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Biomedical subjects

G A Wobeser

Publications and source records attributed to G A Wobeser.

15 recordsLinked to original sources
PubMed2000

Histology and ultrastructure of the chorioallantoic membrane of the mallard duck (Anas platyrhynchos).

The histology and fine structure of the chorioallantoic membrane of the mallard duck (Anas platyrhynchos), and the density of vessels per millimeter of membrane were assessed between days 12 and 24 of incubation. Light and transmission electron microscopy of the chorioallantoic membrane of the mallard duck after various days of incubation was carried out. Blood vessels within the mesoderm were counted per millimeter of membrane by light microscopy (40x). The chorioallantoic membrane had three distinct layers from day 12 to 24 of incubation, the chorionic epithelium, the mesoderm, and the allantoic epithelium. After day 12, chorionic epithelium consisted of two layers of flattened, elongated epithelial cells interfaced by numerous desmosomes, and separated from the underlying mesoderm by a basement membrane. At this stage, the allantoic epithelium consisted of a single layer of flattened, overlapping cells. Blood capillaries were observed in the mesoderm close to the chorionic epithelium on days 12 and 13; by day 14, these capillaries were located within the chorionic epithelium, forming a capillary sinus. Between days 14 and 16, the chorion underwent cellular and cytological differentiation into three cell types: capillary covering cells, villus cavity cells, and less differentiated basal cells. The mesoderm was composed of a loose matrix of mesenchymal cells and collagen fibrils through which coursed blood and lymphatic vessels. The vascular density in the mesoderm increased rapidly from 4.2+/-0.6 vessels per mm (n = 12) on day 12 to a maximum of 9.4+/-0.3 vessels per mm (n = 15) by day 16. From day 16, the allantoic epithelium had two to three layers of elongated and overlapping cells. The luminal layer of allantoic epithelial cells had microvillus projections and varying numbers of membrane-bound dense vesicles at all stages from day 12 onward. The histologic and ultrastructural features of mallard duck chorioallantoic membrane from day 12 to 24 of incubation were very similar to those described in the chorioallantoic membrane of the chicken (Gallus gallus) from day 8 to 20 of incubation. Much of the information available concerning the CAM of the chicken also may apply to the CAM of the mallard, with timing adjusted to match the developmental time-frame recorded here.

Age Factors↗
PubMed1998

Intracellular survival of Haemophilus somnus in bovine blood monocytes and alveolar macrophages.

The mechanisms used by Haemophilus somnus to survive and multiply within bovine mononuclear phagocytes are not fully understood. In order to study the interaction between bovine mononuclear phagocytes and H. somnus, a colorimetric assay using 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenylItetrazolium bromide (MTT) was developed to assess the survival of H. somnus within cultured bovine blood monocytes (BBM). Using this system, it was found that H. somnus was able to survive within BMM in vitro, and the kinetics of its survival were similar to that seen in BBM isolated from experimentally infected cattle. Using ultrastructural studies, it was possible to demonstrate the survival of H. somnus in freshly isolated bovine mononuclear phagocytes in membrane-bound vacuoles. To determine if activation of macrophage function would result in elimination of intracellular H. somnus, BBM were treated with E. coli lipopolysaccharide (LPS) or recombinant bovine (rBo) cytokines, interferon-gamma (IFN-gamma), granulocyte macrophage colony stimulating factor (GM-CSF), tumour necrosis factor-alpha (TNF-alpha) or interleukin-1beta (IL-1beta). Treatment of BBM with rBoIFN-gamma, rBoGM-CSF or E. coli LPS resulted in decreased intracellular survival of H. somnus at 18 and 48 h, whereas BBM treated with rBoTNF-alpha or rBoIL-1beta had reduced intracellular survival of H. somnus only at 18 h. However, none of these treatments resulted in complete elimination of the intracellular bacteria. The ability of H. somnus to survive and multiply in both freshly isolated and cytokine-treated cultured BBM demonstrated the capability of H. somnus to escape from macrophage killing mechanisms. This capability may play a role in the dissemination of H. somnus infection in the body.

Animals↗
PubMed1997

Modulation of phagocytic function of bovine mononuclear phagocytes by Haemophilus somnus.

