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Background: Jamestown Canyon virus (JCV; Peribunyaviridae, Orthobunyavirus) is a mosquito-borne pathogen belonging to the California serogroup. The virus is endemic in North America and increasingly recognized as a public health concern. In this study, we determined the vector competence of Anopheles (An.) quadrimaculatus and Aedes (Ae.) albopictus for five JCV strains belonging to the two lineages circulating in the Northeast. Methods: An. quadrimaculatus and Ae. albopictus were fed blood meals containing two lineage A strains and three lineage B strains. Vector competence of both mosquito species was evaluated at 7- and 14-days post-feeding (dpf) by testing for virus presence in bodies, legs, and saliva. Results: Our results demonstrated that Ae. albopictus mosquitoes are a competent vector for both lineages, with similar transmission levels for all strains tested. Variable levels of infection (46–83%) and dissemination (17–38%) were measured in An. quadrimaculatus, yet no transmission was detected for the five JCV strains evaluated. Conclusions: Our results demonstrate that establishment of Ae. albopictus in the Northeast could increase the risk of JCV but suggest An. quadrimaculatus are not a competent vector for JCV. [ABSTRACT FROM AUTHOR]

Exposure of the developing fetus to Zika virus (ZIKV) results in a set of brain abnormalities described as the congenital Zika syndrome. Although microcephaly is the most obvious outcome, neuropathologies, such as intracranial calcifications and polymicrogyria, can occur in the absence of microcephaly. Moreover, the full impact of exposure on motor, social, and cognitive skills during development remains uncharacterized. We examined the long-term neurobehavioral consequences of neonatal ZIKV exposure in four genetically divergent inbred mouse strains (C57BL/6J, 129Sl/SvImJ, FVB/NJ, and DBA/2J). Male and female mice were infected on postnatal day 1, considered comparable with exposure late in the second trimester of humans. We demonstrate strain differences in early susceptibility to the virus and the time course of glial reaction in the brain. These changes were associated with strain- and sex-dependent differences in long-term behavioral abnormalities that include hyperactivity, impulsiveness, and motor incoordination. In addition, the adult brains of susceptible mice exhibited widespread calcifications that may underlie the behavioral deficits observed. Characterization of the neuropathological sequelae of developmental exposure to the Zika virus in different immunocompetent mouse strains provides a foundation for identifying genetic and immune factors that contribute to long-term neurobehavioral consequences in susceptible individuals. [ABSTRACT FROM AUTHOR]

Zika virus (ZIKV) (Flaviviridae, Flavivirus) has become one of the most medically important mosquito-borne viruses because of its ability to cause microcephaly in utero and Guillain-Barré syndrome in adults. This virus emerged from its sylvatic cycle in Africa to cause an outbreak in Yap, Federated States of Micronesia in 2007, French Polynesia in 2014, and most recently South America in 2015. The rapid expansion of ZIKV in the Americas largely has been due to the biology and behavior of its vector, Aedes aegypti. Other arboviruses transmitted by Ae. aegypti include the 2 flaviviruses dengue virus and yellow fever virus and the alphavirus chikungunya virus, which are also (re)emerging viruses in the Americas. This mosquito vector is highly domesticated, living in close association with humans in urban households. Its eggs are desiccation resistant, and the larvae develop rapidly in subtropical and tropical environments. Climate warming is facilitating range expansion of Ae. aegypti, adding to the threat this mosquito poses to human health, especially in light of the difficulty controlling it. Aedes albopictus, another highly invasive arbovirus vector that has only been implicated in one country (Gabon), is an important vector of ZIKV, but because of its wide geographic distribution may become a more important vector in the future. This article discusses the historical background of ZIKV and the biology and ecology of these 2 vectors. [ABSTRACT FROM AUTHOR]

In this review, we highlight biological characteristics of Aedes aegypti and Aedes albopictus, 2 invasive mosquito species and primary vectors of chikungunya virus (CHIKV), that set the tone of these species' invasiveness, vector competence, and vectorial capacity (VC). The invasiveness of both species, as well as their public health threats as vectors, is enhanced by preference for human blood. Vector competence, characterized by the efficiency of an ingested arbovirus to replicate and become infectious in the mosquito, depends largely on vector and virus genetics, and most A. aegypti and A. albopictus populations thus far tested confer vector competence for CHIKV. VC, an entomological analog of the pathogen's basic reproductive rate (R0), is epidemiologically more important than vector competence but less frequently measured, owing to challenges in obtaining valid estimates of parameters such as vector survivorship and host feeding rates. Understanding the complexities of these factors will be pivotal in curbing CHIKV transmission. [ABSTRACT FROM AUTHOR]

Background: Climate change is predicted to alter the transmission of many vector-borne pathogens. The quantitative impact of climate change is usually estimated by measuring the temperature-performance relationships for a single population of vectors, and then mapping this relationship across a range of temperatures or locations. However, life history traits of different populations often differ significantly. Specifically, performance across a range of temperatures is likely to vary due to local adaptation to temperature and other factors. This variation can cause spatial variation in pathogen transmission and will influence the impact of climate change on the transmission of vector-borne pathogens. Methods: We quantified variation in life history traits for four populations of Culex pipiens (Linnaeus) mosquitoes. The populations were distributed along altitudinal and latitudinal gradients in the eastern United States that spanned ~3 °C in mean summer temperature, which is similar to the magnitude of global warming expected in the next 3-5 decades. We measured larval and adult survival, development rate, and biting rate at six temperatures between 16 and 35 °C, in a common garden experiment. Results: Temperature had strong and consistent non-linear effects on all four life history traits for all four populations. Adult female development time decreased monotonically with increasing temperature, with the largest decrease at cold temperatures. Daily juvenile and adult female survival also decreased with increasing temperature, but the largest decrease occurred at higher temperatures. There was significant among-population variation in the thermal response curves for the four life history traits across the four populations, with larval survival, adult survival, and development rate varying up to 45, 79, and 84 % among populations, respectively. However, variation was not correlated with local temperatures and thus did not support the local thermal adaptation hypothesis. Conclusion: These results suggest that the impact of climate change on vector-borne disease will be more variable than previous predictions, and our data provide an estimate of this uncertainty. In addition, the variation among populations that we observed will shape the response of vectors to changing climates. [ABSTRACT FROM AUTHOR]

