Serologic Evidence of West Nile Virus and St. Louis Encephalitis Virus Infections in White-Tailed Deer (Odocoileus virginianus) from New Jersey, 2001

Emerging tickborne viruses vectored by Amblyomma americanum (Ixodida: Ixodidae): Heartland and Bourbon viruses

Heartland (HRTV) and Bourbon (BRBV) viruses are newly identified tick-borne viruses, isolated from serious clinical cases in 2009 and 2014, respectively. Both viruses originated in the lower Midwest United States near the border of Missouri and Kansas, cause similar disease manifestations, and are presumably vectored by the same tick species, Amblyomma americanum Linnaeus (Ixodida: Ixodidae). In this article, we provide a current review of HRTV and BRBV, including the virology, epidemiology, and ecology of the viruses with an emphasis on the tick vector. We touch on current challenges of vector control and surveillance, and we discuss future directions in the study of these emergent pathogens.

North American Arboviruses and White-Tailed Deer (Odocoileus virginianus): Associated Diseases and Role in Transmission

Background: Arboviral disease is of increasing concern to human and animal health professionals as emerging and re-emerging arboviruses are more frequently recognized. Wildlife species are known to play a role in the transmission and maintenance of arboviruses and infections can result in morbidity and mortality in wildlife hosts. Materials and Methods: In this review, we detail existing evidence of white-tailed deer (Odocoileus virginianus) as an important host to a diverse collection of arboviruses and evaluate the utility of this species as a resource to better understand the epidemiology of related viral diseases. Results: Relevant veterinary and zoonotic viral pathogens endemic to North America include epizootic hemorrhagic disease virus, bluetongue virus, orthobunyaviruses, vesicular stomatitis virus, Eastern equine encephalitis virus, West Nile virus, and Powassan virus. Exotic viral pathogens that may infect white-tailed deer are also identified with an emphasis on zoonotic disease risks. The utility of this species is attributed to the high degree of contact with humans and domestic livestock and evidence of preferential feeding by various insect vectors. Conclusions: There is mounting evidence that white-tailed deer are a useful, widely available source of information regarding arboviral circulation, and that surveillance and monitoring of deer populations would be of value to the understanding of certain viral transmission dynamics, with implications for improving human and domestic animal health.

Spatiotemporal distribution, abundance, and host interactions of two invasive vectors of arboviruses, Aedes albopictus and Aedes japonicus, in Pennsylvania, USA

Background

Aedes albopictus and Aedes japonicus, two invasive mosquito species in the United States, are implicated in the transmission of arboviruses. Studies have shown interactions of these two mosquito species with a variety of vertebrate hosts; however, regional differences exist and may influence their contribution to arbovirus transmission.

Methods

We investigated the distribution, abundance, host interactions, and West Nile virus infection prevalence of Ae. albopictus and Ae. japonicus by examining Pennsylvania mosquito and arbovirus surveillance data for the period between 2010 and 2018. Mosquitoes were primarily collected using gravid traps and BG-Sentinel traps, and sources of blood meals were determined by analyzing mitochondrial cytochrome b gene sequences amplified in PCR assays.

Results

A total of 10,878,727 female mosquitoes representing 51 species were collected in Pennsylvania over the 9-year study period, with Ae. albopictus and Ae. japonicus representing 4.06% and 3.02% of all collected mosquitoes, respectively. Aedes albopictus was distributed in 39 counties and Ae. japonicus in all 67 counties, and the abundance of these species increased between 2010 and 2018. Models suggested an increase in the spatial extent of Ae. albopictus during the study period, while that of Ae. japonicus remained unchanged. We found a differential association between the abundance of the two mosquito species and environmental conditions, percent development, and median household income. Of 110 Ae. albopictus and 97 Ae. japonicus blood meals successfully identified to species level, 98% and 100% were derived from mammalian hosts, respectively. Among 12 mammalian species, domestic cats, humans, and white-tailed deer served as the most frequent hosts for the two mosquito species. A limited number of Ae. albopictus acquired blood meals from avian hosts solely or in mixed blood meals. West Nile virus was detected in 31 pools (n = 3582 total number of pools) of Ae. albopictus and 12 pools (n = 977 total pools) of Ae. japonicus.

