Epidemiologic and environmental characterization of the Re-emergence of St. Louis Encephalitis Virus in California, 2015-2020.

St. Louis encephalitis virus (SLEV) is an endemic flavivirus in the western and southeastern United States, including California. From 1938 to 2003, the virus was detected annually in California, but after West Nile virus (WNV) arrived in 2003, SLEV was not detected again until it re-emerged in Riverside County in 2015.

Mosquito blood-feeding patterns and nesting behavior of American crows, an amplifying host of West Nile virus.

Background: Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population.

Diagnostic applications of molecular and serological assays for bluetongue and African horse sickness.

The availability of rapid, highly sensitive and specific molecular and serologic diagnostic assays, such as competitive enzyme-linked immunosorbent assay (cELISA), has expedited the diagnosis of emerging transboundary animal diseases, including bluetongue (BT) and African horse sickness (AHS), and facilitated more thorough characterisation of their epidemiology. The development of assays based on real-time, reverse-transcription polymerase chain reaction (RT-PCR) to detect and identify the numerous serotypes of BT virus (BTV) and AHS virus (AHSV) has aided in-depth studies of the epidemiology of BTV infection in California and AHSV infection in South Africa. The subsequent evaluation of pan-serotype, real-time, RT-PCR-positive samples through the use of serotype-specific RT-PCR assays allows the rapid identification of virus serotypes, reducing the need for expensive and time-consuming conventional methods, such as virus isolation and serotype-specific virus neutralisation assays.

West Nile virus in California, 2003-2018: A persistent threat.

The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California.

Overwintering of West Nile Virus in the United States.

The establishment of a tropical virus such as West Nile (WNV; Flaviviridae: Flavivirus) within the temperate latitudes of the continental United States was unexpected and perhaps contingent, in part, upon the ability of this invasive virus to persist during winter when temperatures become too cold for replication and vector mosquito gonotrophic activity. Our Forum article reviews research examining possible overwintering mechanisms that include consistent reintroduction and local persistence in vector mosquitoes and avian hosts, mostly using examples from research conducted in California. We conclude that the transmission of WNV involves so many vectors and hosts within different landscapes that multiple overwintering pathways are possible and collectively may be necessary to allow this virus to overwinter consistently within the United States.

N-linked glycosylation of the West Nile virus envelope protein is not a requisite for avian virulence or vector competence.

The N-linked glycosylation motif at amino acid position 154-156 of the envelope (E) protein of West Nile virus (WNV) is linked to enhanced murine neuroinvasiveness, avian pathogenicity and vector competence. Naturally occurring isolates with altered E protein glycosylation patterns have been observed in WNV isolates; however, the specific effects of these polymorphisms on avian host pathogenesis and vector competence have not been investigated before. In the present study, amino acid polymorphisms, NYT, NYP, NYF, SYP, SYS, KYS and deletion (A'DEL), were reverse engineered into a parental WNV (NYS) cDNA infectious clone to generate WNV glycosylation mutant viruses.

Comparative fitness of West Nile virus isolated during California epidemics.

West Nile virus (WNV) has been circulating in California since its first detection in 2003, causing repeated outbreaks affecting public, wildlife and veterinary health. Epidemics of WNV are difficult to predict due to the multitude of factors influencing transmission dynamics among avian and mosquito hosts. Typically, high levels of WNV amplification are required for outbreaks to occur, and therefore associated viral strains may exhibit enhanced virulence and mortality in competent bird species resulting in increased mosquito infection prevalence.

Flanders hapavirus in western North America.

Flanders virus (FLAV; family Rhabdoviridae) is a mosquito-borne hapavirus with no known pathology that is frequently isolated during arbovirus surveillance programs. Here, we document the presence of FLAV in Culex tarsalis mosquitoes and a Canada goose (Branta canadensis) collected in western North America, outside of the currently recognized range of FLAV. Until now, FLAV-like viruses detected in the western United States were assumed to be Hart Park virus (HPV, family Rhabdoviridae), a closely related congener.

Detection of Arbovirus Transmission via Sugar Feeding in a Laboratory Setting.

Most species of mosquitoes consume sugar to survive and during sugar feeding can expectorate virus. Scientists have used this behavior to develop novel methods of mosquito control and arbovirus surveillance. In this study, we use sugar feeding and corresponding viral expectoration to develop an affordable method of monitoring individual mosquitoes for longitudinal data collection.

Avian malaria co-infections confound infectivity and vector competence assays of Plasmodium homopolare.

Currently, there are very few studies of avian malaria that investigate relationships among the host-vector-parasite triad concomitantly. In the current study, we experimentally measured the vector competence of several Culex mosquitoes for a newly described avian malaria parasite, Plasmodium homopolare. Song sparrow (Melospiza melodia) blood infected with a low P.