West Nile virus (WNV; Flavivirus; Flaviviridae) is the cause of the most widespread arthropod-borne viral disease in the world and the largest outbreak of neuroinvasive disease ever observed. Mosquito-borne outbreaks are influenced by intrinsic (e.g., vector and viral genetics, vector and host competence, vector life-history traits) and extrinsic (e.g., temperature, rainfall, human land use) factors that affect virus activity and mosquito biology in complex ways. The concept of vectorial capacity integrates these factors to address interactions of the virus with the arthropod host, leading to a clearer understanding of their complex interrelationships, how they affect transmission of vector-borne disease, and how they impact human health. Vertebrate factors including host competence, population dynamics, and immune status also affect transmission dynamics. The complexity of these interactions are further exacerbated by the fact that not only can divergent hosts differentially alter the virus, but the virus also can affect both vertebrate and invertebrate hosts in ways that significantly alter patterns of virus transmission. This chapter concentrates on selected components of the virus-vector-vertebrate interrelationship, focusing specifically on how interactions between vector, virus, and environment shape the patterns and intensity of WNV transmission. [ABSTRACT FROM AUTHOR]

Abstract: Dengue and West Nile viruses are enveloped RNA viruses that belong to genus Flavivirus (family Flaviviridae) and are considered important mosquito-borne viral pathogenic agents worldwide. A potential target for intervention strategies is the virus cell entry mechanism. Previous studies of flavivirus entry have focused on the effects of biochemical and molecular inhibitors on viral entry leading to controversial conclusions suggesting that the process is dependent upon endocytosis and low pH mediated membrane fusion. In this study we analyzed the early events in the infection process by means of electron microscopy and immuno-gold labeling of viral particles during cell entry, and used as a new approach for infecting cells with viruses obtained directly from mosquitoes. The results show that Dengue and West Nile viruses may infect cells by a mechanism that involves direct penetration of the host cell plasma membrane as proposed for alphaviruses. [Copyright &y& Elsevier]

Background: The genus Flavivirus currently consists of approximately 80 single-strand positive-sense RNA viruses. These replicate in a range of hosts including myriad vertebrate, insect, and tick species. As a consequence of this broad host range, the majority of flaviviruses can be propagated in most vertebrate and insect cell cultures. This ability to infect arthropods and vertebrates usually is essential for maintenance of these viruses in nature. But recently, there has been the discovery of a number of flaviviruses that infect mosquitoes but not vertebrates. It remains largely unknown why certain flaviviruses infect vertebrates and mosquitoes while others infect mosquitoes or vertebrates exclusively. Methods: Here, we initiated in vitro host range studies of Rabensburg virus (RABV), an intermediate between the mosquito-specific and horizontally transmitted flaviviruses, to provide information on the factor(s) that underlie the varying host range of flaviviruses. RABV is an intermediate between the mosquito-specific and horizontally transmitted flaviviruses because it does not infect mammalian or avian cell cultures, house sparrows, or chickens, but it does share genetic characteristics with the Japanese Encephalitis serogroup of flaviviruses. Results: In vitro growth kinetic assays revealed the complete abrogation of RABV growth on Vero and E6 cells incubated at temperatures 35°C and higher, but surprisingly RABV infected, replicated efficiently, and displayed overt cytopathic effects (CPE) on Vero and E6 cell cultures incubated below 35°C. In contrast, RABV was fully viable, replicated efficiently, and displayed overt CPE on C6/36 cells incubated at 28°C or 37°C, thus implicating temperature as an important factor limiting the host range of RABV. Conclusions: These data are critical for further study to more fully identify the determinants that mediate the evolution of biological transmission among flaviviruses. It also will be useful for studies that look to provide a comprehensive molecular definition of flavivirus-host cell interactions. And it will provide a cadre of information to design wet lab experiments to investigate the genetic changes that facilitate host switching, which may lead to new vertebrate pathogens or transmission pathways. [ABSTRACT FROM AUTHOR]

Background: Temperature is known to induce changes in mosquito physiology, development, ecology, and in some species, vector competence for arboviruses. Since colonized mosquitoes are reared under laboratory conditions that can be significantly different from their field counterparts, laboratory vector competence experiments may not accurately reflect natural vector-virus interactions. Methods: We evaluated the effects of larval rearing temperature on immature development parameters and vector competence of two Culex tarsalis strains for West Nile virus (WNV). Results: Rearing temperature had a significant effect on mosquito developmental parameters, including shorter time to pupation and emergence and smaller female body size as temperature increased. However, infection, dissemination, and transmission rates for WNV at 5, 7, and 14 days post infectious feeding were not consistently affected. Conclusions: These results suggest that varying constant larval rearing temperature does not significantly affect laboratory estimates of vector competence for WNV in Culex tarsalis mosquitoes. [ABSTRACT FROM AUTHOR]

Arthropod-borne viruses (arboviruses) are maintained in nature by cycling between vertebrate hosts and haematophagous invertebrate vectors. These viruses are responsible for causing a significant public health burden throughout the world, with over 100 species having the capacity to cause human disease. Arbovirus outbreaks in previously naïve environments demonstrate the potential of these pathogens for expansion and emergence, possibly exacerbated more recently by changing climates. These recent outbreaks, together with the continued devastation caused by endemic viruses, such as Dengue virus which persists in many areas, demonstrate the need to better understand the selective pressures that shape arbovirus evolution. Specifically, a comprehensive understanding of host-virus interactions and how they shape both host-specific and virus-specific evolutionary pressures is needed to fully evaluate the factors that govern the potential for host shifts and geographic expansions. One approach to advance our understanding of the factors influencing arbovirus evolution in nature is the use of experimental studies in the laboratory. Here, we review the contributions that laboratory passage and experimental infection studies have made to the field of arbovirus adaptation and evolution, and how these studies contribute to the overall field of arbovirus evolution. In particular, this review focuses on the areas of evolutionary constraints and mutant swarm dynamics; how experimental results compare to theoretical predictions; the importance of arbovirus ecology in shaping viral swarms; and how current knowledge should guide future questions relevant to understanding arbovirus evolution. [ABSTRACT FROM AUTHOR]

Perpetuation, overwintering, and extinction of eastern equine encephalitis virus (EEEV) in northern foci are poorly understood. We therefore sought to describe the molecular epidemiology of EEEV in New York State during current and past epizootics. To determine whether EEEV overwinters, is periodically reintroduced, or both, we sequenced the E2 and partial NSP3 coding regions of 42 EEEV isolates from New York State and the Eastern Seaboard of the United States. Our phylogenetic analyses indicated that derived subclades tended to contain southern strains that had been isolated before genetically similar northern strains, suggesting southern to northern migration of EEEV along the Eastern Seaboard. Strong clustering among strains isolated during epizootics in New York from 2003-2005, as well as from 1974-1975, demonstrates that EEEV has overwintered in this focus. This study provides molecular evidence for the introduction of southern EEEV strains to New York, followed by local amplification, perpetuation, and overwintering. [ABSTRACT FROM AUTHOR]

