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PubMed2006

Life-history and ecological correlates of geographic variation in egg and clutch mass among passerine species.

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study.

Animals↗

PubMed1976

Hormone concentrating cells in vocal control and other areas of the brain of the zebra finch ( Poephila guttata).

Using the autoradiographic method in the zebra finch (poephila guttata), areas of the brain were identified which contain cells which accumulate testosterone. Among these areas are the caudal nucleus of the hyperstriatum ventrale, nucleus intercollicularis of the midbrain, and the tracheosyringeal portion of the hypoglossal nucleus of the medulla (nXIIts). These three are known to control or influence androgen dependent song and other vocalizations of passeriform birds, and nXIIts is composed of the motoneurons innervating the vocal (syringeal) muscles. Other areas containing hormone-concentrating cells are the medial preoptic area, nucleus periventricularis magnocellularis of the hypothalamus, dorsal infundibular layers, dorsomedial thalamus, lateral septum, magnocellular nucleus of the anterior neostriatum, periventricular medial neostriatum, nucleus taeniae of the archistriatum, and ventral paleostriatum augmentatum. Accumulation by cells in the preoptic area, hypothalamus, and limbic forebrain is consistent with a general vertebrate pattern of distribution of brain cells which accumulate sex steroids. Some of these same areas may be involved in the control of androgen dependent events such as courtship, copulation, aggression, and feedback regulation of the hypophysis.

Animals↗

PubMed1993

Estrogen receptors in the avian brain: survey reveals general distribution and forebrain areas unique to songbirds.

Estrogens play an important role in the control and differentiation of species-typical behavior and in endocrine homeostasis of birds, but the distribution and evolution of cells that contain estrogen receptors in the avian brain are poorly understood. This study therefore surveys 26 species in the avian orders Anseriformes (1 species), Galliformes (2), Columbiformes (3), Psittaciformes (1), Apodiformes (2), and Passeriformes (3 suboscines, 14 oscines). Indirect immunocytochemistry with the estrogen receptor (ER) antibody H222Spy revealed a general pattern of ER-antibody-immunoreactive cells (ER-IRC) in all 26 species, with ER-IRC in consistent, well-defined locations in the limbic forebrain, the midbrain striatum, the hippocampus, the hindbrain, and especially in the preoptic area and the tuberal hypothalamus. For some species, the microdistribution of ER-IRC in some of these general areas differed, such as in the hippocampus and the anterior hypothalamus of suboscine species and in the preoptic area of the Japanese quail. Brains of oscine songbirds of both sexes, unlike brains of nonsongbirds, had ER-IRC in three specific structures of the nonlimbic forebrain: in the area surrounding the nucleus robustus archistriatalis; in the rostral forebrain; and, for all individuals, in the caudale neostriatum, including the nucleus hyperstriatalis ventrale, pars caudale (HVc). Among songbird families or subfamilies, adult males of the Estrildinae had much lower numbers of ER-IRC in HVc than did adult males of the Fringillidae, Paridae, Sturnidae, and Ploceinae. Differences occurred, too, among closely related species: the songbird canary (Serinus canaria) had an ER-IRC area in the rostral forebrain that was lacking in all other songbird species, including other cardueline finches. The cells with ER that are found only in the songbird forebrain but not in reptiles, nonpasserine birds, and nonoscine passerine birds very likely coevolved with steroid-dependent differentiation of vocal control areas. The songbird-specific expression of ER in the forebrain could be an example in which taxon-specific behavior is due to taxon specific neurochemical properties of the brain.

Age Factors↗

PubMed1987

Spontaneous continuous release of spermatozoa and its predawn surge in male passerine birds.

Spontaneous, continuous release of morphologically normal spermatozoa occurs in males of species of passerine (order Passeriformes) birds that were examined. It was demonstrated and studied quantitatively in temporarily captive and isolated house sparrows and house finches by means of repetitive cloacal lavages and extraction of excreta. It is suggested that this phenomenon could be exploited to facilitate comparative and quantitative evaluations of release of spermatozoa in relation to diverse environmental, physiological, and social factors.

