Lead exposure among mothers and their newborns in Toronto.

Recent studies have suggested that a fetal blood lead level of 0.48 mumol/L (much lower than 1.21 mumol/L, which is the level previously believed to be toxic to the developing brain) may impair brain development permanently. We measured the maternal and umbilical cord blood levels of lead and free erythrocyte protoporphyrin (FEP) among 95 consecutive mother-infant pairs to determine whether neonates in Toronto are in the high-risk group. There was a significant correlation between the maternal and the cord blood lead levels (r = 0.59, p less than 0.0001). Most (99%) of the infants had cord blood lead levels below 0.34 mumol/L; in 11 cases the levels were below the detection limit of 0.01 mumol/L. The cord blood FEP levels were higher than the maternal levels. The US Centers for Disease Control, Atlanta, currently finds acceptable a blood FEP level of 0.62 mumol/L among children up to 10 years of age; however, this is not applicable to newborns since their higher FEP levels apparently reflect immature heme synthesis and increased erythrocyte volume rather than lead poisoning. Our data suggest that living in Toronto does not impose increased teratogenic risk from intrauterine exposure to lead; however, residents in high-risk areas should be followed up.     

Protoporphyrin IX and oxidative stress

The short- and long-term pro-oxidant effect of protoporphyrin IX (PROTO) administration to mice was studied in liver. A peak of liver porphyrin accumulation was found 2 h after the injection of PROTO (3.5 mg/kg, i.p.); then the amount of porphyrins diminished due to biliar excretion. After several doses of PROTO (1 dose every 24 h up to 5 doses) a sustained enhancement of liver porphyrins was observed. The activity of δ-amino-levulinic acid synthetase was induced 70–90% over the control values 4 h after the first injection of PROTO and stayed at these high levels throughout the period of the assay. Administration of PROTO induced rapid liver damage, involving lipid peroxidation. Hepatic GSH content was increased 2 h after the first injection of PROTO, but then decreased below the control values which were maintained after several doses of porphyrin. After a single dose of PROTO, Cu-Zn superoxide dismutase (SOD) was rapidly induced, suggesting that superoxide radicals had been generated. Increased levels of hydrogen peroxide coming from the reaction catalyzed by SOD and lipid peroxides as a consequence of membrane peroxidation, induced the activity of catalase and glutathione peroxidase (GPx), while decreased GSH levels induced glutathione reductase (GRed) activity. However after 5 doses of PROTO, the activity of SOD was reduced reaching control values. GPx and catalase activities slowly went down, while GRed continued increasing as long as the levels of GSH were kept very low. TBARS values, although lower than those observed after a single dose of PROTO, remained above control values; Glutathione S-transferase activity was instead greatly diminished, indicating sustained liver damage.

Our findings would indicate that accumulation of PROTO in liver induces oxidative stress, leading to rapid increase in the activity of the antioxidant enzymes to avoid or revert liver damage. However, constant accumulation of porphyrins provokes a liver damage so severe that the antioxidant system is compromised.     

Protoporphyrin IX and oxidative stress

The short- and long-term pro-oxidant effect of protoporphyrin IX (PROTO) administration to mice was studied in liver. A peak of liver porphyrin accumulation was found 2 h after the injection of PROTO (3.5 mg/kg, i.p.); then the amount of porphyrins diminished due to biliar excretion. After several doses of PROTO (1 dose every 24 h up to 5 doses) a sustained enhancement of liver porphyrins was observed. The activity of δ-amino-levulinic acid synthetase was induced 70-90% over the control values 4 h after the first injection of PROTO and stayed at these high levels throughout the period of the assay. Administration of PROTO induced rapid liver damage, involving lipid peroxidation. Hepatic GSH content was increased 2 h after the first injection of PROTO, but then decreased below the control values which were maintained after several doses of porphyrin. After a single dose of PROTO, Cu-Zn superoxide dismutase (SOD) was rapidly induced, suggesting that superoxide radicals had been generated. Increased levels of hydrogen peroxide coming from the reaction catalyzed by SOD and lipid peroxides as a consequence of membrane peroxidation, induced the activity of catalase and glutathione peroxidase (GPx), while decreased GSH levels induced glutathione reductase (GRed) activity. However after 5 doses of PROTO, the activity of SOD was reduced reaching control values. GPx and catalase activities slowly went down, while GRed continued increasing as long as the levels of GSH were kept very low. TBARS values, although lower than those observed after a single dose of PROTO, remained above control values; Glutathione S-transferase activity was instead greatly diminished, indicating sustained liver damage.