West Nile virus (WNV) Flavivirus: Flaviviridae) is the most widespread arbovirus in the world. A significant range expansion occurred beginning in 1999 when the virus was introduced into New York City. This review highlights recent research into WNV epizootiology and epidemiology, including recent advances in understanding of the host-virus interaction at the molecular, organismal, and ecological levels. Vector control strategies, vaccines, and antivirals, which now must be considered on a global scale, are also discussed. [ABSTRACT FROM AUTHOR]

Summary: West Nile virus is a mosquito-borne flavivirus originally isolated in 1937 from the blood of a febrile woman in the West Nile province of Uganda. The virus is widely distributed in Africa, Europe, Australia, and Asia, and, since 1999, it has spread rapidly throughout the western hemisphere, including the USA, Canada, Mexico, and the Caribbean and into parts of Central and South America. Before 1994, outbreaks of West Nile virus were sporadic and occurred primarily in the Mediterranean region, Africa, and east Europe. Since 1994, outbreaks have occurred with a higher incidence of severe human disease, particularly affecting the nervous system. In North America, the virus has caused meningitis, encephalitis, and poliomyelitis, resulting in significant morbidity and mortality. The goal of this Review is to highlight recent advances in our understanding of West Nile virus virology, ecology, clinical disease, diagnosis, and development of potential vaccines and antiviral therapies. [Copyright &y& Elsevier]

West Nile virus (WNV) has caused repeated large-scale human epidemics in North America since it was first detected in 1999 and is now the dominant vector-borne disease in this continent. Understanding the factors that determine the intensity of the spillover of this zoonotic pathogen from birds to humans (via mosquitoes) is a prerequisite for predicting and preventing human epidemics. We integrated mosquito feeding behavior with data on the population dynamics and WNV epidemiology of mosquitoes, birds, and humans. We show that Culex pipiens, the dominant enzootic (bird-to-bird) and bridge (bird-to-human) vector of WNV in urbanized areas in the northeast and north-central United States, shifted its feeding preferences from birds to humans by 7-fold during late summer and early fall, coinciding with the dispersal of its preferred host (American robins, Turdus migratorius) and the rise in human WNV infections. We also show that feeding shifts in Cx. tarsalis amplify human WNV epidemics in Colorado and California and occur during periods of robin dispersal and migration. Our results provide a direct explanation for the timing and intensity of human WNV epidemics. Shifts in feeding from competent avian hosts early in an epidemic to incompetent humans after mosquito infection prevalences are high result in synergistic effects that greatly amplify the number of human infections of this and other pathogens. Our results underscore the dramatic effects of vector behavior in driving the transmission of zoonotic pathogens to humans. [ABSTRACT FROM AUTHOR]

In the northeast United States, control of West Nile virus (WNV) vectors has been unfocused because of a lack of accurate knowledge about the roles different mosquitoes play in WNV transmission. We analyzed the risk posed by 10 species of mosquitoes for transmitting WNV to humans by using a novel risk-assessment measure that combines information on the abundance, infection prevalence, vector competence, and biting behavior of vectors. This analysis suggests that 2 species (Culex pipiens L. and Cx. restuans Theobald [Diptera: Cilicidae]) not previously considered important in transmitting WNV to humans may be responsible for up to 80% of human WNV infections in this region. This finding suggests that control efforts should be focused on these species which may reduce effects on nontarget wetland organisms. Our risk measure has broad applicability to other regions and diseases and can be adapted for use as a predictive tool of future human WNV infections. [ABSTRACT FROM AUTHOR]

West Nile (WN) virus was detected in the metropolitan New York City (NYC) area during the summer and fall of 1999. Sixty-two human cases, 7 fatal, were documented. The New York State Department of Health initiated a departmental effort to implement a statewide mosquito and virus surveillance system. During the 2000 arbovirus surveillance season, we collected 317,676 mosquitoes, submitted 9,952 pools for virus testing, and detected 363 WN virus-positive pools by polymerase chain reaction (PCR). Eight species of mosquitoes were found infected. Our mosquito surveillance system complemented other surveillance systems in the state to identify relative risk for human exposure to WN virus. PCR WN virus-positive mosquitoes were detected in NYC and six counties in the lower Hudson River Valley and metropolitan NYC area. Collective surveillance activities suggest that WN virus can disperse throughout the state and may impact local health jurisdictions in the state in future years. [ABSTRACT FROM AUTHOR]

Background: Past findings demonstrate that arthropods can egest midgut microbiota into the host skin leading to dual colonization of the vertebrate host with pathogens and saliva microbiome. A knowledge gap exists on how the saliva microbiome interacts with the pathogen in the saliva. To fill this gap, we need to first define the microbial composition of mosquito saliva. Methods: The current study aimed at analyzing and comparing the microbial profile of Aedes albopictus saliva and midgut as well as assessing the impact of Zika virus (ZIKV) infection on the midgut and saliva microbial composition. Colony-reared Ae. albopictus strains were either exposed to ZIKV infectious or noninfectious bloodmeal. At 14 ays postinfection, the 16S V3–V4 hypervariable rRNA region was amplified from midgut and saliva samples and sequenced on an Illumina MiSeq platform. The relative abundance and diversity of midgut and saliva microbial taxa were assessed. Results: We observed a richer microbial community in the saliva compared with the midgut, yet some of the microbial taxa were common in the midgut and saliva. ZIKV infection did not impact the microbial diversity of midgut or saliva. Further, we identified Elizabethkingia spp. in the Ae. albopictus saliva. Conclusions: This study provides insights into the microbial community of the Ae. albopictus saliva as well as the influence of ZIKV infection on the microbial composition of its midgut and saliva. The identification of Elizabethkingia spp., an emerging pathogen of global health significance, in Ae. albopictus saliva is of medical importance. Future studies to assess the interactions between Ae. albopictus saliva microbiome and ZIKV could lead to novel strategies for developing transmission barrier tools. [ABSTRACT FROM AUTHOR]