Animals↗

PubMed2000

Avian dependence on sound pressure level as an auditory distance cue.

Sound pressure level (SPL) has received little attention as a distance cue or signal for communication because of the methodological difficulty of determining source SPL from free-ranging signallers and because SPL is presumed to be unreliable as a distance cue. Eastern towhees, Pipilo erythrophthalmus (Emberizidae, Passeriformes), in south-central Florida give a simple call during territorial interactions. I obtained measurements of call-source SPL with a calibrated microphone positioned 100+/-10 cm from caged male eastern towhees. Measurements of source SPL were highly variable, but much of this variation can be predicted from measurements of call duration or call frequency variables (spectrotemporal variables). Male towhees accurately perceived the distance of a speaker after it played synthetic calls that matched the amplitude and structure of natural 84-dB and 78-dB call types. Subjects flew further in response to an attenuated (-6 or -12 dB) version of an otherwise identical 84-dB call and flew shorter in response to an amplified (+6 dB) version of this same call. Towhees misjudged speaker distance in approximately half of the trials that included a discrepancy (-6, -12 or +6 dB SPL) between playback source SPL and predicted spectrotemporal variables. These distance errors suggest that towhees assess auditory distance partly from the difference between perceived SPL and source SPL, determined from spectrotemporal variables. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1997

Estrogen synthesis and secretion in the brown-headed cowbird (Molothrus ater).

Estrogens exert profound effects on vertebrate physiology and behavior. In most vertebrates, including birds, estrogens derived from ovarian tissue circulate at high levels during discrete periods of reproductive activity, and estrogen levels in males are low. In some songbirds (Passeriformes) plasma estrogens are high in both males and females. In the zebra finch, aromatase (estrogen-synthetase) is expressed abundantly in several regions of the male and female telencephalon and contributes to peripheral estrogen titers. To determine if this pattern of neural aromatase and estrogen synthesis is found in other songbirds, we have examined the patterns of estrogen synthesis in various tissues of another songbird, the common North American cowbird (Molothrus ater). Radiolabeled aromatizable androgenic substrate was injected in vivo or provided in vitro to telencephalic and gonadal tissue from adult male and female cowbirds. Estrogenic products were assayed in blood from the carotid artery and jugular vein, and in the telencephalon, ovary, and testes. Additionally, the presence of aromatase mRNA was studied in the brain using in situ hybridization. Radiolabeled androgenic substrate, injected in vivo, was readily converted to estrogens with higher amounts in the jugular compared to carotid blood, suggesting that the brain contains relatively high levels of aromatase. Further, radiolabeled androgens, provided in vitro to telencephalic, ovarian, and testicular tissue, resulted in the formation of radiolabeled estrogens. Aromatase mRNA is distributed widely in several areas of the cowbird telencephalon including the hippocampus, caudomedial neostriatum (including Field L), and nucleus taeniae. This pattern of neural aromatase expression resembles what we found previously in the zebra finch. Telencephalic aromatase may be characteristic of passerine songbirds and may function to provide local estrogenic cues to estrogen-sensitive neural loci, and/or contribute to peripheral estrogen titers in male and female songbirds.

Animals↗

PubMed1998

The passerine hippocampus is a site of high aromatase: inter- and intraspecies comparisons.

The vertebrate hippocampus (HP) plays a critical role in the organization of memory. Estrogens alter synaptic morphology and function in the mammalian HP and may potentiate memory performance. Previous studies suggest that the songbird HP itself is a site of significant aromatase expression, intimating that local estrogen synthesis may provide a source of this steroid to estrogen-sensitive neural circuits. To explore the potential role of local estrogen synthesis on HP structure and function, we have characterized aromatase message and activity in the zebra finch HP. Toward this end we have compared (a) HP aromatase mRNA with that at other neural loci, (b) HP aromatase activity between adults of both sexes, and (c) HP and hypothalamic preoptic area (HPOA) aromatase activity among songbirds and nonsongbirds. Finally we asked whether aromatase activity was intrinsic to the HP by maintaining it in culture, isolated from the rest of the telencephalon. The HP of every songbird studied expresses aromatase, with comparable levels across sexes. Notably, aromatase activity was found at higher levels in the songbird HP than in the HPOA. In both nonsongbird species investigated, however, HP aromatase activity was undetectable under identical assay conditions. Additionally, the developing songbird HP continues to express aromatase when cultured in isolation from the rest of the telencephalon. The data suggest that HP aromatase is characteristic of passeriformes and, as in the HPOA, may represent a mechanism whereby estrogen is made available to neural circuits. Passerines may prove invaluable animal models for investigations of the estrogenic modulation of HP structure and function.

