Persistence of antibodies to West Nile virus in naturally infected rock pigeons (Columba livia)

Naturally induced humoral immunity to West Nile virus infection in raptors

West Nile virus (WNV) infection can be fatal to many bird species, including numerous raptors, though population- and ecosystem-level impacts following introduction of the virus to North America have been difficult to document. Raptors occupy a diverse array of habitats worldwide and are important to ecosystems for their role as opportunistic predators. We documented initial (primary) WNV infection and then regularly measured WNV-specific neutralizing antibody titers in 16 resident raptors of seven species, plus one turkey vulture. Most individuals were initially infected and seroconverted between July and September of 2003, though three birds remained seronegative until summer 2006. Many of these birds became clinically ill upon primary infection, with clinical signs ranging from loss of appetite to moderate neurological disease. Naturally induced WNV neutralizing antibody titers remained essentially unchanged in some birds, while eight individuals experienced secondary rises in titer presumably due to additional exposures at 1, 2, or 3 years following primary infection. No birds experienced clinical signs surrounding or following the time of secondary exposure, and therefore antibodies were considered protective. Results of this study have implications for transmission dynamics of WNV and health of raptor populations, as well as the interpretation of serologic data from free-ranging and captive birds. Antibodies in raptors surviving WNV may persist for multiple years and protect against potential adverse effects of subsequent exposures.

Nestling passerines are not important hosts for amplification of West Nile Virus in Chicago, Illinois

Nestling birds have been hypothesized to be important hosts for mosquito-borne arboviruses, but the role of nestlings for West Nile virus (WNV) amplification remains unclear. We sampled open-cup and cavity-nesting passerines in Chicago, Illinois, an area of intense WNV transmission, to determine infection rates in nestlings and mosquitoes, and to test whether mosquitoes are attracted to nesting birds. Analysis of Culex pipiens mosquito populations demonstrated WNV amplification to high mosquito infection rates during both years of the study near the locations where nestlings were sampled. Nevertheless, of 194 nestlings representing 12 species, only one 8-day-old house wren was positive for WNV RNA, and only one 10-day-old mourning dove was seropositive for antibodies to WNV, but at a low titer (1:20). The number of mosquitoes captured in nest box traps and control traps was not significantly different. These combined results suggest that nestling passerines play no evident role in WNV amplification and transmission in the Chicago area.

Urban land use predicts West Nile virus exposure in songbirds

Urbanization is a widespread phenomenon that is likely to influence the prevalence and impact of wildlife pathogens, with implications for wildlife management and public health policies toward zoonotic pathogens. In this study, wild songbird populations were sampled at 14 sites along an urban rural gradient in the greater metropolitan Atlanta (Georgia, USA) area and tested for antibodies to West Nile virus (WNV). The level of urbanization among sites was quantitatively assessed using a principal component analysis of key land use characteristics. In total, 499 individual birds were tested during the spring and summer over three years (2004-2006). Antibody prevalence of WNV increased from rural to urban sites, and this trend was stronger among adult birds relative to juveniles. Furthermore, antibody prevalence among Northern Cardinals (Cardinalis cardinalis) was significantly higher than in other songbird species along the urban gradient. Findings reported here indicate that ecological factors associated with urbanization can influence infection patterns of this vector-borne viral disease, with likely mechanisms including changes in host species diversity and the tolerance or recovery of infected animals.

Magpies as hosts for West Nile virus, southern France

European magpies (Pica pica) from southern France were tested for antibodies to West Nile virus (WNV) and viral shedding in feces during spring–autumn 2005. Results suggest that this peridomestic species may be a suitable sentinel species and a relevant target for additional investigations on WNV ecology in Europe.