Our findings would indicate that accumulation of PROTO in liver induces oxidative stress, leading to rapid increase in the activity of the antioxidant enzymes to avoid or revert liver damage. However, constant accumulation of porphyrins provokes a liver damage so severe that the antioxidant system is compromised.     

Low genetic differentiation and close evolutionary connection between Anas platyrhynchos and Anas poecilorhyncha: data from RAPD-PCR analysis

Using RAPD-PCR, we examined genetic diversity and phylogenetic relationships in two groups of river ducks: Anas platyrhynchos, A. poecilorhyncha, A. strepera and A. crecca, A. formosa, A. querquedula. Molecular taxon-specific markers were found for teals (A. crecca, A. formosa, A. querquedula) and gadwall (A. strepera). Each of the species examined was shown to exhibit high genetic diversity. The mean levels of intraspecific genetic polymorphism in the groups of mallards (P = 77%) and teals (P = 74.5%) were approximately equal whereas the mean interspecific genetic distances in teals were significantly higher than in mallards (D = 0.432 and D = 0.336, respectively). The levels of interspecific genetic differentiation in the species groups were also different. The genetic distances between the teal species and between gadwall and mallards were equal to 0.668-0.971 while the genetic distance between mallard A. platyrhynchos and spot-billed duck A. poecilorhyncha was 0.401, which slightly exceeds the intraspecific values for mallards (0.356-0.377). The RAPD patterns for this species pair showed high variability and a lack of fixed differences. This was adequately reflected on both intra- and interspecific differences and on phylogenetic constructions in which the morphological species did not form their own clusters but were intermixed. In contrast to mallards, the other species, which showed high genetic variability, were reliably separated in phenogenetic and phylogenetic reconstructions. The possible explanations of the low genetic differentiation of A. platyrhynchos and A. poecilorhyncha are discussed.     

Low Genetic Differentiation of and Close Evolutionary Relationships between Anas platyrhynchos and Anas poecilorhyncha: RAPD–PCR Evidence

Using RAPD–PCR, we examined genetic diversity and phylogenetic relationships in two groups of river ducks: Anas platyrhynchos, A. poecilorhyncha, A. streperaand A. crecca, A. formosa, A. querquedula. Molecular taxon-specific markers were found for teals (A. crecca, A. formosa, A. querquedula) and gadwall (A. strepera). Each of the species examined was shown to exhibit high genetic diversity. The mean levels of intraspecific genetic polymorphism in the groups of mallards (P = 77%) and teals (P = 74.5%) were approximately equal whereas the mean interspecific genetic distances in teals were significantly higher than in mallards (D = 0.432 and D= 0.336, respectively). The levels of interspecific genetic differentiation in the species groups were also different. The genetic distances between the teal species and between gadwall and mallards were equal to 0.668–0.971 while the genetic distance between mallard A. platyrhynchos and spot-billed duck A. poecilorhyncha was 0.401, which slightly exceeds the intraspecific values for mallards (0.356–0.377). The RAPD patterns for this species pair showed high variability and a lack of fixed differences. This was adequately reflected on both intra- and interspecific differences and on phylogenetic constructions in which the morphological species did not form their own clusters but were intermixed. In contrast to mallards, the other species, which showed high genetic variability, were reliably separated in phenogenetic and phylogenetic reconstructions. The possible explanations of the low genetic differentiation of A. platyrhynchos and A. poecilorhynchaare discussed.     

Efficacy of a type C botulism vaccine in green-winged teal

We tested the efficacy of a single dose of Botumink toxoid for protecting wild green-winged teal (Anas crecca) during botulism epizootics caused by Clostridium botulinum type C. We challenged control and immunized ducks with four different doses of type C botulinum toxin to determine the LD50 for this species and to evaluate vaccine protection. Fewer immunized ducks were affected with botulism than control ducks, indicating that a single dose of Botumink toxoid could increase the survival of ducks during epizootics. However, the frequency of immunized ducks with signs of botulism increased with the challenge dose of botulinum toxin. Even at doses of botulinum toxin approximately 2 to 4 green-winged teal LD50, about 50% of the immunized ducks were affected. We believe an improved vaccine or a better delivery system is required to justify immunization of wild birds for experimental survival studies.     

