Emerging Avian Disease: Published for the Cooper Ornithological Society
126
Emerging Avian Disease: Published for the Cooper Ornithological Society
126eBook
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Overview
Product Details
| ISBN-13: | 9780520952201 |
|---|---|
| Publisher: | University of California Press |
| Publication date: | 05/02/2012 |
| Series: | Studies in Avian Biology , #42 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 126 |
| File size: | 3 MB |
About the Author
Read an Excerpt
Emerging Avian Disease
By Ellen Paul
UNIVERSITY OF CALIFORNIA PRESS
Copyright © 2012 Cooper Ornithological SocietyAll rights reserved.
ISBN: 978-0-520-95220-1
CHAPTER 1
Ecological Associations of West Nile Virus and Avian Hosts in an Arid Environment
Holly B. Vuong, Donald F. Caccamise, Marta Remmenga, and Rebecca Creamer
Abstract. We evaluated disease associations of West Nile virus (WNV) with avian hosts in four key habitats of southern New Mexico (agriculture, desert, riparian, and urban). Our goal was to examine the role of avian life history traits in transmission of WNV and to evaluate possible mechanisms to explain differences in seroprevalence among avian communities. Seroprevalence was highest in Summer Tanagers (Piranga rubra, 39%) and American Robins (Turdus migratorius, 33%). Serosurveys of bird communities indicated differences among habitats, age, and resident status. Urban and agricultural habitats had higher seroprevalence than desert and riparian habitats. After-hatch-year birds had higher seroprevalence than hatch-year birds. Seroprevalence in permanent resident and local breeding species were higher than migrants and winter residents. Males had higher seroprevalence in 2004, while females were higher in 2005. Analyses among communities indicated negative relationships between seroprevalence and avian species diversity and richness. Desert and riparian habitats had higher diversity and lower seroprevalence compared to urban and agriculture. This study revealed associations between WNV and avian life history traits, providing insights into mechanisms of transmission in the arid Southwest. In addition, we found relationships between complexity of avian host communities (e.g., species diversity, species richness) and patterns in seroprevalence of WNV in avian host species.
Key Words: avian community, desert, habitat, life history, seroprevalence, southern New Mexico, West Nile virus, WNV.
Asociaciones Ecológicas del Virus del Nilo Occidental y sus Aves Hospedadoras en un Ambiente Árido
Resumen. Evaluamos las asociaciones de la enfermedad del virus del Nilo Occidental (VNO) con sus aves hospedadoras en cuatro hábitats clave del Sur de Nuevo México (agrícola, desértico, ripario y urbano). Nuestro objetivo fue examinar el papel que juegan las características de las historias de vida de las aves en la transmisión del VNO, y evaluar los posibles mecanismos que expliquen las diferencias de la seroprevalencia entre las distintas comunidades de aves. La seroprevalencia más alta se observó en la Tángara Roja migratoria (Piranga rubra, 39%), y en el Zorzal Pechirrojo (Turdus migratorius, 33%). El estudio serológico de las comunidades de aves indicó que existen diferencias entre hábitats, edad, y estatus de residencia. Las aves de hábitats urbanos y agrícolas presentaron una seroprevalencia mayor que las de hábitats desérticos y riparios. La seroprevalencia fue mayor en aves adultas que en juveniles. La seroprevalencia de las especies residentes y de las especies que se reproducen localmente fue mayor que la de las especies migratorias y las residentes invernales. Los machos mostraron una mayor seroprevalencia en 2004, mientras que las hembras tuvieron una mayor seroprevalencia en 2005. Los análisis para las diferentes comunidades indicaron que existe una relación negativa entre la seroprevalencia y la diversidad y riqueza de especies de aves. Los hábitats desérticos y riparios presentaron una mayor diversidad y menor seroprevalencia que los hábitats urbanos y agrícolas. Este estudio reveló la existencia de asociaciones entre el VNO y las características de las historias de vida de las aves, proporcionando información sobre los mecanismos de transmisión en el ambiente árido del Suroeste de los Estado Unidos. Además, encontramos relaciones entre la complejidad de las comunidades de aves hospedadoras (por ejemplo, la diversidad y riqueza de especies) y los patrones de seroprevalencia del VNO en las especies de aves infectadas.
Palabras Clave: comunidad aviar, desierto, hábitat, historia de vida, meridional, Nuevo México, seroprevalencia, Virus del Nilo Occidental, VNO.
