Host-Feeding Behavior of Mosquitoes in the Florida Everglades

Background: West Nile virus (WNV), Everglades virus (EVEV), and five species of Orthobunyavirus were isolated from mosquitoes collected in the Everglades in 2016-2017. Prior studies of blood meals of mosquitoes in southern Florida have related findings to acquisition and transmission of EVEV, St. Louis encephalitis virus, and WNV, but not the Orthobunyavirus viruses associated with the subgenus Melanoconion of the genus Culex. Materials and Methods: In the present study, blood-fed mosquitoes were collected in the Everglades in 2016, 2017, 2021, and 2022, and from an industrial site in Naples, FL in 2017. Blood meals were identified to host species by PCR assays using mitochondrial cytochrome b gene. Results: Blood meals were identified from Anopheles crucians complex and 11 mosquito species captured in the Florida Everglades and from 3 species collected from an industrial site. The largest numbers of blood-fed specimens were from Culex nigripalpus, Culex erraticus, Culex cedecei, and Aedes taeniorhynchus. Cx. erraticus fed on mammals, birds, and reptiles, particularly American alligator. This mosquito species could transmit WNV to American alligator in the wild. Cx. nigripalpus acquired blood meals primarily from birds and mammals and frequently fed on medium-sized mammals and white-tailed deer. Water and wading birds were the primary avian hosts for Cx. nigripalpus and Cx. erraticus in the Everglades. Wading birds are susceptible to WNV and could serve as reservoir hosts. Cx. cedecei fed on five species of rodents, particularly black and hispid cotton rats. EVEV and three different species of Orthobunyavirus have been isolated from the hispid cotton rat and Cx. cedecei in the Everglades. Cx. cedecei is likely acquiring and transmitting these viruses among hispid cotton rats and other rodents. The marsh rabbit was a frequent host for An. crucians complex. An. crucians complex, and other species could acquire Tensaw virus from rabbits. Conclusions: Our study contributes to a better understanding of the host and viral associations of mosquito species in southwestern Florida.

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.

A ticking time bomb hidden in plain sight

The deer tick transmits nearly half of the known tick-borne pathogens in the United States, and its expanding geographic range increases the risk of human infection. To decrease the abundance of and infection risk from deer ticks, approaches that include vaccines for human use and for animal hosts are desired.

Seasonal Dynamics of Mosquito-Borne Viruses in the Southwestern Florida Everglades, 2016, 2017

Mosquitoes were collected for 12 consecutive months beginning June 2016, from 11 locations in the Florida Everglades, Collier County, and tested for viruses by isolation in Vero cells and subsequent identification. One species complex and 31 species of mosquitoes were identified from 668,809 specimens. Ochlerotatus taeniorhynchus comprised 72.2% of the collection. Other notable species were Anopheles crucians complex, Culex nigripalpus, Cx. erraticus, and Cx. cedecei. Seven species of virus were identified from 110 isolations: Everglades, Gumbo Limbo, Mahogany Hammock, Pahayokee, Shark River, Tensaw, and West Nile viruses. Everglades, West Nile, Tensaw, and Mahogany Hammock viruses were most frequently isolated. Largest numbers of viruses were identified from Cx. cedecei, Cx. nigripalpus, and An. crucians complex. Five species of virus were isolated from Cx. cedecei. Viruses were isolated from mangrove, cypress swamp, hardwood hammock, and sawgrass habitats. West Nile virus was isolated August through October when Cx. nigripalpus was most abundant. Everglades virus was the most frequently isolated virus from nine species of mosquitoes collected from June through August. Tensaw virus was isolated primarily from Anopheles species. Isolations were made in July, August, January, February, and April, suggesting that this virus may be present in host-seeking mosquitoes throughout the year. Mahogany Hammock, Shark River, Gumbo Limbo, and Pahayokee viruses were isolated primarily from Cx. cedecei from June through December. Shotgun metagenomic sequencing was used to document that seven pools of Cx. cedecei were infected with two arboviruses. As communities expand into the Everglades, more humans will become exposed to arboviruses.

