Public Health Response to Aedes aegypti and Ae. albopictus Mosquitoes Invading California, USA

A validated triplex RT-qPCR protocol to simultaneously detect chikungunya, dengue and Zika viruses in mosquitoes

BACKGROUND & OBJECTIVES

Recently, the incidences of chikungunya, dengue and Zika infections have increased due to globalization and urbanization. It is vital that reliable detection tools become available to assess the viral prevalence within mosquito populations.

METHODS

Based on the previous publications on clinical diagnosis in human infections, for the first time, we described a customized triplex RT-qPCR protocol for simultaneous detection of chikungunya virus (CHIKV), dengue virus serotypes 1-4 (DENV1-4) and Zika virus (ZIKV) in mosquitoes.

RESULTS

In preliminary assessment to determine the specificity and sensitivity of primers and probes, all six targets were detected individually with the following thresholds as indicated by calculated pfu equivalents: 3.96x10⁰ for CHIKV, 3.80x10¹ for DENV1, 3.20x10¹ for DENV2, 8.00x10⁴ for DENV3, 1.58x10⁰ for DENV4, and 6.20x10⁰ for ZIKV When tested in a full combination of six targets (CDZ mix), CHIKV, DENV1-4 mix or ZIKV were all detected with the thresholds of 1.32x10⁰ for CHIKV, 3.79x10⁰ for DENV1-4 and 2.06x10⁰ for ZIKV All targets, individually or in full combination were detected in the mixtures of Aedes aegypti (L.) homogenate and viral lysates. A robust evaluation with three replicates in each of three plates for CHIKV, DENV1-4 and ZIKV individually or in full combination was conducted. In individual assays, CHIKV was detected to 3.96x10^-1, DENV1-4 to 1.14x10⁰ and ZIKV to 3.20x10⁰. In full combination assays, CHIKV was detected to 1.32x10⁴, DENV1-4 to 3.79x10¹ and ZIKV to 1.07x10⁰.

INTERPRETATION & CONCLUSION

This triplex RT-qPCR assay appears to consistently detect all six targets and does not cross react with Ae. aegypti homogenate, making it a feasible, practical, and immediately adoptable protocol for use among vector control and other entities, particularly in the endemic areas of CHIKV, DENVs and ZIKV.

Detection and Establishment of Aedes notoscriptus (Diptera: Culicidae) Mosquitoes in Southern California, United States

Aedes notoscriptus (Skuse), the Australian backyard mosquito, is a pestiferous daytime-biting species native to Australia and the surrounding southwestern Pacific region. It is suspected to play a role in the transmission of several arboviruses and is considered a competent vector of dog heartworm, Dirofilaria immitis (Leidy). This highly adaptable mosquito thrives in natural and artificial water-holding containers in both forested and urbanized areas, from tropical to temperate climates, and has benefitted from a close association with humans, increasing in abundance within its native range. It invaded and successfully established in New Zealand as well as in previously unoccupied temperate and arid regions of Australia. Ae. notoscriptus was discovered in Los Angeles County, CA, in 2014, marking the first time this species had been found outside the southwestern Pacific region. By the end of 2019, immature and adult mosquitoes had been collected from 364 unique locations within 44 cities spanning three southern California counties. The discovery, establishment, and rapid spread of this species in urban areas may signal the global movement and advent of a new invasive container-inhabiting species. The biting nuisance, public health, and veterinary health implications associated with the invasion of southern California by this mosquito are discussed.

Aedes aegypti in the Mediterranean container ports at the time of climate change: A time bomb on the mosquito vector map of Europe

