Next generation sequencing improves the resolution of detecting mixed host blood meal sources in field collected arboviral mosquito vectors

Accurate knowledge of blood meal hosts of different mosquito species is critical for identifying potential vectors and establishing the risk of pathogen transmission. We compared the performance of Miseq next generation sequencing approach relative to conventional Sanger sequencing approach in identification of mosquito blood meals using genetic markers targeting the 12S rRNA and cytochrome oxidase I (COI) genes. We analysed the blood meals of three mosquito vector species (Aedes aegypti, Aedes simpsoni s.l. and Culex pipiens s.l.) collected outdoors, and compared the frequency of single- versus multiple-blood feeding. Single host blood meals were mostly recovered for Sanger-based sequencing of the mitochondrial 12S rRNA gene, whereas Miseq sequencing employing this marker and the COI marker detected both single and multiple blood meal hosts in individual mosquitoes. Multiple blood meals (two or more hosts) which mostly included humans were detected in 19%-22.7% of Ae. aegypti samples. Most single host blood meals for this mosquito species were from humans (47.7%-57.1%) and dogs (9.1%-19.0%), with livestock, reptile and rodent hosts collectively accounting for 4.7%-28.9% of single host blood meals. The frequency of two or more host blood meals in Ae. simpsoni s.l. was 26.3%-45.5% mostly including humans, while single host blood meals were predominantly from humans (31.8%-47.4%) with representation of rodent, reptile and livestock blood meals (18.2%-68.2%). Single host blood meals from Cx. pipiens s.l. were mostly from humans (27.0%-39.4%) and cows (11.5%-27.36%). Multiple blood meal hosts that mostly included humans occurred in 21.2%-24.4% of Cx. pipiens s.l. samples. Estimated human blood indices ranged from 53%-76% for Ae. aegypti, 32%-82% for Ae. simpsoni s.l. and 26%-61% for Cx. pipiens s.l. and were consistently lower for Sanger-based sequencing approach compared to Miseq-based sequencing approach. These findings demonstrate that Miseq sequencing approach is superior to Sanger sequencing approach as it can reliably identify mixed host blood meals in a single mosquito, improving our ability to understand the transmission dynamics of mosquito-borne pathogens.

Aedes (Ochlerotatus) scapularis, Aedes japonicus japonicus, and Aedes (Fredwardsius) vittatus (Diptera: Culicidae): Three Neglected Mosquitoes with Potential Global Health Risks

More than 3550 species of mosquitoes are known worldwide, and only a fraction is involved in the transmission of arboviruses. Mosquitoes in sylvatic and semi-sylvatic habitats may rapidly adapt to urban parks and metropolitan environments, increasing human contact. Many of these mosquitoes have been found naturally infected with arboviruses from the Alphaviridae, Flaviviridae, and Bunyaviridae families, with many being the cause of medically important diseases. However, there is a gap in knowledge about the vector status of newly invasive species and their potential threat to human and domestic animal populations. Due to their rapid distribution, adaptation to urban environments, and anthropophilic habits, some neglected mosquito species may deserve more attention regarding their role as secondary vectors. Taking these factors into account, we focus here on Aedes (Ochlerotatus) scapularis (Rondani), Aedes japonicus japonicus (Theobald), and Aedes (Fredwardsius) vittatus (Bigot) as species that have the potential to become important disease vectors. We further discuss the importance of these neglected mosquitoes and how factors such as urbanization, climate change, and globalization profoundly alter the dynamics of disease transmission and may increase the participation of neglected species in propagating diseases.