In the US, 326 bird species in 57 families and 23 orders have tested positive for West Nile virus (WNV) infection since the virus was first detected in New York City in 1999 (CDC 2009). As an emerging disease in the U.S., WNV expanded across the Western Hemisphere, developing new host–virus associations along the way. Initial studies in the U.S. documented the spread of WNV and were based mainly on surveillance for dead birds (Bernard et al. 2001; Eidson et al. 2001a, 2001b). Such studies provided information on the impact of infection on individual species, but they failed to examine the ecological dynamics of WNV in relation to host communities. More recently, research efforts have focused on the role of individual species in the associations between WNV and avian host communities (Beveroth et al. 2006, Ezenwa et al. 2006, Marshall et al. 2006, Harris and Sleeman 2007, Wilcox et al. 2007). In addition, reservoir competency studies under laboratory conditions provided information on the susceptibility of individual species to WNV and their potential role in the transmission cycle (Komar et al. 2003). Studies based on capture of free-living birds have provided information on exposure to the virus under natural conditions (Ringia et al. 2004, Beveroth et al. 2006, Marshall et al. 2006).
The life history traits of birds, including residency status, habitat, age, and sex, can influence disease prevalence. Resident birds have been shown to have higher seroprevalence for WNV (Ringia et al. 2004, Beveroth et al. 2006, Gibbs et al. 2006) and other mosquito-borne encephalitic viruses (Crans et al. 1994, Goddard et al. 2002, Reisen et al. 2004b) that may be due to the longer seasonal overlap of residents with mosquito vectors. Nonetheless, migratory birds may be key players in transporting the virus to new areas (Rappole et al. 2000). Studies of habitat effects for WNV have focused primarily on urban versus rural areas (Taylor et al. 1956, McIntosh and Jupp 1982, Tsai et al. 1998, Ringia et al. 2004). These past field studies demonstrated that seroprevalence in humans and avian hosts and WNV prevalence in mosquitoes tend to be higher in urban habitats.
Several similar arboviruses, such as eastern equine encephalitis (EEE; Crans et al. 1994), St. Louis encephalitis (SLE; Gruwell et al. 2000, Reisen et al. 2000), and western equine encephalitis (WEE; Reisen et al. 2000), along with WNV (Ringia et al. 2004, Beveroth et al. 2006, Gibbs et al. 2006), have shown differences in seroprevalence between age classes, with after-hatch-year birds (AHY) generally showing higher rates than hatch-year (HY) birds. Nonetheless, HY birds are important in the transmission cycle of arboviruses because they are naïve, susceptible hosts when they enter the population, and could serve to amplify disease transmission and help maintain the pathogen for extended periods (Reed and Crans 1998, Hamer et al. 2008). A sex bias in seroprevalence might provide new insights into the ecology of host–pathogen interactions. The first study to show sexual differences in seroprevalence reported that female Northern Cardinals (Cardinalis cardinalis) in Ohio had higher WNV seroprevalence than males (Marshall et al. 2006). The authors suggested that this pattern appeared because females may be more exposed to mosquitoes during incubation. Other studies on WNV (Ringia et al. 2004, Beveroth et al. 2006, Gibbs et al. 2006) and similar arboviruses (Crans et al. 1994; Gruwell et al. 2000; Reisen et al. 2000, 2001, 2005) have not found differences in seroprevalence between sexes.
The importance of avian hosts in disease transmission can vary in relation to both community complexity and host responses to variations in local ecological conditions. When few primary reservoirs are associated with host communities, disease risk may be reduced. For example, risk of Lyme disease in humans is inversely related to complexity of host communities (Ostfeld and Keesing 2000, LoGuidice et al. 2003). The authors suggested that risk might decline if the primary competent host is relatively less abundant in more complex communities. A similar relationship was also shown with hantavirus (Mills 2006) and WNV (Ezenwa et al. 2006).
As WNV spread into New Mexico, we expected that differences in life history traits among avian hosts would result in variations in seroprevalence. Furthermore, we predicted that seroprevalence would vary among habitat types based on differences in the composition of avian host communities. Therefore, the goals of this study were to (1) evaluate the variation in disease associations of avian hosts among four key habitats of southern New Mexico (riparian, agriculture, urban, and desert), (2) examine the role of avian life history traits in the transmission of WNV, and (3) evaluate the relationships between complexity of avian host communities and patterns in seroprevalence.
