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PubMed2006

Molecular analysis of clock gene expression in the avian brain.

Birds are equipped with a complex circadian pacemaking system that regulates the rhythmicity of physiology and behavior. As with all organisms, transcriptional and translational feedback loops of clock genes represent the basic molecular mechanism of rhythm generation in birds. To investigate avian clock gene expression, partial cDNA sequences of six mammalian clock gene homologs (Bmal1, Clock, Per2, Per3, Cry1, and Cry2) and a novel avian cryptochrome gene (Cry4) were cloned from the house sparrow, a model system in circadian research. Expression patterns were analyzed by semi-quantitative RT-PCR and RNase protection assays using total RNA extracted from adult male house sparrow brains. With the exception of Cry4, pronounced rhythmic mRNA expression of all the clock genes analyzed was encountered, with mRNA levels varying considerably between the various genes. Although some basic features of the molecular circadian feedback loop appear to be similar between mammals and birds, the precise phase relationships of the clock gene mRNA rhythms relative to each other and to the light zeitgeber differ significantly between the house sparrow and mammals. Our results point to the existence of differences in the organization of avian and mammalian circadian clock mechanisms.

ARNTL Transcription Factors↗
PubMed2006

Bird-baited traps for surveillance of West Nile mosquito vectors: effect of bird species, trap height, and mosquito escape rates.

Host-seeking mosquitoes were sampled in bird-baited traps at four sites in New York state in 2003-2004. Trap placement and efficacy of chickens, Gallus gallus domesticus L., as bait compared with house sparrows, Passer domesticus L., an important reservoir of West Nile virus (family Flaviviridae, genus Flavivirus, WNV), was evaluated. Each site had a chicken-baited trap near ground level (approximately 1.5 m) and in the tree canopy (approximately 9 m), and a house sparrow-baited trap at ground level and canopy level. Each trap allowed mosquito access to birds on one end, and an inner mesh screen blocked bird access on the other end. The two most abundant mosquitoes, Culex restuans Theobald and Culex pipiens pipiens L., were differentiated using molecular characters. In 2003, Cx. restuans and Cx. p. pipiens made up 88% of total mosquito catch. In 2004, Cx. restuans comprised 43% of total catch and Cx. p. pipiens comprised 33%. The remaining species representing at least 1% of total catch were Ochlerotatus trivittatus (Coquillett), Coquilletidia perturbans (Walker), and Culiseta morsitans (Theobald). Capture rates were similar for chicken and house sparrow-baited traps; however, significantly more mosquitoes were captured in the canopy for both bird species. Cx. restuans preferred canopy traps, whereas equal numbers of Cx. p. pipiens were captured at ground and canopy levels. Mosquitoes were more likely to escape (74%) when excluded from birds than when allowed free access to birds (54%). Sentinel bird surveillance for WNV can be improved by trapping in the tree canopy in addition to ground level to capture the most important avian vectors.

Animals↗
PubMed2006

The relationship between migratory behaviour, memory and the hippocampus: an intraspecific comparison.

It has been hypothesized that memory-demanding ecological conditions might result in enhanced memory and an enlarged hippocampus, an area of the brain involved in memory processing, either via extensive memory experience or through evolutionary changes. Avian migration appears to represent one of such memory-demanding ecological conditions. We compared two subspecies of the white-crowned sparrow: migratory Zonotrichia leucophrys gambelii and non-migratory Z. l. nuttalli. Compared to non-migratory Z. l. nuttalli, migratory Z. l. gambelii showed better memory performance on spatial one-trial associative learning tasks and had more hippocampal neurons. Migratory subspecies also had larger hippocampi relative to the remainder of the telencephalon but not relative to body mass. In adults, the differences between migratory and non-migratory sparrows were especially pronounced in the right hippocampus. Juvenile migratory Z. l. gambelii had relatively larger hippocampal volume compared to juvenile non-migratory Z. l. nuttalli. Adult migratory Z. l. gambelii had more neurons in their right hippocampus compared to juveniles but such differences were not found in non-migratory Z. l. nuttalli. Our results suggest that migratory behaviour might be related to enhanced spatial memory and an enlarged hippocampus with more neurons, and that differences in the hippocampus between migratory and non-migratory sparrows might be experience-dependent. Furthermore, for the first time our results suggest that the right hippocampus, which encodes global spatial information, might be involved in migratory behaviour.

