Modification of immunologic and hematologic variables by method of CO2 euthanasia

BACKGROUND AND PURPOSE

The major goal was to determine whether variations in the method of CO2 euthanasia would induce significant immunologic differences.

METHODS

Young adult C57BL/6 mice (n = 40) were euthanized, using four regimens: 70% CO2/30% O2; 70% CO2/30% O2-->100% CO2; 100% CO2-naïve chamber; and 100% CO2 pre-charged chamber. Time to recumbency and euthanasia and body, liver, lung, spleen, and thymus masses were determined. Blood and spleen were further evaluated for leukocyte, lymphocyte, and thrombocyte counts, erythrocyte characteristics, distribution of lymphocyte subpopulations, spontaneous and mitogen-induced blastogenesis, complement activity, and cytokine production.

RESULTS

Time to euthanasia was five- to eightfold longer in mice exposed to 70% CO2/30% O2 than that for any other group. There were slight increases in mean erythrocyte volume (MCV) and mean erythrocyte hemoglobin (MCH) for all groups, compared with those for the 100% CO2 pre-charged group. Circulating cytotoxic T (CD8+) lymphocyte percentages and numbers, and spontaneous blastogenesis of leukocytes in blood and spleen, also were affected by euthanasia method.

CONCLUSIONS

The method of CO2 euthanasia can result in significant differences in immunologic/hematologic variables. Thus, consistency in euthanasia procedures may be important in accurate interpretation of research data.

Glucagonoma in a jaguar (Panthera onca)

An obese adult jaguar (Panthera onca) was euthanized because of progressive lameness. Two 3-cm-diameter pancreatic nodules were identified as islet cell tumors, which were positive with immunohistochemical stains for glucagon, neuron-specific enolase, chromogranin A, and synaptophysin. The jaguar did not present clinical evidence of hyperglucagonemia.

Operation-management factors associated with early-postnatal mortality of US foals

Of 7320 equine foals reported born alive during 1997 on 1043 operations that had equids on 1 January 1997, and that participated in the United States National Animal Health Monitoring System (NAHMS) Equine 1998 Study, 120 foals were reported to have died (by either euthanasia or natural causes) within the first 2 days of a live birth. The weighted estimate was 1.7% mortality (standard error=0.5) within the first 2 days of live birth for all foals born on operations in the 28 states included in the study.A multivariable logistic-regression model revealed that foals born in the southern region were more likely to have been reported to have died within the first 2 days of live birth than in the western region. In addition, the following operation-level factors were associated with increased odds of a foal dying within the first 2 days of live birth: not routinely testing newborn foals for adequate absorption of colostral immunoglobulins during the first 2 days of life; adding new resident equids to the operation during 1997; having non-resident equids stay on the operation for 1-30 days during 1997; never requiring an official health certificate (for operations that had non-resident equids stay on the operation for 1-30 days); using something other than straw or hay as the predominant bedding type; and feeding equids a vitamin-mineral supplement/premix with forage and/or grain.

The 1997/1998 epizootic of swine fever in the Netherlands: control strategies under a non-vaccination regimen

The 1997/1998 epizootic of classical swine fever (CSF) in an area with high pig density in the Netherlands is described. The epizootic, which numbered 429 outbreaks, was controlled and finally eradicated after 14 months without resorting to vaccination. A further almost 1300 herds (1.1 million pigs) at close proximity of confirmed outbreaks were preventively culled because of the risk of having been infected. The pros and cons of this so-called "pre-emptive slaughter" are discussed. The long-lasting movement restrictions caused severe overcrowding especially in breeding farms. For reasons of animal welfare 6.5 million weaners and adult pigs had to be killed and destroyed, whereas another 2.6 million 3-17 days old piglets were euthanised to save long-term destruction capacity. The presumed routes of infection and factors influencing the epizootic are explained, as well as the various methods to bring the epizootic to a halt. The strategy for detecting outbreaks in an early stage, and the type of samples to be collected for laboratory diagnosis are emphasised from the general point of application. The direct costs of the epizootic, losses of exports not included, are estimated at US$ 2 billion.

Evaluation of brain damage resulting from penetrating and non-penetrating captive bolt stunning using lambs

OBJECTIVE

To compare the brain damage in sheep resulting from penetrating and non-penetrating captive bolt stunning.

