of S989P/V1016G (18.27%) and F1534L (17.48%), a relatively high frequency of F1534C (50.61%) and absence of T1520I in the population. Mutations S989P and V1016G were in complete linkage disequilibrium in this population while they were in linkage equilibrium with kdr mutations F1534C and F1534L. The alleles F1534C and F1534L are genetically associated with permethrin resistance.

CONCLUSIONS

A new kdr mutation, F1534L, was found in an Ae. aegypti population from Bengaluru (India), co-occurring with the other three mutations S989P, V1016G and F1534C. The findings of a new mutation have implications for insecticide resistance management.

Chemical composition and larvicidal activity against Aedes mosquitoes of essential oils from Arisaema fargesii

BACKGROUND

Dengue fever is caused by the spread of dengue virus by Aedes mosquito vectors. Currently, the most effective way to control dengue is by preventing mosquitoes from spreading the disease. Arisaema fargesii is a Chinese herbal medicine commonly used to repel mosquitoes. In our laboratory, anti-mosquito chemical components were extracted from A. fargesii, and the effects of these substances on mosquito larvae were examined.

RESULTS

In total, 48 compounds corresponding to 98.79% of the total oil were identified and the major compounds identified were linalool (12.38%), carvacrol (8.27%), eugenol (5.21%), and β-selinene (5.36%). Essential oil had larvicidal activity against Ae. aegypti and Ae. albopictus with LC₅₀ values of 40.49 mg/L, 47.01 mg/L, respectively. The LC₅₀ values of carvacrol, eugenol, linalool and β-selinene were 32.78, 56.34, 70.56, 136.03 mg/L against Ae. aegypti larvae, and 39.08, 52.07, 82.34, 151.74 mg/L, respectively, against Ae. albopictus larvae. Biochemical assays of Aedes larvae showed that the activities of acetylcholinesterase (AChE), monooxygenases (MO), glutathione-S-transferase (GST), p-Nitrophenyl acetate (p-NPA) esterase, α-esterase and β-esterase were significantly affected by carvacrol. Essential oil induced the detoxification mechanism for the action of GST and MO.

CONCLUSION

The result indicates that essential oil of A. fargesii and its isolated constituent have good inhibitory effects on the defense enzymes of Aedes mosquito larvae. A. fargesii essential oil can be used to control Aedes mosquito larvae to prevent the spread of dengue fever. © 2019 Society of Chemical Industry.

CYP-mediated resistance and cross-resistance to pyrethroids and organophosphates in Aedes aegypti in the presence and absence of kdr

Aedes aegypti thrives in urban environments and transmits several debilitating human viral diseases. Thus, our ability to control this mosquito species in endemic areas is of utmost importance. The use of insecticides, mostly pyrethroids and organophosphates (OPs), has long been the primary means of controlling A. aegypti, but widespread insecticide resistance has emerged. The two main mechanisms of pyrethroid resistance in A. aegypti are CYP-mediated detoxification and mutations in the target site, voltage-sensitive sodium channel (Vssc), referred to as knockdown resistance (kdr). Knowledge about the contributions and interactions of these mechanisms to resistance is important for the understanding of the molecular and evolutionary basis of insecticide resistance, and to determine the effectiveness of insecticides. In this study, we address two aims: 1) determine the patterns of CYP-mediated cross-resistance to pyrethroid and OP insecticides, both in the presence and absence of kdr (S989P + V1016G), and 2) determine whether the interaction between the two mechanisms yields a greater than, less than, or additive effect on resistance. We tested seven pyrethroids and four OPs against three congenic strains of A. aegypti: ROCK (susceptible), CYP:ROCK (CR) (resistant due to CYP-mediated detoxification without kdr), and CYP + KDR:ROCK (CKR) (resistant due to both CYPs and kdr), and compared these to the congenic KDR:ROCK strain that was previously reported. We found that resistance ratios (RRs) were variable between pyrethroids and strains, ranging from 6.2- to 42-fold for CR, and 70- to 261-fold for CKR. In general, we found that CYP-mediated resistance alone contributes less to resistance than kdr. The effect of the combined mechanisms on resistance was significantly greater than additive for all pyrethroids except (1R)-trans-fenfluthrin. CYP-mediated pyrethroid resistance conferred cross-resistance to both methyl paraoxon and fenitrothion, and negative cross-resistance to methyl parathion and naled. Based on our results, we recommend that etofenprox and cyfluthrin be avoided for A. aegypti control in areas where these two resistance mechanisms are prevalent.