Analysis of Variance↗
PubMed1992

Seasonal changes of the adrenocortical response to stress in birds of the Sonoran Desert.

Many avian species of the North American Sonoran desert, e.g., the black-throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve-billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50 degrees C). Plasma levels of corticosterone during June were high in black-throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black-throated sparrows, cactus wrens, and curve-billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins.

Adrenal Cortex↗
PubMed1998

Photoperiod and tutor access affect the process of vocal learning.

Song learning in white-crowned sparrows, Zonotrichia leucophrys, involves three steps: memorization of external models, song practice and selection of a song from the practiced repertoire for crystallization. These three events occur in a sequential and predictable order during the first year of life in captive sparrows. To study the external regulation of these events, we raised nestling sparrows under conditions in which photoperiod and tutor exposure were manipulated. We measured plasma testosterone concentration twice a month to study its role in the mediation of vocal learning. We conclude that the timing of song memorization is relatively impervious to photoperiodic manipulation. Song practice and crystallization, however, were readily influenced by both photoperiod and tutor exposure. We suggest that low testosterone concentrations permit acquisition at an older age than would normally occur, and confirm that testosterone propels the transition to production of crystallized song, but is not required for the onset of song practice. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Song types as fundamental units in vocal repertoires.

We investigated whether song types function as fundamental units of song variation in song sparrows, Melospiza melodia. As the size of a male song sparrow's repertoire increases, so does the mean similarity of his song types, as measured by the sharing of minimal units of production (MUPs). It follows that if MUP similarity is important perceptually, then small repertoires (of dissimilar song types) may be functionally equivalent to large repertoires (of similar song types). We performed two experiments to test whether MUP similarity is important perceptually to male song sparrows. Both experiments used a habituation/recovery design, in which recovery in response at a switch in stimuli is used to gauge the subject's perception of the similarity of the stimuli. The results of both experiments indicate that the level of perceived similarity between pairs of songs does not depend on their level of MUP similarity, within the range of MUP similarities found between song types. Songs with high enough MUP similarity to be judged as variants of the same song type are, however, perceived to be much more similar than are any two song types. The results are compatible with a categorical model of song type perception. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Vasotocin and vasoactive intestinal polypeptide modulate aggression in a territorial songbird, the violet-eared waxbill (Estrildidae: Uraeginthus granatina).

Previous research demonstrates that intraseptal administrations of arginine vasotocin (AVT) inhibit male aggression in the territorial field sparrow (Emberizidae: Spizella pusilla) but facilitate aggression in the colonial zebra finch (Estrildidae: Taeniopygia guttata). In order to determine whether this difference may be related to the territorial and colonial social organizations of these two species, the effect of AVT infusions was examined in a territorial Estrildid species, the violet-eared waxbill (Uraeginthus granatina). This species is more closely related to the zebra finch than to the field sparrow and shares most critical features of breeding ecology in common with zebra finches, but differs in social organization. AVT infusions administered via chronic guide cannulae directed at the septum significantly inhibited aggressive behavior, consistent with results in the territorial field sparrow, supporting the hypothesis that social organization is correlated with AVT function. Similar experiments with mesotocin and substance P produced no effects on any of the behaviors measured, but infusions of vasoactive intestinal polypeptide (VIP) significantly facilitated aggression. This result contrasts with the inhibitory effect of septal VIP obtained in the colonial zebra finch, suggesting that VIP function may be correlated with social organization as well.

Aggression↗
PubMed1999

Effects of vasoactive intestinal peptide on plasma prolactin in passerines.

