RESUMEN
Global migrations of diverse animal species often converge along the same routes, bringing together seasonal assemblages of animals that may compete, prey on each other, and share information or pathogens. These interspecific interactions, when energetic demands are high and the time to complete journeys is short, may influence survival, migratory success, stopover ecology, and migratory routes. Numerous accounts suggest that interspecific co-migrations are globally distributed in aerial, aquatic, and terrestrial systems, although the study of migration to date has rarely investigated species interactions among migrating animals. Here, we test the hypothesis that migrating animals are communities engaged in networks of ecological interactions. We leverage over half a million records of 50 bird species from five bird banding sites collected over 8 to 23 y to test for species associations using social network analyses. We find strong support for persistent species relationships across sites and between spring and fall migration. These relationships may be ecologically meaningful: They are often stronger among phylogenetically related species with similar foraging behaviors and nonbreeding ranges even after accounting for the nonsocial contributions to associations, including overlap in migration timing and habitat use. While interspecific interactions could result in costly competition or beneficial information exchange, we find that relationships are largely positive, suggesting limited competitive exclusion at the scale of a banding station during migratory stopovers. Our findings support an understanding of animal migrations that consist of networked communities rather than random assemblages of independently migrating species, encouraging future studies of the nature and consequences of co-migrant interactions.
Asunto(s)
Migración Animal , Aves , Ecosistema , Estaciones del Año , Animales , Migración Animal/fisiología , Aves/fisiologíaRESUMEN
Intraspecific variation in pathogen shedding impacts disease transmission dynamics; therefore, understanding the host factors associated with individual variation in pathogen shedding is key to controlling and preventing outbreaks. In this study, ileum and bursa of Fabricius tissues of wild-bred mallards (Anas platyrhynchos) infected with low-pathogenic avian influenza (LPAIV) were evaluated at various post-infection time points to determine genetic host factors associated with intraspecific variation in viral shedding. By analysing transcriptome sequencing data (RNA-seq), we found that LPAIV-infected wild-bred mallards do not exhibit differential gene expression compared to uninfected birds, but that gene expression was associated with cloacal viral shedding quantity early in the infection. In both tissues, immune gene expression was higher in high/moderate shedding birds compared to low shedding birds, and significant positive relationships with viral shedding were observed. In the ileum, expression for host genes involved in viral cell entry was lower in low shedders compared to moderate shedders at 1 day post-infection (DPI), and expression for host genes promoting viral replication was higher in high shedders compared to low shedders at 2 DPI. Our findings indicate that viral shedding is a key factor for gene expression differences in LPAIV-infected wild-bred mallards, and the genes identified in this study could be important for understanding the molecular mechanisms driving intraspecific variation in pathogen shedding.
Asunto(s)
Virus de la Influenza A , Gripe Aviar , Animales , Patos , Expresión Génica , Virus de la Influenza A/genética , Esparcimiento de VirusRESUMEN
BACKGROUND: Individual heterogeneity in pathogen load can affect disease transmission dynamics; therefore, identifying intrinsic factors responsible for variation in pathogen load is necessary for determining which individuals are prone to be most infectious. Because low pathogenic avian influenza viruses (LPAIV) preferentially bind to alpha-2,3 sialic acid receptors (SAα2,3Gal) in the intestines and bursa of Fabricius in wild ducks (Anas and Spatula spp.), we investigated juvenile mallards (Anas platyrhyncos) and blue-winged teals (Anas discors) orally inoculated with A/northern pintail/California/44221-761/2006 (H5N9) and the virus titer relationship to occurrence frequency of SAα2,3Gal in the intestines and bursa. To test the natural variation of free-ranging duck populations, birds were hatched and raised in captivity from eggs collected from nests of free-ranging birds in North Dakota, USA. Data generated from qPCR were used to quantify virus titers in cloacal swabs, ileum tissue, and bursa of Fabricius tissue, and lectin histochemistry was used to quantify the occurrence frequency of SAα2,3Gal. Linear mixed models were used to analyze infection status, species, and sex-based differences. Multiple linear regression was used to analyze the relationship between virus titer and SAα2,3Gal occurrence frequency. RESULTS: In mallards, we found high individual variation in virus titers significantly related to high variation of SAα2,3Gal in the ileum. In contrast to mallards, individual variation in teals was minimal and significant relationships between virus titers and SAα2,3Gal were not determined. Collectively, teals had both higher virus titers and a higher occurrence frequency of SAα2,3Gal compared to mallards, which may indicate a positive association between viral load and SAα2,3Gal. Statistically significant differences were observed between infected and control birds indicating that LPAIV infection may influence the occurrence frequency of SAα2,3Gal, or vice versa, but only in specific tissues. CONCLUSIONS: The results of this study provide quantitative evidence that SAα2,3Gal abundance is related to LPAIV titers; thus, SAα2,3Gal should be considered a potential intrinsic factor influencing variation in LPAIV load.