Background: Mayaro virus (MAYV; Alphavirus, Togaviridae) is an emerging pathogen endemic in South American countries. The increase in intercontinental travel and tourism-based forest excursions has resulted in an increase in MAYV spread, with imported cases observed in Europe and North America. Intriguingly, no local transmission of MAYV has been reported outside South America, despite the presence of potential vectors. Methods: We assessed the vector competence of Aedes albopictus from New York and Anopheles quadrimaculatus for MAYV. Results: The results show that Ae. albopictus from New York and An. quadrimaculatus are competent vectors for MAYV. However, Ae. albopictus was more susceptible to infection. Transmission rates increased with time for both species, with rates of 37.16 and 64.44% for Ae. albopictus, and of 25.15 and 48.44% for An. quadrimaculatus, respectively, at 7 and 14 days post-infection. Conclusions: Our results suggest there is a risk of further MAYV spread throughout the Americas and autochthonous transmission in the USA. Preventive measures, such as mosquito surveillance of MAYV, will be essential for early detection. [ABSTRACT FROM AUTHOR]

Flaviviruses are a genus within the Flaviviridae family of positive-strand RNA viruses and are transmitted principally through mosquito and tick vectors. These viruses are responsible for hundreds of millions of human infections worldwide per year that result in a range of illnesses from self-limiting febrile syndromes to severe neurotropic and viscerotropic diseases and, in some cases, death. A vaccine against the prototype flavivirus, yellow fever virus, has been deployed for 85 years and is highly effective. While vaccines against some medically important flaviviruses are available, others have proven challenging to develop. The emergence and spread of flaviviruses, including dengue virus and Zika virus, demonstrate their pandemic potential. This review highlights the gaps in knowledge that need to be addressed to allow for the rapid development of vaccines against emerging flaviviruses in the future. [ABSTRACT FROM AUTHOR]

Rabensburg virus (RBGV; Flaviviridae, Flavivirus) has been classified as both a novel flavivirus and a unique lineage of West Nile virus (WNV). RBGV and WNV share approximately 76% sequence homology, yet RBGV does not replicate to high viral titers within vertebrate cell lines at physiological temperatures and has not been naturally isolated from a vertebrate host. These unique genetic and biological characteristics make RBGV a viable tool to identify the genetic determinants of flavivirus infectivity and fitness in vertebrate hosts. Using experimental evolution, we characterized mutated variants of RBGV that have altered capacity for infection and replication in various cell lines. Shared genetic differences within these variants were identified throughout the genome, with a large majority found in the NS3 and NS5 genes. Our results support a role for the replication complex in host utilization and suggest that epistatic interactions likely contribute to host-specific fitness and emergence. [ABSTRACT FROM AUTHOR]

Powassan virus is an emerging tick-borne virus of concern for public health, but very little is known about its transmission patterns and ecology. Here, we expanded the genomic dataset by sequencing 279 Powassan viruses isolated from Ixodes scapularis ticks from the northeastern United States. Our phylogeographic reconstructions revealed that Powassan virus lineage II was likely introduced or emerged from a relict population in the Northeast between 1940 and 1975. Sequences strongly clustered by sampling location, suggesting a highly focal geographical distribution. Our analyses further indicated that Powassan virus lineage II emerged in the northeastern United States mostly following a south-to-north pattern, with a weighted lineage dispersal velocity of ~3 km/y. Since the emergence in the Northeast, we found an overall increase in the effective population size of Powassan virus lineage II, but with growth stagnating during recent years. The cascading effect of population expansion of white-tailed deer and I. scapularis populations likely facilitated the emergence of Powassan virus in the northeastern United States. [ABSTRACT FROM AUTHOR]

Although infections of vertebrate hosts by arthropod-borne viruses may lead to pathogenic outcomes, infections of vector mosquitoes result in persistent infections, where the virus replicates in the host without causing apparent pathological effects. It is unclear how persistent infections are established and maintained in mosquitoes. Several reports revealed the presence of flavivirus-like DNA sequences in the mosquito genome, and recent studies have shown that DNA forms of RNA viruses restrict virus replication in Drosophila , suggesting that DNA forms may have a role in developing persistent infections. Here, we sought to investigate whether arboviruses generate DNA forms following infection in mosquitoes. Our results with West Nile, Dengue, and La Crosse viruses demonstrate that DNA forms of the viral RNA genome are generated in mosquito cells; however, not the entire viral genome, but patches of viral RNA in DNA forms can be detected 24 h post infection. [ABSTRACT FROM AUTHOR]

In July 2019, Bourbon virus RNA was detected in an Amblyomma americanum tick removed from a resident of Long Island, New York, USA. Tick infection and whitetailed deer (Odocoileus virginianus) serosurvey results demonstrate active transmission in New York, especially Suffolk County, emphasizing a need for surveillance anywhere A. americanum ticks are reported. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Dengue in Travelers," by A. Wilder-Smith and E. Schwartz in the September 1, 2005 issue.

Introduction: In New York State (NYS), Eastern equine encephalitis (EEE) was first reported in a human in 1971, in horses in 1970, and in pheasants in 1952. Material and Method: Following work for the interval from 1970 to 1991, we identified cases in vertebrates from 1992 to 2012, through a passive surveillance system involving veterinarians in clinical practice, county health departments, and the Departments of Agriculture and Markets, Environmental Conservation, and Health, of the State of New York. Result: During an 11-year hiatus, from 1992 to 2002, no case in any vertebrate was observed. In a re-emergence, from 2003 to 2012, disease occurred in 12 counties, including 7 counties where disease had never been documented. Vertebrate cases included 4 cases in humans and 77 nonhuman occurrences; in 58 horses, Equus ferus caballus L.; 2 deer, Odocoileus virginianus Zimmermann; 6 dogs, Canis familiaris; 10 birds; and 1 flock of pheasants, Phasianus colchicus L. These were the first reported cases in NYS in white-tailed deer, the domestic dog, and in five species of birds: American crow, Corvus brachyrhynchos Brehm; American goldfinch, Carduelis tristis L.; bald eagle, Haliaeetus leucocephalus L.; blue jay, Cyanocitta cristata (L.); and red-tailed hawk, Buteo jamaicensis Gmelin. One crow was dually infected with EEE virus and West Nile virus. The northern, southern, and southeastern borders of the state were newly affected. Conclusion: The geographic area, time periods, and vertebrate species with risk of EEE disease expanded from 1992 to 2012. [ABSTRACT FROM AUTHOR]