Conclusions

Extensive distribution, high abundance, and frequent interactions with mammalian hosts suggest potential involvement of Ae. albopictus and Ae. japonicus in the transmission of human arboviruses including Cache Valley, Jamestown Canyon, La Crosse, dengue, chikungunya, and Zika should any of these viruses become prevalent in Pennsylvania. Limited interaction with avian hosts suggests that Ae. albopictus might occasionally be involved in transmission of arboviruses such as West Nile in the region.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05151-8.

Serologic Survey of Mosquito-Borne Viruses in Hunter-Harvested White-Tailed Deer (Odocoileus virginianus), New York State

Sera from white-tailed deer (WTD, Odocoileus virginianus) hunter-harvested throughout New York State (NYS), 2007-2015, were tested by plaque reduction neutralization for antibodies against nine mosquito-borne viruses from the families Peribunyaviridae, Flaviviridae, and Togaviridae. Overall, 76.1% (373/490) of sampled WTD were seropositive against at least one virus, and 38.8% were exposed to multiple viruses. The seropositivity rate in adult WTD (78.0%) was significantly greater (P < 0.0001) than that in fawns (47.7%). Neutralizing antibodies against California serogroup viruses were most common in WTD sampled across all regions (67.1%), followed by the Bunyamwera serogroup (BUN) (37.6%). Jamestown Canyon and Cache Valley orthobunyaviruses were responsible for most California and BUN infections, respectively. Seroprevalence rates to West Nile virus were higher in samples originating from Long Island (LI) (19.0%) than in those originating from the central (7.3%), western (5.0%), and Hudson Valley (4.4%) regions of NYS. Antibodies to Eastern equine encephalitis virus were seen primarily in WTD from central NYS (5.1%), where annual enzootic activity occurs, but low rates were documented in western NYS (1.4%) and LI (1.7%). Low rates of Potosi and LaCrosse orthobunyavirus, and Highlands J virus antibodies were detected over the course of this investigation. St. Louis encephalitis virus (or a closely related virus) antibodies were detected in samples collected from central and western NYS, suggesting local virus transmission despite a lack of evidence from routine mosquito surveillance. Serologic results demonstrate the value of WTD in NYS as an indicator of arbovirus distribution and recent transmission on a relatively fine spatial scale.

Serological Evidence of West Nile Virus Infection in White-Tailed Deer in Central Texas

White-tailed deer (WTD) are abundant mammals widely distributed across the United States. As a result, WTD are considered to be excellent sentinels for detecting arboviral activity in certain geographic areas. Evidence of West Nile virus (WNV) antibody in WTD has been reported previously in several states. However, WNV infection in WTD has not been reported from Texas, where the incidence of human West Nile (WN) cases is among the highest in the United States. Therefore, the aim of this study was to determine the prevalence of WNV antibody in WTD in central Texas. Sera samples (n = 644) were collected from deer during the fall and winter in western Travis County, Texas from 2014 to 2018 and tested for WNV immunoglobulin G (IgG) antibody by an indirect enzyme-linked immunosorbent assay (ELISA). ELISA antibody-positive samples were further tested for WNV and St. Louis encephalitis virus (SLEV) antibodies by an 80% plaque-reduction neutralization tests (PRNT80). Overall, 9% (n = 58) and 0.31% (n = 2) of the deer samples had serological evidence of WNV and SLEV infections, respectively. WNV seroprevalence differed significantly by age (p < 0.05), but there was no significant difference between sex. Interestingly, 3.1% (n = 20) of the samples were positive for Flavivirus IgG antibody by ELISA, but negative for SLEV and WNV antibodies, suggesting that other Flaviviruses may be circulating among WTD in Texas. Finally, these results supported WNV infection among WTD and highlight their potential role as sentinels for the detection of WNV in Texas and warrant further studies to determine the role WTD play in the maintenance and transmission of WNV.

West Nile Virus Associations in Wild Mammals: An Update

Although West Nile virus (WNV) is generally thought to circulate among mosquitoes and birds, several historic and recent works providing evidence of WNV activity in wild mammals have been published. Indeed, a previous review tabulated evidence of WNV exposure in at least 100 mammalian species. Herein, we provide an update on WNV activity in wild and select other mammals that have been reported since the last major review article on this subject was published in early 2013. Of interest, new species, such as Hoffman’s two-toed sloths (Choloepus hoffmanni), are now included in the growing list of wild mammals that have been naturally exposed to WNV. Furthermore, new instances of WNV viremia as well as severe disease presumably caused by this virus have been reported in wild mammals (e.g., the Virginia opossum [Didelphis virginiana]) from natural and semi-captive (e.g., zoological institution) settings. Regrettably, few recent challenge studies have been conducted on wild mammals, which would provide key information as to their potential role(s) in WNV cycles. Largely based on these recent findings, important future lines of research are recommended to assess which mammalian species are commonly exposed to WNV, which mammal species develop viremias sufficient for infecting mosquitoes, and which mammal species might be negatively affected by WNV infection at the species or population level.