Vasoactive intestinal peptide (VIP) is a potent releaser of prolactin (PRL) in domestic fowl, turkey, and ring doves. However, few comparative studies have investigated this in wild species. We tested the effects of intravenously administered chicken VIP on plasma PRL concentrations in four passerine species: the white-crowned sparrow (Zonotrichia leucophrys gambelii), the dark-eyed junco (Junco hyemalis), the Florida scrub-jay (Aphelocoma coerulescens), and the western scrub-jay (A. californica). In the white-crowned sparrow, junco, and Florida scrub-jay, which were tested during the breeding season, VIP induced a rapid increase in plasma PRL. Serial plasma samples taken after VIP injection in the white-crowned sparrow show a 10-fold increase in PRL within 2 min of treatment, followed by a gradual decline. Effects of VIP, as compared to saline, remained significant for at least 20 min after treatment. Western scrub-jays did not respond to intravenous VIP with a significant rise in PRL secretion, possibly because they were tested after termination of the breeding season. This study indicates that VIP control of PRL release may be widespread among avian species, and that seasonal changes in plasma PRL may be mediated in part at the level of the pituitary. In addition, analysis of the control data revealed no increase in plasma PRL as a result of injection or restraint, suggesting that unlike in mammals, PRL is not released during acute stress in passerines.

Animals↗
PubMed2000

Pharmacological adrenalectomy with mitotane.

The potential of mitotane (ortho, para'-DDD, commonly used to treat adrenal carcinomas in humans and dogs) was investigated as an alternative to surgical adrenalectomy in birds, salamanders, and lizards. House sparrows (Passer domesticus) were injected twice daily with vehicle or one of two doses of mitotane (225 or 450 mg/kg), and basal and stress-induced levels of corticosterone (CORT) were measured 3 and 5 days after injections. Mitotane reduced basal CORT levels to nondetectable and abolished stress-induced CORT increases by the 3rd day of treatment. In another study, a single injection of mitotane was effective in lowering endogenous CORT levels 36 h later, but levels had apparently recovered by 10 days after the injection. Mitotane did not effect testicular weights and had no detectable effect on testosterone levels. In contrast to its effects on house sparrows, mitotane did not lower endogenous CORT levels in either tiger salamanders (Ambystoma tigrinum) or tree lizards (Urosaurus ornatus), even at doses much higher than those used in house sparrows.

Adrenalectomy↗
PubMed2001

Dehydroepiandrosterone in songbird plasma: seasonal regulation and relationship to territorial aggression.

Many male animals are territorial in the breeding season, when plasma testosterone (T) levels are high, and nonterritorial in the nonbreeding season, when plasma T levels are basal. In contrast to this common pattern, male song sparrows (Melospiza melodia morphna) are territorial year-round, except briefly during molt. Song sparrows are highly aggressive in the nonbreeding season (autumn and winter), even though plasma T, 5 alpha-dihydrotestosterone, androstenedione (AE), and 17beta-estradiol levels are undetectable (<or=0.1 ng/ml). Castration has no effect on nonbreeding territoriality. However, aromatase inhibitors decrease aggression in the nonbreeding season, indicating a role for estrogens in winter. The androgenic substrate for brain aromatase in winter is unclear, because plasma T and AE levels are basal. Here, we measured plasma levels of dehydroepiandrosterone (DHEA). DHEA is a precursor to AE and T, and the avian brain can convert DHEA into sex steroids. In nonbreeding male song sparrows, plasma levels of DHEA were detectable and several times higher than plasma AE and T levels. Plasma DHEA levels were similar in the breeding and nonbreeding seasons, but significantly lower during molt, which parallels seasonal changes in male aggression. Adrenal glands and testes from nonbreeding males had high concentrations of DHEA, suggesting that both tissues may secrete DHEA. However, stress and gonadotropin-releasing hormone (GnRH) did not increase plasma DHEA in nonbreeding birds. We hypothesize that in the nonbreeding season, circulating DHEA, possibly of adrenal origin, is converted into active sex steroids by steroidogenic enzymes in the brain. This mechanism would create high local levels of sex steroids in the brain to support winter aggression.

Adrenal Glands↗
PubMed2002

Dehydroepiandrosterone (DHEA) increases territorial song and the size of an associated brain region in a male songbird.