West Nile virus (WNV; Flaviviridae, Flavivirus ) is the most geographically widespread arthropod-borne virus (arbovirus) in the world and is found in multiple ecologically distinct settings. Despite the likelihood of frequent exposure to novel hosts, studies evaluating the capacity and correlates of host range expansions or shifts of WNV and other arboviruses are generally lacking. We utilized experimental evolution of WNV in an Amblyomma americanum tick cell line to model an invertebrate host shift and evaluate the adaptive potential of WNV outside of its primary transmission cycle. Our results demonstrate that highly significant gains in replicative ability in ixodid tick cells are attainable for WNV but are also associated with widespread genetic change and significant phenotypic costs in vitro . Decreased fitness in primary hosts could represent a barrier to frequent exploitation of hard ticks by WNV in nature. [ABSTRACT FROM AUTHOR]

Predicting pathogen emergence and spillover risk requires understanding the determinants of a pathogens' host range and the traits involved in host competence. While host competence is often considered a fixed species-specific trait, it may be variable if pathogens diversify across hosts. Balancing selection can lead to maintenance of pathogen polymorphisms (multiple-niche-polymorphism; MNP). The causative agent of Lyme disease, Borrelia burgdorferi (Bb), provides a model to study the evolution of host adaptation, as some Bb strains defined by their outer surface protein C (ospC) genotype, are widespread in white-footed mice and others are associated with non-rodent vertebrates (e.g. birds). To identify the mechanisms underlying potential strain × host adaptation, we infected American robins and white-footed mice, with three Bb strains of different ospC genotypes. Bb burdens varied by strain in a host-dependent fashion, and strain persistence in hosts largely corresponded to Bb survival at early infection stages and with transmission to larvae (i.e. fitness). Early survival phenotypes are associated with cell adhesion, complement evasion and/or inflammatory and antibody-mediated removal of Bb, suggesting directional selective pressure for host adaptation and the potential role of MNP in maintaining OspC diversity. Our findings will guide future investigations to inform eco-evolutionary models of host adaptation for microparasites. [ABSTRACT FROM AUTHOR]

Cache Valley virus (CVV) is a mosquitoborne virus that infects livestock and humans. We report results of surveillance for CVV in New York, USA, during 2000-2016; full-genome analysis of selected CVV isolates from sheep, horse, humans, and mosquitoes from New York and Canada; and phenotypic characterization of selected strains. We calculated infection rates by using the maximum-likelihood estimation method by year, region, month, and mosquito species. The highest maximum-likelihood estimations were for Anopheles spp. mosquitoes. Our phylogenetic analysis identified 2 lineages and found evidence of segment reassortment. Furthermore, our data suggest displacement of CVV lineage 1 by lineage 2 in New York and Canada. Finally, we showed increased vector competence of An. quadrimaculatus mosquitoes for lineage 2 strains of CVV compared with lineage 1 strains. [ABSTRACT FROM AUTHOR]

Background Culex pipiens L. complex mosquitoes have a global distribution and are primary vectors of pathogens of public health significance. In the U.S., Cx. pipiens bioformes, Cx. pipiens form pipiens and Cx. pipiens form molestus, as well as Cx. quinquefasciatus, are primary vectors of West Nile virus (WNV; Flaviviridae, Flavivirus). These mosquitoes reside in distinct but overlapping ecological niches and readily hybridize in areas where they coexist. Although species and population-specific differences in vector competence of Culex mosquitoes for WNV have been identified, the extent to which hybridization within this complex alters WNV transmission potential has not been well characterized. Findings WNV vector competence of laboratory colonies of Cx. p. f. pipiens, Cx. p. f. molestus, and Cx. quinquefasciatus was assessed and compared to hybrid populations created from reciprocal mating of these lines. The results demonstrate that hybridization has a significant effect on WNV infection, dissemination, and, particularly, transmission in Culex pipiens L. complex mosquitoes. Specifically, enhanced transmission of WNV was measured in all hybrid populations relative to one or both parental stains. Conclusion These findings demonstrate that environmental or anthropogenic changes resulting in fluctuations in the distribution and extent of hybrid populations of Culex mosquitoes could have a significant impact on transmission patterns of WNV in nature. [ABSTRACT FROM AUTHOR]

During 2018, Heartland virus RNA was detected in an Amblyomma americanum tick removed from a resident of Suffolk County, New York, USA. The person showed seroconversion. Tick surveillance and white-tailed deer (Odocoileus virginianus) serosurveys showed widespread distribution in Suffolk County, emphasizing a need for disease surveillance anywhere A. americanum ticks are established or emerging. [ABSTRACT FROM AUTHOR]

Powassan/deer tick virus (POWV/DTV), a tick-borne flavivirus, is emerging in the United States. However, little work has assessed spatial distribution and infection prevalence and density of infected vector ticks in Pennsylvania (PA). Therefore, we conducted active surveillance for Ixodes scapularis in every PA county and screened for pathogen presence by real-time RT-PCR. A total of 1,672 pools were assayed for 5,588 adult I. scapularis collected. We detected POWV/ DTV in three counties. Minimum infection rates (MIRs) ranged between 1.01 and 1.47%. Mean statewide MIR was 0.06% ± 0.28%, well below infection estimates from more northern studies, suggesting a relatively more recent emergence of POWV/ DTV in PA. These data should help efforts to raise awareness among regional public health practitioners of POWV/DTV prevalence and distribution. [ABSTRACT FROM AUTHOR]

Background: Vector-borne pathogens must survive and replicate in the hostile environment of an insect's midgut before successful dissemination. Midgut microbiota interfere with pathogen infection by activating the basal immunity of the mosquito and by synthesizing pathogen-inhibitory metabolites. Methods: The goal of this study was to assess the influence of Zika virus (ZIKV) infection and increased temperature on Aedes albopictus midgut microbiota. Aedes albopictus were reared at diurnal temperatures of day 28 °C/night 24 °C (L) or day 30 °C/night 26 °C (M). The mosquitoes were given infectious blood meals with 2.0 × 108 PFU/ml ZIKV, and 16S rRNA sequencing was performed on midguts at 7 days post-infectious blood meal exposure. Results: Our findings demonstrate that Elizabethkingia anophelis albopictus was associated with Ae. albopictus midguts exposed to ZIKV infectious blood meal. We observed a negative correlation between ZIKV and E. anophelis albopictus in the midguts of Ae. albopictus. Supplemental feeding of Ae. albopictus with E. anophelis aegypti and ZIKV resulted in reduced ZIKV infection rates. Reduced viral loads were detected in Vero cells that were sequentially infected with E. anophelis aegypti and ZIKV, dengue virus (DENV), or chikungunya virus (CHIKV). Conclusions: Our findings demonstrate the influence of ZIKV infection and temperature on the Ae. albopictus microbiome along with a negative correlation between ZIKV and E. anophelis albopictus. Our results have important implications for controlling vector-borne pathogens. [ABSTRACT FROM AUTHOR]

