A Review of the Control of Aedes aegypti (Diptera: Culicidae) in the Continental United States.

Aedes aegypti (L) is an anthropophilic mosquito involved in the transmission of a variety of viral pathogens worldwide including dengue, chikungunya, yellow fever, and Zika viruses. This species, native to Africa, is well established in the continental U.S. (CONUS) and occasionally contributes to localized outbreaks of viral diseases. In the last seven decades, mosquito control programs in the CONUS have been focused on vectors of eastern equine encephalitis, St. Louis encephalitis, and West Nile viruses, as well as nuisance species. Aedes aegypti receives little control focus except during outbreak periods, which has led to a lack of information on appropriate and effective control options targeting Ae. aegypti in the CONUS. As such, in the event of an Ae. aegypti-borne arboviral outbreak in the CONUS, there are limited evidence-based control recommendations or protocols in place. Autochthonous outbreaks of Ae. aegypti-borne pathogens have occurred recently in the CONUS, including dengue outbreaks in 2010 and 2013, a chikungunya outbreak in 2014, and the 2016 outbreak of Zika virus. The increasing frequency of Ae. aegypti-borne outbreaks necessitates increased attention and research on control of this species to prevent and mitigate future outbreaks. This review consolidates and synthesizes the available literature on control of Ae. aegypti, specifically within the CONUS, focusing on data generated through operational applications as well as field and semifield experiments. The purpose of this review is to identify and highlight areas where additional research is needed. The review covers chemical control and insecticide resistance, biological control, source reduction, trapping, and alternative techniques.

Culex interfor and Culex saltanensis (Diptera: Culicidae) are susceptible and competent to transmit St. Louis encephalitis virus (Flavivirus: Flaviviridae) in central Argentina.

BACKGROUND: St. Louis encephalitis virus (SLEV) is endemic and autochthonous on the American continent. Culex pipiens quinquefasciatus is a vector of SLEV; however, Culex interfor and Culex saltanensis have also been found to be naturally infected with SLEV. The aim of this study was to determine the vector competence of C. interfor and C. saltanensis for SLEV from Argentina compared with C. p. quinquefasciatus. METHODS: Female of the Culex species were orally infected by feeding on viraemic chicks that had been inoculated with SLEV. Abdomens, legs and saliva blood-fed mosquitoes were analysed by viral plaque assay. RESULTS: Mosquitoes were susceptible to orally acquired infection, dissemination and transmission of SLEV in the saliva. CONCLUSIONS: Our results demonstrate that C. saltanensis and C. interfor are susceptible to SLEV and competent for its transmission.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit.

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Silent Circulation of the Saint Louis Encephalitis Virus among Humans and Equids, Southeast Brazil.

Saint Louis encephalitis virus (SLEV) is a mosquito-borne flavivirus that occurs throughout the Americas, and is considered a public health threat. In Brazil, SLEV has been detected from human cases associated with dengue-like disease, but no neurological symptoms were reported. Furthermore, the epidemiology of SLEV in human populations is still poorly explored in the country. We reported serological and molecular detection of SLEV in a healthy population of equids and humans from rural areas in Southeast Brazil. A plaque reduction neutralization test was applied, and neutralizing antibodies were detected in 11 individuals (4.6%) and 60 horses (21.5%). A qPCR targeting the 5'UTR region and reverse transcription-PCR (RT-PCR) targeting the non-structural protein (NS5) gene were performed and three individuals tested positive in both assays. Subsequent phylogenetic analysis confirmed SLEV circulation and its findings suggest the occurrence of an asymptomatic or subclinical presence in human and animal cases, correlating with the risks for outbreaks and consequently burden of SLEV infections to public health. Preventive strategies should include improved surveillance in regions with a high probability of SLEV occurrence, improvement in diagnostic methods, and evaluation of exposure/risk factors that can favor SLEV emergence.

Vector Competence for West Nile Virus and St. Louis Encephalitis Virus (Flavivirus) of Three Tick Species of the Genus Amblyomma (Acari: Ixodidae).