Asunto(s)
Virus de la Influenza A/metabolismo , Gripe Aviar/virología , Receptores de Superficie Celular/metabolismo , Carga Viral/veterinaria , Animales , Bolsa de Fabricio/virología , Patos , Femenino , Virus de la Influenza A/fisiología , Intestinos/virología , Masculino , Especificidad de la EspecieRESUMEN
The relationship between stress and disease is thought to be unambiguous: chronic stress induces immunosuppression, which likely increases the risk of infection. However, this link has not been firmly established in wild animals, particularly whether stress hormones affect host responses to zoonotic pathogens, which can be transmitted to domesticated animal, wildlife and human populations. Due to the dynamic effects of stress hormones on immune functions, stress hormones may make hosts better or poorer amplifying hosts for a pathogen contingent on context and the host species evaluated. Using an important zoonotic pathogen, West Nile virus (WNV) and a competent host, the Northern Cardinal (Cardinalis cardinalis), we tested the effects of exogenous corticosterone on response to WNV infection. Corticosterone was administered at levels that individuals enduring chronic stressors (i.e., long-term inclement weather, food shortage, anthropogenic pollution) might experience in the wild. Corticosterone greatly impacted mortality: half of the corticosterone-implanted cardinals died between five - 11 days post-inoculation whereas only one of nine empty-implanted (control) birds died. No differences were found in viral titer between corticosterone- and empty-implanted birds. However, cardinals that survived infections had significantly higher average body temperatures during peak infection than individuals that died. In sum, this study indicates that elevated corticosterone could affect the survival of WNV-infected wild birds, suggesting that populations may be disproportionately at-risk to disease in stressful environments.
Asunto(s)
Enfermedades de las Aves/virología , Corticosterona/metabolismo , Tolerancia Inmunológica , Pájaros Cantores , Fiebre del Nilo Occidental/veterinaria , Virus del Nilo Occidental/aislamiento & purificación , Animales , Enfermedades de las Aves/inmunología , Enfermedades de las Aves/mortalidad , Ensayo de Inmunoadsorción Enzimática/veterinaria , Femenino , Técnicas para Inmunoenzimas/veterinaria , Masculino , Michigan , Viremia/inmunología , Viremia/mortalidad , Viremia/veterinaria , Viremia/virología , Fiebre del Nilo Occidental/inmunología , Fiebre del Nilo Occidental/mortalidad , Fiebre del Nilo Occidental/virologíaRESUMEN
Intraspecific variation in host infectiousness affects disease transmission dynamics in human, domestic animal, and many wildlife host-pathogen systems including avian influenza virus (AIV); therefore, identifying host factors related to host infectiousness is important for understanding, controlling, and preventing future outbreaks. Toward this goal, we used RNA-seq data collected from low pathogenicity avian influenza virus (LPAIV)-infected blue-winged teal (Spatula discors) to determine the association between host gene expression and intraspecific variation in cloacal viral shedding magnitude, the transmissible fraction of virus. We found that host genes were differentially expressed between LPAIV-infected and uninfected birds early in the infection, host genes were differentially expressed between shed level groups at one-, three-, and five-days post-infection, host gene expression was associated with LPAIV infection patterns over time, and genes of the innate immune system had a positive linear relationship with cloacal viral shedding. This study provides important insights into host gene expression patterns associated with intraspecific LPAIV shedding variation and can serve as a foundation for future studies focused on the identification of host factors that drive or permit the emergence of high viral shedding individuals.