Abstract: The transmission of vector-borne pathogens is greatly influenced by the ecology of their vector, which is in turn shaped by genetic ancestry, the environment, and the hosts that are fed on. One group of vectors, the mosquitoes in the Culex pipiens complex, play key roles in the transmission of a range of pathogens including several viruses such as West Nile and St. Louis encephalitis viruses, avian malaria (Plasmodium spp.), and filarial worms. The Cx. pipiens complex includes Culex pipiens pipiens with two forms, pipiens and molestus, Culex pipiens pallens, Culex quinquefasciatus, Culex australicus, and Culex globocoxitus. While several members of the complex have limited geographic distributions, Cx. pipiens pipiens and Cx. quinquefasciatus are found in all known urban and sub-urban temperate and tropical regions, respectively, across the world, where they are often principal disease vectors. In addition, hybrids are common in areas of overlap. Although gaps in our knowledge still remain, the advent of genetic tools has greatly enhanced our understanding of the history of speciation, domestication, dispersal, and hybridization. We review the taxonomy, genetics, evolution, behavior, and ecology of members of the Cx. pipiens complex and their role in the transmission of medically important pathogens. The adaptation of Cx. pipiens complex mosquitoes to human-altered environments led to their global distribution through dispersal via humans and, combined with their mixed feeding patterns on birds and mammals (including humans), increased the transmission of several avian pathogens to humans. We highlight several unanswered questions that will increase our ability to control diseases transmitted by these mosquitoes. [Copyright &y& Elsevier]

Abstract: A duplex TaqMan real-time reverse transcriptase polymerase chain reaction (PCR) assay was developed for the detection of California (CAL) serogroup viruses and Cache Valley virus (CVV), for use in human surveillance. The targets selected for the assay were the sequences encoding the nucleocapsid protein of CAL and the G1 glycoprotein of CVV. Conserved regions were selected by aligning genetic sequences from various strains available in the GenBank database. Primers and probes were selected in conserved regions. The assay sensitivity was 75 gene copies (gc)/reaction for CAL serogroup viruses and 30 gc/reaction for CVV. The performance of the assay was linear over at least 6 log10 gc. The assay was specific, given that it did not cross-react with a variety of pathogens. It did, however, detect 11 viruses within the CAL serogroup and 12 CVV isolates. The use of an internal control ensured that possible inefficiency in nucleic acid extraction or PCR inhibition would be detected. [Copyright &y& Elsevier]

Abstract: A duplex TaqMan real-time reverse transcriptase polymerase chain reaction (PCR) assay was developed for the detection of St. Louis encephalitis virus (SLEV) and eastern equine encephalitis virus (EEEV), for use in human and vector surveillance. The respective targets selected for the assay were the conserved NS5 and E1 genes of the 2 viruses. Because of the insufficient number of NS5 sequences from SLEV strains in the GenBank database, we determined the sequence of an approximately 1-kb region for each of 25 strains of SLEV to select primers and probes in a conserved region. Our assay has a sensitivity of 5 gene copies (gc)/reaction for EEEV and 10 gc/reaction for SLEV, and its performance is linear for at least 6 log10 gc. The assay is specific and detected all strains of SLEV (69) and EEEV (12) that were tested. An internal control ensures detection of efficient nucleic acid extraction and possible PCR inhibition. [Copyright &y& Elsevier]

We examined West Nile virus (WNV) seroprevalence in wild mammals along a forest-to-urban gradient in the US mid-Atlantic region. WNV antibody prevalence increased with age, urbanization, and date of capture for juveniles and varied significantly between species. These findings suggest several requirements for using mammals as indicators of transmission. [ABSTRACT FROM AUTHOR]

Abstract: To define the impact of mosquitoes and birds on intrahost WNV population dynamics, the mutant spectra that arose as a result of 20 serial in vivo passages in Culex pipiens and young chickens were examined. Genetically homogeneous WNV was serially passaged 20 times in each host. Genetic diversity was greater in mosquito-passaged WNV compared to chicken-passaged WNV. Changes in the viral consensus sequence occurred in WNV passaged in mosquitoes earlier and more frequently than in chicken-passaged WNV. Analysis of synonymous and nonsynonymous variation suggested that purifying selection was relaxed during passage in mosquitoes. Mortality in mice was significantly negatively correlated with the size of the WNV mutant spectrum. These studies suggest that mosquitoes serve as sources for WNV genetic diversity, that birds are selective sieves, and that both the consensus sequence and the mutant spectrum contribute to WNV phenotype. [Copyright &y& Elsevier]

Pathogens are transmitted from one host to another either by vertical transmission (VT) or horizontal transmission (HT). Mosquito-borne arboviruses (arthropod-borne viruses), including several clinically important viruses such as dengue, Zika, West Nile and chikungunya viruses persist in nature by both VT and HT. VT may also serve as an essential link in the transmission cycle during adverse environmental conditions. VT rates (VTRs) vary between virus families and even among viruses within the same genus. The mechanism behind these differences in VTRs among viruses is poorly understood. For efficient VT to occur, viruses must infect the mosquito germline. Here, we show that Zika virus infects mosquito ovaries and is transmitted vertically at a low rate. The infected progeny derive from mosquitoes with infected ovaries. The prevalence of ovary infection increases after a second non-infectious blood meal following an infectious blood meal. • Zika virus infects Ae. aegypti ovaries. • Infections are infrequent at 10 days post infections, but common in the 18-day samples. • The prevalence of ovary infection increases following a second non-infectious blood meal. • Zika virus vertical transmission rate is low and infected offspring are produced by mosquitoes with infected ovaries. [ABSTRACT FROM AUTHOR]

In spring 2002, an intensive avian serosurvey was initiated in Jamaica, Puerto Rico, and Mexico. We collected >1,600 specimens from resident and nonresident neotropical migratory birds before their northerly migrations. Plaque reduction neutralization test results indicated specific neutralizing antibodies to West Nile virus in 11 resident species from Jamaica. [ABSTRACT FROM AUTHOR]