DESIGN

The unrestrained heads of anaesthetised lambs were impacted in the temporal region with penetrating and non-penetrating captive bolt pistols (humane stunners) using a constant charge. Two hours after head impact, brains were perfusion-fixed with 4% paraformaldehyde. Coronal sections were stained with haematoxylin and eosin and immunohistochemically for amyloid precursor protein, a sensitive marker of axonal and neuronal reaction in brains after trauma. Pathological changes in these brains were then quantified by morphometric analysis.

RESULTS

The skull was fractured in 50% of lambs after a non-penetrating head impact and in all animals after a penetrating head wound. Impact contusions were present in 80% of lambs receiving a non-penetrating head injury and in all of those with a penetrating wound. Total contusion area was similar in both groups. Amyloid precursor protein-positive axons and neurons, and haemorrhage, were widely distributed in the brain after both head impact types, but there was no statistically significant difference between the two groups. Multifocal necrosis of the cerebellar granular layer was found in all lambs with non-penetrating head injury, but in none with a penetrating injury.

CONCLUSIONS

The structural brain damage, a mixture of focal and diffuse injury, produced by penetrating and non-penetrating captive bolt pistols was overall similar and of sufficient severity to suggest that both types of weapon are acceptable for euthanasia.

Use of sevoflurane for anesthetic management of horses during thoracotomy

OBJECTIVE

To evaluate sevoflurane as an inhalation anesthetic for thoracotomy in horses.

ANIMALS

18 horses between 2 and 15 years old.

PROCEDURE

4 horses were used to develop surgical techniques and were euthanatized at the end of the procedure. The remaining 14 horses were selected, because they had an episode of bleeding from their lungs during strenuous exercise. General anesthesia was induced with xylazine (1.0 mg/kg of body weight, IV) followed by ketamine (2.0 mg/kg, IV). Anesthesia was maintained with sevoflurane in oxygen delivered via a circle anesthetic breathing circuit. Ventilation was controlled to maintain PaCO2 at approximately 45 mm Hg. Neuromuscular blocking drugs (succinylcholine or atracurium) were administered to eliminate spontaneous breathing efforts and to facilitate surgery. Cardiovascular performance was monitored and supported as indicated.

RESULTS

2 of the 14 horses not euthanatized died as a result of ventricular fibrillation. Mean (+/- SD) duration of anesthesia was 304.9 +/- 64.1 minutes for horses that survived and 216.7 +/- 85.5 minutes for horses that were euthanatized or died. Our subjective opinion was that sevoflurane afforded good control of anesthetic depth during induction, maintenance, and recovery.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of sevoflurane together with neuromuscular blocking drugs provides stable and easily controllable anesthetic management of horses for elective thoracotomy and cardiac manipulation.

Meningeal osteosarcoma in a dog

A meningeal osteosarcoma was diagnosed in a dog displaying neurologic signs compatible with a space-occupying cerebellar lesion. Gross lesions, restricted to the brain, consisted of a solitary, compressive mass attached to the dura mater overlying the left cerebellum. The mass was composed of single and multinucleated, atypical polygonal cells that lined or rested within lacuna surrounded by eosinophilic, mineralized matrix. The matrical component stained dark green-yellow to blue with Movat's pentachrome stain, deep blue to red with Heidenhain aniline blue stain, and brown-black with Von Kossa stain. Results of these stains were interpreted as tumor osteoid. Foci of dural mineralization and osseous metaplasia were present at the point of tumor attachment. The microscopic observations were interpreted as an osteosarcoma of extraskeletal origin. To our knowledge, these findings represent the first documented case of a meningeal osteosarcoma in a domestic animal species.

Use of injectable potassium chloride for euthanasia of American lobsters (Homarus americanus)

Potassium chloride (KCl: 330 mg/ml) was assessed as an euthanasia agent in American lobsters (Homarus americanus). Two groups of 10 lobsters (408.2 to 849.9 g) were maintained at 11.9 to 12.1 degrees C ('warm') and 1.5 to 2.5 degrees C ('cold') to evaluate the possible effect of ambient temperature on response to KCl. Death was defined as time of cardiac arrest, as viewed and measured by use of ultrasound. The KCl solution was injected (100 mg of KCl/100 g of body weight) at the base of the second walking leg to flood the hemolymph sinus containing the ventral nerve cord with potassium. Disruption of this 'central nervous system' was immediate, followed by cardiac arrest within 60 to 90 seconds. Group median ( +/- SD) baseline heart rate was 42 +/- 14 'warm' and 36 +/- 5 'cold' beats per minute. Time until cardiac arrest ranged from 35 to 90 (57 +/- 18) seconds in the 'warm' group and from 40 to 132 (53 +/- 34) seconds in the 'cold' group. There was no significant difference between group medians for either parameter. Histologic lesions were limited to mild to moderate acute degeneration, characterized by cell swelling, loss of contraction bands, and occasional mild cytoplasmic vacuolation of skeletal muscle at the injection site. Injectable KCl solution was an effective, reliable method for euthanasia of H. americanus.