West Nile and St. Louis encephalitis viral genetic determinants of avian host competence.

West Nile virus (WNV) and St. Louis encephalitis (SLEV) virus are enzootically maintained in North America in cycles involving the same mosquito vectors and similar avian hosts. However, these viruses exhibit dissimilar viremia and virulence phenotypes in birds: WNV is associated with high magnitude viremias that can result in mortality in certain species such as American crows (AMCRs, Corvus brachyrhynchos) whereas SLEV infection yields lower viremias that have not been associated with avian mortality.

Guidance for Evaluating the Safety of Experimental Releases of Mosquitoes, Emphasizing Mark-Release-Recapture Techniques.

Experimental releases of mosquitoes are performed to understand characteristics of populations related to the biology, ability to transmit pathogens, and ultimately their control. In this article, we discuss considerations related to the safety of experimental releases of living mosquitoes, applying principles of good practice in vector biology that protect human health and comfort. We describe specific factors of experimental releases of mosquitoes that we believe are critical to inform institutional biosafety committees and similar review boards to which proposals to conduct mosquito release experiments have been submitted.

LOW PREVALENCE OF WEST NILE VIRUS ANTIBODIES IN SELECT NORTHERN CALIFORNIA OWL SPECIES (2007-2014).

The objective of this study was to determine evidence of previous West Nile virus (WNV) infection in northern California owls. Owl serum samples were collected from birds presenting to a veterinary medical teaching hospital between 2007 and 2014 and were screened for the presence of WNV antibodies by an indirect enzyme immunoassay (EIA). Only one of 71 samples (1.

Increases in the competitive fitness of West Nile virus isolates after introduction into California.

To investigate the phenotypic evolution of West Nile virus (WNV) in California, we competed sixteen isolates made during 2007-08 against COAV997-5nt, a genetically marked clone from the founding 2003 California isolate COAV997-2003. Using in vivo fitness competitions in House Finches (HOFI) and Culex tarsalis mosquitoes, we found that the majority of WNV WN02 and SW03 genotype isolates exhibited elevated replicative fitness in both hosts compared to COAV997-5nt. Increased replicative capacity in HOFIs was not associated with increased mortality, indicating that these isolates had not gained avian virulence.

Abundance and Bloodfeeding Patterns of Mosquitoes (Diptera: Culicidae) in an Oak Woodland on the Eastern Slope of the Northern Coast Range of California.

The abundance and bloodfeeding patterns of mosquitoes was studied from 2008 to 2010 at an 18 ha. oak woodland in Lake County, CA. Host-seeking females were collected weekly from sunset to sunrise by paired dry-ice-baited CDC style traps, whereas resting females were aspirated from paired walk-in red boxes.

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

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

Evaluation of Nucleic Acid Preservation Cards for West Nile Virus Testing in Dead Birds.

The California West Nile virus (WNV) Dead Bird Surveillance Program (DBSP) is an important component of WNV surveillance in the state. We evaluated FTA™ and RNASound™ cards as an alternative method for sampling dead birds for WNV molecular testing as these cards allow for more cost effective, rapid, and safer diagnostic sampling than the shipment of bird carcasses. To evaluate accuracy of results among avian sampling regimes, Reverse-Transcription Polymerase Chain Reaction (RT-PCR) results from FTA™ and RNASound™ cards were compared with results from kidney tissue, brain tissue, or oral swabs in lysis buffer in 2012-2013.

Field Methods and Sample Collection Techniques for the Surveillance of West Nile Virus in Avian Hosts.

Avian hosts play an important role in the spread, maintenance, and amplification of West Nile virus (WNV). Avian susceptibility to WNV varies from species to species thus surveillance efforts can focus both on birds that survive infection and those that succumb. Here we describe methods for the collection and sampling of live birds for WNV antibodies or viremia, and methods for the sampling of dead birds.

West Nile Virus Fitness Costs in Different Mosquito Species.

West Nile virus (WNV) remains an important public health problem causing annual epidemics in the United States. Grubaugh et al. observed that WNV genetic divergence is dependent on the vector mosquito species.

Surveys for Antibodies Against Mosquitoborne Encephalitis Viruses in California Birds, 1996-2013.

From 1996 through 2013, 54,546 individual birds comprising 152 species and 7 orders were banded, bled, and released at four study areas within California, from which 28,388 additional serum samples were collected at one or more recapture encounters. Of these, 142, 99, and 1929 birds from 41 species were positive for neutralizing antibodies against western equine encephalomyelitis virus (WEEV), St. Louis encephalitis virus (SLEV), or West Nile virus (WNV) at initial capture or recapture, respectively.