In the past, Aedes aegypti was present in Southern Europe. Although the mosquito was eradicated from the Mediterranean region, its regional ecotype survived the second half of the 20th century in the eastern Black Sea area. The aim of the study was to model the changes in the altering climatic suitability, ontogenetic development time and the survival rate of Aedes aegypti from first-stage larvae to adulthood in Southern Europe. The modelled present climatic suitability patterns of the mosquito show that large areas of the lower altitude Mediterranean regions, including the coastal areas of the Balkan Peninsula, South France, and large regions of the Apennines and the Iberian Peninsulas could be suitable for Ae. aegypti. The future (2041-2060 and 2061-2080) projections predict the potential northward shift of the northern occurrence of the species in the circum-Mediterranean and Black Sea areas. Both, the potential development time, and survival rate of Ae. aegypti in the late 19th and the early 20th century could be like in the present times along the Mediterranean coast. The current climatic conditions cannot explain the absence of the mosquito in wide areas of the Mediterranean and sub-Mediterranean ecoregions. The future models predict the notable increase in the development time and survival rate of the mosquito in the southern and central regions of Europe. In general, the container ports of the Alboran, Balearic, and Aegean seas seem to be the most suitable sites for the re-colonization of the mosquito, and such northern parts of the Mediterranean Sea like the Gulf of Lion, the Ligurian, and Adriatic Seas are in less extent.

Establishment of the Invasive Aedes aegypti (Diptera: Culicidae) in the West Valley Area of San Bernardino County, CA

The yellow fever mosquito, Aedes aegypti (Linnaeus, 1762), is the most aggressive invasive mosquito species with worldwide distribution. In addition to being a notorious nuisance species, it can pose significant public health concern because of its ability to transmit various viral pathogens. The first adult capture in the West Valley area of San Bernardino County, CA, occurred in September 2015 in Montclair. A strategic surveillance plan was implemented accordingly by the West Valley Mosquito and Vector Control District to document the infestation. The Biogent Sentinel (BG-2) trap augmented with BG-Lure and carbon dioxide (CO2) was deployed as a routine surveillance tool during 2017-2019. Extensive trapping revealed an expanding infestation, when positive trap nights (TN) increased from 14.2% in 2017 to 23.9% in 2018 and 55.6% in 2019. The average counts/TN increased from 0.65 in 2017 and 0.90 in 2018 to 3.83 in 2019. The cities of Montclair, Chino, and Ontario had much higher infestation than other cities in the district with the highest positive TN of 46.0% in Montclair, and highest average trap count of 3.23/TN in Chino. It was interesting to note that males coincided with females with more profound trend during warmer months of July to October when ratios of males ranged 28.4-35.0%. The BG-2 trap significantly outperformed the CO2 trap and gravid trap. The establishment of this invasive species in semiarid inland Southern California was further confirmed by concurrent larval collections.

Wolbachia in mosquitoes from the Central Valley of California, USA

BACKGROUND

Wolbachia bacteria are widely distributed throughout terrestrial arthropod species. These bacteria can manipulate reproduction and influence the vector competence of their hosts. Recently, Wolbachia have been integrated into vector control programmes for mosquito management. A number of supergroups and strains exist for Wolbachia, and they have yet to be characterized for many mosquito species. In this study, we examined Wolbachia prevalence and their phylogenetic relationship to other Wolbachia, using mosquitoes collected in Merced County in the Central Valley of California.

METHODS

Adult mosquitoes were collected from 85 sites in Merced County, California in 2017 and 2018. Traditional and quantitative PCR were used to investigate the presence or absence and the density of Wolbachia, using Wolbachia-specific 16S rRNA and Wolbachia-surface protein (wsp) genes. The supergroup of Wolbachia was determined, and Multilocus Sequence Typing (MLST) by sequencing five housekeeping genes (coxA, gatB, ftsZ, hcpA and fbpA) was also used to determine Wolbachia supergroup as well as strain.

RESULTS

Over 7100 mosquitoes of 12 species were collected: Aedes melanimon, Ae. nigromaculis, Ae. vexans, Ae. aegypti, Culex pipiens, Cx. stigmatosoma, Cx. tarsalis, Anopheles franciscanus, An. freeborni, An. punctipennis, Culiseta incidens and Cs. inornata. Eight showed evidence of Wolbachia. To our knowledge, this study is the first to report detection of Wolbachia in five of these species (Ae. melanimon, Cx. stigmatosoma, Cx. tarsalis, Cs. incidens and Cs. inornata). Culex pipiens and Cx. stigmatosoma had a high frequency and density of Wolbachia infection, which grouped into supergroup B; Cs. inornata clustered with supergroup A. MLST comparisons identified Cx. pipiens and Cx. stigmatosoma as wPip strain type 9 supergroup B. Six species had moderate to low (< 14%) frequencies of Wolbachia. Four species were negative, Ae. nigromaculis, An. franciscanus, An. freeborni and Ae. aegypti.