The interactions between bovine mononuclear cells and Haemophilus somnus are known to be complex. To study this interaction, a flow cytometric assay was developed to assess the effect of H. somnus on phagocytosis of killed opsonized Staphylococcus aureus by bovine alveolar macrophages and blood monocytes. Using this in vitro system, it was found that log phase H. somnus significantly inhibited the phagocytosis of killed opsonized S. aureus by bovine alveolar macrophages obtained both from healthy calves and from cattle experimentally infected with H. somnus. However, killed log-phase H. somnus, in vitro passaged and stationary phase H. somnus had no effect on the phagocytic activity of these cells. In contrast to bovine alveolar macrophages, blood monocytes showed a significant increase in their phagocytic activity following in vitro exposure to either log or stationary phase H. somnus. Using a lypophilic, non-toxic fluorophore PKH2 to label live H. somnus, it was possible to simultaneously measure the uptake of both S. aureus and H. somnus. Stationary and log phase H. somnus were taken up by macrophages equally well, even though phagocytosis of S. aureus was inhibited by only log phase H. somnus. These results demonstrate the ability of H. somnus to modulate bovine mononuclear phagocytic function which might contribute towards the pathogenesis of bovine hemophilosis.

Animals↗
PubMed1997

Effect of Haemophilus somnus on nitric oxide production and chemiluminescence response of bovine blood monocytes and alveolar macrophages.

Haemophilus somnus is able to survive and multiply in bovine blood monocytes (BBM) and alveolar macrophages (BAM), but the mechanisms used by H. somnus to evade killing mechanisms of bovine mononuclear phagocytes are not completely understood. To study the bactericidal ability of bovine mononuclear phagocytes following interaction with H. somnus, in vitro assay systems were developed to detect the luminol-dependent chemiluminescence response (LDCL) and nitric oxide (NO) production of BBM and BAM. Live logarithmically growing or stationary phase H. somnus inhibited the LDCL of BBM and BAM costimulated with opsonized Staphylococcus aureus. Inhibition of the LDCL response of BBM and BAM was not mediated by live H. somnus opsonized with hyperimmune serum, or by killed bacteria. H. somnus stimulated both BBM and BAM to produce NO at levels comparable with Escherichia coli lipopolysaccharide. While NO was being produced, viable H. somnus could still be isolated from the cell cultures. The ability of H. somnus to inhibit LDCL of both BBM and BAM, and resistance to NO killing may be an important mechanism that contributes to survival of the organism following ingestion by bovine mononuclear phagocytes.

Animals↗
PubMed1997

The Canadian Cooperative Wildlife Health Centre and surveillance of wild animal diseases in Canada.

The Canadian Cooperative Wildlife Health Centre (CCWHC) was established in 1992 as an organization among Canada's 4 veterinary colleges, with a mandate to apply veterinary medicine to wildlife management and conservation in Canada. A major function of the CCWHC is nation-wide surveillance of wild animal diseases. Disease surveillance is conceived as consisting of 4 different activities: detection, diagnosis, information management, and use of information. In the CCWHC surveillance program, detection of disease is carried out by a wide range of professional and avocational field personnel, and much effort is expended to stimulate and support this activity. Diagnosis is done by personnel of provincial and federal veterinary laboratories and the CCWHC. Information management is achieved through a national database of wildlife disease incidents developed and maintained by the CCWHC. Use of information is enabled through established channels for distribution of information derived from the surveillance program to persons responsible for wildlife programs and policies, and to the public. There has been a high demand for the services of the CCWHC since its establishment. The CCWHC responds to approximately 2000 requests for information annually, distributes its newsletter to over 1700 recipients, examines approximately 1200 wild animal submissions each year, and has accumulated records of over 5000 disease incidents in its database. Technical information from the CCWHC has benefited federal, provincial/territorial, and nongovernment wildlife agencies; endangered species recovery programs; federal and provincial veterinary services; and federal and provincial public health programs.

Animal Diseases↗
PubMed1996

Immunotoxicity studies in mink (Mustela vison) chronically exposed to dietary bleached kraft pulp mill effluent.

