Analysis of the Knockdown Resistance Locus (kdr) in Anopheles stephensi, An. arabiensis, and Culex pipiens s.l. for Insight Into the Evolution of Target-site Pyrethroid Resistance in Eastern Ethiopia

The malaria vector, Anopheles stephensi, which is typically restricted to South Asia and the Middle East, was recently detected in the Horn of Africa. Addressing the spread of this vector could involve integrated vector control that considers the status of insecticide resistance of multiple vector species in the region. Previous reports indicate that the knockdown resistance mutations (kdr) in the voltage-gated sodium channel (vgsc) are absent in both pyrethroid-resistant and pyrethroid-sensitive An. stephensi in eastern Ethiopia; however, similar information about other vector species in the same areas is limited. In this study, kdr and the neighboring intron were analyzed in An. stephensi, An. arabiensis, and Culex pipiens s.l. collected between 2016 and 2017 to determine the evolutionary history of kdr in eastern Ethiopia. A sequence analysis revealed that all of Cx. pipiens s.l. (N = 42) and 71.6% of the An. arabiensis (N = 67) carried kdr L1014F, which is known to confer target-site pyrethroid resistance. Intronic variation was only observed in An. stephensi (six segregating sites, three haplotypes), which was previously shown to have no kdr mutations. In addition, no evidence of non-neutral evolutionary processes was detected at the An. stephensi kdr intron, thereby further supporting the target-site mechanism not being a major resistance mechanism in this An. stephensi population. Overall, these results show key differences in the evolution of target-site pyrethroid/dichlorodiphenyltrichloroethane resistance mutations in populations of vector species from the same region. Variations in insecticide resistance mechanism profiles between eastern Ethiopian mosquito vectors may lead to different responses to insecticides used in integrated vector control.

High incidence of Trypanosoma cruzi infections in dogs directly detected through longitudinal tracking at 10 multi-dog kennels, Texas, USA

Canine Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is increasingly recognized as a health concern for dogs in the USA, and infected dogs may signal geographic regions of risk for human disease. Dogs living in multi-dog kennel environments (kennels with more than one dog) where triatomine vectors are endemic may be at high risk for infection. We monitored a cohort of 64 T. cruzi-infected and uninfected dogs across 10 kennels in Texas, USA, to characterize changes in infection status over one year. We used robust diagnostic criteria in which reactivity on multiple independent platforms was required to be considered positive. Among the 30 dogs enrolled as serologically- and/or PCR-positive, all but one dog showed sustained positive T. cruzi diagnostic results over time. Among the 34 dogs enrolled as serologically- and PCR-negative, 10 new T. cruzi infections were recorded over a 12-month period. The resulting incidence rate for dogs initially enrolled as T. cruzi-negative was 30.7 T. cruzi infections per 100 dogs per year. This study highlights the risk of T. cruzi infection to dogs in kennel environments. To protect both dog and human health, there is an urgent need to develop more integrated vector control methods as well as prophylactic and curative antiparasitic treatment options for T. cruzi infection in dogs.

Development of an RNAi-based microalgal larvicide for the control of Aedes aegypti

Background Mosquito-borne diseases affect over half of the human population globally. Multiple studies have shown that chemical insecticides are ineffective because of resistance. Therefore, environmentally safe mosquito population control tools need to be developed. Ribonucleic acid interference (RNAi) is a reverse genetic mechanism recently introduced as a new pest control tool. This technique represents a new class of biorational technology that could combat the increased global incidence of insecticide resistance. The technique has the potential of becoming a critical component of integrated vector control programs. Methods A 3-hydroxykynurenine transaminase (3-HKT) RNAi expression plasmid was constructed, generated and transformed into Chlamydomonas and Chlorella algae. The transgenic algae were then used to feed Ae. aegypti mosquito larvae. The feeding experiments were conducted on a small and large scale with 10 and about 300 larvae, respectively. The mortality rate of the larvae was calculated over 30 days. In addition, histological examination of the insect tissues was performed to examine the extent of tissue damage. Results The integumentary system and midguts of larvae fed with transgenic Chlamydomonas were severely damaged. The mortality rate of the larvae fed with transgenic Chlamydomonas ranged from 60 to 100% in small-scale tests. The survival rate of adult mosquitoes was 0.0% in a large-scale feeding experiment when the larvae were fed with transgenic Chlamydomonas. Moreover, when the larvae were fed with transgenic Chlorella, the mortality rate ranged from 6.7% to 43% compared to that fed wild-type Chlorella. Conclusions 3HKT RNAi transgenic algae are in some scales lethal to Ae. aegypti. The findings of this study indicate that technology based on microalgae RNAi may provide a new way to control mosquito populations. Graphical Abstract

The Zika Virus

This chapter offers a contextual narrative to the Zika outbreak and justifies a pertinent case study for gender analysis in global health security. It contends that Zika was constructed as a security threat at multiple levels of analysis. This framing perpetuated an exclusion and problematization of women in global health security more broadly. The chapter argues that the key policies developed—integrated vector control, vaccine development and behavioural requests around reproduction, to paraphrase, ‘clean your houses and don’t get pregnant’—were inherently gendered given the activities required are socially prescribed women’s activities. It further argues that although the outbreak revolved around women, gender was not mainstreamed into any of the policies developed, and the securitised policies failed to protect those women most at risk from the disease.