The Effect of Occupational Lead Exposure on Blood Levels of Zinc, Iron, Copper, Selenium and Related Proteins

The study objective was to evaluate the effect of occupational lead exposure on blood concentrations of zinc, iron, copper, selenium and proteins related to them, such as transferrin, caeruloplasmin and haptoglobin. The examined group consisted of 192 healthy male employees of zinc?Clead works. By the degree of lead exposure, the exposed group was subdivided into three subgroups. The control group was composed of 73 healthy male administrative workers. The markers of lead exposure (blood levels of lead and zinc protoporphyrin) were significantly elevated in the exposed group compared with the control group. Additionally, concentrations of copper and caeruloplasmin were raised. The significant increase in haptoglobin level was observed only in the low exposure group. Selenium levels were significantly decreased, whereas iron, zinc and transferrin levels were unchanged in the exposed group compared with the control group. There were positive correlations between the lead toxicity parameters and the copper and caeruloplasmin levels. In conclusion, the effect of occupational exposure to lead on the metabolism of trace metals appears to be limited. However, significant associations between lead exposure and levels of copper and selenium were shown. Changed levels of positive acute-phase proteins, such as caeruloplasmin and haptoglobin, were also observed.     

Avian paramyxoviruses from migrating and resident ducks in coastal Louisiana

Cloacal and tracheal swabs were collected from 1,409 hunter-killed ducks in Cameron Parish, Louisiana, during the 1986 and 1987 waterfowl seasons. Thirty avian paramyxoviruses (PMV's) were isolated from 605 blue-winged teal (Anas discors), 75 mottled ducks (A. fulvigula), 375 gadwalls (A. strepera), 334 green-winged teal (A. crecca), and 20 mallards (A. platyrhynchos). Prevalence of PMV decreased (P = 0.042) from September (4%) through November (2%) to December and January (1%). Juveniles had a higher prevalence of PMV (P less than 0.0001) than adults. An isolate from resident mottled ducks documents transmission of PMV's on the coastal wintering areas of Louisiana. The four serotypes isolated, PMV-1, PMV-4, PMV-6, and PMV-8, were typical of PMV's commonly associated with free-living waterfowl.     

Comparative toxicity of lead shot in black ducks (Anas rubripes) and mallards (Anas platyrhynchos)

In winter, pen-reared and wild black ducks (Anas rubripes), and game farm and wild mallards (Anas platyrhynchos), maintained on pelleted feed, were sham-dosed or given one number 4 lead shot. After 14 days, dosed birds were redosed with two or four additional lead shot. This dosing regimen also was repeated in summer using pen-reared black ducks and game farm mallards. Based upon mortality, overt intoxication, weight change, delta-aminolevulinic acid dehydratase activity and protoporphyrin concentration, black ducks and mallards were found to be equally tolerant to lead shot. However, captive wild ducks were more sensitive than their domesticated counterparts, as evidenced by greater mortality and weight loss following lead shot administration. This difference may be related to stress associated with captivity and unnatural diet.     

High-performance liquid chromatographic determination of protoporphyrin and zinc protoporphyrin in blood

Zinc protoporphyrin and protoporphyrin free acid in blood were determined by high-performance liquid chromatography on a C₁₈ column. Results for 63 human blood samples obtained through a lead poisoning detection program compared favorably with the widely-used ethyl acetate—acetic acid extraction determination. Blood from 16 rats which had been maintained on water heavily spiked with chloroform or bromodichloromethane and blood from a lead-poisoned cow were examined by this procedure.     

Presence of fish affects lake use and breeding success in ducks

Several previous studies indicate that presence of fish has negative effects on waterbirds breeding on lakes, owing either to competition for common invertebrate prey or fish predation on ducklings/chicks. However, others have reported results to the contrary and it remains unresolved what factors trigger, inhibit, and modulate fish–waterbird interactions. The present study was designed to test the effect of fish presence per se, with a minimum of variation in possibly confounding environmental variables. Thus, after stratifying for area, depth, altitude, pH, and total phosphorus we compared 13 lakes with and 12 without fish (mainly pike Esox lucius and perch Perca fluviatilis) with respect to (i) general species richness of waterbirds, (ii) species-specific utilization and breeding success of two dabbling ducks (mallard Anas platyrhynchos and teal Anas crecca) and a diving duck (goldeneye Bucephala clangula). General species richness of waterbirds was higher on fishless lakes. Overall use (bird days) and brood number of teal and goldeneye were higher on fishless lakes. The latter also had more benthic and free-swimming prey invertebrates compared to lakes with fish. Mallard use, mallard brood number, and abundance of emerging insects did not differ between lake groups. Generalized linear models including fish presence as factor and considering seven environmental variables as covariates, confirmed that all waterbird variables except mallard days and broods were negatively correlated to fish presence. There was also a residual positive relationship of lake area on general species richness, teal days, and teal broods. Our data demonstrate a stronger effect of fish presence on diving ducks and small surface feeding ducks than on large surface-feeding ducks. We argue that observed patterns were caused by fish predation on ducks rather than by fish–duck competition for common prey.     