Animals↗

PubMed1994

DNA-DNA hybridization-based phylogeny for "higher" nonpasserines: reevaluating a key portion of the avian family tree.

A matrix of delta T mode values for 10 birds, including 9 nonpasserines and a suboscine passerine flycatcher, was generated by DNA-DNA hybridization. Within the most derived lineages, all bootstrapped and jackknifed FITCH trees lend strong support to sister-groupings of the two swift families, of hummingbirds to swifts, and of these to a clade containing both owls and night-hawks. The outgroup duck roots the tree between the woodpecker (Piciformes) and the remaining taxa, indicating that Piciformes are among the earliest branches within nonpasserines. However, the succeeding branches to kingfisher, mousebird, and suboscine passerine flycatcher are based on short internodes that are poorly supported by bootstrapping and that give inconsistent results in jackknifing. Although these 3 orders may have arisen through rapid or near-simultaneous divergence, placement of the "advanced" Passeriformes deep within a more "primitive" radiation indicates that nonpasserines are paraphyletic, echoing the same distinction for reptiles with respect to their advanced descendants. Despite significant rate variation among different taxa, these results largely concur with those obtained with the same technique by Sibley and Ahlquist, who used the delta T50H measure and UPGMA analysis. This agreement lends credence to some of their more controversial claims.

Animals↗

PubMed1997

Re: Congruence and phylogenetic reanalysis of perching bird cytochrome b sequences.

In a study of the phylogenetic relationships among perching bird mtDNA sequences, Edwards et al. (1991; Proc. R. Soc. London Ser B. 243: 99-107) sequenced part of the mitochondrial cytochrome b gene from 13 perching birds (Passeriformes) and a woodpecker outgroup. However, recently the validity of part of the sequence of the hermit thrush (Catharus guttatus) in that study has been questioned. To determine the effect of inclusion of this apparently chimeric sequence on the conclusions of the original analysis, we reanalyzed these sequences using a different published hermit thrush sequence. In addition, we applied tests of congruence to examine the possibility that the aberrant phylogenetic behavior of chimeric mtDNA sequences might be detected. The reanalysis confirms the ability of slow evolving first and second codon positions of cytochrome b sequences to resolve deep branches in the avian tree. The fact that the new data set does not reject the DNA hybridization tree of these species probably indicates poor ability of the cytochrome b sequences to discriminate among alternative trees, rather than consistency among data sets. Statistical testing of trees based on individual amplified segments of mtDNA indicates that congruence tests may be one useful way of identifying chimeric mtDNA sequences when they have not been detected in the laboratory or during standard phylogenetic analysis.

Animals↗

PubMed1997

Molecular systematics of tanagers (Thraupinae): evolution and biogeography of a diverse radiation of neotropical birds.

The tanagers (Passeriformes: Emberizidae: Thraupinae) are a diverse group of mostly Neotropical birds with a wide range of feeding morphologies, behaviors, plumage patterns and colors, and habitat preferences. Phylogenetic relationships of genera in this lineage were investigated using cytochrome b sequence data. This study indicates that the genera Euphonia and Chlorophonia (traditionally considered part of Thraupinae) do not form a monophyletic group with the other tanagers. Within the rest of Thraupinae, several monophyletic groups are identified that agree with traditional sequential taxonomies. Other monophyletic groups provide novel interpretations of biogeographic patterns and morphological evolution within tanagers. In several lineages, plumage patterns and colors persist despite dramatic changes in bill morphology. Phylogenetic structure and estimated timings of divergence events indicate that tanagers probably originated on Caribbean islands and later diversified throughout Central and South America during the mid-Tertiary.