In many species, male territorial aggression is tightly coupled with gonadal secretion of testosterone (T). In contrast, in song sparrows (Melospiza melodia morphna), males are highly aggressive during the breeding (spring) and nonbreeding (autumn and early winter) seasons, but not during molt (late summer). In aggressive nonbreeding song sparrows, plasma T levels are basal (< or = 0.10 ng/ml), and castration has no effect on aggression. However, aromatase inhibitors reduce nonbreeding aggression, indicating a role for estrogen in wintering males. In the nonbreeding season, the substrate for brain aromatase is unclear, because plasma T and androstenedione levels are basal. Aromatizable androgen may be derived from plasma dehydroepiandrosterone (DHEA), an androgen precursor. DHEA circulates at elevated levels in wintering males (approximately 0.8 ng/ml) and might be locally converted to T in the brain. Moreover, plasma DHEA is reduced during molt, as is aggression. Here, we experimentally increased DHEA in wild nonbreeding male song sparrows and examined territorial behaviors (e.g., singing) and discrete neural regions controlling the production of song. A physiological dose of DHEA for 15 days increased singing in response to simulated territorial intrusions. In addition, DHEA treatment increased the volume of a telencephalic brain region (the HVc) controlling song, indicating that DHEA can have large-scale neuroanatomical effects in adult animals. The DHEA treatment also caused a slight increase in plasma T. Exogenous DHEA may have been metabolized to sex steroids within the brain to exert these behavioral and neural effects, and it is also possible that peripheral metabolism contributed to these effects. These are the first results to suggest that exogenous DHEA increases male-male aggression and the size of an entire brain region in adults. The data are consistent with the hypothesis that DHEA regulates territorial behavior, especially in the nonbreeding season, when plasma T is basal.

Aggression↗
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↗
PubMed1993

Dietary amino acid complementation as a foraging strategy for wild birds.

Foraging birds finding foods containing protein of various quality could satisfy their amino acid needs by either 1) choosing only those foods that contain a suitable array of essential amino acids, or 2) choosing foods in amounts that permit complementation of constituent amino acids. We studied the abilities of sparrows (Zonotrichia leuchophrys gambelii) to use dietary amino acid complementation as a foraging strategy. We conducted two series of tests: 1) to determine if sparrows could select adequate portions from food pairs in order to compensate for reciprocal dietary deficiencies of either valine and lysine or lysine and threonine, and 2) to evaluate to what extent fortuitous (passive) complementation of dietary amino acids was constrained in sparrows by the magnitude of the dietary amino acid deficiency and the schedule of daily intakes of complementary foods. Small birds appear to have limited abilities to actively exploit dietary amino acid complementation. Birds offered a choice of two foods deficient in either lysine, valine, or threonine but of complementary compositions, reduced their daily intakes of food and body masses, but to a lesser extent (ca. one-half to one-third, and ca. one-quarter as much, respectively) than when either of the deficient foods were offered alone. Even passive complementation of dietary amino acids was severely constrained by both the magnitude of the dietary amino acid deficiency and the time course of feeding. The greater the amino acid deficiency, the less effective the complementation of dietary amino acids. The time course for effective and efficient complementation of dietary essential amino acids in these small, metabolically active animals was less than 2 h.

Amino Acids↗
PubMed1987

Molecular analysis of the hemagglutinin genes of Australian H7N7 influenza viruses: role of passerine birds in maintenance or transmission?

In 1985 a fowl plague-like disease occurred in chickens in Lockwood, Victoria, Australia and caused high mortality. An H7N7 influenza virus was isolated from the chickens (A/Chicken/Victoria/1/85); additionally, an antigenically similar virus was isolated from starlings (A/Starling/Victoria/5156/85) and serological evidence of H7N7 virus infection was found in sparrows. Antigenic analysis with monoclonal antibodies to H7, oligonucleotide mapping of total vRNA, and sequence analysis of the HA genes established that the chicken and starling influenza viruses were closely related and probably came from the same source. There was high nucleotide sequence homology (95.3%) between the HA genes of A/Chick/Vic/85 and a fowl plague-like virus isolated from chickens in Victoria 9 years earlier [A/Fowl/Vic/76 (H7N7)]. The sequence homologies indicated that the A/Chick/Vic/85 and A/Fowl/Vic/76 were derived from a common recent ancestor, while another recent H7N7 virus, Seal/Mass/1/80 originated from a different evolutionary lineage. Experimental infection of chickens and starlings with A/Chick/Vic/1/85 (H7N7) was associated with high mortality (100%), transmission to contact birds of the same species, and virus in all organs. In sparrows one-third of the birds died after infection and virus was isolated from most organs; transmission to contact sparrows did not occur. In contrast, the H7N7 virus replicated in ducks and spread to contact ducks but caused no mortality. These studies establish that the host species plays a role in determining the virulence of avian influenza viruses, and provide the first evidence for transmission of virulent influenza viruses between domestic poultry and passerine birds. They support the hypothesis that potentially virulent H7N7 influenza viruses could be maintained in ducks where they cause no apparent disease and may sometimes spread to other wild birds and domestic poultry.