Pathogens possess the ability to adapt and survive in some host species but not in others–an ecological trait known as host tropism. Transmitted through ticks and carried mainly by mammals and birds, the Lyme disease (LD) bacterium is a well-suited model to study such tropism. Three main causative agents of LD, Borrelia burgdorferi, B. afzelii, and B. garinii, vary in host ranges through mechanisms eluding characterization. By feeding ticks infected with different Borrelia species, utilizing feeding chambers and live mice and quail, we found species-level differences in bacterial transmission. These differences localize on the tick blood meal, and specifically complement, a defense in vertebrate blood, and a polymorphic bacterial protein, CspA, which inactivates complement by binding to a host complement inhibitor, Factor H (FH). CspA selectively confers bacterial transmission to vertebrates that produce FH capable of allele-specific recognition. CspA is the only member of the Pfam54 gene family to exhibit host-specific FH-binding. Phylogenetic analyses revealed convergent evolution as the driver of such uniqueness, and that FH-binding likely emerged during the last glacial maximum. Our results identify a determinant of host tropism in Lyme disease infection, thus defining an evolutionary mechanism that shapes host-pathogen associations. Author summary: The evolution of pathogens in response to a host environment often leads to a specificity of these pathogens to survive in particular hosts, known as host tropism. However, the mechanisms of host tropism remain unclear. The Lyme disease (LD) bacterium is an ideal model to study such mechanisms because the causative agent of this disease (bacteria species) are transmitted by ticks and carried by multiple vertebrates, including mammals and birds. We found that different LD bacteria species vary in their ability to survive in mice and quail, and in ticks fed on human or quail blood after transmission. We also showed that such a variation is dependent on whether tick blood meals have functional complement, an innate defense in vertebrate blood. We attributed such species-to-species differences of transmission to the polymorphisms of a bacterial complement inactivating protein, CspA: CspA, by inactivating vertebrate complement in tick blood meals in a species-specific manner, allows bacterial transmission to selective vertebrates. We further demonstrated that this CspA-mediated bacterium species-specific complement evasion arose through convergent evolution, as an evolutionary mechanism to permit such vertebrate-bacteria interaction. The mechanisms defined in this multi-disciplinary work provide new insights into the host-pathogen interactions. [ABSTRACT FROM AUTHOR]

Background: Transmission of pathogens by vector mosquitoes is intrinsically linked with mosquito's reproductive strategy because anautogenous mosquitoes require vertebrate blood to develop a batch of eggs. Each cycle of egg maturation is tightly linked with the intake of a fresh blood meal for most species. Mosquitoes that acquire pathogens during the first blood feeding can transmit the pathogens to susceptible hosts during subsequent blood feeding and also vertically to the next generation via infected eggs. Large-scale gene-expression changes occur following each blood meal in various tissues, including ovaries. Here we analyzed mosquito ovary transcriptome following a blood meal at three different time points to investigate blood-meal induced changes in gene expression in mosquito ovaries. Results: We collected ovaries from Aedes aegypti that received a sugar meal or a blood meal on days 3, 10 and 20 post blood meal for transcriptome analysis. Over 4000 genes responded differentially following ingestion of a blood meal on day 3, and 660 and 780 genes on days 10 and 20, respectively. Proteins encoded by differentially expressed genes (DEGs) on day 3 include odorant binding proteins (OBPs), defense-specific proteins, and cytochrome P450 detoxification enzymes. In addition, we identified 580 long non-coding RNAs that are differentially expressed at three time points. Gene ontology analysis indicated that genes involved in peptidase activity, oxidoreductase activity, extracellular space, and hydrolase activity, among others were enriched on day 3. Although most of the DEGs returned to the nonsignificant level compared to the sugar-fed mosquito ovaries following oviposition on days 10 and 20, there remained differences in the gene expression pattern in sugar-fed and blood-fed mosquitoes. Conclusions: Enrichment of OBPs following blood meal ingestion suggests that these genes may have other functions besides being part of the olfactory system. The enrichment of immune-specific genes and cytochrome P450 genes indicates that ovaries become well prepared to protect their germ line from any pathogens that may accompany the blood meal or from environmental contamination during oviposition, and to deal with the detrimental effects of toxic metabolites. [ABSTRACT FROM AUTHOR]

All 4 dengue viruses (DENV) cause sporadic outbreaks of human disease in the Rio Grande Valley along the US-Mexico border. In addition, West Nile virus (WNV) is enzootic in most border communities, and is the only arbovirus known to cause human disease in the El Paso, Texas community. In an effort to determine if DENV were also endemic in the El Paso community, a serosurvey was conducted among mothers at the time of delivery of their babies in selected hospitals. Cord-blood plasma samples obtained from mothers were tested for DENV antibody by an enzyme-linked immuno-sorbent assay (ELISA), plaque reduction neutralization test (PRNT) and a multiplex microsphere immunoassay. All DENV antibody positive plasma samples were also tested for WNV antibody by the same assays to consider the possibility that DENV antibody positive samples reflected WNV cross reactive antibody. The results indicated that 0.74% (11/1,472) of the mothers had a previous DENV infection and that 3.3% (48/1,472) had a previous WNV infection. Of these mothers, 0.20% (3/1,472) had antibody to both DENV and WNV as evidence of infection by both viruses. The results indicated that 0.2% (3/1472) of the mothers were positive for antibody to only WNV envelope, thus suggesting an undetermined flavivirus infection. Although 6 of the 11 DENV antibody positive mothers did not have a history of travel to a DENV endemic country, the findings of this survey provided further evidence of local transmission of WNV and suggested the possibility of focal autochthonous transmission of DENV in the El Paso community. [ABSTRACT FROM AUTHOR]