The importance of immediate destruction in epidemics of foot and mouth disease

Foot and mouth disease is still prevalent in many parts of the world, as emphasised by the recent devastating epidemic in pig farms in Taiwan. A discrete time mechanistic model has been used to describe the spread of infection in both this epidemic and the 1967 to 1968 epidemic in the UK. The force of infection and basic reproduction number are estimated and the sensitivity of these results to the distributions of both the latent and infectious periods of the disease is examined. Epidemic simulations were performed to evaluate the disease control policy whereby all herds are slaughtered on the same day as disease confirmation. These simulations showed that implementing this policy could have resulted in a dramatic reduction (of over 60 per cent) in the number of pig farms affected in the Taiwan epidemic. It is thus imperative that the necessary resources are available to implement this policy, should an outbreak occur.

Surgical treatment of 45 horses affected by squamous cell carcinoma of the penis and prepuce

The medical records of 45 horses treated for suspected squamous cell carcinoma of the penis and/or prepuce were reviewed. The age of 40 horses was known, and these had a mean age of 17.4 years. The duration of neoplasia was known for only 3 of the 45 horses. The results of histological evaluation of lesions, available for 35 horses, confirmed that the diseased tissue was squamous cell carcinoma. The location of gross neoplastic lesions was recorded for 43 horses; the glans penis was involved in 24 horses, the body of the penis or the inner lamina of the preputial fold in 27 horses, and the external fold of the prepuce in 10 horses. Surgical treatments of these horses included phallectomy (penile amputation) in 35 horses, segmental posthectomy in 4 horses, phallectomy plus segmental posthectomy in 2 horses, and en bloc resection of the penis, prepuce and superficial inguinal lymph nodes with penile retroversion in 4 cases. Short-term complications in the immediate postoperative period included preputial oedema and haemorrhage at the end of urination. One horse developed acute urinary retention because of severe urethral oedema. Long-term (>1 year) follow-up information was obtained for 31 horses. Neoplasia of the penis and/or prepuce recurred in 6 of these 31 horses (19%), and in 5 of these the recurrence necessitated euthanasia of the horse.

Anti-plakin and desmoglein autoantibodies in a dog with pemphigus vulgaris

Paraneoplastic pemphigus was suspected in a 14-year-old Labrador retriever because of mucocutaneous erosions, microscopic suprabasal acantholysis, and keratinocyte apoptosis. In this patient, circulating IgG autoantibodies recognized plakin (envoplakin, periplakin) and desmoglein (desmoglein-1 and -3) antigens. Necropsy, however, failed to confirm the concurrent existence of hematopoietic or solid neoplasia. The diagnosis of pemphigus vulgaris therefore was proposed. This study illustrates that such a combination of clinicopathologic lesions and plakin/desmoglein-specific autoantibodies is not restricted to canine paraneoplastic pemphigus but can also be detected in another form of suprabasal pemphigus.

T-cell-rich B-cell lymphoma in a ring-tailed lemur (Lemur catta)

A 13-yr-old ring-tailed lemur (Lemur catta) was evaluated for depression, anorexia, polyuria, and polydipsia. The lemur was in poor body condition and was anemic, hypoalbuminemic, and hyponatremic. Cytologic examination of aspirates of the spleen, liver, and bone marrow and histopathologic examination of liver and bone marrow biopsies revealed a disseminated round cell tumor. After euthanasia, necropsy revealed hepatomegaly, splenomegaly, and mesenteric lymphadenomegaly. Neoplastic cells were present within the spleen, liver, kidneys, multiple lymph nodes, bone marrow, lung, small intestine, pancreas, and testicle and were composed of large anaplastic round cells in a background of small well-differentiated lymphocytes. Immunohistochemical analysis revealed that the small well-differentiated lymphocytes labeled for the anti-human T-cell marker, CD3, and the large anaplastic round cells labeled with the anti-human B-cell marker, CD79a. On the basis of the immunohistochemical staining results and morphologic appearance, a diagnosis of a T-cell-rich B-cell lymphoma was made.