Amino Acid Sequence↗
PubMed2005

Timing of incorporation of docosahexaenoic acid into brain and muscle phospholipids during precocial and altricial modes of avian development.

We investigated the possibilities that the proportion of docosahexaenoic acid (DHA) in phospholipids of brain and skeletal muscle at hatch, and the ontogenetic timing of the DHA accretion spurt in these tissues, might serve as indices of neonatal functional maturity that discriminate between precocial and altricial avian developmental modes. Comparison of the fatty acid profiles of the initial and residual yolks of two free-living altricial species, the swallow (Hirundo rustica) and the sparrow (Passer domesticus), reveals that, in contrast to precocial birds, there is no preferential uptake of DHA from the yolk during embryonic development. At hatch, the proportions of DHA in brain phospholipid (wt.% of fatty acids) of the swallow and sparrow, at 8.1% and 5.0%, respectively, are far lower than the values (16.9-19.6%) reported for non-altricial species. This reflects a marked difference in the timing of the brain DHA accretion spurt, which occurs during the first half of the embryonic period of precocial birds, but is largely delayed until after hatching in the altricial species. By the time of fledging, the proportion of DHA in the swallow brain phospholipid has increased to 14.3%. For non-altricial birds, the brain DHA concentration at hatch shows little interspecies variation, despite major differences in yolk DHA content. The proportions of DHA in leg muscle phospholipid of the newly hatched swallow and sparrow, at 2.9% and 2.5%, respectively, are far lower than the value (6.7%) for the precocial chicken. Again, this relates to differences in developmental timing, with muscle DHA accretion occurring in the first half of the chicken's embryonic period, whereas, in the swallow, this increase is delayed until after hatching. By the time of fledging in the swallow, DHA forms 9.3% of muscle phospholipid fatty acids, equivalent to the level attained in chicken muscle at the mid-embryo stage. The results indicate a clear distinction between altricial and non-altricial avian species in the timing of tissue DHA accretion during development, presumably reflecting differences in neonatal functional maturity.

Animals↗
PubMed2005

Results and evaluation of the first study of organochlorine contaminants (PCDDs, PCDFs, PCBs and DDTs), heavy metals and metalloids in birds from Baja California, México.

Organochlorine compounds (OCs) including polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p-p'-DDE), heavy metals (Pb, Cd, Zn, Cu), and arsenic were measured in house sparrows (Passer domesticus) and common ground doves (Columbina passerina) from Baja California Sur, México. Concentrations of PCDD/Fs were low, with 21 pg/g for house sparrows, and 7.7 pg/g for common ground doves. Non-ortho-PCB concentrations in house sparrow and common ground doves were 58 and 254 pg/g, respectively, and are within the highest concentrations reported in species that are in the low levels of food webs. The major differences in organochlorine levels between species were found for ortho-PCBs and DDTs. ortho-PCB levels were higher in the seedeater species, whereas DDT levels were higher in the omnivorous species. Heavy metal levels were far below those associated with negative effects.

Animals↗
PubMed2002

Latitudinal variation in plasma testosterone levels in birds of the genus Zonotrichia.

