Test of Recrudescence Hypothesis for Overwintering of Eastern Equine Encephalomyelitis Virus in Gray Catbirds

Abstract

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.

Characterizing areas of potential human exposure to eastern equine encephalitis virus using serological and clinical data from horses

“…The phenomenon of recurrence of EEE three years in a row in southern Lanaudière would warrant further investigations on the potential mechanisms driving EEEV endemicity. The potential for transovarial transmission of EEEV in mosquito vectors is not well supported in the literature [14, 25, 26] and, although a number of authors have hypothesized that EEEV could overwinter in various vertebrate hosts [27–29], the overwintering mechanism of EEEV have not been clearly elucidated.…”

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

“…This possibility requires further validation. Owen et al (2011) could not document persistent infections and viral recrudesce in experimentally infected gray catbirds, except for the detection of viral RNA from a single cloacal sample. In a study by Howard et al (2004) , wild birds inhabiting the toad harbor swamp in central NY were captured from 1986 to 1990 and screened for the presence of EEEV antibodies and live virus.…”

“…Moreover, EEEV is listed as a select agent, which creates additional regulatory oversight and hurdles when conducting research with this virus. Nevertheless, a handful of studies have been published to report that virtually all passerine bird species tested supported sufficient viremias (>10 3 PFU/ml) required to infect susceptible mosquitoes ( Davis 1940 , Kissling et al 1954 , Komar et al 1999 , Owen et al 2011 ). Species tested included house sparrow ( Passer domesticus ), brown-headed cowbird ( Molothrus ater ), northern cardinal ( Cardinalis cardinalis ), common grackle ( Quiscalus quiscula ), gray catbird ( Dumetella carolinensis ), European starling ( Sturnus vulgaris ), red-winged blackbird ( Agelaius phoeniceus ), American robin, and song sparrow ( Melospiza melodia ), but sample sizes were small ( n < 3) for some of these species.…”

Baseline corticosterone is positively related to juvenile survival in a migrant passerine bird

“…We did not validate the assay for the thrush and instead used assay conditions found to be effective for several other songbird species [white‐crowned sparrow ( Zonotrichia leucophrys ): Wada, Hahn & Breuner ; house sparrow ( Passer domesticus ): Kuhlman & Martin ; grey catbird ( Dumetella carolinensis ) Owen et al . , ]. Briefly, we added a 10% steroid displacement reagent (5 μL) to 5 μL of plasma; 5 min later, we added an assay buffer (240 μL) to each sample, vortexed and aliquoted in duplicate (100 μL per well) to assay plates.…”

“…At the completion of fieldwork, we shipped samples to the University of South Florida on dry ice where all laboratory analysis took place. We used a commercially available enzyme immunoassay (EIA) kit (cat# 900-097; Assay Designs, Ann Arbor, MI, USA) to measure corticosterone in plasma (Breuner et al 2006 Owen et al 2010Owen et al , 2011. Briefly, we added a 10% steroid displacement reagent (5 lL) to 5 lL of plasma; 5 min later, we added an assay buffer (240 lL) to each sample, vortexed and aliquoted in duplicate (100 lL per well) to assay plates.…”