Leukoencephalitis and vasculitis with perivascular demyelination in a Weimaraner dog

Aseptic and noninfectious diseases of the central nervous system are being recognized with increasing frequency. After multiple episodes of neurologic illness, this 7-year-old Weimaraner dog was euthanatized and submitted for postmortem examination. Lesions in the central nervous system were found mainly in the white matter of the cerebral cortex and cervical spinal cord and represented acute and more chronic injury. Necrotizing vasculitis with fibrinoid change and a marked neutrophilic infiltrate dominated the acute lesions. More chronic changes consisted of perivascular demyelination and accumulation of foamy macrophages with positive staining for myelin. An immune-complex (Arthus-type) vasculitis is suspected.

Treatment of fibrosarcoma in a maned wolf (Chrysocyon brachyurus) by rostral maxillectomy

A 12-yr-old captive intact male maned wolf (Chrysocyon brachyurus) was diagnosed with a fibrosarcoma of the incisive bones. The mass was excised by rostral maxillectomy, and the wolf remained normal and on display with good function and cosmetics for 7 mo. Subsequently, it became weak, ataxic, and dyspneic and was euthanatized. At necropsy, there was a small regrowth of the maxillary tumor, a metastatic mediastinal mass, and multiple metastatic lung masses, suggesting that oral fibrosarcoma in maned wolves behaves similarly to oral fibrosarcoma in domestic canines. Aggressive surgical treatment of oral fibrosarcoma in this species can achieve good functional and cosmetic results.

Isolation and characterization of an antigenically distinct 68-kd protein from nonviral intracytoplasmic inclusions in Boa constrictors chronically infected with the inclusion body disease virus (IBDV: Retroviridae)

The relationship between a retroviral infection and the development of nonviral intracytoplasmic inclusion bodies was studied in a Boa constrictor model. Twelve juvenile age- and size-matched inclusion body disease (IBD)-negative boas were randomly divided into three groups. Each group was inoculated intraperitoneally with 1 ml of an IBD virus (IBDV)-infected liver homogenate or 1 ml of normal boa liver homogenate (sham-inoculated control) or was left untreated. All boas were monitored for development of IBD by daily examination and serial liver biopsy over 1 year. The 4 IBDV-inoculated boas became IBDV and inclusion positive by 10 weeks postinoculation. The average size and density of inclusion bodies increased with the duration of infection. Ultrastructurally, inclusion bodies <2 microm in diameter consisted of intracytoplasmic aggregates of granular electron-dense material that were not membrane limited. Larger inclusions (3-6 microm in diameter) were characterized as membrane-bound aggregates of amorphous to granular electron-dense material admixed with membranelike fragments. The sham-inoculated and untreated control snakes did not become inclusion or IBDV positive. Direct comparison of the protein electrophoretograms of IBDV-infected and normal boa tissues demonstrated a prominent 68-kd protein band unique to infected inclusion-positive tissues. Monoclonal antibodies directed against the 68-kd protein band specifically labeled inclusion bodies. The results of this study demonstrate that IBD inclusions represent an intracytoplasmic accumulation of an antigenically distinct IBDV-associated protein.

Progression of an orbital T-cell rich B-cell lymphoma to a B-cell lymphoma in a dog

An 11-year-old Shetland Sheepdog was presented for exophthalmos caused by a locally extensive, poorly defined mass located behind the right eye. The primary orbital mass was identified by light microscopy and immunohistochemistry as a T-cell rich B-cell lymphoma (TCRBCL) composed predominantly of BLA.36-positive large neoplastic lymphoid cells admixed with fewer CD3- and CD79a-positive small lymphocytes. The dog was treated for lymphoma, but 6 months after presentation it was euthanatized for suspected hepatic and gastrointestinal metastasis. Gross findings revealed an enlarged liver with multiple well-demarcated, randomly distributed 0.1-1.5-cm white nodules, five firm white submucosal jejunal nodules, and ileocecal, mediastinal, and hilar lymphadenopathy. Metastatic liver lesions consisted of sheets of monomorphic large neoplastic lymphoid cells that effaced and expanded portal and centrilobular zones. These cells were morphologically similar to the large neoplastic cells of the original orbital tumor and were CD3-negative and variably BLA.36-positive, consistent with B-cell lineage. Similar cells comprised the jejunal nodules and effaced the lymph nodes. The progression of TCRBCL to a diffuse B-cell lymphoma in this case is consistent with reported human cases and has not been previously reported in the dog.