Many species of Amblyomma ticks are commonly found infesting wild birds in South America, where birds are important hosts for several arboviruses, such as West Nile virus (WNV) and St. Louis encephalitis virus (SLEV). In this study, WNV and SLEV transmission experiments were performed to evaluate the vector competence of three South American tick species: Amblyomma ovale, Amblyomma tigrinum, and Amblyomma tonelliae. Larval and nymphal ticks of each species were allowed to feed on chicks needle inoculated with WNV or SLEV. All three Amblyomma species acquired either WNV or SLEV through larval feeding, with infection rates varying from 3.1% to 100% for WNV and from 0% to 35.7% for SLEV in engorged larvae. Transstadial perpetuation of the viruses was demonstrated in the molted nymphs, with WNV infection rates varying from 0% to 33.7% and SLEV infection rates from 13.6% to 23.8%. Although nymphal ticks also acquired either virus through feeding, transstadial perpetuation to adult ticks was lower, with virus detection in only 3.2% of A. tigrinum and 11.5% of A. tonelliae unfed adult ticks. On the other hand, vector competence for nymphs (exposed to WNV or SLEV through larval feeding) and adult ticks (exposed to WNV or SLEV through larval or nymphal feeding) was null in all cases. Although our results indicate transstadial perpetuation of WNV or SLEV in the three tick species, the ticks were not competent to transmit these agents to susceptible hosts. The role of these ixodid tick species in the epidemiology of WNV and SLEV might be insignificant, even though at least A. ovale and A. tigrinum are frequent bird ticks in Latin America, so the virus could survive winter in the fed larvae. However, future studies are required to determine the implications that this could have, as well as analyze the vector competence of other common bird tick species in South America.

Reemergence of St. Louis Encephalitis Virus in the Americas.

We summarize and analyze historical and current data regarding the reemergence of St. Louis encephalitis virus (SLEV; genus Flavivirus) in the Americas. Historically, SLEV caused encephalitis outbreaks in the United States; however, it was not considered a public health concern in the rest of the Americas. After the introduction of West Nile virus in 1999, activity of SLEV decreased considerably in the United States. During 2014-2015, SLEV caused a human outbreak in Arizona and caused isolated human cases in California in 2016 and 2017. Phylogenetic analyses indicate that the emerging SLEV in the western United States is related to the epidemic strains isolated during a human encephalitis outbreak in Córdoba, Argentina, in 2005. Ecoepidemiologic studies suggest that the emergence of SLEV in Argentina was caused by the introduction of a more pathogenic strain and increasing populations of the eared dove (amplifying host).

St. Louis Encephalitis Virus Disease in the United States, 2003-2017.

St. Louis encephalitis virus (SLEV), an arthropod-borne flavivirus, can cause disease presentations ranging from mild febrile illness through severe encephalitis. We reviewed U.S. national SLEV surveillance data for 2003 through 2017, including human disease cases and nonhuman infections. Over the 15-year period, 198 counties from 33 states and the District of Columbia reported SLEV activity; 94 (47%) of those counties reported SLEV activity only in nonhuman species. A total of 193 human cases of SLEV disease were reported, including 148 cases of neuroinvasive disease. A median of 10 cases were reported per year. The national average annual incidence of reported neuroinvasive disease cases was 0.03 per million. States with the highest average annual incidence of reported neuroinvasive disease cases were Arkansas, Arizona, and Mississippi. No large outbreaks occurred during the reporting period. The most commonly reported clinical syndromes were encephalitis (N = 116, 60%), febrile illness (N = 35, 18%), and meningitis (N = 25, 13%). Median age of cases was 57 years (range 2-89 years). The case fatality rate was 6% (11/193) and all deaths were among patients aged > 45 years with neuroinvasive disease. Nonhuman surveillance data indicated wider SLEV activity in California, Nevada, and Florida than the human data alone suggested. Prevention depends on community efforts to reduce mosquito populations and personal protective measures to decrease exposure to mosquitoes.