Culicoides Midge Abundance across Years: Modeling Inter-Annual Variation for an Avian Feeder and a Candidate Vector of Hemorrhagic Diseases in Farmed Wildlife

(1) Background: Epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) are orbiviruses that cause hemorrhagic disease (HD) with significant economic and population health impacts on domestic livestock and wildlife. In the United States, white-tailed deer (Odocoileus virginianus) are particularly susceptible to these viruses and are a frequent blood meal host for various species of Culicoides biting midges (Diptera: Ceratopogonidae) that transmit orbiviruses. The species of Culicoides that transmit EHDV and BTV vary between regions, and larval habitats can differ widely between vector species. Understanding how midges are distributed across landscapes can inform HD virus transmission risk on a local scale, allowing for improved animal management plans to avoid suspected high-risk areas or target these areas for insecticide control. (2) Methods: We used occupancy modeling to estimate the abundance of gravid (egg-laden) and parous (most likely to transmit the virus) females of two putative vector species, C. stellifer and C. venustus, and one species, C. haematopotus, that was not considered a putative vector. We developed a universal model to determine habitat preferences, then mapped a predicted weekly midge abundance during the HD transmission seasons in 2015 (July-October) and 2016 (May-October) in Florida. (3) Results: We found differences in habitat preferences and spatial distribution between the parous and gravid states for C. haematopotus and C. stellifer. Gravid midges preferred areas close to water on the border of well and poorly drained soil. They also preferred mixed bottomland hardwood habitats, whereas parous midges appeared less selective of habitat. (4) Conclusions: If C. stellifer is confirmed as an EHDV vector in this region, the distinct spatial and abundance patterns between species and physiological states suggest that the HD risk is non-random across the study area.

Everglades virus: an underrecognized disease-causing subtype of Venezuelan equine encephalitis virus endemic to Florida, USA

Everglades virus (EVEV) is subtype II of the Venezuelan equine encephalitis virus (VEEV) complex (Togaviridae: Alphavirus), endemic to Florida, USA. EVEV belongs to a clade that includes both enzootic and epizootic/epidemic VEEV subtypes. Like other enzootic VEEV subtypes, muroid rodents are important vertebrate hosts for EVEV and certain mosquitoes are important vectors. The hispid cotton rat Sigmodon hispidus and cotton mouse Peromyscus gossypinus are important EVEV hosts, based on natural infection (virus isolation and high seropositivity), host competence (experimental infections), and frequency of contact with the vector. The mosquito Culex (Melanoconion) cecedei is the only confirmed vector of EVEV based upon high natural infection rates, efficient vector competence, and frequent feeding upon muroid rodents. Human disease attributed to EVEV is considered rare. However, cases of meningitis and encephalitis are recorded from multiple sites, separated by 250 km or more. Phylogenetic analyses indicate that EVEV is evolving, possibly due to changes in the mammal community. Mutations in the EVEV genome are of concern, given that epidemic strains of VEEV (subtypes IAB and IC) are derived from enzootic subtype ID, the closest genetic relative of EVEV. Should epizootic mutations arise in EVEV, the abundance of Aedes taeniorhynchus and other epizootic VEEV vectors in southern Florida provides a conducive environment for widespread transmission. Other factors that will likely influence the distribution and frequency of EVEV transmission include the establishment of Culex panocossa in Florida, Everglades restoration, mammal community decline due to the Burmese python, land use alteration by humans, and climate change.

Consumption of endemic arbovirus mosquito vectors by bats in the southeastern United States

Mosquitoes affect human health and well-being globally through their roles as disease-causing pathogen vectors. Utilizing genetic techniques, we conducted a large-scale dietary study of three bat species common to the southeastern U.S.A., Lasiurus seminolus (Seminole bat), Nycticeius humeralis (evening bat), and Myotis austroriparius (southeastern myotis). Through next-generation sequencing of a 180 bp portion of cytochrome oxidase subunit I (COI) of mitochondrial DNA from 180 bat guano samples, we documented consumption of 17 species of mosquitoes by bats, including six endemic arbovirus vectors. Culex quinquefasciatus, Culex coronator, Culiseta melanura, Culex salinarius, Culex erraticus, and Coquillettidia perturbans were consumed by 51.3%, 43.7%, 27.2%, 22.8%, 18.0%, and 12.7% of bats sampled, respectively. Consumption of two of these mosquito species was explained by spatial variables reflecting the prevalence of mosquito larval habitat, five were explained by bat traits (bat mass, bat species), and two were explained by these factors plus temporal variables (maximum daily temperature, time since sunset, date), making it challenging to offer specific guidance on how best to promote bats as a means of reducing arbovirus vector species. Our results show that common bat species of the southeastern U.S.A. consume endemic, but not exotic, arbovirus mosquito vectors. Future studies are needed to understand the impact of bat consumption on mosquito numbers and public health.