CONCLUSIONS

New records of Wolbachia detection were found in mosquitoes from Merced County, California. Culex stigmatosoma and Cs. inornata were new records for Wolbachia supergroup B and A, respectively. Other species with Wolbachia occurred with low frequency and low density. Detection of Wolbachia in mosquitoes can be used to inform potential vector control applications. Future study of Wolbachia within Cx. stigmatosoma and Cs. inornata in California and through the range of these species could further explore Wolbachia infection in these two species.

A potential global surveillance tool for effective, low-cost sampling of invasive Aedes mosquito eggs from tyres using adhesive tape

BACKGROUND

The international movement of used tyres is a major factor responsible for global introductions of Aedes invasive mosquitoes (AIMs) (Diptera: Culicidae) that are major disease vectors (e.g. dengue, Zika, chikungunya and yellow fever). Surveillance methods are restricted by expense, availability and efficiency to detect all life stages. Currently, no tested method exists to screen imported used tyres for eggs in diapause, the life stage most at risk from accidental introduction. Here we test the efficiency of adhesive tape as an affordable and readily available material to screen tyres for eggs, testing its effect on hatch rate, larval development, DNA amplification and structural damage on the egg surface.

RESULTS

We demonstrated that the properties of adhesive tape can influence pick up of dormant eggs attached to dry surfaces. Tapes with high levels of adhesion, such as duct tape, removed eggs with high levels of efficiency (97% ± 3.14). Egg numbers collected from cleaned used tyres were found to explain larval hatch rate success well, particularly in subsequent larval to adult emergence experiments. The strength of this relationship decreased when we tested dirty tyres. Damage to the exochorion was observed following scanning electron microscopy (SEM), possibly resulting in the high variance in the observed model. We found that five days was the optimal time for eggs to remain on all tested tapes for maximum return on hatch rate success. Tape type did not inhibit amplification of DNA of eggs from three, five or ten days of exposure. Using this DNA, genotyping of AIMs was possible using species-specific markers.

CONCLUSIONS

We demonstrated for the first time that adhesive tapes are effective at removing AIM eggs from tyres. We propose that this method could be a standardised tool for surveillance to provide public health authorities and researchers with an additional method to screen tyre cargo. We provide a screening protocol for this purpose. This method has a global applicability and in turn can lead to increased predictability of introductions and improve screening methods at high risk entry points.

Identification of Molecular Determinants of Resistance to Pyrethroid Insecticides in Aedes aegypti (Diptera: Culicidae) Populations in California, USA

The first breeding populations of Aedes aegypti (Linnaeus) were identified in California in 2013, and have since been detected in 13 counties. Recent studies suggest two introductions likely occurred, with genetically distinct populations in the central and southern regions of the state. Given the threat of dengue, chikungunya, and Zika virus transmission, it is imperative to understand if these populations harbor genes that could confer resistance to pyrethrin-based insecticides, known as pyrethroids, the most commonly used class of adulticides in the state. In 2017, the California Department of Public Health initiated a pesticide resistance screening program for Ae. aegypti to assess the presence of specific mutations on the sodium channel gene (V1016I and F1534C) associated with knockdown resistance to pyrethroids. Mosquitoes collected between 2015 and 2017 from 11 counties were screened for mutations using real-time polymerase chain reaction assays. Results revealed distinctly different resistance profiles between the central and southern regions. The central population displayed nearly fixed resistant mutations at both loci, whereas the southern population was more variable. The relative proportion of resistant alleles observed in sampled mosquitoes collected in southern California increased each year from 2015 through 2017, indicating potential increases in resistance across this region. The presence of these mutations indicates that these mosquitoes may be predisposed to surviving pyrethroid treatments. Additional biological and biochemical assays will help better elucidate the mechanisms underlying insecticide resistance in California Ae. aegypti and prompt the use of pesticides that are most effective at controlling these mosquitoes.