Evaluation of Argentinean Bird Species as Amplifying Hosts for St. Louis Encephalitis Virus (Flavivirus, Flaviviridae).

St.Louis encephalitis virus (SLEV) is an emerging human pathogen flavivirus in Argentina. Recently, it has reemerged in the United States. We evaluated the role as amplifying host of six resident bird species and analyzed their capacity as host during the 2005 encephalitis outbreak of SLEV in Córdoba. Eared Dove, Picui Ground Dove, and House Sparrow were the three species with highest host competence index. At a city level, Eared Dove and Picui Ground Dove were the most important amplifying hosts during the 2005 SLEV human outbreak in Córdoba city. This finding highlighted important differences in the SLEV ecology between Argentina and the United States. Characterizing and evaluating the SLEV hosts contribute to our knowledge about its ecology and could help us to understand the causes that promote its emergence as a human pathogen in South America.

St. Louis encephalitis virus possibly transmitted through blood transfusion-Arizona, 2015.

BACKGROUND: St. Louis encephalitis virus is a mosquito-borne flavivirus that infrequently causes epidemic central nervous system infections. In the United States, blood donors are not screened for St. Louis encephalitis virus infection, and transmission through blood transfusion has not been reported. During September 2015, St. Louis encephalitis virus infection was confirmed in an Arizona kidney transplant recipient. An investigation was initiated to determine the infection source. STUDY DESIGN AND METHODS: The patient was interviewed, and medical records were reviewed. To determine the likelihood of mosquito-borne infection, mosquito surveillance data collected at patient and blood donor residences in timeframes consistent with their possible exposure periods were reviewed. To investigate other routes of exposure, organ and blood donor and recipient specimens were obtained and tested for evidence of St. Louis encephalitis virus infection. RESULTS: The patient presented with symptoms of central nervous system infection. Recent St. Louis encephalitis virus infection was serologically confirmed. The organ donor and three other organ recipients showed no laboratory or clinical evidence of St. Louis encephalitis virus infection. Among four donors of blood products received by the patient via transfusion, one donor had a serologically confirmed, recent St. Louis encephalitis virus infection. Exposure to an infected mosquito was unlikely based on the patient's minimal outdoor exposure. In addition, no St. Louis encephalitis virus-infected mosquito pools were identified around the patient's residence. CONCLUSION: This investigation provides evidence of the first reported possible case of St. Louis encephalitis virus transmission through blood product transfusion. Health care providers and public health professionals should maintain heightened awareness for St. Louis encephalitis virus transmission through blood transfusion in settings where outbreaks are identified.

Acute larvicidal toxicity of five essential oils (Pinus nigra, Hyssopus officinalis, Satureja montana, Aloysia citrodora and Pelargonium graveolens) against the filariasis vector Culex quinquefasciatus: Synergistic and antagonistic effects.

Mosquito vector control is facing a number of important and timely challenges, mainly due to the rapid development of pesticide resistance and environmental concerns. In this scenario, screening of botanical resources for their mosquitocidal activity may offer effective and eco-friendly tools against Culicidae vectors. Culex quinquefasciatus Say (Diptera: Culicidae) is a vector of lymphatic filariasis and of dangerous arboviral diseases, such as West Nile and St. Louis encephalitis. In this study, the chemical composition of five essential oils obtained from different plants, namely Pinus nigra J.F. Arnold var. italica (Pinaceae), Hyssopus officinalis L. subsp. aristatus (Lamiaceae), Satureja montana L. subsp. montana (Lamiaceae), Aloysia citriodora Palau (Verbenaceae) and Pelargonium graveolens L'Hér (Geraniaceae), was investigated by GC-MS analysis. Furthermore, it was evaluated their acute toxicity on larvae of C. quinquefasciatus. Then, the most effective oils were selected, in order to focus on the potential synergistic and antagonistic effects, testing them in binary mixtures on C. quinquefasciatus larvae. Results showed that the higher effectiveness was obtained by S. montana subsp. montana essential oil (LC50=25.6µL·L-1), followed by P. nigra var. italica (LC50=49.8µL·L-1) and A. citriodora (LC50=65.6µL·L-1), while the other essential oils showed LC50 values higher than 90µL·L-1. The larvicidal effectiveness can be enhanced by preparing simple binary mixtures of essential oils, such as S. montana+A. citriodora (ratio 1:1), which showed higher larvicidal toxicity (LC50=18.3µL·L-1). On the other hand, testing S. montana+P. nigra (1:1) an antagonistic effect was detected, leading to a LC50 (72.5µL·L-1) higher than the LC50 values calculated for the two oils tested separately. Overall, our results add useful knowledge to allow the employ of synergistic essential oil blends as effective, cheap and eco-friendly mosquito larvicides.