Characterization of Three New Insect-Specific Flaviviruses: Their Relationship to the Mosquito-Borne Flavivirus Pathogens

Three novel insect-specific flaviviruses, isolated from mosquitoes collected in Peru, Malaysia (Sarawak), and the United States, are characterized. The new viruses, designated La Tina, Kampung Karu, and Long Pine Key, respectively, are antigenically and phylogenetically more similar to the mosquito-borne flavivirus pathogens, than to the classical insect-specific viruses like cell fusing agent and Culex flavivirus. The potential implications of this relationship and the possible uses of these and other arbovirus-related insect-specific flaviviruses are reviewed.

Lyme disease ecology in a changing world: consensus, uncertainty and critical gaps for improving control

Lyme disease is the most common tick-borne disease in temperate regions of North America, Europe and Asia, and the number of reported cases has increased in many regions as landscapes have been altered. Although there has been extensive work on the ecology and epidemiology of this disease in both Europe and North America, substantial uncertainty exists about fundamental aspects that determine spatial and temporal variation in both disease risk and human incidence, which hamper effective and efficient prevention and control. Here we describe areas of consensus that can be built on, identify areas of uncertainty and outline research needed to fill these gaps to facilitate predictive models of disease risk and the development of novel disease control strategies. Key areas of uncertainty include: (i) the precise influence of deer abundance on tick abundance, (ii) how tick populations are regulated, (iii) assembly of host communities and tick-feeding patterns across different habitats, (iv) reservoir competence of host species, and (v) pathogenicity for humans of different genotypes of Borrelia burgdorferi Filling these knowledge gaps will improve Lyme disease prevention and control and provide general insights into the drivers and dynamics of this emblematic multi-host-vector-borne zoonotic disease.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Human rickettsial pathogen modulates arthropod organic anion transporting polypeptide and tryptophan pathway for its survival in ticks

The black-legged tick Ixodes scapularis transmits the human anaplasmosis agent, Anaplasma phagocytophilum. In this study, we show that A. phagocytophilum specifically up-regulates I. scapularis organic anion transporting polypeptide, isoatp4056 and kynurenine amino transferase (kat), a gene involved in the production of tryptophan metabolite xanthurenic acid (XA), for its survival in ticks. RNAi analysis revealed that knockdown of isoatp4056 expression had no effect on A. phagocytophilum acquisition from the murine host but affected the bacterial survival in tick cells. Knockdown of the expression of kat mRNA alone or in combination with isoatp4056 mRNA significantly affected A. phagocytophilum survival and isoatp4056 expression in tick cells. Exogenous addition of XA induces isoatp4056 expression and A. phagocytophilum burden in both tick salivary glands and tick cells. Electrophoretic mobility shift assays provide further evidence that A. phagocytophilum and XA influences isoatp4056 expression. Collectively, this study provides important novel information in understanding the interplay between molecular pathways manipulated by a rickettsial pathogen to survive in its arthropod vector.

Ticks elicit variable fibrinogenolytic activities upon feeding on hosts with different immune backgrounds

Ticks secrete several anti-hemostatic factors in their saliva to suppress the host innate and acquired immune defenses against infestations. Using Ixodes scapularis ticks and age-matched mice purchased from two independent commercial vendors with two different immune backgrounds as a model, we show that ticks fed on immunodeficient animals demonstrate decreased fibrinogenolytic activity in comparison to ticks fed on immunocompetent animals. Reduced levels of D-dimer (fibrin degradation product) were evident in ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Increased engorgement weights were noted for ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Furthermore, the LC-MS/MS and quantitative real-time-PCR analysis followed by inhibitor and antibody-blocking assays revealed that the arthropod HSP70-like molecule contributes to differential fibrinogenolysis during tick feeding. Collectively, these results not only indicate that ticks elicit variable fibrinogenolysis upon feeding on hosts with different immune backgrounds but also provide insights for the novel role of arthropod HSP70-like molecule in fibrinogenolysis during blood feeding.

Genetic characterization, molecular epidemiology, and phylogenetic relationships of insect-specific viruses in the taxon Negevirus

The recently described taxon Negevirus is comprised of a diverse group of insect-specific viruses isolated from mosquitoes and phlebotomine sandflies. In this study, a comprehensive genetic characterization, molecular, epidemiological and evolutionary analyses were conducted on nearly full-length sequences of 91 new negevirus isolates obtained in Brazil, Colombia, Peru, Panama, USA and Nepal. We demonstrated that these arthropod restricted viruses are clustered in two major phylogenetic groups with origins related to three plant virus genera (Cilevirus, Higrevirus and Blunevirus). Molecular analyses demonstrated that specific host correlations are not present with most negeviruses; instead, high genetic variability, wide host-range, and cross-species transmission were noted. The data presented here also revealed the existence of five novel insect-specific viruses falling into two arthropod-restrictive virus taxa, previously proposed as distinct genera, designated Nelorpivirus and Sandewavirus. Our results provide a better understanding of the molecular epidemiology, evolution, taxonomy and stability of this group of insect-restricted viruses.