Aedes aegypti Males as Vehicles for Insecticide Delivery

Aedes aegypti continues to spread globally and remains a challenge to control, in part due to its ‘cryptic behavior’ in that it often deposits eggs (oviposits) in larval habitats that are difficult to find and treat using traditional methods. Auto-dissemination strategies target these cryptic breeding sites by employing mosquitoes to deliver lethal doses of insecticide. This report describes the initial field trials of an application known as Autodissemination Augmented by Males (ADAM), utilizing A. aegypti males dusted with pyriproxyfen (PPF). Findings presented here are drawn from both caged and field trial studies. Together, these trials examined for the ability of A. aegypti males to disseminate PPF and to impact field populations. PPF-dusted males were able to effectively deliver lethal doses of PPF to oviposition sites under the conditions tested. Results from field trials in Florida and California demonstrated reduced A. aegypti populations in treated areas, compared to areas where PPF-treated males were not released. These results indicate that the release of PPF-dusted A. aegypti males can impact A. aegypti populations as measured by both reduced larval survival and lower numbers of adult female A. aegypti. We propose the ADAM approach as an addition to existing mosquito control techniques targeting A. aegypti and other mosquitoes that utilize cryptic larval habitats.

Susceptibility Profile of Aedes aegypti L. (Diptera: Culicidae) from Montclair, California, to Commonly Used Pesticides, With Note on Resistance to Pyriproxyfen

The peridomestic anthropophilic Aedes aegypti L. (Diptera: Culicidae) is originated from the wild zoophilic subspecies Aedes aegypti formosus in sub-Saharan Africa, and currently has a broad distribution in human-modified environments of the tropics and subtropics worldwide. In California, breeding populations were initially detected in 2013 in the cities of Fresno, Madera, and San Mateo, and now can be found in 188 cities of 12 counties in the state. Recent genetic studies suggest that this species invaded California on multiple occasions from several regions of the United States and northern Mexico prior to initial detection. As an invasive species and vector for numerous arboviruses, Ae. aegypti is a primary target of surveillance and control in California. In southern California city of Montclair, a population was identified in September 2015, from which a short-term colony was established in an insectary. The susceptibility of this field population to commonly used pesticides with various modes of action, including 15 formulations against larvae and four against adults, was determined, in reference to a susceptible laboratory colony of the same species. No resistance was shown to most pesticides tested. However, tolerance or reduced susceptibility to spinosad, spinetoram, diflubezuron, and fipronil was detected, and modest levels of resistance to pyriproxyfen (resistance ratio = 38.7-fold at IE50 and 81.5-fold at IE90) was observed. Results are discussed based on the field usage and modes of action of the pesticides tested. Strategic selection and application of pesticides against this population of Ae. aegypti in the urban environments should be taken into consideration.

Travel-Associated Zika Cases and Threat of Local Transmission during Global Outbreak, California, USA

Zika and associated microcephaly among newborns were reported in Brazil during 2015. Zika has since spread across the Americas, and travel-associated cases were reported throughout the United States. We reviewed travel-associated Zika cases in California to assess the potential threat of local Zika virus transmission, given the regional spread of Aedes aegypti and Ae. albopictus mosquitoes. During November 2015-September 2017, a total of 588 travel-associated Zika cases were reported in California, including 139 infections in pregnant women, 10 congenital infections, and 8 sexually transmitted infections. Most case-patients reported travel to Mexico and Central America, and many returned during a period when they could have been viremic. By September 2017, Ae. aegypti mosquitoes had spread to 124 locations in California, and Ae. albopictus mosquitoes had spread to 53 locations. Continued human and mosquito surveillance and public health education are valuable tools in preventing and detecting Zika virus infections and local transmission in California.

Mother-to-child transmission of Chikungunya virus: A systematic review and meta-analysis

BACKGROUND

Chikungunya virus (CHIKV) is an emerging arboviral infection with a global distribution and may cause fetal and neonatal infections after maternal CHIKV-infections during gestation.

METHODOLOGY

We performed a systematic review to evaluate the risk for: a) mother-to-child transmission (MTCT), b) antepartum fetal deaths (APFD), c) symptomatic neonatal disease, and d) neonatal deaths from maternal CHIKV-infections during gestation. We also recorded the neonatal clinical manifestations after such maternal infections (qualitative data synthesis). We searched PubMed (last search 3/2017) for articles, of any study design, with any of the above outcomes. We calculated the overall risk of MTCT, APFDs and risk of symptomatic neonatal disease by simple pooling. For endpoints with ≥5 events in more than one study, we also synthesized the data by random-effect-model (REM) meta-analysis.