The immunotoxic potential of bleached kraft pulp mill effluent (BKME) to cell-mediated immunity in mink (Mustela vison) was investigated October 1993 through May 1994. For 26 weeks, 20 mink were fed a diet based upon fish caught within 6 km downstream of a bleached kraft mill in Saskatchewan, Canada. Water for this group contained 25% softwood-run BKME. Twenty control mink were fed nutritionally matched diets based upon fish from lakes receiving no municipal or industrial effluent and tap water. Using in vitro and in vivo immunotoxicity assays, the proliferative response of mink peripheral blood mononuclear cells (PBMC) to mitogens was optimal, at 72 hr with 10 micrograms/ml Concanavalin A, 1/80 dilution pokeweed mitogen, and 1/80 dilution phytohemagglutinin. Bacterial cell wall Escherichia coli lipopolysaccharide did not stimulate mitosis of the mink PBMC. No difference (P < 0.05) in PBMC proliferation was seen between the control and BKME-exposed mink with any of the mitogens used. Delayed type hypersensitivity (DTH), a cell mediated response, was assessed in mink vaccinated with live bacille Calmette-Guérin (BCG) and then challenged by intradermal toe web injection with 200 micrograms of sonicated BCG approximately 6 weeks later. The DTH response in the BKME-exposed mink was impaired based upon assessment using skin thickness measurements, histopathological assessment and image analyzer technology. This decreased response is evidence for suboptimal immune function associated with BKME exposure, which could affect the competitive fitness of piscivorous mammals naturally exposed to BKME.

Animal Feed↗
PubMed1988

An adenovirus infection of the kidney of Franklin's ground squirrels (Spermophilus franklini) in Saskatchewan, Canada.

During routine pathological studies of Franklin's ground squirrels (Spermophilus franklini) collected during a predator control program, basophilic intranuclear inclusions were found in the collecting tubule epithelium of the renal papillae in seven of 13 squirrels. This was associated with marked karyomegaly in affected cells. An inflammatory response was not seen in the adjacent tissues. Electron microscopic examination of affected cells demonstrated that the enlarged nuclei contained numerous virus-like particles. Autoculture and serial passage of renal medullary cells resulted in the isolation of virus particles producing intranuclear inclusions and cytopathic effect. The virus possessed properties typical of adenoviruses, but showed no evidence of hemagglutinating activity with a range of species of erythrocytes tested under several temperature conditions. The isolates were relatively host-cell specific; they failed to grow in hamster and rabbit kidney cell lines and in ground squirrel kidney cortical cells.

Adenoviridae Infections↗
PubMed1987

Labile neurotoxin in serum of calves with "nervous" coccidiosis.

Mouse inoculation was used to test for the presence of a toxin in the serum, cerebrospinal fluid, and intestinal contents collected from cases of bovine enteric coccidiosis, with and without neurological signs, and from control calves. Intravenous inoculation of mice with 10 mL/kg of serum from calves showing nervous signs caused effects significantly different from those caused by the inoculation of serum from calves not showing nervous signs and from control calves. The effect was particularly evident in female mice. At this dosage severe neurological signs such as loss of righting reflex, seizures and death occurred only with serum from calves with "nervous coccidiosis". The results suggest that serum from the calves with neurological signs contains a neurotoxin. This toxin appears to be highly labile. It was not present in the cerebrospinal fluid at levels comparable to those in the serum. The significance of this labile neurotoxin with respect to the pathogenesis of the neurological signs associated with bovine enteric coccidiosis is unknown.

Animals↗
PubMed1987

Characteristics of the labile neurotoxin associated with nervous coccidiosis.

Reported are the results of preliminary attempts to characterize the molecular weight, heat sensitivity and other features of a labile neurotoxin identified in the serum of calves exhibiting neurological signs in association with coccidial enteritis. The labile neurotoxin activity is heat labile (60 degrees C for 30 min) and is lost upon exposure to acidic pH (5.5) and cysteine (1.75 g/100 mL serum). Activity can be recovered from the precipitate of a 30% wt/vol solution of (NH4)2SO4 in serum. Ultrafiltration trials suggest that labile neurotoxin activity may be linked to a molecule of over 300,000 MW.

Animals↗
PubMed1987

Pathogenesis of neurological signs associated with bovine enteric coccidiosis: a prospective study and review.