Reemergence of St. Louis Encephalitis Virus, California, 2015.

St. Louis encephalitis virus infection was detected in summer 2015 in southern California after an 11-year absence, concomitant with an Arizona outbreak. Sequence comparisons showed close identity of California and Arizona isolates with 2005 Argentine isolates, suggesting introduction from South America and underscoring the value of continued arbovirus surveillance.

Multiplex qRT-PCR for the Detection of Western Equine Encephalomyelitis, St. Louis Encephalitis, and West Nile Viral RNA in Mosquito Pools (Diptera: Culicidae).

Following the introduction of West Nile virus into California during the summer of 2003, public health and vector control programs expanded surveillance efforts and were in need of diagnostics capable of rapid, sensitive, and specific detection of arbovirus infections of mosquitoes to inform decision support for intervention. Development of a multiplex TaqMan or real-time semiquantitative reverse transcription polymerase chain reaction (RT-PCR) assay in which three virus specific primer-probe sets were used in the same reaction is described herein for the detection of western equine encephalomyelitis, St. Louis encephalitis and West Nile viral RNA. Laboratory validation and field data from 10 transmission seasons are reported. The comparative sensitivity and specificity of this multiplex assay to singleplex RT-PCR as well as an antigen detection (rapid analyte measurement platform) and standard plaque assays indicate this assay to be rapid and useful in providing mosquito infection data to estimate outbreak risk.

St. Louis Encephalitis virus mosquito vectors dynamics in three different environments in relation to remotely sensed environmental conditions.

In Argentina the St. Louis Encephalitis virus (SLEV) is an endemic and widely distributed pathogen transmitted by the cosmopolitan mosquito Culex quinquefasciatus. During two outbreaks in Córdoba city, in 2005 and 2010, Culex interfor was also found infected, but its role as vector of SLEV is poorly known. This mosquito species is distributed from central Argentina to southern Brazil. The primary aim of this study was to analyze the population dynamic of Cx. interfor and Cx. quinquefasciatus in three different environments (urban, suburban and non-urban) in relation to remotely sensed environmental data for vegetation (NDVI and NDWI) and temperature (brightness temperature). Cx. quinquefasciatus and Cx. interfor were found at the three sampled sites, being both the most abundant Culex species, with peaks in early and midsummer. Temporal distribution patterns of both mosquito species were highly correlated in a non-urban area of high SLEV risk transmission. Cx. quinquefasciatus and Cx. interfor were associated with the most urbanized site and the non-urban environment, respectively; high significant correlations were detected between vegetation indices and abundance of both mosquito species confirming these associations. These data provide a foundation for building density maps of these two SLEV mosquito vectors using remotely sensed data to help inform vector control programs.

Detección molecular de virus de encefalitis de Saint Louis en mosquitos de Buenos Aires, Argentina

Durante el mes de marzo de 2013 una población de palomas torcazas (Zenaida auriculata) se instaló en una zona céntrica de la ciudad de Buenos Aires. Conociendo el rol que poseen estas aves como hospedadores competentes del virus de la encefalitis de Saint Louis (SLEV), fue colocada en el lugar una trampa de luz tipo CDC, a fin de realizar una vigilancia entomológica. Durante ese mes,fueron capturados 5 grupos de mosquitos (n = 48), 3 correspondieron a la especie Culex pipiens (n = 10) y 2 a Culex spp.(n = 38), no pudiéndose determinar en estos últimos con precisión la especie por encontrarse dañados. En un grupo de mosquitos Culex spp. se detectó el SLEV por técnicas moleculares. Posteriormente fue secuenciado y clasificado como perteneciente al genotipo III.