PRINCIPAL FINDINGS

Among 563 identified articles, 13 articles from 8 cohorts were included in the quantitative data synthesis and 33 articles in the qualitative data synthesis. Most cohorts reported data only on symptomatic rather than on all neonatal infections. By extrapolation also of these data, the overall pooled-MTCT-risk across cohorts was at least 15.5% (206/1331), (12.6% by REMs). The pooled APFD-risk was 1.7% (20/1203); while the risk of CHIKV-confirmed-APFDs was 0.3% (3/1203). Overall, the pooled-risk of symptomatic neonatal disease was 15.3% (203/1331), (11.9% by REMs). The pooled risk of symptomatic disease was 50.0% (23/46) among intrapartum vs 0% (0/712) among antepartum/peripartum maternal infections. Infected newborns, from maternal infections during gestation were either asymptomatic or presented within their first week of life, but not at birth, with fever, irritability, hyperalgesia, diffuse limb edema, rashes and occasionally sepsis-like illness and meningoencephalitis. The pooled-risk of neonatal death was 0.6% (5/832) among maternal infections and 2.8% (5/182) among neonatal infections; long-term neurodevelopmental delays occurred in 50% of symptomatic neonatal infections.

CONCLUSIONS/SIGNIFICANCE

Published cohorts with data on the risk to the fetus and/or newborn from maternal CHIKV-infections during gestation were sparse compared to the number of recently reported CHIKV-infection outbreaks worldwide; however perinatal infections do occur, at high rates during intrapartum period, and can be related to neonatal death and long-term disabilities.

Driving towards ecotechnologies

The prospect of using genetic methods to target vector, parasite, and reservoir species offers tremendous potential benefits to public health, but the use of genome editing to alter the shared environment will require special attention to public perception and community governance in order to benefit the world. Public skepticism combined with the media scrutiny of gene drive systems could easily derail unpopular projects entirely, especially given the potential for trade barriers to be raised against countries that employ self-propagating gene drives. Hence, open and community-guided development of thoughtfully chosen applications is not only the most ethical approach, but also the most likely to overcome the economic, social, and diplomatic barriers. Here we review current and past attempts to alter ecosystems using biological methods, identify key determinants of social acceptance, and chart a stepwise path for developers towards safe and widely supported use.

Modeling the Environmental Suitability for Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae) in the Contiguous United States

The mosquitoes Aedes (Stegomyia) aegypti (L.)(Diptera:Culicidae) and Ae. (Stegomyia) albopictus (Skuse) (Diptera:Culicidae) transmit dengue, chikungunya, and Zika viruses and represent a growing public health threat in parts of the United States where they are established. To complement existing mosquito presence records based on discontinuous, non-systematic surveillance efforts, we developed county-scale environmental suitability maps for both species using maximum entropy modeling to fit climatic variables to county presence records from 1960-2016 in the contiguous United States. The predictive models for Ae. aegypti and Ae. albopictus had an overall accuracy of 0.84 and 0.85, respectively. Cumulative growing degree days (GDDs) during the winter months, an indicator of overall warmth, was the most important predictive variable for both species and was positively associated with environmental suitability. The number (percentage) of counties classified as environmentally suitable, based on models with 90 or 99% sensitivity, ranged from 1,443 (46%) to 2,209 (71%) for Ae. aegypti and from 1,726 (55%) to 2,329 (75%) for Ae. albopictus. Increasing model sensitivity results in more counties classified as suitable, at least for summer survival, from which there are no mosquito records. We anticipate that Ae. aegypti and Ae. albopictus will be found more commonly in counties classified as suitable based on the lower 90% sensitivity threshold compared with the higher 99% threshold. Counties predicted suitable with 90% sensitivity should therefore be a top priority for expanded mosquito surveillance efforts while still keeping in mind that Ae. aegypti and Ae. albopictus may be introduced, via accidental transport of eggs or immatures, and potentially proliferate during the warmest part of the year anywhere within the geographic areas delineated by the 99% sensitivity model.