Insecticide resistance mapping in the vector of lymphatic filariasis, Culex quinquefasciatus Say from northern region of West Bengal, India

Culex quinquefasciatus is a vector of lymphatic filariasis and vector control strategies normally involve the use of synthetic insecticides targeted against them. Extensive and uncontrolled use of these synthetic insecticides has led to the development of insecticide resistance in the mosquito vectors. In this context, to study the resistance status of Cx. quinquefasciatus, field populations were collected from three districts of Northern part of West Bengal and tested against insecticides (5% malathion, 0.05% deltamethrin, 0.05% lambdacyhalothrin,0.75% permethrin, 0.1% propoxur, 4% DDT and Temephos). Qualitative and quantitative enzyme assay was also conducted in order to find the role of detoxifying enzymes behind the development of insecticide resistance. This study revealed the presence of widespread resistance amongst the field populations of Cx. quinquefasciatus throughout the studied regions. Moreover, the result of native PAGE and biochemical enzyme assay may be linked to some extent in the involvement of the detoxifying enzymes in conferring resistance against insecticides in most of the tested Cx. quinquefasciatus populations. The present study involving the survey of resistance status may be of immense help during the implementation of vector control strategies throughout this region.

Prevalence of kdr mutations and insecticide susceptibility among natural population of Aedes aegypti in West Bengal

BACKGROUND

Aedes albopictus and Aedes aegypti are the major vectors of arboviral diseases. As effective vaccines are not available for most of the arboviral diseases, vector control by using insecticides play the key role to reduce the disease transmission. The emergence and spread of resistance to different classes of insecticides by the vectors is a major obstacle to control the disease transmission. Information about vector susceptibility to different insecticides and their mechanisms are very important for formulating proper vector control measures. The present study was designed to assess the susceptibility of Ae. aegypti against three different classes of adulticides, one larvicidal agent available and polymorphisms in the voltage-gated sodium channel (VGSC) gene related to insecticide resistance.

METHODS

Immature stages of Ae. aegypti were collected from three dengue endemic municipal areas of West Bengal and reared in the laboratory. Larvae and adults (F1 progeny) were used for insecticide bioassay as per WHO protocols. Knock down resistance gene (kdr) mutations were assessed by direct sequencing of PCR products.

RESULTS

The Ae. aegypti population was found to be susceptible to type II pyrethroids and malathion but highly resistant to DDT. A high rate of polymorphisms in the VGSC gene was observed among the collected mosquitoes. A double mutant V1016G + F1534C was found to be associated with DDT resistance but neither V1016G nor F1534C alone showed the same association. Association between the kdr mutations and the susceptibility status of pyrethroids could not be established due to very small sample size. A low to moderate level of resistance was noticed against temephos among the larval population based on WHO criteria.

CONCLUSION

The replacement of DDT by type II pyrethroids for the management of dengue vectors is an appropriate decision taken by the national program which is supported by the findings of a higher level of resistance to DDT. Persistence of polymorphisms in the VGSC gene might be an indication of emergence of resistance against pyrethroid insecticides that should be monitored at a regular interval. Attempts should be made to determine the effectiveness of other larvicides for replacement of temephos if needed in future. Along with the chemical insecticides different biological vector control methods as well as biopesticides should also be used in vector control programmes.