Various hypotheses have been proposed for the pathogenesis of the neurological signs associated with bovine enteric coccidiosis. We undertook a prospective study of cases of bovine enteric coccidiosis with and without nervous signs to test the validity of these hypotheses and explore other possible pathophysiological mechanisms. Clinical, pathological and toxicological data from 12 calves with, and 15 calves without, neurological signs were compared. Calves with neurological signs had a lower liver Cu concentration (p less than 0.01) and a higher plasma glucose concentration (p less than 0.05) than did calves without neurological signs. Hyperglycemia and Cu deficiency may increase the susceptibility to central nervous system damage, but are not likely to account for the onset of neurological signs in calves with enteric coccidiosis. The results of the study suggest that the following are not involved in the pathogenesis of "nervous coccidiosis": disturbance of serum Na, K, Ca, P, or Mg concentration, vitamin A deficiency, thiamine deficiency, anemia, lead intoxication, uremia, Haemophilus somnus meningoencephalitis, severity of coccidial infection, gross alterations in intestinal bacterial flora and hepatopathy.

Animals↗
PubMed1983

Subacute toxic effects of dietary T-2 toxin in young mallard ducks.

Young Mallard ducks (Anas platyrhynchos) were fed diets containing purified T-2 toxin at levels of 20 or 30 ppm for two or three weeks. Ingestion of T-2 toxin was associated with reduced weight gain and delayed development of adult plumage. Affected ducks developed caseonecrotic plaques throughout the upper alimentary tract, especially in oropharynx and ventriculus. Several ducks also developed severe ulcerative, proliferative esophagitis and proventriculitis. Generalized atrophy of all lymphoid tissues consistently occurred. The manifestations of T-2 mycotoxicosis in Mallard ducks were mostly attributable to irritant toxicity to the alimentary mucosa. The T-2 toxin caused neither hematopoietic suppression nor a hemorrhagic syndrome in ducks. These alimentary lesions of T-2 mycotoxicosis in ducks do not resemble diseases of native waterfowl presently being recognized in routine surveillance of waterfowl mortality in Saskatchewan.

Animal Feed↗
PubMed1982

Tularemia in Canada with a focus on Saskatchewan.

Although rare among humans in Canada, tularemia is often endemic in wildlife. The inhabitants of rural areas are especially likely to be exposed to the causative bacterium, Francisella tularensis, through trapping or through the bites of arthropods. Muskrats have replaced rabbits as the principal source of infection, as illustrated by a familial outbreak of oropharyngeal tularemia in Saskatchewan. In humans the disease has six distinct forms and can be asymptomatic, but it generally comes to medical attention as fever, persistent ulcers and enlarged lymph nodes. Serologic tests will confirm the diagnosis.Bien que la tularémie soit rare chez l'homme au Canada, elle existe souvent à l'état endémique parmi les animaux sauvages. Les habitants des régions rurales sont particuliérement susceptibles d'être exposés à l'agent étiologique, Francisella tularensis, lors du trappage ou par les morsures d'arthropodes. Le rat musqué a maintenant remplacé le lapin comme principale source d'infection, tel que l'illustre une poussée de tularémie oropharyngienne chez une famille de Saskatchewan. Chez l'humain la maladie prend six formes distinctes, et elle peut être asymptomatique, mais elle se présente généralement à l'attention du médecin comme une fièvre accompagnée d'ulcères persistants et d'une tuméfaction ganglionnaire. Les épreuves sérologiques confirment le diagnostic.

Agglutination Tests↗
PubMedDate not supplied

Redescription of the sarcocysts of Sarcocystis rileyi (Apicomplexa: Sarcocystidae).

The intermediate hosts for Sarcocystis rileyi (Stiles 1893) Minchin 1913 are ducks (Anas spp.), and the striped skunk (Mephitis mephitis) is its definitive host. The structure of sarcocysts from an experimentally infected shoveler duck (Anas cylpeata) fed sporocysts from an experimentally-infected M. mephitis was studied and compared with type specimens from a naturally infected duck. The experimentally infected duck was killed 154 d after feeding sporocysts. By light microscopy the sarcocyst wall was 3-5 microm thick with indistinct villar protrusions. Ultrastructurally, the sarcocyst wall was a type-23 cyst wall with anastomosing villar protrusions that were up to 7.5 microm long. The villar projections contained filamentous structures. The bradyzoites were 12-14 microm long. Structurally, the sarcocyst from the naturally infected and experimentally infected ducks appeared similar.

Animals↗