Birds breeding in northern latitudes generally have elevated plasma testosterone levels throughout the breeding season with a peak at the onset of the breeding season. In contrast, tropical birds tend to have extremely low plasma testosterone levels year round with only a slight increase during breeding. While these patterns have been consistent in the species investigated, closely related species have not been investigated across a range of latitudes. Birds of the genus Zonotrichia present an ideal opportunity to investigate latitudinal variation in plasma testosterone levels as breeding populations occur from northern Alaska to southern Argentina. We studied three taxa of Zonotrichia: (1) Gambel's white-crowned sparrows, Zonotrichia leucophrys gambelii, breeding at high latitude in northern Alaska, (2) Puget Sound white-crowned sparrows, Z. l. pugetensis, breeding at mid-latitude in Washington state, and (3) an equatorial population of the rufous-collared sparrow, Z. capensis, in Ecuador. To compare both baseline breeding and maximal testosterone levels, males from the three taxa were either bled immediately upon capture during the breeding season or first challenged with gonadotropin-releasing hormone (GnRH) and then bled. As a control, another group of birds experienced a saline challenge. Two-way ANCOVA, with treatment and taxa as factors and testis volume as a covariate, showed a significant effect of treatment on plasma testosterone levels. There was also a significant interaction between taxa and treatment. Contrary to expectations, the equatorial species exhibited greater plasma testosterone levels in response to the GnRH challenge than the high latitude species. There were no differences between the mid- and high-latitude species. The equatorial species had the smallest average testis size and within each taxa there were no relationships between plasma testosterone and testis size. These data suggest that latitudinal clines in plasma testosterone levels in Zonotrichia do not follow previously described patterns and that tropical birds can have levels of testosterone similar to northern latitude species.

Animals↗
PubMed1997

Experimental induction of equine protozoal myeloencephalitis in horses using Sarcocystis sp. sporocysts from the opossum (Didelphis virginiana).

Sarcocystis sp. sporocysts isolated from eight feral opossums (Didelphis virginiana) were pooled and fed to 18 commercially reared budgerigars (Melopsittacus undulatus), 14 wild-caught sparrows (Passer domesticus), one wild-caught slate-colored Junco (Junco hyemalis) and five weanling horses (Equus caballus). All budgerigars died within 5 weeks post inoculation (wpi). Histologic examination revealed meronts within the pulmonary epithelia and typical Sarcocystis falcatula sarcocysts developing in the leg muscles. Sparrows were euthanized 13 and 17 wpi and their carcasses were fed to four laboratory raised opossums. Sporocysts were detected in the feces of two opossums on 15 days post inoculation (dpi) and in a third opossum on 40 dpi. Fecal samples from the fourth opossum remained negative; however, sporocysts were found in intestinal digests from all four opossums. Sporocysts were not found in feces or intestinal digest of an additional opossum that was fed three uninoculated sparrows. Five foals were fed sporocysts (Foals 2, 3, 4, 5, and 7) and two foals were maintained as uninoculated controls (Foals 1 and 6). Sporocysts from two additional feral opossums also were fed to foals. Foal 5 was given 0.05 mg kg-1 dexamethasone sodium phosphate daily beginning 2 days before inoculation for a total of 2 weeks. Horse sera were tested three times per week, and cerebrospinal fluid (CSF) samples were tested biweekly for anti-Sarcocystis neurona antibodies by Western blot analysis. No foals had any S. neurona-specific antibodies by Western blot analysis prior to sporocysts ingestion. Seroconversion occurred in Foals 3, 5, and 7 by 24 dpi, followed by positive CSF tests on 28 dpi. Foals 2 and 4 seroconverted by 40 dpi. Cerebrospinal fluid from Foal 2 tested positive by 42 dpi, but Foal 4 remained seronegative throughout the study. Sera and CSF from control Foals 1 and 6 remained seronegative. All foals with positive CSF developed neurologic clinical signs. Neurologic disease was evident in Foals 2 and 3 by 42 dpi and in Foal 7 by 28 dpi. The severity of clinical signs progressed to marked spasticity, hypermetria and ataxia in Foal 7 by the end of the trial. Necropsy examination of inoculated foals did not reveal gross lesions; however, microscopic lesions consistent with equine protozoal myeloencephalitis (EPM) were found in Foals 2, 3, and 7. Protozoa were not observed in the tissue sections. Microscopic lesions consistent with EPM were not found in Foals 4 and 5 or in uninoculated control Foals 1 and 6. Foal 5 had unilateral non-inflammatory lesions in the cervical and thoracic spinal cord consistent with cord compression. These data indicate that the opossum is a definitive host of S. neurona.

Animals↗