Predicting the potential distribution of Culex (Melanoconion) cedecei in Florida and the Caribbean using ecological niche models

Everglades virus (EVEV), an enzootic subtype of Venezuelan equine encephalitis virus, along with its endemic mosquito vector, Culex cedecei, is known only from South Florida. The taxonomy of Cx. cedecei is complex and was once synonymous with Culex opisthopus and Culex taeniopus. We modeled potential distribution of Cx. cedecei in Florida and the Caribbean using an ecological niche model and compared this distribution to the recorded distribution of EVEV in Florida as well as historical records of Cx. opisthopus/Cx. taeniopus. We used recent collections and occurrence data from scientific publications and temperature/precipitation variables and vegetation greenness values to calibrate models. We found mean annual temperature contributed the greatest to model performance. Everglades virus in humans and wildlife corresponded with areas predicted suitable for Cx. cedecei in Florida but not with incidence of antibodies reported in dogs. Most records of Cx. opisthopus/Cx. taeniopus in the Caribbean did not correspond to areas predicted suitable for Cx. cedecei, which may be due to mean annual temperature values in the Caribbean exceeding values within the calibration region, imposing model constraints. Results indicated that this model may adequately predict the distributions of Cx. cedecei within Florida but cannot predict areas suitable in the Caribbean.

Ecology and Epidemiology of Eastern Equine Encephalitis Virus in the Northeastern United States: An Historical Perspective

In the current review, we examine the regional history, ecology, and epidemiology of eastern equine encephalitis virus (EEEV) to investigate the major drivers of disease outbreaks in the northeastern United States. EEEV was first recognized as a public health threat during an outbreak in eastern Massachusetts in 1938, but historical evidence for equine epizootics date back to the 1800s. Since then, sporadic disease outbreaks have reoccurred in the Northeast with increasing frequency and northward expansion of human cases during the last 20 yr. Culiseta melanura (Coquillett) (Diptera: Culicidae) serves as the main enzootic vector that drives EEEV transmission among wild birds, but this mosquito species will occasionally feed on mammals. Several species have been implicated as bridge vectors to horses and humans, with Coquilletstidia perturbans (Walker) as a leading suspect based on its opportunistic feeding behavior, vector competence, and high infection rates during recent disease outbreaks. A diversity of bird species are reservoir competent, exposed to EEEV, and serve as hosts for Cs. melanura, with a few species, including the wood thrush (Hlocichia mustelina) and the American robin (Turdus migratorius), contributing disproportionately to virus transmission based on available evidence. The major factors responsible for the sustained resurgence of EEEV are considered and may be linked to regional landscape and climate changes that support higher mosquito densities and more intense virus transmission.

Ecology of Eastern Equine Encephalitis Virus in the Southeastern United States: Incriminating Vector and Host Species Responsible for Virus Amplification, Persistence, and Dispersal

Eastern equine encephalitis virus (EEEV; family Togaviridae, genus Alphavirus) is a mosquito-borne pathogen found in eastern North America that causes severe disease in humans and horses. The mosquito Culiseta melanura (Coquillett) (Diptera: Culicidae) is the primary enzootic vector of EEEV throughout eastern North America while several mosquito species belonging to diverse genera serve as bridge vectors. The ecology of EEEV differs between northern and southern foci, with respect to phenology of outbreaks, important vertebrate hosts, and bridge vector species. Active transmission is limited to roughly half of the year in northern foci (New York, New Hampshire, Massachusetts, Connecticut), while year-round transmission occurs in the southeastern region (particularly Florida). Multiple phylogenetic analyses indicate that EEEV strains circulating in northern foci are likely transported from southern foci by migrating birds. Bird species that overwinter or migrate through Florida, are bitten by Cs. melanura in late spring, and arrive at northern breeding grounds in May are the most likely candidates to disperse EEEV northward. Available data indicate that common yellowthroat and green heron satisfy these criteria and could serve as virus dispersers. Understanding the factors that drive the phenology of Cs. melanura reproduction in the south and the timing of avian migration from southern foci could provide insight into how confluence of these biological phenomena shapes outbreaks of EEE throughout its range. This information could be used to develop models predicting the likelihood of outbreaks in a given year, allowing vector control districts to more efficiently marshal resources necessary to protect their stakeholders.