Interspecific interactions and co-existence in dabbling ducks: observations and an experiment

We studied the possible role of resource limitation and interspecific competition in assemblages of dabbling ducks on breeding lakes in Finland and Sweden with observational and experimental data. After initial vegetation mapping and yearly censuses of ducks in 1985–1990, we collected observational data in 1991–1994 from 28 lakes with natural populations of mallard Anas platyrhynchos and teal A. crecca. Mallard and teal co-occur over vast areas in the Holarctic and they are the only breeding dabbling ducks on many oligotrophic lakes. Both species are migratory in our study regions, teal arriving later in spring than mallards. Log-linear model analysis of observational presence/absence data revealed a positive, not a negative, association between the species. This association was independent of habitat diversity as well as of lake size. Mallard-teal interaction was also studied in a cross-over introduction experiment in 32 other lakes in two years. Wing-clipped mallards were introduced to breeding lakes before the arrival of teal to induce resource limitation and interspecific competition, hypothesized to reduce lake use by teal. The density of mallard pairs on experimental lakes was 2.9–8.0 times higher than on controls, but there was no negative response by teal to the treatment. This is the first combined observational-experimental demonstration of lack of interspecific competition in waterfowl. Our results indicate that heterospecific attraction may affect species co-existence in dabbling ducks. Received: 28 October 1996 / Accepted: 13 January 1997     

Dual‐wavelength excitation for fluorescence‐based quantification of zinc protoporphyrin IX and protoporphyrin IX in whole blood

Quantification of erythrocyte zinc protoporphyrin IX (ZnPP) and protoporphyrin IX (PPIX), individually or jointly, is useful for the diagnostic evaluation of iron deficiency, iron‐restricted erythropoiesis, lead exposure, and porphyrias. A method for simultaneous quantification of ZnPP and PPIX in unwashed blood samples is described, using dual‐wavelength excitation to effectively eliminate background fluorescence from other blood constituents. In blood samples from 35 subjects, the results of the dual‐wavelength excitation method and a reference high performance liquid chromatography (HPLC) assay were closely correlated both for ZnPP (r_s = 0.943, p < 0.0001; range 37–689 μmol ZnPP/mol heme, 84–1238 nmol/L) and for PPIX (r_s = 0.959, p < 0.0001; range 42–4212 μmol PPIX/mol heme, 93–5394 nmol/L). In addition, for ZnPP, the proposed method is compared with conventional single‐wavelength excitation and with commercial front‐face fluorimetry of washed erythrocytes and whole blood. We hypothesize that dual‐wavelength excitation fluorimetry will provide a new approach to the suppression of background fluorescence in blood and tissue measurements of ZnPP and PPIX. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of Avian Paramyxoviruses Isolated from Feral Ducks in Northern Japan: The Presence of Three Distinct Viruses in Nature

Seventy-eight strains of avian paramyxoviruses (PMV) were isolated from cloacal and/or tracheal swabs taken from 1,342 feral ducks, comprised of spot-bill ducks, mallards, pintails, teals, falcated teals, wigeons and buffie-heads, in Wakuya-cho, Miyagi Prefecture, Japan, between 1976 and 1979. Five and a half percent of the ducks were positive for virus. Serological and structural characterization indicated that three different avian paramyxoviruses arc prevalent in the Japanese feral duck population. The first group of PMV was Newcastle disease virus (NDV), and in vivo pathogenecity tests in embryonated chicken eggs and 1-day-old chicks revealed that all the NDV strains isolated were avirulent. The second and most prevalent strain was closely related to PMV-4, duck/Hong Kong/D3/75 strain. The viruses of the third group were recovered only from pintails. They cross-reacted antigenically with PMV-3 when antisera to the PMV-3 reference strains, turkey/Wisconsin/68 and parakeet/Netherlands/449/75, were employed. However, no cross-reaction was observed when antiserum to pintail/ Wakuya/20/78, the prototype of this group, was used. The viruses of the third group also differed in viral polypeptide profile from the reference strains of PMV-3.     

