Experimental inoculation of three arboviruses in black-bellied whistling ducks (Dendrocygna autumnalis)

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

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

Epidemic Alphaviruses: Ecology, Emergence and Outbreaks

Over the past century, the emergence/reemergence of arthropod-borne zoonotic agents has been a growing public health concern. In particular, agents from the genus Alphavirus pose a significant risk to both animal and human health. Human alphaviral disease presents with either arthritogenic or encephalitic manifestations and is associated with significant morbidity and/or mortality. Unfortunately, there are presently no vaccines or antiviral measures approved for human use. The present review examines the ecology, epidemiology, disease, past outbreaks, and potential to cause contemporary outbreaks for several alphavirus pathogens.

Venous Blood Analytes and Osmolality of Rehabilitated Juvenile Black-bellied Whistling Ducks (Dendrocygna autumnalis)

Venous blood samples were collected from 129 apparently healthy, rehabilitated juvenile black-bellied whistling ducks (Dendrocygna autumnalis) immediately before release from rehabilitation. Blood gas, electrolyte, and select biochemical and hematologic values were analyzed by using a point-of-care analyzer, and complete blood cell counts and osmolality were determined. Most biochemical analyte values were distributed parametrically, while most hematologic values were nonparametrically distributed. Calculated osmolality values were in poor agreement with measured osmolality values, and values of packed cell volume had poor agreement with hematocrit values determined with the i-STAT 1. The physiologic values reported provide vital information to assess individual duck health and guide fluid therapy in captivity and may prove useful to assess free-living population health of this duck species.

Field investigations of winter transmission of eastern equine encephalitis virus in Florida

Studies investigating winter transmission of Eastern equine encephalitis virus (EEEV) were conducted in Hillsborough County, Florida. The virus was detected in Culiseta melanura and Anopheles quadrimaculatus in February 2012 and 2013, respectively. During the winter months, herons were the most important avian hosts for all mosquito species encountered. In collections carried out in the summer of 2011, blood meals taken from herons were still common, but less frequently encountered than in winter, with an increased frequency of mammalian- and reptile-derived meals observed in the summer. Four wading bird species (Black-crowned Night Heron [Nycticorax nycticorax], Yellow-crowned Night Heron [Nyctanassa violacea], Anhinga [Anhinga anhinga], and Great Blue Heron [Ardea herodias]) were most frequently fed upon by Cs. melanura and Culex erraticus, suggesting that these species may participate in maintaining EEEV during the winter in Florida.

Test of recrudescence hypothesis for overwintering of eastern equine encephalomyelitis virus in gray catbirds

Eastern equine encephalitis virus (EEEV; family Togaviridae, genus Alphavirus) epizootics are infrequent, but they can lead to high mortality in infected horses and humans. Despite the importance of EEEV to human and animal health, little is known about how the virus overwinters and reinitiates transmission each spring, particularly in temperate regions where infected adult mosquitoes are unlikely to survive through the winter. One hypothesis to explain the mechanism by which this virus persists from year to year is the spring recrudescence of latent virus in avian reservoir hosts. In this study, we tested the recrudescence hypothesis with gray catbirds (Dumatella carolinensis) captured in northern Ohio (July-August 2007). Birds were experimentally infected with EEEV on 1 October 2007. In January 2008, they were then exposed to exogenous testosterone and/or extended photoperiod to initiate reactivation of latent EEEV infection. All birds became viremic with EEEV, with mean viremia of 6.0 log10 plaque-forming units/ml serum occurring at 1 d postinoculation. One male in the testosterone, long-day treatment group had EEEV viral RNA in a cloacal swab collected on 18 January 2008. Otherwise, no other catbirds exhibited reactivated infections in cloacal swabs or blood. Antibody titers fluctuated over the course of the study, with lowest titers observed in January 2008, which corresponded with the lowest mean weight of the birds. No EEEV viral RNA was detected in the blood, kidney, spleen, brain, liver, and lower intestine upon necropsy at 19 wk postinfection.

West Nile virus activity in the United States, 2001

West Nile virus (WNV) first appeared in the naive environment of the Western Hemisphere in 1999 in New York. Genetic analysis determined that the virus was introduced into the United States from the Mediterranean Basin. This review discusses the spread of the virus in 2001 from the initial focus in Queens, New York, to widespread activity in the eastern and midwestern United States. It concentrates on viral ecology, epizootiology, pathology, prediction, and prevention. Research questions to further our understanding of the transmission cycle of WNV are discussed, including host-preference studies, molecular confirmation of implicated mosquito vectors, and survival of WNV in the temperate environment of the United States. Comparisons are drawn with two other arboviruses enzootic in the United States, eastern equine encephalitis, and St. Louis encephalitis viruses. Although not recently introduced, these two viruses also demonstrated increased activity in the United States in 2001.

Method of infection does not alter response of chicks and house finches to western equine encephalomyelitis and St. Louis encephalitis viruses

The effects of method of infection and virus dose on the viremia and antibody responses of 1-wk-old chicks and after-hatching-year house finches to infection with western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were studied under laboratory conditions. Using a capillary tube technique, females from 2 strains of Culex tarsalis Coquillett mosquitoes were estimated to expectorate from 1.0 to 1.7 log10 plaque forming units (PFU) of WEE and from 1.9 to 2.2 log10 PFU of SLE. Based on the proportion of parenterally infected females that transmitted and the number that blood fed during each experiment, virus doses per bird were estimated to be 1.0-1.9 log10 PFU for WEE and 1.4-2.3 log10 PFU for SLE. When infected with comparable doses of WEE by subcutaneous inoculation, there was no significant difference in the duration or magnitude of the viremia response between birds infected by mosquito bite or syringe; few birds developed a viremia response after infection with SLE, precluding analysis. In chickens, increasing the syringe dose of WEE from 0.3 to 1.7 log10 PFU/0.1 ml shortened the time when viremia first appeared from 3 to 1 d postinfection and increased the duration of the viremia period from 1 to 3 d, but did not alter the maximum viremia titer. In house finches, increasing the syringe dose of WEE from 2.6 to 3.3 log10 PFU/0.1 ml did not alter markedly the viremia response. Most birds developed antibody detected by enzyme immunoassay (EIA) or plaque reduction neutralization test (PRNT). In chickens, WEE EIA levels and PRNT titers were higher for birds infected by syringe than by mosquito bite, whereas in house finches the pattern was reversed. For birds infected with SLE, there was overlap among groups infected by mosquito bite or syringe. These results indicate that subcutaneous syringe inoculation provides a biologically sound mode of infection that did not alter viremia and antibody responses when compared with infection by mosquito bite.