Serologic Evidence of Various Arboviruses Detected in White-Tailed Deer (Odocoileus virginianus) in the United States

White-tailed deer (Odocoileus virginianus) are an abundant mammal with a wide geographic distribution in the United States, which make them good sentinels for monitoring arboviral activity across the country. Exposure to various arboviruses has been detected in white-tailed deer, typically in conjunction with another diagnostic finding. To better assess the exposure of white-tailed deer to seven arboviruses, we tested 1,508 sera collected from 2010 to 2016 for antibodies to eastern equine encephalitis (2.5%), Powassan (4.2%), St. Louis encephalitis, (3.7%), West Nile (6.0%), Maguari (19.4%), La Crosse (30.3%), and bluetongue (7.8%) viruses. At least one arbovirus was detected in 51.3%, and exposure to more than one arbovirus was identified in 17.6% of the white-tailed deer sampled.

Spatio-temporal trends and risk factors affecting West Nile virus and related flavivirus exposure in Spanish wild ruminants

Background

During the last decade, the spread of many flaviviruses (Genus Flavivirus) has been reported, representing an emerging threat for both animal and human health. To further study utility of wild ruminant samples in West Nile virus (WNV) surveillance, we assessed spatio–temporal trends and factors associated with WNV and cross-reacting flaviviruses exposure, particularly Usutu virus (USUV) and Meaban virus (MBV), in wild ruminants in Spain. Serum samples from 4693 wild ruminants, including 3073 free-living red deer (Cervus elaphus), 201 fallow deer (Dama dama), 125 mouflon (Ovis aries musimon), 32 roe deer (Capreolus capreolus) and 1262 farmed red deer collected in 2003–2014, were screened for WNV and antigenically-related flavivirus antibodies using a blocking ELISA (bELISA). Positive samples were tested for neutralizing antibodies against WNV, USUV and MBV by virus micro-neutralization tests.

Results

Mean flavivirus seroprevalence according to bELISA was 3.4 ± 0.5 % in red deer, 1.0 ± 1.4 % in fallow deer, 2.4 ± 2.7 % in mouflon and 0 % in roe deer. A multivariate logistic regression model revealed as main risk factors for seropositivity in red deer; year (2011), the specific south-coastal bioregion (bioregion 5) and presence of wetlands. Red deer had neutralizing antibodies against WNV, USUV and MBV.

Conclusions

The results indicate endemic circulation of WNV, USUV and MBV in Spanish red deer, even in areas without known flavivirus outbreaks. WNV antibodies detected in a free-living red deer yearling sampled in 2010, confirmed circulation this year. Co-circulation of WNV and USUV was detected in bioregions 3 and 5, and of WNV and MBV in bioregion 3. Sampling of hunted and farmed wild ruminants, specifically of red deer yearlings, could be a complementary way to national surveillance programs to monitor the activity of emerging flaviviruses.

Serological evidence for Saint Louis encephalitis virus in free-ranging New World monkeys and horses within the upper Paraná River basin region, Southern Brazil

INTRODUCTION

Saint Louis encephalitis virus (SLEV) primarily occurs in the Americas and produces disease predominantly in humans. This study investigated the serological presence of SLEV in nonhuman primates and horses from southern Brazil.

METHODS

From June 2004 to December 2005, sera from 133 monkeys (Alouatta caraya, n=43; Sapajus nigritus, n=64; Sapajus cay, n=26) trap-captured at the Paraná River basin region and 23 blood samples from farm horses were obtained and used for the serological detection of a panel of 19 arboviruses. All samples were analyzed in a hemagglutination inhibition (HI) assay; positive monkey samples were confirmed in a mouse neutralization test (MNT). Additionally, all blood samples were inoculated into C6/36 cell culture for viral isolation.