Animals↗

PubMed1999

Molecular phylogeny of Palearctic-African Acrocephalus and Hippolais Warblers (Aves: Sylviidae).

Phylogenetic relationships of the reed warbler group (genera Acrocephalus, Hippolais, Chloropeta; Aves: Passeriformes) and their potential relatives were studied using nucleotide sequences (1 kb) of the mitochondrial cytochrome b gene. This species-rich but morphologically poorly differentiated group of insectivorous passerines is distributed in Eurasia, Africa, and Australasia. Intergeneric relationships were poorly resolved, but monophyly of the reed warbler group (including Chloropeta) versus other Sylviidae was strongly supported. A basal polytomy within the reed warbler group consists of seven branches and may indicate a rapid early radiation. In the genus Acrocephalus three major clades were identified, which corresponded to phenotypic groups characterized by body size and plumage patterns. However, current delimitation of some subgenera (Acrocephalus, Lusciniola, Bebrornis) is at variance with our phylogeny estimate, and appropriate revisions are proposed. The genus Hippolais, which may or may not be monophyletic, consisted of two well-supported clades of four species each. Some Acrocephalus taxa whose species status had been doubted (griseldis, tangorum, orientalis, australis) proved to be highly distinct genetically. Genetic distances between members of two pairs of allopatric Hippolais taxa (caligata/rama; opaca/elaeica) were as large or larger than between other closely related warbler species. Overall, cytochrome b sequences resolved phylogenetically young relationships quite well, whereas more ancient nodes remained poorly resolved.

Africa↗

PubMed1983

Innervation of the avian pineal organ. A comparative study.

The innervation of the pineal organ was studied in 26 avian species under particular consideration of comparative aspects. A population of nerve cells and their pinealofugal (afferent) fiber systems were stained by means of the acetylcholinesterase method, while catecholamine-containing pinealopetal (efferent) fibers were demonstrated with the use of the glyoxylic acid method. Afferent axons were mainly found in the postero-proximal portion of the organ, and the patterns of their distribution were classified into three groups according to the characteristic densities of the reaction product. The number of acetylcholinesterase-positive neurons in the avian pineal organs examined in this study varied extremely from species to species, ranging from 0 to 362. Catecholamine-containing nerve fibers penetrating the antero-lateral walls of the pineal follicles accompanied blood vessels and were arranged more densely in the distal portion of the organ, in contrast to the distribution of the acetylcholinesterase-positive nerve fibers. Three-dimensional reconstruction of the distributional patterns of both types of neural projections was performed for the pineal organ of every avian species examined. In avian species possessing a relatively conspicuous afferent projection, such as Passeriformes, Nycticorax, and Milvus, terminals of catecholamine-containing nerve fibers were observed exclusively in the interfollicular and perivascular tissues. In Galliformes, which display only few pineal afferents, catecholamine-containing fibers terminate not only in the interfollicular space, but also in the neuroepithelial parenchyma. The regional differences in the innervation in the avian pineal organ suggest that the pinealocytes ranging from more sensory-like to more secretory-like elements are arranged in a mosaic-like pattern.

Acetylcholinesterase↗

PubMed1998

The complete mitochondrial genome of Rhea americana and early avian divergences.

The complete mitochondrial DNA, mtDNA, molecule of the greater rhea, Rhea americana, was sequenced. The size of the molecule is 16,710 nucleotides. The organization of the molecule conforms with that described for the chicken and the ostrich. It has been shown previously that relative to other vertebrates the NADH3 gene of the ostrich has an insertion of one nucleotide in position 174 of the gene. The same observation was made in the rhea and in the newly sequenced NADH3 gene of the emu, Dromaius novaehollandiae. Comparison with the NADH3 gene of the chicken and the rook suggests that the inserted nucleotide may be deleted by RNA editing. The divergence between the two struthioniform species, the ostrich and the rhea, was molecularly dated at approximately 51 million years before present, MYBP. This dating is more recent than commonly acknowledged. Phylogenetic analysis of the complete cytochrome b genes of seven avian orders placed the Passeriformes basal in the avian tree with the Struthioniformes among the remaining Neognathae. These findings challenge the commonly accepted notion that the most basal avian divergence is that between the Palaeognathae and Neognathae.

