Socio-ecology of the marsh rice rat (Oryzomys palustris) and the spatio-temporal distribution of Bayou virus in coastal Texas.

Along the southeastern coast of the United States of America (USA), the marsh rice rat (Oryzomys palustris) is the primary host for the hantavirus, genotype Bayou. According to the socio-ecological model for a territorial, polygamous species, females should be distributed across space and time by habitat resources and predation risks, whereas males should space themselves according to the degree of female aggregation and reproductive synchrony. To investigate how females affect the male-male transmission paradigm of Bayou virus, rodents were captured, marked, released in two macrohabitat types and followed across a 30-month period. Microhabitat cover variables were quantified around the individual trap stations. A geodatabase was created from habitat and rodent capture data and analysed in a geographical information system. The ratio of breeding to non-breeding females was ~1:1, with breeding females overly dispersed and non-breeding females randomly dispersed. Spatial analyses revealed both macro- and microhabitat preferences in females. Compared to seronegatives, higher proportions of seropositive adult males were found consistently within closer proximities to breeding females but not to non-breeding females, indicating that male locations were not driven simply by habitat selection. Activities to acquire dispersed receptive females could be an important driver of Bayou virus transmission among male hosts. Herein, we describe an interdisciplinary effort providing a novel approach to elucidate the complexity of hantavirus trafficking and maintenance in rodent populations of a coastal marsh ecosystem.

Bayou virus detected in non-oryzomyine rodent hosts: an assessment of habitat composition, reservoir community structure, and marsh rice rat social dynamics.

In the United States, Bayou virus (BAYV) ranks second only to Sin Nombre virus (SNV) in terms of hantavirus pulmonary syndrome (HPS) incidents, having been confirmed in cases from Texas and Louisiana since its discovery in 1994. This study on BAYV infection among sympatric, non-oryzomyine rodents ("spillover") in Freeport, TX, is the first to link patterns of hantavirus interspecific spillover with the spatiotemporal ecology of the primary host (marsh rice rat, Oryzomys palustris). Mark-recapture and/or harvest methods were employed from March 2002 through May 2004 in two macrohabitat types. Rodent blood samples were screened for the presence of IgG antibody to BAYV antigen by IFA after which Ab-positive blood, saliva, and urine were analyzed for the presence of viral RNA by nested RT-PCR. From 727 non-oryzomyine captures, five seropositive (but not viral RNA positive) individuals were detected: one each of Baiomys taylori, Peromyscus leucopus, and Reithrodontomys fulvescens; and two Sigmodon hispidus. Spillover hosts were not associated with macrohabitat where O. palustris abundance, density, or seroprevalence was highest. Rather, spillover occurred in the macrohabitat indicative of greater overall disturbance (as indicated by grazing and exotic plant diversity) and overall biodiversity. Spillover occurred during periods of high seroprevalence detected elsewhere within the study region. Spillover locations differed significantly from all other capture locations in terms of percent water, shrub, and grass cover. Although greater habitat and mammal diversity of old-fields may serve to reduce seroprevalence levels by tempering intraspecific contacts between rice rats, greater diversity also may create an ecologically opportunistic setting for BAYV spillover. Impacts of varying levels of disturbance and biodiversity on transmission dynamics represent a vastly uncharacterized component of the evolutionary ecology of hantaviruses.

A longitudinal study of Bayou virus, hosts, and habitat.

What is currently known about the ecology of North American hantaviruses has come largely from studies on Sin Nombre virus (SNV). We conducted a longitudinal study of Bayou virus (BAYV), the second-leading agent of hantavirus pulmonary syndrome in the United States. Antibodies to hantavirus were detected from Oryzomys palustris (most commonly infected species), Sigmodon hispidus, Peromyscus leucopus, Reithrodontomys fulvescens, and Baiomys taylori. However, only O. palustris had viral RNA in tissues and excreta, suggesting that antibodies detected in other species may have resulted from spill-over infection. Seroprevalence rates averaged around 16% for O. palustris and varied seasonally. The heaviest males exhibited the highest levels of seroprevalence. Seroprevalence was higher in coastal prairie (20.0%) than old-fields (10.5%) and was associated with host abundance. These patterns are similar to those of SNV and can be used in identification of potentially at-risk areas.