RESULTS

Positive seroreactivity was only observed for SLEV. A prevalence of SLEV antibodies in sera was detected in Alouatta caraya (11.6%; 5/43), Sapajus nigritus (12.5%; 8/64), and S. cay (30.8%; 8/26) monkeys with the HI assay. Of the monkeys, 2.3% (1/42) of A. caraya, 6.3% 94/64) of S. nigritus, and 15.4% (4/26) of S. cay were positive for SLEV in the MNT. Additionally, SLEV antibodies were detected by HI in 39.1% (9/23) of the horses evaluated in this study. Arboviruses were not isolated from any blood sample.

CONCLUSIONS

These results confirmed the presence of SLEV in nonhuman primates and horses from southern Brazil. These findings most likely represent the first detection of this virus in nonhuman primates beyond the Amazon region. The detection of SLEV in animals within a geographical region distant from the Amazon basin suggests that there may be widespread and undiagnosed dissemination of this disease in Brazil.

Vector-host interactions of Culex pipiens complex in northeastern and southwestern USA

Studies on the vector-host interactions of Culex pipiens complex mosquitoes by sequencing portions of mitochondrial cytochrome b gene indicate that Cx. p. pipiens f. pipiens predominantly feed on avian hosts (93.1%), and focus feeding activity on several key bird species, in particular the American robin, the gray catbird, and the house sparrow in Connecticut. However, Cx. p. quinquefasciatus indiscriminately feed on both birds and mammals. Culex p. quinquefasciatus in Harris County - Texas and southern California acquired 39.1% and 88.2% of bloodmeals from birds, respectively. Mammalian-derived bloodmeals constituted 52.5% and 9.6% in the two regions, respectively. The most frequent avian hosts for this mosquito species in the southwestern U.S. were the mourning dove, the white-winged dove, the house sparrow and the house finch. Humans infrequently served as the source of bloodmeals for Cx. p. pipiens and Cx. p. quinquefasciatus. Microsatellite analysis of mosquitoes from Chicago, Illinois showed that Cx. p. pipiens f. pipiens with mammalian- derived bloodmeals had significantly higher ancestry and proportion of hybrids from Cx. p. pipiens f. molestus than did those with avian-derived bloodmeals.

Do wild ungulates allow improved monitoring of flavivirus circulation in Spain?

As a response to the need for improved and cost-efficient West Nile virus (WNV) and other flavivirus surveillance tools, we tested 887 juvenile free-living red deer, 742 free-living juvenile wild boar, and 327 farmed deer, to detect temporal variability in exposure to these viruses. Thirty of 742 wild boar samples (4%; 95% CI 2.8,5.7) yielded a positive ELISA result. Antibody-positive individuals had been sampled between 2003 and 2011 in localities from central and southern Spain. No wild boar from the northern half of Spain (n=120) tested positive. Regarding juvenile wild red deer, only two out of 887 samples yielded a positive ELISA result (0.2%; 95% CI 0.1,0.8). These two samples came from the same site and sampling year. The likelihood of detecting contact with WNV or cross-reacting flaviviruses was 18 times higher among juvenile wild boar than among juvenile red deer. ELISA positivity among farmed deer increased 10-fold after local flavivirus outbreaks recorded in the summer and autumn of 2010. This survey demonstrated the potential usefulness of juvenile wild ungulates, particularly wild boar, as suitable flavivirus sentinels in southwestern Europe, and that systematic serum banking of samples from hunter-harvested wildlife or from individual farmed ungulates provides valuable material for retrospective epidemiological surveys and future disease monitoring.

Larviciding offshore islands reduces adulticidal treatment of populated areas adjacent to national wildlife refuges

The Florida Keys Mosquito Control District has conducted larvicide missions on uninhabited offshore islands of the Great White Heron National Wildlife Refuge and the National Key Deer Refuge since 2003. The objective of these missions is to reduce the need to apply adulticides on nearby populated islands where private lands are interspersed with refuge lands that support a diverse assemblage of native butterflies and insect-pollinated plants on Big Pine Key, No Name Key, Little Torch Key, Middle Torch Key, and Big Torch Key (the Torch Keys). More than 800 visits were made to refuge islands by Florida Keys Mosquito Control District personnel; 334 aerial larvicide missions were flown. From 2003 to 2010, a marked reduction in adult mosquito numbers was seen on Big Pine Key, and to a lesser extent on No Name Key. Seasonal distribution of mosquitoes was not different, however. Number of aerial adulticide missions flown on Big Pine Key, No Name Key, and the Torch Keys was 2, 1, and 2 in 2003; 9, 10, and 7 in 2004; 4, 4, and 2 in 2005; 6, 6, and 7 in 2006; 1, 0, and 0 in 2007; 3, 2, and 4 in 2008; 4, 3, and 4 in 2009; and 1, 1, and 3 in 2010, respectively. This is a dramatic reduction from prior years; from 1998 to 2002, 57 aerial adulticide missions were flown on Big Pine Key, 45 missions were flown on No Name Key, and 38 on the Torch Keys. Larviciding is an important component of an integrated approach to mosquito management that seeks to reduce environmental impacts on the national wildlife refuges.