Metabolism of Magnesium Protoporphyrin Monomethyl Ester in Chlamydomonas reinhardtii

The y-1 mutant of Chlamydomonas reinhardtii is defective in the conversion of protochlorophyllide (Pchlide) to chlorophyllide in the dark. Aerobic δ-aminolevulinic acid (ALA) feeding of y-1 cells causes protoporphyrin monomethyl ester (PME) to accumulate in addition to increased levels of Pchlide. y-1 cell homogenates are not capable of methylating protoporphyrin (PROTO) to form PME but can methylate magnesium protoporphyrin (MgP) to form magnesium protoporphyrin monomethyl ester (MgPME). Anaerobic ALA feeding of y-1 causes concomitant accumulation of PME and MgPME. y-1 cells treated with α,α′-dipyridyl (DP) accumulate MgPME but not PROTO or PME. A mutant strain (bme) of Chlamydomonas has been isolated which has very little chlorophyll and accumulates PME. bme Cell homogenates can methylate MgP but not PROTO. We propose that: (a) in Chlamydomonas, PME is the initial breakdown product of MgPME; (b) both the breakdown of MgPME to PME and the conversion of MgPME to Pchlide require O₂; (c) the breakdown of MgPME to PME appears to require Fe; and (d) the PME accumulated in the bme mutant is the result of an increased breakdown of MgPME.     

Divergence and gene flow in the globally distributed blue‐winged ducks

The ability to disperse over long distances can result in a high propensity for colonizing new geographic regions, including uninhabited continents, and lead to lineage diversification via allopatric speciation. However, high vagility can also result in gene flow between otherwise allopatric populations, and in some cases, parapatric or divergence‐with‐gene‐flow models might be more applicable to widely distributed lineages. Here, we use five nuclear introns and the mitochondrial control region along with Bayesian models of isolation with migration to examine divergence, gene flow, and phylogenetic relationships within a cosmopolitan lineage comprising six species, the blue‐winged ducks (genus Anas), which inhabit all continents except Antarctica. We found two primary sub‐lineages, the globally‐distributed shoveler group and the New World blue‐winged/cinnamon teal group. The blue‐winged/cinnamon sub‐lineage is composed of sister taxa from North America and South America, and taxa with parapatric distributions are characterized by low to moderate levels of gene flow. In contrast, our data support strict allopatry for most comparisons within the shovelers. However, we found evidence of gene flow from the migratory, Holarctic northern shoveler A. clypeata and the more sedentary, African Cape shoveler A. smithii into the Australasian shoveler A. rhynchotis, although we could not reject strict allopatry. Given the diverse mechanisms of speciation within this complex, the shovelers and blue‐winged/cinnamon teals can serve as an effective model system for examining how the genome diverges under different evolutionary processes and how genetic variation is partitioned among highly dispersive taxa.     

Oxidative stress and neurological disorders in relation to blood lead levels in children

Oxidative stress plays a pivotal role in the pathogenesis of neurological disorders. Free radical generation appears to be the mode of lead toxicity. We evaluated the effects of blood lead levels on oxidative stress parameters in children suffering from neurological disorders. Thirty children (aged 3-12 years) with neurological disorders (cerebral palsy [n = 12], seizures [n = 11], and encephalopathy [n = 7]) were recruited in the study group. Sixty healthy children (aged 3-12 years) from similar socio-economic environments and not suffering from any chronic disease were taken as the controls. Blood lead levels and oxidant/antioxidant status were determined. Mean blood lead level was significantly higher while delta-aminolevulinic acid dehydratase (delta-ALAD) activity, a biomarker for lead exposure, was significantly lower in the study group as compared to the control group (P < 0.05 for each). Malondialdehyde (MDA) levels, an end-product of lipid peroxidation, were significantly higher while the antioxidant glutathione (GSH) levels were significantly lower in the study group as compared to the control group (P < 0.05 for each). Activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were significantly higher in the study group than those of the control group (P < 0.05 for each). There were significant negative correlations of blood lead levels with delta-ALAD (r = -0.35; P < 0.05) and GSH (r = -0.31; P < 0.05), and positive correlations with MDA (r = 0.37; P < 0.05), SOD (r = 0.53; P < 0.05), and CAT (r = 0.31; P < 0.05). In turn, delta-ALAD had significant negative correlations with MDA (r = -0.29; P < 0.05), SOD (r = -0.28; P < 0.05) and CAT (r = -0.34; P < 0.05), but positive correlation with GSH (r = 0.32; P < 0.05). Although a causal pathway can not be determined from the present study, our findings indicate lead-induced oxidative stress in blood of children with neurological disorders. Lead-induced oxidative stress as an underlying mechanism for neurological diseases in children warranted further investigation.     