Animals↗

PubMed2004

Avian mortality events in the United States caused by anticholinesterase pesticides: a retrospective summary of National Wildlife Health Center records from 1980 to 2000.

We reviewed the U.S. Geological Survey National Wildlife Health Center (NWHC) mortality database from 1980 to 2000 to identify cases of poisoning caused by organophosphorus and carbamate pesticides. From the 35,022 cases from which one or more avian carcasses were submitted to the NWHC for necropsy, we identified 335 mortality events attributed to anticholinesterase poisoning, 119 of which have been included in earlier reports. Poisoning events were classified as confirmed (n = 205) when supported by findings of > or =50% inhibition of cholinesterase (ChE) activity in brain tissue and the detection of a specific pesticide in the gastrointestinal contents of one or more carcasses. Suspected poisonings (n = 130) were defined as cases where brain ChE activity was > or =50% inhibited or a specific pesticide was identified in gastrointestinal contents. The 335 avian mortality events occurred in 42 states. Washington, Virginia, and Ohio had the highest frequency of events, with 24 (7.2%), 21 (6.3%), and 20 (6.0%) events, respectively. A total of 8877 carcasses of 103 avian species in 12 orders was recovered. Because carcass counts underestimate total mortality, this represents the minimum actual mortality. Of 24 different pesticides identified, the most frequent were famphur (n = 59: 18%), carbofuran (n = 52; 15%), diazinon (n = 40; 12%), and fenthion (n = 17; 5.1%). Falconiformes were reported killed most frequently (49% of all die-offs) but Anseriformes were found dead in the greatest numbers (64% of 8877 found dead). The majority of birds reported killed by famphur were Passeriformes and Falconiformes, with the latter found dead in 90% of famphur-related poisoning events. Carbofuran and famphur were involved in mortality of the greatest variety of species (45 and 33, respectively). Most of the mortality events caused by diazinon involved waterfowl.

Acetylcholinesterase↗

PubMed2000

Mhc diversity in two passerine birds: no evidence for a minimal essential Mhc.

Humans express an array of Mhc genes, while the chicken has an Mhc that is relatively small and compact with fewer expressed genes. Here we ask whether the "minimal essential Mhc" of the chicken is representative for birds. We investigated the RFLP genotypes in 55 great reed warblers Acrocephalus arundinaceus and 10 willow warblers Phylloscopus trochilus to obtain an overview of the number of class II B genes. There were 13-17 bands per individual in the great reed warblers and 25-30 in the willow warblers, and every individual had a unique RFLP genotype. The high number of RFLP bands indicates that both species have a large number of class II B genes although some may be pseudogenes. Seven different class II B sequences were detected in a great reed warbler cDNA library. There was considerable sequence divergence between the cDNA sequences in exon 2 (peptide-binding region, PBR), whereas they were very similar in exon 3. The cDNA sequences were easily alignable to a classical chicken class II B sequence, and balancing selection was acting in the PBR. One of the cDNA sequences had two deletions and is likely nonfunctional. Finally, the polymorphic class I and class II B RFLP fragments seemed to be linked in the five studied great reed warbler families. These and previous results suggest that birds of the order Passeriformes in general have more Mhc class I and II B genes than birds of the order Galliformes. This difference could be caused by their phylogenetic past, and/or by variance in the selection pressure for maintaining a high number of Mhc genes.

Amino Acid Sequence↗

PubMed2002

A comparative study of avian auditory brainstem responses: correlations with phylogeny and vocal complexity, and seasonal effects.