Interannual dynamics of antibody levels in naturally infected long-lived colonial birds

Little is known about the long-term persistence of specific antibodies (Ab) in natural host-parasite systems despite its potential epidemiological and ecological importance. In long-lived species, knowledge of the dynamics of individual immunological profiles can be important not only for interpreting serology results, but also for assessing transmission dynamics and the potential selective pressures acting on parasites. The aim of this paper was to investigate temporal variation in levels of specific Ab against the bacterium Borrelia burgdorferi sensu lato in adults of a long-lived colonial seabird, the Black-legged Kittiwake Rissa tridactyla. In wild populations, adults are naturally exposed each breeding season to a Borrelia vector, the tick Ixodes uriae. Breeding birds were captured during four consecutive breeding seasons, and parasite infestation quantified. Using enzyme-linked immunosorbent assay (ELISA) and immunoblots, we found that the immunological profiles of anti-Borrelia Ab were highly repeatable among years, reflecting the interannual persistence of Ab levels. We nevertheless also observed that year-to-year changes of Ab levels were related to exposure to ticks in the previous year. The long-term persistence of Ab levels may be an important mechanism of individual protection against future exposure to the microparasite. It will also affect the availability of susceptible hosts, and thus the transmission dynamics of the bacterium. These results illustrate the need to consider the dynamics of the immune response in order to better understand the evolutionary ecology of host-parasite interactions in natural populations.

Seroconversion in wild birds and local circulation of West Nile virus, Spain

A serosurvey for neutralizing antibodies against West Nile virus (WNV) in common coots (Fulica atra) was conducted in Doñana, Spain. Antibody prevalence was highest in 2003, intermediate in 2004, and lowest in 2005. Some birds seroreverted <1 year after first capture. Seroconversion of birds suggests local circulation of the virus.

Prevalence of West Nile virus neutralizing antibodies in colonial aquatic birds in southern Spain

The rapid expansion of West Nile virus (WNV) throughout the New World has raised interest in understanding the population dynamics and patterns of dispersal of emerging infectious diseases by wildlife. WNV affects humans, although its main reservoirs are various species of birds. Here we analyse the prevalence of WNV-neutralizing antibodies in nearly full-grown chicks belonging to seven different species of colonial waterbirds at three localities in southern Spain. Chicks with neutralizing antibodies against WNV were detected in three species and at all three localities. However, the low antibody titres suggest the presence of antibodies is probably due to maternal transfer of antibody, presumably from exposure of the adult birds to WNV or a similar flavivirus at some stage of their lives. The analyses of the movements of tagged birds confirmed that all species with antibody visit regions that have had reports of WNV infection over the past decade.

PASSIVE TRANSFER OF MATERNAL ANTIBODIES TO WEST NILE VIRUS IN FLAMINGO CHICKS (PHOENICOPTERUS CHILENSIS AND PHOENICOPTERUS RUBER RUBER)

Passive transfer of maternal antibodies against West Nile virus (WNV) was studied in a captive population of Chilean (Phoenicopterus chilensis) and Caribbean flamingos (Phoenicopterus ruber ruber). Transfer of WNV antibodies from hens to chicks was documented and measured by plaque-reduction neutralization test. Hen titers were significantly correlated to chick titers. Mean half-life of maternal WNV antibodies was 13.4 days in chicks for which half-life was measurable.

West Nile virus antibodies in avian species of Georgia, USA: 2000-2004

West Nile virus (WNV) was first isolated in the state of Georgia in the summer of 2001. As amplifying hosts of WNV, avian species play an important role in the distribution and epidemiology of the virus. The objective of this study was to identify avian species that are locally involved as potential amplifying hosts of WNV and can serve as indicators of WNV transmission over the physiographic and land use variation present in the southeastern United States. Avian serum samples (n=14,077) from 83 species of birds captured throughout Georgia during the summers of 2000-2004 were tested by a plaque reduction neutralization test for antibodies to WNV and St. Louis encephalitis virus. Over the 5-year period, WNV-neutralizing antibodies were detected in 869 (6.2%) samples. The WNV seroprevalence increased significantly throughout the study and was species dependent. The highest antibody prevalence rates were detected in rock pigeons (Columba livia), northern cardinals (Cardinalis cardinalis), common ground doves (Columbina passerina), grey catbirds (Deumetella carolinensis), and northern mockingbirds (Mimus polyglottos). Northern cardinals, in addition to having high geometric mean antibody titers and seroprevalence rates, were commonly found in all land use types and physiographic regions. Rock pigeons, common ground doves, grey catbirds, and northern mockingbirds, although also having high seroprevalence rates and high antibody titers against WNV, were more restricted in their distribution and therefore may be of more utility when attempting to assess exposure rates in specific habitat types. Of all species tested, northern cardinals represent the best potential avian indicator species for widespread serologic-based studies of WNV throughout Georgia due to their extensive range, ease of capture, and high antibody rates and titers. Due to the large geographic area covered by this species, their utility as a WNV sentinel species may include most of the eastern United States.