Identification of bloodmeals in Anopheles quadrimaculatus and Anopheles punctipennis from eastern equine encephalitis virus foci in northeastern U.S.A

The host-feeding patterns of Anopheles quadrimaculatus Say and Anopheles punctipennis (Say) were examined in order to evaluate their potential contributions to the transmission of eastern equine encephalitis virus (EEEv) and other arboviruses in the northeastern U.S.A. Engorged mosquitoes of the two species were collected from EEEv foci in central New York (NY) and throughout New Jersey (NJ), and their bloodmeals were identified using a polymerase chain reaction (PCR)-based assay and sequencing portions of the mitochondrial cytochrome b gene. Analysis of 131 An. quadrimaculatus and 107 An. punctipennis from NY revealed that 97.7% and 97.2%, respectively, had acquired blood solely from mammalian hosts. Similarly, examination of 288 An. quadrimaculatus and 127 An. punctipennis from NJ showed 100% and 96.0%, respectively, contained mammalian-derived bloodmeals. Mosquitoes containing mixed bloodmeals from both avian and mammalian hosts were detected in 1.6% of An. quadrimaculatus from NY, and 2.8% and 4.0% of An. punctipennis from NY and NJ, respectively. White-tailed deer (Odocoileus virginianus) constituted the most common vertebrate host for these anopheline mosquitoes, accounting for 85.8-97.7% of all bloodmeals identified. The predominance of white-tailed deer as a source of bloodmeals supports enzootic amplification of deer-associated arboviruses in this region, including Jamestown Canyon, Cache Valley and Potosi viruses. One horse- and two human-derived bloodmeals were also detected in An. quadrimaculatus collected in NJ. Limited avian-derived bloodmeals were detected from mourning dove (Zenaida macroura), sharp-shinned hawk (Accipiter striatus) and house finch (Carpodacus mexicanus), mostly in mixed bloodmeals. Occasional feeding on avian hosts suggests that these mosquitoes may participate as epizootic-epidemic bridge vectors of EEEv from viraemic birds to mammalian hosts of concern, including horses and humans. An isolate of EEEv was recovered from the head and thorax of an An. punctipennis mosquito collected in NY.

Human bloodfeeding by the recently introduced mosquito, Aedes japonicus japonicus, and public health implications

Knowledge of the host-feeding behavior and extent of interactions with human hosts are important in evaluating the role and vector potential of invasive mosquitoes in transmission of native arboviruses. We collected blood-engorged females of the recently established exotic species Aedes japonicus japonicus from sites in New Jersey during 2000 to 2007 and identified the sources of vertebrate blood meals by sequencing portions of the cytochrome b gene of mitochondrial DNA. Over 1/3 (36%, n = 36) of the engorged mosquitoes acquired blood meals from humans. Other mammalian hosts included white-tailed deer (53%), fallow deer (5%), horse (3%), and Virginia opossum (3%). No avian, amphibian, reptilian, or mixed blood meals were identified. Our detection of a comparatively high prevalence of human bloodfeeding in Ae. j. japonicus in association with its local abundance, vector competence, and repeated detection of West Nile virus from field-collected specimens illustrates the potential for this invasive mosquito to serve as a "bridge" vector in transmission of West Nile and other mosquito-borne viruses in North America.

Wild deer as a source of infection for livestock and humans in the UK

Wild deer can feature in the epidemiology of a wide range of livestock and human diseases in the United Kingdom by representing a source of disease via various transmission routes. This review highlights current and possible future infections of deer in the UK which may have an impact on livestock and/or human health. Increases in deer abundance as well as range expansion are likely to exacerbate the potential for disease persistence due to the formation of multi-species deer assemblages, which may act as disease reservoirs. Climatic changes are likely to have a direct impact on the presence and abundance of various pathogens and their vectors, so that with a warming climate exotic diseases may play a role in future UK livestock and wildlife disease management. This paper highlights the need for a monitoring strategy for wildlife diseases, in particular infections in wild deer, in the UK.