Asunto(s)
Virus de la Influenza A , Gripe Aviar , Animales , Humanos , Esparcimiento de Virus , Patos , Virus de la Influenza A/genética , Expresión GénicaRESUMEN
West Nile virus (WNV; Flavivirus, Flaviviridae) was introduced to New York State (NYS) in 1999 and rapidly expanded its range through the continental United States (US). Apart from the displacement of the introductory NY99 genotype with the WN02 genotype, there has been little evidence of adaptive evolution of WNV in the US. WNV NY10, characterized by shared amino acid substitutions R1331K and I2513M, emerged in 2010 coincident with increased WNV cases in humans and prevalence in mosquitoes. Previous studies demonstrated an increase in frequency of NY10 strains in NYS and evidence of positive selection. Here, we present updated surveillance and sequencing data for WNV in NYS and investigate if NY10 genotype strains are associated with phenotypic change consistent with an adaptive advantage. Results confirm a significant increase in prevalence in mosquitoes though 2018, and updated sequencing demonstrates a continued dominance of NY10. We evaluated NY10 strains in Culex pipiens mosquitoes to assess vector competence and found that the NY10 genotype is associated with both increased infectivity and transmissibility. Experimental infection of American robins (Turdus migratorius) was additionally completed to assess viremia kinetics of NY10 relative to WN02. Modelling the increased infectivity and transmissibility of the NY10 strains together with strain-specific viremia demonstrates a mechanistic basis for selection that has likely contributed to the increased prevalence of WNV in NYS.
Asunto(s)
Fiebre del Nilo Occidental , Virus del Nilo Occidental , Animales , Humanos , Mosquitos Vectores , New York/epidemiología , Prevalencia , Virus del Nilo Occidental/genéticaRESUMEN
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.
Asunto(s)
Culicidae/virología , Virus de la Encefalitis Equina del Este/fisiología , Pájaros Cantores/virología , Animales , Enfermedades de las Aves/virología , Clima Frío , Virus de la Encefalitis Equina del Este/genética , Virus de la Encefalitis Equina del Este/crecimiento & desarrollo , Virus de la Encefalitis Equina del Este/aislamiento & purificación , Encefalomielitis Equina Oriental/epidemiología , Femenino , Masculino , Mosquiteros , Ohio/epidemiología , Estaciones del Año , Pájaros Cantores/sangre , Testosterona/sangre , Viremia/virologíaRESUMEN
The blue-winged teal (Spatula discors) is a recreationally and ecologically important dabbling duck species in North America. Transcriptomic data of this species can be used in public and animal health studies given its role as a natural reservoir host for avian influenza, which can be a zoonotic disease of high concern. Ileum and bursa of Fabricius tissues were sampled from six captive raised blue-winged teals, four of the six who were experimentally infected with low-pathogenic avian influenza virus H5N9. RNAseq data were generated from extracted total mRNA from each tissue and pooled to create a de novo assembly of the transcriptome using Trinity. A total of 571,105 transcripts were identified at 449,956 unique unigenes that have been functionally annotated. This transcriptome will be useful for future blue-winged teal gene expression research, especially in hypothesis driven differential expression studies to determine the driving forces of avian influenza host-pathogen interactions, spatial distribution, and transmission.
RESUMEN
West Nile virus (WNV) infections in free-ranging birds were studied in Slidell, St. Tammany Parish, Louisiana, after a human encephalitis outbreak peaked there in July 2002. Seroprevalence in resident, free-ranging wild birds in one suburban site was 25% and 24% in August and October, respectively, indicating that most transmission had ceased by early August. Mortality rates, seroprevalence rates, host competence, and crude population estimates were used in mathematical models to predict actual infection rates, population impacts, and importance as amplifying hosts for several common passerine birds. Northern cardinal (Cardinalis cardinalis) and house sparrow (Passer domesticus) were the principal amplifying hosts, but blue jay (Cyanocitta cristata) and northern mockingbird (Mimus polyglottos) also contributed. The blue jay population was reduced by an estimated 47%. A variety of passerine bird species combined to play an important role as amplifying hosts in the WNV transmission cycle.