High insecticide resistance mediated by different mechanisms in Culex quinquefasciatus populations from the city of Yaoundé, Cameroon

Culex mosquitoes particularly Culex quinquefasciatus are important arboviral and filariasis vectors, however despite this important epidemiological role, there is still a paucity of data on their bionomics. The present study was undertaken to assess the insecticide resistance status of Cx. quinquefasciatus populations from four districts of Yaoundé (Cameroon). All Culex quinquefasciatus populations except one displayed high resistance to bendiocarb and malathion with mortalities ranging from 0 to 89% while high resistance intensity against both permethrin and deltamethrin was recorded. Molecular analyses revealed high frequencies of the ACE-1 G119S mutation (ranging from 0 to 33%) and kdr L1014F allele (ranging from 55 to 74%) in all Cx. quinquefasciatus populations. Significant overexpression was detected for cytochrome P450s genes CYP6AA7 and CYP6Z10, as well as for Esterase A and Esterase B genes. The total cuticular hydrocarbon content, a proxy of cuticular resistance, was significantly increased (compared to the S-lab strain) in one population. The study confirms strong insecticide resistance mediated by different mechanisms in Cx. quinquefasciatus populations from the city of Yaoundé. The expansion of insecticide resistance in Culex populations could affect the effectiveness of current vector control measures and stress the need for the implementation of integrated vector control strategies in urban settings.

Malaria en route to elimination in two endemic coastal environments of southern India: an eco-epidemiological analysis from 2004 to 2019

Background Coastal environment and climatic condition are more suitable in propagation of mosquito vectors, and malaria parasite transmission throughout the year. In the present investigation, malaria prevalence in two endemic coastal localities of India viz., Besant Nagar (Chennai district) and Pamban (Rameshwaram district) were analysed from 2004 to 2019. Methods Malaria surveillance data and entomological data from malaria clinic were used to investigate epidemiological parameters. The annual malaria cases were correlated with highest maximum temperature. Results The analysis showed that the malaria case (P.v. and P.f.) report were directly proportional to the temperature increase. Malaria cases were remarkably increased from 2004 to 2011 and subsequently, both P.v. and P.f. cases were drastically reduced till 2019. P. vivax was higher than P. falciparum and male population was found to be more affected. Mixed infection of P.v. & P.f. was observed only in Besant Nagar site (0.3%). The most affected age group was adult age group (15 years and above) in both Besant Nagar (76.1%) and Pamban (69.5%). Conclusions Improved surveillance, complete treatment and integrated vector control activities showed declining trend of malaria cases in both the coastal sites towards malaria elimination.

Anopheles gambiae s.l. insecticide susceptibility status in Umudike, Ikwuano LGA, Abia State, Nigeria

This study was conducted in order to determine the insecticide susceptibility status of Anopheles gambiae in Umudike, Abia State, Nigeria. Larval and pupal stages of An. gambiae mosquitoes were collected from different points within Umudike, and reared to adult stage in the laboratory. The adults that emerged were tested on four types of WHO bioassay test papers impregnated with recommended diagnostic concentrations of 4% DDT (Organochlorines); 0.1% bendiocarb (Carbamates); 0.25% Primiphos-methyl (Organophosphates); and 0.05% Deltamethrin (Pyrethroids) procured from National Abovirus and Vector Research Institute Enugu. Twenty 10% sugar solution fed female Anopheles gambiae mosquitoes aged 3-5days were used for the bioassay which was replicated four times with two control of same population without insecticide treatment. Knockdown was recorded at five minutes post-exposure, and then at 10 minutes interval for 1 hour and then maintained for 24 hours post-exposure on 10% sugar solution, after which a final mortality was recorded. The Knockdown Times (KDT50 and KDT90) were determined by Probit analysis. An. gambiae was resistant to DDT, primiphos-methyl and Deltamethrin with 24 hours post exposure percentage mortalities of 4.65, 11.85, and 24.83 respectively.In contrary the mosquitoes were susceptible to bendiocarb which killed 98.88% of the mosquitoes 24 hours after exposure. Bendiocarb is hence recommended as the most effective insecticide for the control of Anopheles gambiae in Umudike, while there were need for the investigation of the mechanism behind the resistance displayed by this mosquito. Furthermore, routine surveillance of insecticide susceptibility/resistance in mosquito population is advocated in line with integrated vector control strategy. Keywords: Insecticide; susceptibility; Anopheles gambiae; Umudike; Abia State; Nigeria