During March 2013 a population of eared doves (Zenaida auriculata) was established in the center of City of Buenos Aires. Considering the role of these birds as host competent for Saint Louis encephalitis virus (SLEV), a CDC light trap was put in place to perform entomologic surveillance. During this month 5 pools of mosquitoes (n = 48) were collected and taxonomically determined. Three of them were classified as Culex pipiens (n = 10) and the other two were Culex spp. (n = 38). In this case, the mosquitoes species could not be determined due to that individuals were damaged. One of the Culex spp. pool was found to be positive for Saint Louis encephalitis virus by molecular techniques. This was then sequenced and classified as genotype III.

[Molecular detection of Saint Louis encephalitis virus in mosquitoes in Buenos Aires]. / Detección molecular de virus de encefalitis de Saint Louis en mosquitos de Buenos Aires, Argentina.

During March 2013 a population of eared doves (Zenaida auriculata) was established in the center of City of Buenos Aires. Considering the role of these birds as host competent for Saint Louis encephalitis virus (SLEV), a CDC light trap was put in place to perform entomologic surveillance. During this month 5 pools of mosquitoes (n = 48) were collected and taxonomically determined. Three of them were classified as Culex pipiens (n = 10) and the other two were Culex spp. (n = 38). In this case, the mosquitoes species could not be determined due to that individuals were damaged. One of the Culex spp. pool was found to be positive for Saint Louis encephalitis virus by molecular techniques. This was then sequenced and classified as genotype III.

Nesting bird "host funnel" increases mosquito-bird contact rate.

Increases in vector-host contact rates can enhance arbovirus transmission intensity. We investigated weekly fluctuations in contact rates between mosquitoes and nesting birds using the recently described Nest Mosquito Trap (NMT). The number of mosquitoes per nestling increased from < 1 mosquito per trap night to 36.2 in the final 2 wk of the nesting season. Our evidence suggests the coincidence of the end of the avian nesting season and increasing mosquito abundances may have caused a "host funnel," concentrating host-seeking mosquitoes to the few remaining nestlings. The relative abundance of mosquitoes collected by the NMT suggests that significantly more Aedes albopictus (Skuse) and Culex pipiens (L.) /restuans (Theobald) sought nesting bird bloodmeals than were predicted by their relative abundances in CO2-baited Centers for Disease Control and Prevention light and gravid traps. Culex salinarius (Coquillett) and Culex erraticus Dyar and Knab were collected in NMTs in proportion to their relative abundances in the generic traps. Temporal host funnels and nesting bird host specificity may enhance arbovirus amplification and explain observed West Nile virus and St. Louis encephalitis virus amplification periods.

Transmission of endemic St Louis encephalitis virus strains by local Culex quinquefasciatus populations in Cordoba, Argentina.

BACKGROUND: St Louis encephalitis virus (SLEV) is a re-emerging human pathogen widely distributed in the American continent. Although it is not fully understood, the SLEV transmission network may involve Culex quinquefasciatus mosquitoes as vectors and Columbidae species as hosts. METHODS: To calculate infection rates, we inoculated Cx. quinquefasciatus mosquitoes from Córdoba, Argentina by feeding them on viremic chicks. RESULTS: We observed differences in infection rate among the viral strains, the highest rate (78/87 mosquitoes, 90.8%) being seen in strain 78V-6507. After re-feeding on susceptible chicks, mosquitoes were able to transmit the virus. CONCLUSION: Our findings suggest that Cx. quinquefasciatus populations are susceptible to and able to transmit different SLEV strains.