West Nile virus antibody prevalence in American crows (Corvus brachyrhynchos) and fish crows (Corvus ossifragus) in Georgia, USA

Crows have been the centerpiece of avian West Nile virus (WNV) surveillance and research in North America. This work has demonstrated variation in susceptibility to WNV infection between American (Cor vus brachyrhynchos) andFish Crows (Corvus ossifragus). The higher WNV-associated mortality rate in American Crows compared with Fish Crows suggests that WNV antibody prevalence would be greater in the Fish Crow population. The objectives of this study were to 1) determine whether Fish Crows had higher WNV antibody prevalencethan American Crows, 2 ) determine th e persistence o f antibodies to WNV in naturally infected Fish Crows, and 3) develop a technique to distinguish Fish Crows from American Crows on the basis of sequence analysis and restriction enzyme digestion of a mitochondrial DNA fragment. West Nile virus antibody prevalence was 16.5% (n = 97) in Fish Crows and 5.7% in American Crows (n = 53) collected from Georgia between 2004 and 2006. Antibodies persisted at high titers for 12 mo in Fish Crows. This is the first report of WNV antibody persistence in a crow species. A polymerase chain reaction technique paired with restriction enzyme digestion easily distinguished American Crows from Fish Crows on the basis of a mitochondrial DNA fragment.

Bird Species Potentially Involved in Introduction, Amplification, And Spread of West Nile Virus in A Mediterranean Wetland, The Camargue (Southern France)

West Nile virus (WNV) is a mosquito-transmitted Flavivirus with a transmission cycle involving birds as amplifying hosts. Wild birds are also believed to carry WNV over large distances and are able to introduce it into new areas during migration and dispersal. In this paper, our objective is to provide lists of birds potentially involved in the introduction, the amplification and the spread of WNV in the Camargue, a Mediterranean wetland in the south of France where several WNV outbreaks have occurred since the 1960s. Bird species were classified according to the following ecological factors: migratory status and provenance area, used biotopes, abundance and period of presence in the Camargue. The obtained lists of bird species potentially involved in the introduction, amplification and spread of WNV should prove useful to determine target species on which further studies on WNV ecology in birds could be focused.

West Nile virus: recent trends in diagnosis and vaccine development

West Nile virus (WNV) is a mosquito-borne flavivirus, native to Africa, Europe, and Western Asia. In many respects, WNV is an outstanding example of a zoonotic pathogen that has leaped geographical barriers and can cause severe disease in human and horse. Before the emergence of WNV in the USA, only few methods of diagnosis were available. Recently, many changes in the fields of WN diagnosis and prevention have happened. This paper will review all these new tools. After a description of the main concerns in WNV and West Nile (WN) disease in humans and animals, this review will present the main available tests for serology and virology detection, from gold standard tests to more recently developed methods. Finally, licensed vaccines and candidate vaccines developed in humans, horses and birds will also been described.

West Nile virus epizootiology, central Red River Valley, North Dakota and Minnesota, 2002-2005

West Nile virus (WNV) epizootiology was monitored from 2002 through 2005 in the area surrounding Grand Forks, North Dakota. Mosquitoes were tested for infection, and birds were surveyed for antibodies. In 2003, WNV was epidemic; in 2004, cool temperatures precluded WNV amplification; and in 2005, immunity in passerines decreased, but did not preclude, WNV amplification.

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.

Passive West Nile Virus Antibody Transfer from Maternal Eastern Screech-Owls (Megascops asio) to Progeny

Transovarial antibody transfer in owls has not been demonstrated for West Nile virus (WNV). We sampled chicks from captive adult WNV-antibody-positive Eastern Screech-Owls (Megascops asio) to evaluate the prevalence of transovarial maternal antibody transfer, as well as titers and duration of maternal antibodies. Twenty-four owlets aged 1 to 27 days old circulated detectable antibodies with neutralizing antibody titers ranging from 20 to 1600 (median 1:40). Demonstrating that WNV antibodies are passively transferred transovarially is important for accurate interpretation of serologic data from young birds.