Induction of heme oxygenase-1 improves cold preservation effect of liver graft

We have examined the protective effect and mechanisms of heme oxygenase-1 (HO-1) induction in rat liver model of ex vivo cold ischemia preservation using cobalt protoporphyrin (CoPP) as HO-1 inducer and zinc protoporphyrin (ZnPP) as HO-1 inhibitor. There was a decrease in both aspartate transaminase and lactate dehydrogenase activities and in malondialdehyde level in liver of the CoPP-treated group compared with controls (p < 0.05). In the CoPP-treated rats, the histological signs of reperfusion injury were much lower than in control. Up-regulation of HO-1 expression was also associated with reduced levels of tumor necrosis factor α and interleukin-6. Markedly fewer apoptotic liver cells (determined by TUNEL assay) could be detected in CoPP-treated group compared with the control group. These protective effects were prevented by administration of ZnPP. In conclusion, induction of HO-1 provides protection against liver injury during cold ischemia preservation and improves the preservation of liver graft. The mechanisms underlying these beneficial effects include reduction of oxidative injury and of inflammatory response and prevention of apoptosis. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 5, pp. 674–681.     

Experimental duck plague in blue-winged teal and Canada geese

Ten adult blue-winged teal (Anas discors) and six Canada goose (Branta canadensis) goslings were inoculated with liver tissue from a natural case of duck plague in a wild mallard (Anas platyrhynchos). Four additional teal were placed in contact with the inoculated ducks. Inoculated teal died 63.5-68 hr after inoculation; two of the contact teal died 161-162 hr after exposure. Three of the goslings died 119-133 hr after inoculation, the others were killed when moribund 90-133 hr postinfection. The clinical course of disease was extremely rapid in both species. Signs were limited to sudden onset of profound weakness, ataxia, tremors and terminal convulsions. The only consistent gross lesion in the teal was a small dark spleen; half the teal also had inconspicuous foci of epithelial necrosis in the distal esophagus and in the cloaca. Goslings had more severe lesions, with focal hepatic necrosis visible in all, and mucosal necrosis over the intestinal lymphoid tissue, and intestinal hemorrhage in three birds each. Microscopic lesions in both species were similar to those reported in mallards. Duck plague might be overlooked at necropsy of blue-winged teal, because of the paucity of gross lesions.     

Ecological studies on Cyathocotyle bushiensis (Digenea) and Sphaeridiotrema globulus (Digenea), possible pathogens of dabbling ducks in southern Québec

Over the past 20 yr, recurrent late-summer mortality of dabbling ducks in southern Québec has been attributed to the digenean parasite Cyathocotyle bushiensis. This study attempted to determine whether this parasite was still implicated in the epizootics, and examined aspects of the ecology of the parasite in the definitive host. Comparison of prevalence and mean intensity of infection of all species of Digenea between salvaged carcasses and hunter-shot ducks revealed that C. bushiensis and a second digenean Sphaeridiotrema globulus were both significantly more prevalent in salvaged ducks. Mean intensity of infection was consistently higher for S. globulus in the salvaged carcasses than in hunter-shot ducks. These data provide strong circumstantial support for the hypothesis that C. bushiensis continues to contribute to the annual mortality, but also strongly suggest that S. globulus may be involved. Comparison of the relative numbers of each species of duck between the salvaged carcass sample and the hunter-shot sample revealed that blue-winged teal (Anas discors) occurred significantly more frequently in the salvaged carcass sample whereas wood ducks (Aix sponsa) were common in the hunter-shot sample but were never found in the salvaged carcass sample. A comparison of susceptibility to experimental infection with C. bushiensis revealed that mallards (Anas platyrhynchos), black ducks (Anas rubripes), blue-winged teal, pintail (Anas acuta) and lesser scaup (Aythya affinis) had similar susceptibilities but that wood ducks were significantly less susceptible to infection. Experimental infections also showed that age of mallards significantly influenced the number of parasites obtained 7 days postinfection; ducklings were most heavily infected. Significant differences were detected in the gross pathology caused by C. bushiensis among duck species. Data obtained from sentinel ducks placed in the field for 24 hr revealed that transmission of both C. bushiensis and S. globulus occurs at least between mid-May and mid-September and that large, potentially lethal, infections can be acquired in as little as 24 hr. Finally evidence is presented to suggest that ducks acquire resistance to challenge infections of C. bushiensis.