Both mosquito species-specific differences and virus strain -specific differences impact vector competence. Previous results in our laboratory with individual populations of N. American mosquitoes support studies suggesting Aedes aegypti are more competent than Ae. albopictus for American Zika virus (ZIKV) strains and demonstrate that U.S. Ae. albopictus have higher competence for an ancestral Asian ZIKV strain. A982V, an amino acid substitution in the NS1 gene acquired prior to the American outbreak, has been shown to increase competence in Ae. aegypti. We hypothesized that variability in the NS1 could therefore contribute to species-specific differences and developed a reverse genetics system based on a 2016 ZIKV isolate from Honduras (ZIKV-WTic) to evaluate the phenotypic correlates of individual amino acid substitutions. In addition to A982V, we evaluated G894A, which was acquired during circulation in the Americas. Reversion of 982 and 894 to ancestral residues increased infectivity, transmissibility and viral loads in Ae. albopictus but had no effect on competence or replication in Ae. aegypti. In addition, while host cell-specific differences in NS1 secretion were measured, with significantly higher secretion in mammalian cells relative to mosquito cells, strain-specific differences in secretion were not detected, despite previous reports. These results demonstrate that individual mutations in NS1 can influence competence in a species-specific manner independent of differences in NS1 secretion and further indicate that ancestral NS1 residues confer increased competence in Ae. albopictus. Lastly, experimental infections of Ifnar1-/- mice demonstrated that these NS1 substitutions can influence viral replication in the host and, specifically, that G894A could represent a compensatory change following a fitness loss from A982V with some viral genetic backgrounds. Together these data suggest a possible role for epistatic interactions in ZIKV fitness in invertebrate and vertebrate hosts and demonstrate that strains with increased transmission potential in U.S. Ae. albopictus could emerge. Author summary: The factors that facilitated the emergence and rapid dissemination of ZIKV in the Americas, and the specific role of strain variation and adaptive evolution in ZIKV transmission, are not fully understood. It has been shown that an amino acid substitution in the NS1 gene acquired prior to the American outbreak confers increased infectivity in Ae. aegypti. Therefore, we hypothesized that variability in the NS1 could contribute to species-specific differences. To investigate the role of the ZIKV NS1 in competence of both Ae. aegypti and Ae. albopictus we utilized reverse genetics to revert to the ancestral NS1 residues and characterized the resultant mutant strains. Reversions increased infectivity, transmissibility and viral loads in Ae. albopictus but had no effect on competence or replication in Ae. aegypti. Additionally, we assessed the effect of these mutations on NS1 secretion and both virulence and viremia kinetics using a ZIKV mouse model. NS1 secretion, as well as vertebrate morbidity or mortality, were similar among strains, yet strain-specific differences in viremia levels were identified. These results demonstrate that individual mutations in NS1 can influence competence in a species-specific manner independent of differences in NS1 secretion and further indicate that ancestral NS1 residues confer increased competence in Ae. albopictus. Moreover, contrasting these data with previous studies suggests a role for epistatic interactions in ZIKV fitness in invertebrate and vertebrate hosts. [ABSTRACT FROM AUTHOR]

Identifying viruses in synanthropic animals is necessary for understanding the origin of many viruses that can infect humans and developing strategies to prevent new zoonotic infections. The white-footed mouse, Peromyscus leucopus, is one of the most abundant rodent species in the northeastern United States. We characterized the serum virome of 978 free-ranging P. leucopus mice caught in Pennsylvania. We identified many new viruses belonging to 26 different virus families. Among these viruses was a highly divergent segmented flavivirus whose genetic relatives were recently identified in ticks, mosquitoes, and vertebrates, including febrile humans. This novel flavi-like segmented virus was found in rodents and shares ≤70% aa identity with known viruses in the highly conserved region of the viral polymerase. Our data will enable researchers to develop molecular reagents to further characterize this virus and its relatives infecting other hosts and to curtail their spread, if necessary. [ABSTRACT FROM AUTHOR]

We characterized the first microsatellite loci in the white-dotted mosquito, Culex restuans, a critical early spring West Nile virus vector. An enrichment protocol yielded 960 positive clones of which we sequenced 300. We designed primers to amplify 29 unique di-, tri- and tetranucleotide microsatellites and chose 17 that amplified consistently across populations and were polymorphic. We developed three multiplex primer combinations for all 17 loci. A survey of 44 individuals revealed two to 20 alleles across loci, and expected heterozygosity ranging from 0.17 to 0.89. These markers will allow examination of the life history of this mysterious early season encephalitis vector. [ABSTRACT FROM AUTHOR]

COVID-19 vaccines under the International Health Regulations - We must use the WHO International Certificate of Vaccination or Prophylaxis. [Extracted from the article]

West Nile virus (WNV; Flaviviridae: Flavivirus) is a widely distributed arthropod-borne virus that has negatively affected human health and animal populations. WNV infection rates of mosquitoes and human cases have been shown to be correlated with climate. However, previous studies have been conducted at a variety of spatial and temporal scales, and the scale-dependence of these relationships has been understudied. We tested the hypothesis that climate variables are important to understand these relationships at all spatial scales. We analyzed the influence of climate on WNV infection rate of mosquitoes and number of human cases in New York and Connecticut using Random Forests, a machine learning technique. During model development, 66 climate-related variables based on temperature, precipitation and soil moisture were tested for predictive skill. We also included 20–21 non-climatic variables to account for known environmental effects (e.g., land cover and human population), surveillance related information (e.g., relative mosquito abundance), and to assess the potential explanatory power of other relevant factors (e.g., presence of wastewater treatment plants). Random forest models were used to identify the most important climate variables for explaining spatial-temporal variation in mosquito infection rates (abbreviated as MLE). The results of the cross-validation support our hypothesis that climate variables improve the predictive skill for MLE at county- and trap-scales and for human cases at the county-scale. Of the climate-related variables selected, mean minimum temperature from July–September was selected in all analyses, and soil moisture was selected for the mosquito county-scale analysis. Models demonstrated predictive skill, but still over- and under-estimated WNV MLE and numbers of human cases. Models at fine spatial scales had lower absolute errors but had greater errors relative to the mean infection rates. [ABSTRACT FROM AUTHOR]

Zika (ZIKV) and dengue (DENV) virus infections elicit a robust but cross-reactive antibody response against the viral envelope protein, while antibody responses against non-structural proteins (NS) are more virus specific. Building on this premise, we have previously developed a flavivirus multiplex microsphere immunoassay (MIA) for the serologic diagnosis of ZIKV and DENV infections. This assay significantly improved diagnostic accuracy; however, MIA could not differentiate more recent from past infections, which still represents a major diagnostic challenge. Therefore, an immunoglobulin G (IgG) based avidity assay was developed and its diagnostic performance evaluated. Specimens from New York State residents were submitted to the Wadsworth Center New York State Department of Health (NYSDOH) for routine clinical testing by Zika IgM ELISA and plaque reduction neutralization test (PRNT). Using our previously developed flavivirus MIA as a platform, we developed an IgG avidity assay to discriminate recent ZIKV from past DENV infections. Zika IgM positive specimens had an average Zika IgG avidity index of 14.8% (95% CI: 11.0-18.4%), while Zika IgM negative but flavivirus MIA and PRNT positive samples had an average Zika IgG avidity index of 34.9% (95% CI: 31.1-38.7%). Specimens positive for dengue antibodies by flavivirus MIA and PRNT had an average dengue IgG avidity index of 68.7% (95% CI: 62.7-75.0%). The IgG avidity assay accurately distinguished recent ZIKV from past DENV infections in patients who traveled to dengue endemic regions. This assay could be very useful in patients with high risk of Zika complications such as pregnant women and monitoring immune responses in vaccine trials. [ABSTRACT FROM AUTHOR]