Closely-related Borrelia burgdorferi (sensu stricto) strains exhibit similar fitness in single infections and asymmetric competition in multiple infections

Background

Wild hosts are commonly co-infected with complex, genetically diverse, pathogen communities. Competition is expected between genetically or ecologically similar pathogen strains which may influence patterns of coexistence. However, there is little data on how specific strains of these diverse pathogen species interact within the host and how this impacts pathogen persistence in nature. Ticks are the most common disease vector in temperate regions with Borrelia burgdorferi, the causative agent of Lyme disease, being the most common vector-borne pathogen in North America. Borrelia burgdorferi is a pathogen of high public health concern and there is significant variation in infection phenotype between strains, which influences predictions of pathogen dynamics and spread.

Methods

In a laboratory experiment, we investigated whether two closely-related strains of B. burgdorferi (sensu stricto) showed similar transmission phenotypes, how the transmission of these strains changed when a host was infected with one strain, re-infected with the same strain, or co-infected with two strains. Ixodes scapularis, the black-legged tick, nymphs were used to sequentially infect laboratory-bred Peromyscus leucopus, white-footed mice, with one strain only, homologous infection with the same stain, or heterologous infection with both strains. We used the results of this laboratory experiment to simulate long-term persistence and maintenance of each strain in a simple simulation model.

Results

Strain LG734 was more competitive than BL206, showing no difference in transmission between the heterologous infection groups and single-infection controls, while strain BL206 transmission was significantly reduced when strain LG734 infected first. The results of the model show that this asymmetry in competition could lead to extinction of strain BL206 unless there was a tick-to-host transmission advantage to this less competitive strain.

Conclusions

This asymmetric competitive interaction suggests that strain identity and the biotic context of co-infection is important to predict strain dynamics and persistence.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1964-9) contains supplementary material, which is available to authorized users.

Assessment of synthetic floral-based attractants and sugar baits to capture male and female Aedes aegypti (Diptera: Culicidae)

Background

The viruses transmitted by Aedes aegypti, including dengue and Zika viruses, are rapidly expanding in geographic range and as a threat to public health. In response, control programs are increasingly turning to the use of sterile insect techniques resulting in a need to trap male Ae. aegypti to monitor the efficacy of the intervention. However, there is a lack of effective and cheap methods for trapping males. Thus, we attempted to exploit the physiological need to obtain energy from sugar feeding in order to passively capture male and female Ae. aegypti (nulliparous and gravid) in free-flight attraction assays. Candidate lures included previously identified floral-based (phenylacetaldehyde, linalool oxide, phenylethyl alcohol, and acetophenone) attractants and an attractive toxic sugar bait-based (ATSB) solution of guava and mango nectars. A free-flight attraction assay assessed the number of mosquitoes attracted to each candidate lure displayed individually. Then, a choice test was performed between the best-performing lure and a water control displayed in Gravid Aedes Traps (GAT).

Results

Results from the attraction assays indicated that the ATSB solution of guava and mango nectars was the most promising lure candidate for males; unlike the floral-based attractants tested, it performed significantly better than the water control. Nulliparous and gravid females demonstrated no preference among the lures and water controls indicating a lack of attraction to floral-based attractants and sugar baits in a larger setting. Although the guava-mango ATSB lure was moderately attractive to males when presented directly (i.e. no need to enter a trap or other confinement), it failed to attract significantly more male, nulliparous female, or gravid female Ae. aegypti than water controls when presented inside a Gravid Aedes Trap.

Conclusions

Our findings suggest that the use of volatile floral-based attractants and sugar mixtures that have been identified in the literature is not an effective lure by which to kill Ae. aegypti at ATSB stations nor capture them in the GAT. Future trapping efforts would likely be more successful if focused on more promising methods for capturing male and female Ae. aegypti.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1946-y) contains supplementary material, which is available to authorized users.