Detection and Establishment of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) Mosquitoes in California, 2011-2015

In 2011, a thriving population of Aedes albopictus (Skuse), the Asian tiger mosquito, was discovered within three cities in Los Angeles County over an estimated 52-km2 urban area. Two years later in 2013, Aedes aegypti (L.), the yellow fever mosquito, was detected within several urban areas of Madera, Fresno, and San Mateo counties. State and local vector control agencies responded with an aggressive effort to eradicate or interrupt the spread of these two invasive mosquitoes; however, known populations continued to expand outward and new infestations were identified at an accelerated pace in central and southern California. By the end of 2015, one or both species had been detected within the jurisdictional boundaries of 85 cities and census-designated places in 12 counties. Herein we report on the discovery and widespread establishment of Ae. aegypti and Ae. albopictus in urban areas of coastal, central, and southern California between 2011 and 2015 and discuss the subsequent rapid changes to the activities and priorities of vector control agencies in response to this unprecedented invasion.

Reported Distribution of Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus in the United States, 1995-2016 (Diptera: Culicidae)

Aedes (Stegomyia) aegypti (L.) and Aedes (Stegomyia) albopictus (Skuse) transmit arboviruses that are increasing threats to human health in the Americas, particularly dengue, chikungunya, and Zika viruses. Epidemics of the associated arboviral diseases have been limited to South and Central America, Mexico, and the Caribbean in the Western Hemisphere, with only minor localized outbreaks in the United States. Nevertheless, accurate and up-to-date information for the geographical ranges of Ae. aegypti and Ae. albopictus in the United States is urgently needed to guide surveillance and enhance control capacity for these mosquitoes. We compiled county records for presence of Ae. aegypti and Ae. albopictus in the United States from 1995-2016, presented here in map format. Records were derived from the Centers for Disease Control and Prevention ArboNET database, VectorMap, the published literature, and a survey of mosquito control agencies, university researchers, and state and local health departments. Between January 1995 and March 2016, 183 counties from 26 states and the District of Columbia reported occurrence of Ae. aegypti, and 1,241 counties from 40 states and the District of Columbia reported occurrence of Ae. albopictus. During the same time period, Ae. aegypti was collected in 3 or more years from 94 counties from 14 states and the District of Columbia, and Ae. albopictus was collected during 3 or more years from 514 counties in 34 states and the District of Columbia. Our findings underscore the need for systematic surveillance of Ae. aegypti and Ae. albopictus in the United States and delineate areas with risk for the transmission of these introduced arboviruses.

Zika in the United States of America and a Fateful 1969 Decision

The United States Gulf Coast's current risk to Zika transmitted by Aedes aegypti mosquitoes can be traced back to some important federal health policy decisions made during the 1960s.

Zika Virus Disease: A CDC Update for Pediatric Health Care Providers

Zika virus is a mosquito-borne flavivirus discovered in Africa in 1947. Most persons with Zika virus infection are asymptomatic; symptoms when present are generally mild and include fever, maculopapular rash, arthralgia, and conjunctivitis. Since early 2015, Zika virus has spread rapidly through the Americas, with local transmission identified in 31 countries and territories as of February 29, 2016, including several US territories. All age groups are susceptible to Zika virus infection, including children. Maternal-fetal transmission of Zika virus has been documented; evidence suggests that congenital Zika virus infection is associated with microcephaly and other adverse pregnancy and infant outcomes. Perinatal transmission has been reported in 2 cases; 1 was asymptomatic, and the other had thrombocytopenia and a rash. Based on limited information, Zika virus infection in children is mild, similar to that in adults. The long-term sequelae of congenital, perinatal, and pediatric Zika virus infection are largely unknown. No vaccine to prevent Zika virus infection is available, and treatment is supportive. The primary means of preventing Zika virus infection is prevention of mosquito bites in areas with local Zika virus transmission. Given the possibility of limited local transmission of Zika virus in the continental United States and frequent travel from affected countries to the United States, US pediatric health care providers need to be familiar with Zika virus infection. This article reviews the Zika virus, its epidemiologic characteristics, clinical presentation, laboratory testing, treatment, and prevention to assist providers in the evaluation and management of children with possible Zika virus infection.