Asunto(s)
Aves/virología , Brotes de Enfermedades , Reservorios de Enfermedades/virología , Encefalitis Viral/epidemiología , Fiebre del Nilo Occidental/epidemiología , Virus del Nilo Occidental/aislamiento & purificación , Animales , Aves/clasificación , Reservorios de Enfermedades/clasificación , Encefalitis Viral/etiología , Encefalitis Viral/transmisión , Encefalitis Viral/virología , Humanos , Louisiana/epidemiología , Fiebre del Nilo Occidental/etiología , Fiebre del Nilo Occidental/transmisión , Fiebre del Nilo Occidental/virologíaRESUMEN
A major challenge in disease ecology is to understand the role of individual variation of infection load on disease transmission dynamics and how this influences the evolution of resistance or tolerance mechanisms. Such information will improve our capacity to understand, predict, and mitigate pathogen-associated disease in all organisms. In many host-pathogen systems, particularly macroparasites and sexually transmitted diseases, it has been found that approximately 20% of the population is responsible for approximately 80% of the transmission events. Although host contact rates can account for some of this pattern, pathogen transmission dynamics also depend upon host infectiousness, an area that has received relatively little attention. Therefore, we conducted a meta-analysis of pathogen shedding rates of 24 host (avian) - pathogen (RNA-virus) studies, including 17 bird species and five important zoonotic viruses. We determined that viral count data followed the Weibull distribution, the mean Gini coefficient (an index of inequality) was 0.687 (0.036 SEM), and that 22.0% (0.90 SEM) of the birds shed 80% of the virus across all studies, suggesting an adherence of viral shedding counts to the Pareto Principle. The relative position of a bird in a distribution of viral counts was affected by factors extrinsic to the host, such as exposure to corticosterone and to a lesser extent reduced food availability, but not to intrinsic host factors including age, sex, and migratory status. These data provide a quantitative view of heterogeneous virus shedding in birds that may be used to better parameterize epidemiological models and understand transmission dynamics.
Asunto(s)
Aves/virología , Modelos Teóricos , Virus ARN/aislamiento & purificación , Esparcimiento de Virus , Animales , Aves/clasificación , Virus ARN/fisiología , Carga ViralRESUMEN
Migrating waterfowl are implicated in the global spread of influenza A viruses (IAVs), and mallards (Anas platyrhynchos) are considered a particularly important IAV reservoir. Prevalence of IAV infection in waterfowl peaks during autumn pre-migration staging and then declines as birds reach wintering areas. Migration is energetically costly and birds often experience declines in body condition that may suppress immune function. We assessed how body condition affects susceptibility to infection, viral shedding and antibody production in wild-caught and captive-bred juvenile mallards challenged with low pathogenic avian influenza virus (LPAIV) H5N9. Wild mallards (nâ=â30) were separated into three experimental groups; each manipulated through food availability to a different condition level (-20%, -10%, and normal ±5% original body condition), and captive-bred mallards (nâ=â10) were maintained at normal condition. We found that wild mallards in normal condition were more susceptible to LPAIV infection, shed higher peak viral loads and shed viral RNA more frequently compared to birds in poor condition. Antibody production did not differ according to condition. We found that wild mallards did not differ from captive-bred mallards in viral intensity and duration of infection, but they did exhibit lower antibody titers and greater variation in viral load. Our findings suggest that reduced body condition negatively influences waterfowl host competence to LPAIV infection. This observation is contradictory to the recently proposed condition-dependent hypothesis, according to which birds in reduced condition would be more susceptible to IAV infection. The mechanisms responsible for reducing host competency among birds in poor condition remain unknown. Our research indicates body condition may influence the maintenance and spread of LPAIV by migrating waterfowl.
Asunto(s)
Susceptibilidad a Enfermedades/fisiopatología , Patos/virología , Virus de la Influenza A/fisiología , Gripe Aviar/virología , Análisis de Varianza , Migración Animal/fisiología , Animales , Tamaño Corporal/fisiología , Dieta , Patos/fisiología , Femenino , Interacciones Huésped-Patógeno , Virus de la Influenza A/genética , Gripe Aviar/fisiopatología , Gripe Aviar/transmisión , Masculino , ARN Viral/genética , ARN Viral/metabolismo , Carga Viral , Esparcimiento de Virus/fisiologíaRESUMEN
The uropygial gland of birds produces secretions that are important in maintaining the health and structural integrity of feathers. Non-volatile components of uropygial secretions are believed to serve a number of functions including waterproofing and conditioning the feathers. Volatile components have been characterized in fewer species, but are particularly interesting because of their potential importance in olfactory interactions within and across species. We used solid-phase microextraction headspace sampling with gas chromatography-mass spectrometry to detect and identify volatiles in uropygial secretions of gray catbirds (Dumetella carolinensis), a North American migratory bird. We consistently detected the following carboxylic acids: acetic, propanoic, 2-methylpropanoic, butanoic, and 3-methylbutanoic. We tested for the effect of lengthened photoperiod and/or exogenous testosterone on volatile signal strength and found a negative effect of lengthened photoperiod on the signal strength of propanoic, 2-methylpropanoic, and butanoic acids, suggesting a trade-off between their production and heightened night-time activity associated with lengthened photoperiod. Signal strength of propanoic and 2-methylpropanoic acids was lower in birds treated with exogenous testosterone than in birds treated with placebos. Sex did not affect signal strength of any of the volatile compounds.