Anaphylactic Reactions Due to Triatoma protracta (Hemiptera, Reduviidae, Triatominae) and Invasion into a Home in Northern California, USA

Simple Summary

Kissing bugs are bloodsucking insects found throughout the Western Hemisphere, including the United States, but also within certain regions of the Western Pacific, India, the Middle East, and Africa. Within the Americas, these insects are known to harbor a parasite known as Trypanosoma cruzi, the causative agent of an infection in humans and other mammals known as Chagas disease. The infection can be spread through the fecal matter of the kissing bug when exposed to the skin or ingested from contaminated food or drink products. Kissing bugs will invade human homes and bite residents and their pets. The bite from a kissing bug can also lead to serious allergic reactions, including anaphylaxis. A potentially life-threatening allergic response typically needs emergency medical attention. We describe a home that was invaded by kissing bugs in northern California where the resident developed serious allergic reactions to the bite. The kissing bugs were identified and a blood meal investigation found the presence of human blood as well as the parasite, Trypanosoma cruzi. The resident was tested extensively for chronic Chagas disease due to his repeated exposure to the kissing bug but was found to not have the disease. Those who live in regions where kissing bugs are found naturally should be aware that their bites can be highly allergenic.

Abstract

Background: Triatoma protracta is a triatomine found naturally throughout many regions of California and has been shown to invade human dwellings and bite residents. A man living in Mendocino County, California, reported developing anaphylactic reactions due to the bite of an “unusual bug”, which he had found in his home for several years. Methods: We conducted environmental, entomological, and clinical investigations to examine the risk for kissing bug invasion, presence of Trypanosoma cruzi, and concerns for Chagas disease at this human dwelling with triatomine invasion. Results: Home assessment revealed several risk factors for triatomine invasion, which includes pack rat infestation, above-ground wooden plank floor without a concrete foundation, canine living in the home, and lack of residual insecticide use. Triatomines were all identified as Triatoma protracta. Midgut molecular analysis of the collected triatomines revealed the detection of T. cruzi discrete typing unit I among one of the kissing bugs. Blood meal PCR-based analysis showed these triatomines had bitten humans, canine and unidentified snake species. The patient was tested for chronic Chagas disease utilizing rapid diagnostic testing and laboratory serological testing, and all were negative. Conclusions: Triatoma protracta is known to invade human dwellings in the western portions of the United States. This is the first report of T. cruzi-infected triatomines invading homes in Mendocino County, California. Triatoma protracta is a known vector responsible for autochthonous Chagas disease within the United States, and their bites can also trigger serious systemic allergic reactions, such as anaphylaxis.

Highlights of Medical Entomology, 2020

Medical Entomology as a field is inherently global - thriving on international and interdisciplinary collaborations and affected dramatically by arthropod and pathogen invasions and introductions. This past year also will be remembered as the year in which the SARS-CoV-2 COVID-19 pandemic affected every part of our lives and professional activities and impacted (or changed, sometimes in good ways) our ability to collaborate and detect or respond to invasions. This incredible year is the backdrop for the 2020 Highlights in Medical Entomology. This article highlights the broad scope of approaches and disciplines represented in the 2020 published literature, ranging from sensory and chemical ecology, population genetics, impacts of human-mediated environmental change on vector ecology, life history and the evolution of vector behaviors, to the latest developments in vector surveillance and control.