Almendravirus: A Proposed New Genus of Rhabdoviruses Isolated from Mosquitoes in Tropical Regions of the Americas

The Rhabdoviridae is a diverse family of negative-sense single-stranded RNA viruses, many of which infect vertebrate hosts and are transmitted by hematophagous arthropods. Others appear to be arthropod specific, circulating only within arthropod populations. Herein, we report the isolation and characterization of three novel viruses from mosquitoes collected from the Americas. Coot Bay virus was isolated from Anopheles quadrimaculatus mosquitoes collected in the Everglades National Park, Florida; Rio Chico virus was isolated from Anopheles triannulatus mosquitoes collected in Panama; and Balsa virus was isolated from two pools of Culex erraticus mosquitoes collected in Colombia. Sequence analysis indicated that the viruses share a similar genome organization to Arboretum virus and Puerto Almendras virus that had previously been isolated from mosquitoes collected in Peru. Each genome features the five canonical rhabdovirus structural protein genes as well as a gene encoding a class 1A viroporin-like protein (U1) located between the G and L genes (3'-N-P-M-G-U1-L-5'). Phylogenetic analysis of complete L protein sequences indicated that all five viruses cluster in a unique clade that is relatively deeply rooted in the ancestry of animal rhabdoviruses. The failure of all viruses in this clade to grow in newborn mice or vertebrate cells in culture suggests that they may be poorly adapted to replication in vertebrates.

A Cost-Effectiveness Tool for Informing Policies on Zika Virus Control

BACKGROUND

As Zika virus continues to spread, decisions regarding resource allocations to control the outbreak underscore the need for a tool to weigh policies according to their cost and the health burden they could avert. For example, to combat the current Zika outbreak the US President requested the allocation of $1.8 billion from Congress in February 2016.

METHODOLOGY/PRINCIPAL FINDINGS

Illustrated through an interactive tool, we evaluated how the number of Zika cases averted, the period during pregnancy in which Zika infection poses a risk of microcephaly, and probabilities of microcephaly and Guillain-Barré Syndrome (GBS) impact the cost at which an intervention is cost-effective. From Northeast Brazilian microcephaly incidence data, we estimated the probability of microcephaly in infants born to Zika-infected women (0.49% to 2.10%). We also estimated the probability of GBS arising from Zika infections in Brazil (0.02% to 0.06%) and Colombia (0.08%). We calculated that each microcephaly and GBS case incurs the loss of 29.95 DALYs and 1.25 DALYs per case, as well as direct medical costs for Latin America and the Caribbean of $91,102 and $28,818, respectively. We demonstrated the utility of our cost-effectiveness tool with examples evaluating funding commitments by Costa Rica and Brazil, the US presidential proposal, and the novel approach of genetically modified mosquitoes. Our analyses indicate that the commitments and the proposal are likely to be cost-effective, whereas the cost-effectiveness of genetically modified mosquitoes depends on the country of implementation.

CONCLUSIONS/SIGNIFICANCE

Current estimates from our tool suggest that the health burden from microcephaly and GBS warrants substantial expenditures focused on Zika virus control. Our results justify the funding committed in Costa Rica and Brazil and many aspects of the budget outlined in the US president's proposal. As data continue to be collected, new parameter estimates can be customized in real-time within our user-friendly tool to provide updated estimates on cost-effectiveness of interventions and inform policy decisions in country-specific settings.

Spatial and Temporal Clustering of Chikungunya Virus Transmission in Dominica

Using geo-referenced case data, we present spatial and spatio-temporal cluster analyses of the early spread of the 2013–2015 chikungunya virus (CHIKV) in Dominica, an island in the Caribbean. Spatial coordinates of the locations of the first 417 reported cases observed between December 15^th, 2013 and March 11^th, 2014, were captured using the Global Positioning System (GPS). We observed a preponderance of female cases, which has been reported for CHIKV outbreaks in other regions. We also noted statistically significant spatial and spatio-temporal clusters in highly populated areas and observed major clusters prior to implementation of intensive vector control programs suggesting early vector control measures, and education had an impact on the spread of the CHIKV epidemic in Dominica. A dynamical identification of clusters can lead to local assessment of risk and provide opportunities for targeted control efforts for nations experiencing CHIKV outbreaks.