We conducted a comparative study of the peripheral auditory system in six avian species (downy woodpeckers, Carolina chickadees, tufted titmice, white-breasted nuthatches, house sparrows, and European starlings). These species differ in the complexity and frequency characteristics of their vocal repertoires. Physiological measures of hearing were collected on anesthetized birds using the auditory brainstem response to broadband click stimuli. If auditory brainstem response patterns are phylogenetically conserved, we predicted woodpeckers, sparrows, and starlings to be outliers relative to the other species, because woodpeckers are in a different Order (Piciformes) and, within the Order Passeriformes, sparrows and starlings are in different Superfamilies than the nuthatches, chickadees, and titmice. However, nuthatches and woodpeckers have the simplest vocal repertoires at the lowest frequencies of these six species. If auditory brainstem responses correlate with vocal complexity, therefore, we would predict nuthatches and woodpeckers to be outliers relative to the other four species. Our results indicate that auditory brainstem responses measures in the spring broadly correlated with both vocal complexity and, in some cases, phylogeny. However, these auditory brainstem response patterns shift from spring to winter due to species-specific seasonal changes. These seasonal changes suggest plasticity at the auditory periphery in adult birds.

Acoustic Stimulation↗

PubMed2006

Auditory feedback is necessary for long-term maintenance of high-frequency sound syllables in the song of adult male budgerigars (Melopsittacus undulatus).

Among avian species that communicate using vocalization, songbirds (oscine Passeriformes), hummingbirds (Trochiliformes), and parrots (Psittaciformes) are vocal learners. Early studies showed that songbirds require auditory feedback for song development in young and maintenance in adults. To determine whether auditory feedback is also necessary for adult song maintenance in non-passerine species, we deprived adult male budgerigars (Psittaciformes) of auditory input by surgical cochlear removal. Songs of the deafened birds changed within 6 months after auditory deprivation. In postoperative songs, high narrowband syllables, which comprised frequency-modulated narrowband elements with relatively high fundamental frequencies of 2-4 kHz, decreased significantly. High harmonic broadband syllables, with fundamental frequencies >/=2 kHz, also decreased. The altered proportions of syllables were subsequently retained, and maintained 12 months after deafening. The sequence linearity score, a parameter representing the stereotypy of the syllable sequence, was higher than that before deafening. The inter-syllable silence was prolonged. Little change was observed in the songs of intact and sham-operated birds. The significant decrease in high-frequency syllables and song alteration followed by stabilization resembled the results with songbirds, although song stabilization took a long time in budgerigars. Therefore, our results suggest that psittacine budgerigars and oscine songbirds require auditory feedback similarly for adult song maintenance.

Acoustic Stimulation↗

PubMed2005

West Nile virus in the vertebrate world.

West Nile virus (WNV), an arthropod-borne virus belonging to the family Flaviviridae, had been recognized in Africa, Asia and the south of Europe for many decades. Only recently, it has been associated with an increasing number of outbreaks of encephalitis in humans and equines as well as an increasing number of infections in vertebrates of a wide variety of species. In this article, the data available on the incidence of WNV in vertebrates are reviewed. Moreover, the role of vertebrates in the transmission of WNV, the control of WNV infections in veterinary medicine as well as future perspectives are discussed. A wide variety of vertebrates, including more than 150 bird species and at least 30 other vertebrate species, are susceptible to WNV infection. The outcome of infection depends on the species, the age of the animal, its immune status and the pathogenicity of the WNV isolate. WNV infection of various birds, especially passeriforms, but also of young chickens and domestic geese, results in high-titred viremia that allows arthropod-borne transmission. For other vertebrate species, only lemurs, lake frogs and hamsters develop suitable viremia levels to support arthropod-borne transmission. The role of vertebrates in direct, non-arthropod-borne transmission, such as via virus-contaminated organs, tissues or excretions is less well characterized. Even though direct transmission can occur among vertebrates of several species, data are lacking on the exact amounts of infectious virus needed. Finally, the increased importance of WNV infections has led to the development of killed, live-attenuated, DNA-recombinant and chimeric veterinary vaccines.

Animal Diseases↗