METHODS
Study Area
The study area lies within the arid Chihuahuan Desert of southern New Mexico, in Doña Ana County (Fig. 1.1). With only four mosquito species making up approximately 85% of the local mosquito community, this area offers a unique opportunity to study WNV where host–vector interactions are relatively simple (Pitzer et al. 2009). The Chihuahuan Desert supports a large diversity of birds that pass through the riparian corridor of the Rio Grande River during fall and spring migrations. The arid climate in the region yields an average of 23.5 cm of rain per year, with 55% falling between July and September, mainly in the form of localized thunderstorms (Western Regional Climate Center 2009). The landcover is composed largely of upland desert mesas dominated by typical desert-shrub vegetation (Dick-Peddie 1999). The Rio Grande River valley bisects Doña Ana County from northwest to southeast and encompasses urbanized areas along with agricultural lands and highly modified riparian habitats adjacent to the river. We located three study sites within each of the four primary cover types in the area, including desert, urban, agricultural, and riparian, for a total of 12 study sites.
Desert sites were located on mesas at 3–25 km from the Rio Grande River. We chose sites with impoundment ponds for cattle watering or natural playas that provide aquatic habitats suitable for mosquito breeding when filled with summer rain. Urban sites were located within the city limits of Las Cruces. We selected residential areas that provided habitats attractive to birds. Vegetation in the residential sites is sustained by irrigation consisting of combinations of drip systems, flood irrigation, and hand watering. All agricultural crops in the Rio Grande valley are irrigated, mainly by flood irrigation. Water arrives to fields through a network of delivery canals and is drained from fields through a system of return canals that lead back to the river. Delivery canals are maintained vegetation free, but return canals have standing water throughout the year and generally support dense vegetation along the banks that is heavily used by birds (Thompson et al. 1994). The lower Rio Grande is channelized so riparian habitats are sparse, occurring where restored wetlands and narrow vegetated patches are adjacent to the river.
Avian Sampling
The field season ran from March through mid-October in 2004 and 2005. Two field crews sampled each of 12 field sites on an 8–10-day rotating schedule. We captured birds using mist nets (12 m × 2.5 m, mesh size 30 mm and 61 mm; AFO Mist Nets, Manomet, Inc., Manomet, MA), as described by Ralph et al. (1993). We set 5–10 nets per site about 30 min before sunrise and checked them every 20 min for approximately 3–4 hr. We recorded species, weight, sex, and age when possible for each captured bird (Pyle 1997, Sibley 2000) and applied a U.S. Geological Survey aluminum leg band.
We obtained a blood sample from each bird to test for WNV antibodies. For birds > 10 g, we used jugular or brachial venipuncture (29 gauge needle) to obtain at least 100 µl of blood. We placed the blood samples into 2-ml microcentrifuge tubes containing 900 µl of 5% bovine serum albumin (BSA) in buffer (PBS containing 0.05% Tween 20) to provide a 1:10 blood dilution. For birds <10 g we used brachial venipuncture by lancet and absorbed blood directly onto filter paper strips (Whatman® 1 Qualitative, Newark, NJ). We kept the blood samples cool while in the field and during transport back to the laboratory. We centrifuged the blood samples at 530 g for 10 min, transferred the plasma to newly labeled microcentrifuge tubes, and stored them at -20°C until testing. We eluted the blood samples from the filter paper strips overnight using 5% BSA buffer at 4°C and centrifuged the samples the next day at 530 g for 10 min. The eluted sera were then transferred into newly labeled tubes and stored at -20°C until testing.
Serological Assays
We used a blocking ELISA (enzyme-linked immunosorbent assay) method described by Jozan et al. (2003) to detect the presence of WNV antibodies. The monoclonal antibody (MAb 3.1112G) used in the ELISA is highly specific to the NS1 epitope of WNV, showing essentially no cross reactivity with SLE (Jozan et al. 2003). We initially tested all samples at 1:20 dilution in Immulon® 2HB plates (96 well, flat bottom Microtiter® Plates; Thermo Labsystems, Franklin, MA). Plates were read by Emax Precision Microplate Reader (Molecular Devices Corporation, Sunnyvale, CA) using program SoftMax Pro (ver. 3.1.1) at 405 nm wavelength to obtain optical density (OD) values. Dilutions of the antigen and monoclonal (generally 1:2,000 and 1:2,500, respectively) were previously determined by titration.