Identification of avian- and mammalian-derived bloodmeals in Aedes vexans and Culiseta melanura (Diptera: Culicidae) and its implication for West Nile virus transmission in Connecticut, U.S.A

To evaluate the host-feeding patterns of Aedes vexans (Meigen) and Culiseta melanura (Coquillett) as secondary vectors of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in Northeastern United States, we identified the source of vertebrate bloodmeals by sequencing portions of the cytochrome b gene of mitochondrial DNA. Analysis of polymerase chain reaction products from a total of 119 Ae. vexans revealed that 92.4% of individuals acquired blood solely from mammalian and 2.5% from avian hosts. Mixed bloodmeals from both avian and mammalian hosts were detected in 5% of individuals of this species. Ae. vexans obtained vertebrate bloodmeals most frequently from white-tailed deer (80%) followed by domestic horse, American robin, eastern cottontail, and domestic cat. In contrast, Cs. melanura fed predominantly on avian species (89.6%) but exhibited some inclination for mammalian blood (4.2%). Individual mosquitoes containing mixed bloodmeals were also identified in 6% of Cs. melanura. American robin was the most common source of vertebrate blood for Cs. melanura (23%), followed by wood thrush and gray catbird. American crow represented only 2% of the bloodmeals identified in Cs. melanura, as was similarly found with other recognized Culex vectors of WNV in the northeast. These findings support the view that Ae. vexans is likely to be a relatively important "bridge vector" to large mammals, including deer and horse, whereas Cs. melanura likely plays a secondary role in enzootic transmission of WNV among free-ranging birds in more rural environs.

Antibodies to West Nile Virus in Feral Swine from Florida, Georgia, and Texas, USA

West Nile virus (WNV) exposure has not yet been reported in feral swine (Sus scrofa) despite the broad geographic range and population density of this species. The objectives of this study were to determine the prevalence of antibodies to WNV in feral pigs, and to evaluate serologic diagnostics as applied to this species. Feral pig serum from three states was evaluated for antibodies to WNV. The overall WNV seroprevalence rate for 222 samples collected in 2001-2004 was 22.5%. Seroprevalence rates in Florida, Georgia, and Texas were 17.2%, 26.3%, and 20.5%, respectively. The results of this study demonstrate that feral pigs could represent useful mammalian sentinels of WNV.

Host feeding patterns of Culex mosquitoes and West Nile virus transmission, northeastern United States

Culex salinarius is a bridge vector to humans, while Cx. pipiens and Cx. restuans are more efficient enzootic vectors.

To evaluate the role of Culex mosquitoes as enzootic and epidemic vectors for WNV, we identified the source of vertebrate blood by polymerase chain reaction amplification and sequencing portions of the cytochrome b gene of mitochondrial DNA. All Cx. restuans and 93% of Cx. pipiens acquired blood from avian hosts; Cx. salinarius fed frequently on both mammals (53%) and birds (36%). Mixed-blood meals were detected in 11% and 4% of Cx. salinarius and Cx. pipiens, respectively. American robin was the most common source of vertebrate blood for Cx. pipiens (38%) and Cx. restuans (37%). American crow represented <1% of the blood meals in Cx. pipiens and none in Cx. restuans. Human-derived blood meals were identified from 2 Cx. salinarius and 1 Cx. pipiens. Results suggest that Cx. salinarius is an important bridge vector to humans, while Cx. pipiens and Cx. restuans are more efficient enzootic vectors in the northeastern United States.

Serologic Evidence of West Nile Virus Infection in Free-Ranging Mammals, Slidell, Louisiana, 2002

After an outbreak of West Nile virus (WNV) infections in Slidell, Louisiana, in 2002, we detected neutralizing antibodies to WNV in 13 of 120 mammals, representing five of six species sampled. Seroprevalence was measured in opossum, Didelphis virginiana (75%, n = 8), raccoons, Procyon lotor (60%, n = 5), black rats, Rattus rattus (6%, n = 36), hispid cotton rats, Sigmodon hispidus (4%, n = 24), and eastern gray squirrels, Sciurus carolinensis (2%, n = 43).