Chikungunya is a disease transmitted by mosquitoes. Currently, there is an epidemic of chikungunya in several islands and countries in the Americas. Despite efforts at understanding and predicting spread, there have been no studies assessing the spatio-temporal spread of chikungunya in any of the Caribbean islands, mainly due to a lack of data. Here, we present a spatio-temporal analysis of the spread of chikungunya virus in Dominica, an island in the Western Hemisphere, using geo-referenced case data. The findings in this study suggest that females are at higher risk for chikungunya virus transmission in Dominica. In addition, there is statistically significant clustering of cases in densely populated areas. Lack of data prevented additional analyses on the impact of mosquito population density, environmental factors and housing conditions on the location and timing of the clusters. This study is relevant for chikungunya control in Dominica, and other regions can use similar methods to assess chikungunya risk at the local level.

Response to Esteve-Gassent et al.: flaB sequences obtained from Texas PCR products are identical to the positive control strain Borrelia burgdorferi B31

Feria-Arroyo et al. had reported previously that, based on PCR analysis, 45 % of Ixodes scapularis ticks collected in Texas and Mexico were infected with the Lyme disease spirochete Borrelia burgdorferi (Parasit. Vectors 2014, 7:199). However, our analyses of their initial data (Parasit. Vectors 2014, 7:467) and a recent response by Esteve-Gassent et al. (Parasit. Vectors 2015, 8:129) provide evidence that the positive PCR results obtained from both ribosomal RNA intergenic sequences and the flagellin gene flaB are highly likely due to contamination by the B. burgdorferi B31 positive control strain.

Association between body size and reservoir competence of mammals bearing Borrelia burgdorferi at an endemic site in the northeastern United States

Background

The reservoirs for the Lyme disease agent, Borrelia burgdorferi, are dominated by several different small to medium sized mammals in eastern North America.

Findings

To experimentally assess the competence of different mammalian species to transmit this pathogen to ticks, we carried out quantitative species-specific PCR of individual nymphal Ixodes scapularis ticks, which had been collected as replete larvae from animals captured at a field site in eastern Connecticut and then allowed to molt in the laboratory. The mammals, in order of increasing body mass, were the white-footed mouse, pine vole, eastern chipmunk, gray squirrel, Virginia opossum, striped skunk, and common raccoon. The prevalence of infection in the nymphs and the counts of spirochetes in infected ticks allometrically scaled with body mass with exponents of −0.28 and −0.29, respectively. By species, the captured animals from the site differed significantly in the mean counts of spirochetes in the ticks recovered from them, but these associations could not be distinguished from an effect of body size per se.

Conclusions

These empirical findings as well as inferences from modeling suggest that small mammals on the basis of their sizes are more competent as reservoirs of B. burgdorferi in this environment than medium-to large-sized mammals.

Borrelia miyamotoi sensu lato seroreactivity and seroprevalence in the northeastern United States

Serum from �%^4% of residents was positive for infection, compared with �%^9% for B. burgdorferi.

Borrelia miyamotoi sensu lato, a relapsing fever Borrelia sp., is transmitted by the same ticks that transmit B. burgdorferi (the Lyme disease pathogen) and occurs in all Lyme disease�?"endemic areas of the United States. To determine the seroprevalence of IgG against B. miyamotoi sensu lato in the northeastern United States and assess whether serum from B. miyamotoi sensu lato�?"infected persons is reactive to B. burgdorferi antigens, we tested archived serum samples from area residents during 1991�?"2012. Of 639 samples from healthy persons, 25 were positive for B. miyamotoi sensu lato and 60 for B. burgdorferi. Samples from �%^10% of B. miyamotoi sensu lato�?"seropositive persons without a recent history of Lyme disease were seropositive for B. burgdorferi. Our resultsA suggest thatA human B. miyamotoiA sensu latoA infection may be common in southern New England and that B. burgdorferi antibody testing is not an effective surrogate for detecting B. miyamotoi sensu lato infection.

Long-term in vitro cultivation of Borrelia miyamotoi

Borrelia are fastidious bacteria some of which are difficult to grow in vitro. Here, we report a method for successful continuous in vitro cultivation of the emerging pathogen Borrelia miyamotoi. The type and quantity of serum as well as the atmosphere were critical for successful in vitro cultivation. Optimal growth was achieved using 50% pooled human serum and an atmosphere of 6% CO2.