We estimated antibody titer by calculating the inhibition level (IL) for the antibodies by:
IL = 100 - [(TS - B/CS - B) × 100]
where TS is the OD of test serum, B is the OD of the background for each test serum, and CS is the OD of negative control. IL provides a measure of the relative number of binding sites blocked by the antibodies and therefore unavailable to the monoclonal antibodies. When we obtained an IL > 45% for our sample at 1:20 dilution, we reconfirmed by further titration (up to 1:80) before categorizing the sample as positive (Jozan et al. 2003).
Statistical Analyses
We grouped each species into one of four categories according to residency status. Permanent residents occur locally year round. Breeding birds spend their breeding period in the area but are absent during the winter. Migrants pass through during migration. Wintering birds spend their winters in southern New Mexico but do not breed locally (Sibley 2000).
We performed logistic regressions with the Genmod procedure in program SAS (ver. 9.1; SAS Institute, Cary, NC) using the binomial distribution and the logit link function to model the probability of each bird being positive for WNV antibodies as a function of habitat, month of capture, age, sex, or residency status. Not all levels of combination were included in this analysis because of too few data points to cover all levels of the interaction. However, logistic regressions on smaller interaction effects were conducted separately. Differences between pairs of proportions were tested with a chi-square test performed by the least square means statement in the Genmod procedure of SAS. We combined samples from March with April and September with October due to low numbers of captures at the start and end of field seasons. Individuals of undetermined age and sex were removed from analyses that included age and sex. Recaptured birds that were positive were only used once in the analyses, but every recapture prior to becoming seropositive was used in the analyses. To determine the importance of HY birds as a source population for virus cycling, we also examined temporal changes of seroprevalence in AHY and HY birds across the seasons.
(Continues...)
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Table of Contents
Contents
Contributors, vii,Foreword Robert G. McLean, xi,
Part I • Environmental and Behavioral Aspects of Transmission,
1 • ECOLOGICAL ASSOCIATIONS OF WEST NILE VIRUS AND AVIAN HOSTS IN AN ARID ENVIRONMENT Holly B. Vuong, Donald F. Caccamise, Marta Remmenga, and Rebecca Creamer, 3,
2 • THE TRANS-ATLANTIC MOVEMENT OF THE SPIROCHETE BORRELIA GARINII: THE ROLE OF TICKS AND THEIR SEABIRD HOSTS Sabir Bin Muzaffar, Robert P. Smith, Jr., Ian L. Jones, Jennifer Lavers, Eleanor H. Lacombe, Bruce K. Cahill, Charles B. Lubelczyk, and Peter W. Rand, 23,
3 • PARASITISM IN THE ENDEMIC GALÁPAGOS DOVE (ZENAIDA GALAPAGOENSIS) AND ITS RELATION TO HOST GENETIC DIVERSITY AND IMMUNE RESPONSE Diego Santiago-Alarcon, Robert E. Ricklefs, and Patricia G. Parker, 31,
Part II • Population-Level Impacts,
4 • PREVALENCE AND EFFECTS OF WEST NILE VIRUS ON WILD AMERICAN KESTREL (FALCO SPARVERIUS) POPULATIONS IN COLORADO Robert J. Dusek, William M. Iko, and Erik K. Hofmeister, 45,
5 • FIRST EXAMPLE OF A HIGHLY PREVALENT BUT LOW-IMPACT MALARIA IN AN ENDEMIC NEW ZEALAND PASSERINE: PLASMODIUM OF TIRITIRI MATANGI ISLAND BELLBIRDS (ANTHORNIS MELANURA) Rosemary K. Barraclough, Taneal M. Cope, Michael A. Peirce, and Dianne H. Brunton, 55,
Part III • Monitoring, Detection, and Research Practices,
6 • PROTOTYPE SYSTEM FOR TRACKING AND FORECASTING HIGHLY PATHOGENIC H5N1 AVIAN INFLUENZA SPREAD IN NORTH AMERICA A. Townsend Peterson, 67,
7 • IMMUNOPHENOTYPING OF AVIAN LYMPHOCYTES: IMPLICATIONS AND FUTURE FOR UNDERSTANDING DISEASE IN BIRDS Jeanne M. Fair, Kirsten J. Taylor-McCabe, Yulin Shou, and Babetta L. Marrone, 81,
8 • ZOONOTIC DISEASES: WHAT ORNITHOLOGISTS AND BIRD BANDERS SHOULD KNOW Ornithological Council, 91,
Index, 103,
Complete Series List, 107,